SUN-EARTH CONNECTION ROADMAP Strategic Planning for From 9057_ /007B 11

Transcription

1 SUN-EARTH CONNECTION ROADMAP Strategic Planning for From 9057_ /007B 11

2 SUN-EARTH CONNECTION GOAL To Understand Our Changing Sun And Its Effects on the Solar System, Life, and Society 9057/007B 2

3 EXECUTIVE SUMMARY We live in the extended atmosphere of an active star. While sunlight enables and sustains life, the Sun s variability produces streams of high-energy particles and radiation that can harm life or alter its evolution. Under the protective shield of a magnetic field and atmosphere, the Earth is an island in the Universe where life has developed and flourished. The origins and fate of life on Earth are intimately connected to the way the Earth responds to the Sun s variations. Understanding the changing Sun and its effects on the Solar System, life, and society is the goal of the Sun-Earth Connection (SEC) Theme. In addition to solar processes, our domain of study includes the interaction of solar plasma and radiation with Earth, the other planets, and the Galaxy. Hence we plan to: 1. Embark on a challenging science program that involves going to new vantage points within the Solar System and even out into the interstellar medium to make critical measurements; and 2. Apply our new scientific knowledge strategically to produce direct and immediate benefits to our increasingly space-dependent society. SEC Challenges: By analyzing the connections between the Sun, solar wind, planetary space environments, and our place in the Galaxy, we are uncovering the fundamental physical processes that occur throughout the Universe. Understanding the connection between the Sun and its planets will allow us to predict the impacts of solar variability on humans, technological systems, and even the presence of life itself. SEC Progress: We have already discovered ways to peer into the internal workings of the Sun and understand how the Earth s magnetosphere responds to solar activity. Our challenge now is to explore the full system of complex interactions that characterize the relationship of the Sun with the Solar System. SEC Relevance: Understanding these connections is especially critical as we contemplate our destiny in 3

4 the third millennium. SEC science is needed to facilitate the accelerated expansion of human experience beyond the confines of our Earthly home. Recent advances in technology allow us, for the first time, to realistically contemplate voyages beyond the Solar System. SEC Approach: Our strategy for understanding this interactive system is organized around four fundamental Quests, designed to answer the questions: I. Why Does the Sun Vary? II. III. IV. How Do the Planets Respond to Solar Variations? How Do the Sun and Galaxy Interact? How Does Solar Variability Affect Life and Society? SEC Program Elements: A combination of interrelated elements is used to answer these questions. They include complementary missions of various sizes; timely development of enabling and enhancing technologies; and acquisition of knowledge through research, analysis, theory, and modeling. Roadmap Implementation: Five near term actions are required to fulfill the objectives of the SEC Roadmap: 1) Study of the Sun, the heliosphere, and geospace as an integrated interacting system. This requires a) Acceleration of the current Solar Terrestrial Probe (STP) missions to an 18-month launch cadence. These missions are Solar B, STEREO, Magnetospheric Multiscale (MMS), Geospace Electrodynamics Connection (GEC), and Magnetotail Constellation (MagCon). b) Inclusion of four new priority missions in the STP line: Inner Magnetospheric Constellation (IMC), ITM Waves, Reconnection and Microscale Probe (RAM), and SONAR. c) Continuation of the current missions, with an emphasis on theory, data analysis, and new integrative approaches to data visualization. 4

5 2) Exploration of both the inner and outer boundaries of the heliosphere. This requires rapid technology development for two Frontier Probes: Interstellar Probe and Solar Polar Imager. 3) Investigation of the interactions between the Sun and the other planets. This can be accomplished by full participation of the SEC community in the Discovery and Outer Planets program. 4) Development of new enabling technologies, including advanced propulsion, next generation spacecraft, scientific instrumentation, and a new type of information architecture. 5) Application of SEC observational techniques and scientific understanding to show how solar variability affects technology, humans in space, and terrestrial climate. This is a multifaceted effort that will require inter-enterprise and inter-agency cooperative programs (e.g., a Space Weather Network). 5

6 Table of Contents COVER... 1 EXECUTIVE SUMMARY... 3 OVERVIEW THE SUN-EARTH CONNECTION: LONG RANGE OBJECTIVES STRATEGY TECHNOLOGY REQUIREMENTS EDUCATION AND PUBLIC OUTREACH IMPLEMENTATION OF THE SEC ROADMAP SCIENTIFIC BACKGROUND THE SUN DYNAMIC GEOSPACE THE EARTH S ATMOSPHERIC SHIELD THE HELIOSPHERE LIFE AND SOCIETY: SPACE WEATHER MEETING THE CHALLENGE RECENT ACHIEVEMENTS QUESTS, CAMPAIGNS, AND MISSIONS QUEST I: WHY DOES THE SUN VARY? OVERVIEW CAMPAIGN 1: UNDERSTAND THE ORIGINS OF SOLAR VARIABILITY Introduction How Do Active Regions Form? What Is the Nature of the Solar Polar Regions? How Do Active Regions Evolve? How Does the Sun Function as a System? CAMPAIGN 2: UNDERSTAND THE EFFECTS OF SOLAR VARIABILITY ON THE CORONA AND SOLAR WIND What Are the Origins of Flares and Coronal Mass Ejections? How Does the Sun Accelerate High-Energy Particles? What Is the Physics of the Solar Wind?...58 QUEST II: HOW DO THE PLANETS RESPOND TO SOLAR VARIABILITY?...62 OVERVIEW...62 CAMPAIGN 3: UNDERSTAND THE GEOSPACE ENVIRONMENT...66 Introduction...66 How Do Microscale Processes Regulate the Transfer of Energy and Mass in Geospace?...68 How Is Energy Generated and Coupled within the ITM System?...68 How Does the Magnetosphere Evolve during Geomagnetic Disturbances?...68 What Factors Influence the Dynamics of the ITM Regions?...69 How Do Global Magnetospheric Disturbances Evolve?...70 CAMPAIGN 4: UNDERSTAND COMPARATIVE PLANETARY SPACE ENVIRONMENTS...74 Introduction...74 What Is the Role of Planetary Ionospheres in the Response of Their Magnetospheres to Solar Variabity?...75 What Effect Do Rapid Planetary Rotation and Large Internal Sources of Plasma Have on Magnetospheric Dynamics?...76 How Do the Plasma Environments and Upper Atmospheres of Planets with Little or No Intrinsic Magnetic Field Respond to Solar Variability?...77 How Does the Planetary Magnetic Dipole Tilt Angle Affect the Response of the Planetary Magnetospheres to Solar Variability?...77 QUEST III: HOW DO THE SUN AND GALAXY INTERACT?...80 OVERVIEW...80 CAMPAIGN 5: UNDERSTAND THE HELIOSPHERIC BOUNDARY AND NEARBY GALACTIC ENVIRONMENT...84 Introduction...84 What Is the Nature of the Boundaries of the Heliosphere and How Do They Respond to Solar Variations?...86 What Are the Properties of the Local Interstellar Medium?...86 What Effect Does the Galaxy Have on the Solar System?

7 QUEST IV: HOW DOES SOLAR VARIABILITY AFFECT LIFE AND SOCIETY? OVERVIEW LONG-TERM GOALS SOLAR VARIABILITY, TECHNOLOGY, AND HUMAN SPACE FLIGHT CAMPAIGN 6: SPACE WEATHER Introduction A Global View of the Sun Transit of the Solar Wind The Global Properties of Geospace A Coordinated Approach TECHNOLOGY REQUIREMENTS INTRODUCTION ADVANCED PROPULSION Solar Sails SPACECRAFT TECHNOLOGY Microsats and Nanosats High-Data-Rate Communications Autonomous Spacecraft Robust, Long-Lived Spacecraft SCIENTIFIC INSTRUMENTATION Advanced Imaging Instruments Miniaturized In Situ Instruments INFORMATION ARCHITECTURE EDUCATION AND PUBLIC OUTREACH HIGH LEVERAGE FOR EPO EFFORTS PARTNERSHIPS WITH EPO NETWORKS SUN-EARTH CONNECTION EDUCATION FORUM EXAMPLES OF FUTURE SEC EPO OPPORTUNITIES IMPLEMENTATION PLAN PROGRAM ELEMENTS PROGRAM REQUIREMENTS RATIONALE FOR ACCELERATING THE STP LINE STP Mission Queue FRONTIER PROBES Discovery and Outer-Planet Missions Ongoing Missions APPENDIX A DAYSIDE BOUNDARY CONSTELLATION GEOSPACE SYSTEM RESPONSE IMAGERS (GSRI) GLOBAL MESOSPHERIC WATER CYCLE PROBE HELIOSPHERIC IMAGER AND GALACTIC GAS SAMPLER (HIGGS) HIGH RESOLUTION SOLAR OPTICAL TELESCOPE INNER HELIOSPHERIC CONSTELLATION (IHC) INNER MAGNETOSPHERIC CONSTELLATION (IMC) INTERSTELLAR PROBE INTERSTELLAR TRAILBLAZER IO ELECTRODYNAMICS ITM WAVES PROBE JUPITER POLAR ORBITER MARS AERONOMY PROBE NEPTUNE ORBITER OUTER HELIOSPHERE RADIO IMAGER (OHRI) PARTICLE ACCELERATION SOLAR OBSERVATORY (PASO) RECONNECTION AND MICROSCALE PROBE (RAM) SOLAR FARSIDE OBSERVER (SFO) SOLAR FLOTILLA SOLAR NEAR-SURFACE ACTIVE REGION RENDERING (SONAR) SOLAR POLAR IMAGER (SPI) STELLAR IMAGER AND SEISMIC PROBE (SISP) SUN-EARTH ENERGY CONNECTOR (SEEC) TROPICAL ITM COUPLER VENUS AERONOMY PROBE APPENDIX B THE SEC ROADMAP PROCESS SUN-EARTH CONNECTION 2000 ROADMAP TEAM ACKNOWLEDGEMENTS SUN-EARTH CONNECTION ADVISORY SUBCOMMITTEE

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10 LIVING WITH A STAR Magnetospheres Comparative Environments The Plasma Universe Humans in Space Satellite Operations Power and Communications Climate Change 9057/007B 16

11 OVERVIEW As we stand at the threshold of a new millennium, we foresee the expansion of humanity beyond the boundaries of our home world. However, significant scientific research and technological advances must be accomplished before this vision can become a reality. In particular, detailed understanding of how our Sun and other stars influence the space and objects within their domains is crucial. We must learn the implications of living with a variable star in preparation for extending human activities in space. We have already conducted preliminary exploration, reconnaissance, and robotic visits to a number of bodies within the Solar System. In the coming decades these missions will become more frequent, will visit a wider variety of places, and will conduct ever more sophisticated studies. Inevitably, humans will travel throughout the Solar System to explore and live on other planets, moons, and asteroids. The human search for greater knowledge and understanding of our place in the Cosmos may eventually lead to voyages to other stars with planetary systems, possibly life, and perhaps even other civilizations. Understanding our changing Sun and its effects on the Solar System, life, and society is the goal of the Sun-Earth Connection (SEC) theme. The attainment of this goal will be valuable for providing fundamental scientific understanding of how our universe works, enhancing our ability to operate space-based technological systems with efficiency, ensuring the safety of humans as they travel beyond the confines of the Earth, understanding fully the contribution of the Sun to climate change, and revealing the effects of solar evolution on the origin and continued evolution of life in the Solar System. 11

12 SEC GRAND CHALLENGES Voyages beyond the Solar System Expanding Our Home in the Solar System 9057/007B 3

13 The Sun-Earth Connection: Long Range Objectives Fundamental and applied research in SEC will lay the groundwork for the future: To advance space science, we will continue to investigate the basic processes that cause solar variations, as well as their consequences for the Solar System. To ensure the safety of humans traveling from Earth, we will seek to understand and forecast the space environments with which they must cope. To take the first steps toward voyaging to nearby stars, we will carry out robotic exploration of interstellar space beyond the heliosphere. To meet these objectives, the SEC theme is dedicated to understanding the physical processes that power the Sun and link the Sun and the Earth. The basic physics concerns the behavior of primarily electrified material and its interaction with magnetic fields on the Sun, in interplanetary space, at the Earth and planets, and in the local galactic environment. The scales in the universe are much larger and the material often much hotter and more tenuous than we can simulate in laboratories or computer experiments on Earth. We can learn about them only by observing them with dedicated instruments in space or by venturing out and exploring these unfamiliar environments with in situ experiments. We are learning that these interactions are far more complicated than we have assumed until now. There are nonlinear coupling processes between very small and very large scales. There is turbulence. Also electromagnetic radiation and waves couple distant locations through the exchange of energy and shock waves form in the hypervelocity flows. The SEC mission ranges from the deep solar interior to the faraway heliopause, where the solar wind impinges on the interstellar medium, and from the Earth s dynamic magnetosphere to the exotic surroundings of Jupiter s moon Io. The knowledge we gain will force us to think in new ways about the world in which we live. It will deepen our understanding of the origin and evolution of the universe, the processes in the Solar System that affect our presence in space, and the vulnerability of our home in space to the changing Sun. 13

14 STRATEGY Quest I: Why Does the Sun Vary? Campaign 1: The Origins of Solar Variability Campaign 2: The Effects of Solar Variability on the Solar Atmosphere and Heliosphere Quest II: How Do the Planets Respond to Solar Variations? Campaign 3: The Geospace Environment Campaign 4: Comparative Planetary Space Environments Quest III: How Do the Sun and Galaxy Interact? Campaign 5: The Heliospheric Boundary and the Nearby Galactic Environment Quest IV: How Does Solar Variability Affect Life and Society? Campaign 6: Space Weather 9057/007B 5

15 Strategy Our strategy for understanding the Sun-Earth system is organized around four primary questions, referred to as Quests. Each Quest focuses on one specific element, although the questions are inherently interconnected. The four SEC Quests are: I. Why Does the Sun Vary? II. III. IV. How Do the Planets Respond to Solar Variability? How Do the Sun and Galaxy Interact? How Does Solar Variability Affect Life and Society? To answer these questions, we need improved understanding, which can only be achieved with new measurements. The plan for the systematic acquisition of this understanding is developed as Campaigns, each of which describes a sequence of missions making new measurements. It is anticipated that as progress is made, the Campaigns will evolve in content and focus. The six SEC Campaigns in this Roadmap are designed to understand: 1. The origins of solar variability 2. The effects of solar variability on the corona and solar wind 3. The geospace environment 4. Comparative planetary space environments 5. The heliospheric boundary and nearby galactic environment 6. Space weather. These Quests, Campaigns, and associated missions are described in detail in subsequent sections. Progress in all these areas is intimately connected with the development of technology as summarized next. 15

16 SEC SCIENTIFIC AND TECHNICAL TRENDS Study of individual scientific question FROM TO Requirements Studying global systems Acceleration of STP line to provide mission overlap Single-point measurements 3-D observations of the evolution of system Microsat constellations 2-D imaging 3-D imaging Advanced propulsion to reach unique vantage point High rate, deep-space communications Focusing on solar atmosphere Expanding to see internal structure Advanced instrumentation Geospace studies Expanding to other planets Cross-theme collaborations Inner heliosphere measurements Modeling of space weather Exploring beyond boundary of solar system Predicting of space weather effects Frontier probe missions Advanced propulsion Space weather network 9057/007B 24

17 Technology Requirements In the course of building the SEC Roadmap, the technology advances that are critical to enable or enhance the proposed SEC missions have been identified and assessed. They fall into several specific categories: Miniature Satellites: Many future SEC missions involve flying constellations of small satellites. The individual spacecraft do not have to be big or complex to achieve the scientific goals of these missions (e.g., Magnetotail Constellation, Inner Heliospheric Constellation and Dayside Boundary Observer). However, they will have to be inexpensive, miniaturized, highly integrated buses and instrument packages to fit within the mission cost guidelines. They will also have to be highly autonomous. Advanced Propulsion: To take instrumentation to some of the remaining unexplored places in the Sun s domain, we need to develop new forms of propulsion. The most promising short-term prospect seems to be solar sails. Extended-Life Components and Redundancy: Several of the SEC missions are designed to last for a solar cycle or longer. Consequently, we must improve the reliability and longevity of our systems. High-Data-Rate Communication from Deep Space: The SEC plan will require putting remotesensing satellites or constellations around the Sun and other planets and in the farthest reaches of the Solar System. Many of the scientific goals depend on high data rates and so will require a high degree of autonomous data processing and selection as well as development of the next generation of deep-space communication techniques. Advanced Instruments: To go along with the first two technology challenges, we need to develop the next generation of advanced instrumentation this primarily involves making smaller, lighter, and more reliable electronics and smart detector systems. Data Visualization and Modeling Techniques: With the advent of missions designed to produce the first 3-D images of the Sun and the geospace environment and even 4-D data, we will have to develop ways to process, visualize, and model such data. Such technical advances will benefit all branches of the NASA program and reduce the cost of commercial ventures in the long term. 17

18 Example SEC EPO Products and Programs SUNBEAMS ISTP Outreach 9057/007A 1 Live@The Version 2.0 Version 2.0 A multimedia presentation on the Sun A for multimedia Windows presentation and Macintosh users (plus on additional the Sun materials) for Windows and Macintosh users (plus additional materials) sohowww.nascom.nasa.gov or sohowww.nascom.nasa.gov sohowww.estec.esa.nl or sohowww.estec.esa.nl Developed by SOHO, the Solar and Heliospheric Observatory -- a mission of Developed international by SOHO, cooperation between NASA the Solar and Heliospheric the European Observatory Space Agency -- a mission of international cooperation between NASA and the European Space Agency Dynamic Sun CD- ROM

19 Education and Public Outreach Space Science Enterprise Vision: Scientists and educators coming together to share new discoveries, the process of doing science - its joys and creativity - and to develop effective strategies for making both the results and the process of science available to educators, students, and the public. Our Roadmap supports SEC Education and Public Outreach (EPO) efforts and delivers new opportunities including individual mission and cross-campaign efforts. In response to NASA s strategic vision for broadly communicating the content, relevancey, and excitement of NASA s missions and discoveries, the Space Science Enterprise has made a strong commitment to a robust EPO program. The SEC science community has enthusiastically responded to the EPO mandate, sharing the excitement and relevance of its discoveries through innovative and effective resources and programs. Our community s unique contribution to education and outreach is through ongoing discoveries and through new knowledge and expertise from our missions, scientists, and research programs. All SEC missions are chartered to include EPO components. SEC scientists representing industry, academia, and government are involved in EPO through support by SR&T grants and/or by their own institutions. EPO provides a unique opportunity for collaboration and synergistic EPO elements across each SEC campaign. SEC EPO Goals: Use SEC missions and research programs and the talents of our community to contribute towards the reform of science, mathematics, and technology education, particularly at the pre-college level, and to the general elevation of scientific and technical understanding. Cultivate and facilitate the development of partnerships between the SEC community and the communities responsible for formal and informal science, mathematics, and technology education. Promote the participation of underserved and underutilized groups in SEC education and outreach, research, and development activities. Share the excitement of discoveries and knowledge generated by SEC missions and research programs by communicating them to the general public. 19

20 Action Plan 1. Study the Sun, heliosphere, and geospace as an interacting system; requiring: a) Acceleration of Solar Terrestrial Probe line to 18-month cadence b) Implementation of next four STP missions (Inner Magnetospheric constellation, ITM Waves Probe, Reconnection and Microscale Probe, and SONAR) c) Use of existing space assets for new SEC objectives 2. Exploration of the extreme boundaries of heliosphere (Interstellar Probe and SPI) 3. Investigation of interaction of the Sun and other planets (SEC participation in Discovery and outer planets programs) 4. Development of new technologies (solar sails, nanosats, advanced instruments, and new data architectures) 5. Development of a space weather network around the Sun and Earth 9057/007B 22

21 Implementation of the SEC Roadmap The roadmap goals will be successfully accomplished if its elements are implemented: Measurement campaigns will provide a variety of observations throughout the Solar System. These campaigns are carried out by means of a carefully coordinated set of missions involving combinations of spacecraft of different capabilities, ranging from Explorer missions through Solar Terrestrial Probes to Frontier Probes. The mission sequences have been developed according to their scientific contribution to the Campaign, synergy with other SEC missions, and technological readiness. A vigorous technology development program is required to ensure timely developments in a) the coordinated use of multiple spacecraft, b) techniques for traveling to currently inaccessible regions of space, and c) the substantial lowering of spacecraft and instrument costs. Major SEC technology thrusts are thus in sensors and instruments, spacecraft systems, deep-space communication, advanced propulsion, and data systems and data visualization. A fundamental research and analysis program, including support of theory and modeling and a robust guest investigator program, is required for effective harvesting of knowledge derived from mission data. These programs must be especially tailored to the integration of data from multiple missions. No program is complete until its results have been effectively communicated. This is accomplished through an active education and public outreach program. 21

22 SOLAR INTERIOR FUNDAMENTAL PHYSICAL PROCESSES SOLAR ATMOSPHERE INTERPLANETARY SPACE EFFECTS ON THE EARTH AND PLANETS HELIOSPHERE PARTICLES INTERSTELLAR MEDIUM GALAXY MAGNETIC FIELDS MAGNETOSPHERES IONOSPHERES ATMOSPHERES PLANETS RADIATION MAGNETOSPHERES IONOSPHERES ATMOSPHERE BIOSPHERE EARTH From 9057_ /007B 4

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24 SOLAR VARIABILITY TIMESCALES Flares & Coronal Mass Ejections: Seconds to Days Solar Cycle: Years to Centuries Active Regions: Days to Months Long-Term Fluctuations: Decades to Billions of Years 9057/007B 6

25 SCIENTIFIC BACKGROUND The Sun The driving force behind changes in the Solar System is the varying solar output of radiation, particles, and magnetic fields. It varies on timescales of seconds to billions of years. The origin of this variation is the Sun s magnetic cycle and the chaotic interactions of the fields it generates. Hence, to understand the changing Sun, it is important to find how magnetic fields are generated beneath its visible surface, how they are transported throughout the body of the Sun, and how they dissipate into space. New Insights: Recent SOHO observations of the solar interior show that the rigidly rotating core is separated from the differentially rotating convection zone by a thin shear region called the tachocline. The tachocline, about 70% of the way out from the core, is probably the seat of the magnetic dynamo that causes the solar cycle. The convection in this outer layer brings thermal energy from below and carries with it the magnetic field. The reason why the activity cycle reaches its peak about every 11 years is unknown. However, this variation affects the rates of flares, coronal mass ejections, and even the solar irradiance. Understanding this process and the resultant phenomena will not only increase our knowledge of our current space environment but also give us insight into the origins and evolution of life on Earth. It should help us discover whether life can evolve near stars that are more active than the Sun. Examining Interfaces Provides a Global View: We need to understand the origin and nature of the solar wind and the eruptive magnetic events that perturb it, since the solar wind provides one of the primary interfaces with the Earth. The other interface is the variable solar radiation flux. To study the wealth of effects that the solar activity cycle provides as clues to its origin and nature, we must study the Sun across the entire spectrum from γ-rays to radio wavelengths. Using an array of high-resolution imaging and spectroscopic instruments as well as in situ particle, wave, and field instruments, we will build a global understanding of the Sun over the next two solar cycles. 25

26 9057/007B 17 THE MAGNETOSPHERE OUR INVISIBLE SHIELD

27 Dynamic Geospace The Earth s magnetic shield - the magnetosphere - protects us from the electrified plasma flowing out from the Sun in the form of the solar wind. Eruptive events on the Sun perturb the solar wind, changing its density, velocity, and composition. Some of the material from these huge events can hit the Earth. Energy in the solar wind can leak past our shield, causing geomagnetic storms and enhancing the Earth s radiation belts. Vast currents manifest themselves as aurorae that are mostly visible at high latitudes on the Earth. However, geomagnetic storms can have much more fundamental effects on our technologically dependent civilization by disrupting communications, causing power outages, and even damaging satellites in Earth orbit. The Solar Wind Transfers Energy to Earth: The flow of energy into the geospace environment, in the form of high-energy particles, is modulated, redirected, and altered by the magnetosphere. Hence, energy is transferred from the solar wind into different forms in the magnetosphere. Currents are induced along the magnetic field lines of the Earth. Particles become trapped in the closed fields, mirroring backwards and forwards, forming the Van Allen radiation belts. Other phenomena such as convection and turbulence are also created. The Required Observations: While these effects have been seen at specific points and particular times by single satellites, they are not easily seen on the large scale. The International Solar Terrestrial Physics (ISTP) program has made the first steps towards obtaining coordinated observations of the Sun and the magnetospheric response to the solar input. The success of this program has demonstrated the power of this approach. Two additional phases are needed to complete the picture, they are: more detailed in situ measurements using satellite clusters to achieve understanding of the physical processes which control the geospace sytem, and global imaging of geospace plasmas 27

28 OUR ATMOSPHERIC SHIELD MAGNETOSPHERE RADIATION CHARGED PARTICLES ALTITUDE (km) THERMOSPHERE THERMOSPHERE IONOSPHERE MESOPAUSE MESOSPHERE X-RAYS EXTREME UV ULTRAVIOLET VISIBLE LIGHT INFRARED GALACTIC COSMIC RAYS AURORAL PARTICLES SOLAR PROTONS 50 STRATOPAUSE GRAVITY WAVES STRATOSPHERE TROPOPAUSE TROPOSPHERE From 9057_ /007B TEMPERATURE ( K)

29 The Earth s Atmospheric Shield The tenuous layers of the Earth s neutral upper atmosphere shield the planet and its biosphere from harmful solar radiation and particles by absorbing and distributing this energy within the ionosphere, thermosphere and mesosphere (ITM) regions. This solar energy input varies over minutes to solar cycles and from the polar cap to the equator resulting in global changes to the ITM neutral composition, plasma state, thermal distribution, and dynamics. As our spacecraft mainly orbit within the ITM region are increasing and therefore will be affected to these changes. It is, therefore, imperative that we understand the processes occurring in our upper atmosphere. The maintenance of this protective shield is sensitive to changes that occur in the chemical makeup of our atmosphere. As anthropogenic sources of methane and carbon dioxide continue to increase, they are transported over time to the upper atmosphere where adverse effects are anticipated. One indicator of such behavior is in the growing presence of noctilucent clouds occurring in the polar summer mesosphere region. Here, methane is transformed to water vapor and carbon dioxide reduces the ambient temperature enabling the formation of these clouds. These visible markers indicate man s influence on the region and imply a potentially broader impact on the region and the overall makeup of the atmospheric shield. The ITM region is subject to a variety of influences, from the sun and magnetosphere, in the form of particles, radiation and electric and magnetic fields, to the troposphere and stratosphere, in the form of wave dynamics and chemistry. Thus, the ITM region often acts as a repository of energy transferred from these very different regions of our environment. These external and disparate influences produce a complex response within the ITM region that is often altitude dependent and regionally diverse. This diversity thus demands global satellite coverage of the ITM region in a series of missions that can address the many faceted aspects of the region from coupling and boundary processes and regional dynamics, to the global response of the ITM region and the geospace environment as a whole. The measurement requirements include the neutral and plasma state variables, particles and electric fields, and energy input into the region. Each mission will involve multiple spacecraft to remove spatial and temporal ambiguities. 29

30 9057/007B 8 THE OUTER FRONTIER

31 The Heliosphere A Unique Laboratory: The domain of the SEC program extends to the very limits of the Sun's influence, to the frontier where our Solar System encounters the plasma, neutral gas, and magnetic field of the interstellar medium. The relevance of the physical understanding gained through the study of Solar System plasmas extends even further, because the plasma processes that we study in our Solar System shock formation, particle acceleration, and magnetic reconnection are fundamental in other astrophysical settings. It is only in the Solar System, however, that these processes can be studied directly, through in situ measurement and close-up imaging. Our Solar System is thus an indispensable laboratory for the investigation of astrophysical plasmas, and the research conducted in it under the aegis of the SEC is vital if we are to advance our knowledge and understanding of the plasma universe. Exploring Interstellar Space: Recent scientific and technical advances have provided the SEC theme with a new connection that we believe is vital, namely, to explore the interaction between the Sun and the Galaxy. The new goal will be to explore the dynamics, properties, and structure of the solar wind as it blows through interplanetary space and interacts with the local interstellar medium to form the heliosphere. Of special interest is the nature of the interface between the solar wind and the interstellar medium and the physical processes that occur there. Exploring Beyond the Solar System: Particularly exciting is the prospect of directly observing that interface and then of penetrating the heliospheric envelope to sample, for the first time, the interstellar medium itself. This important new scientific challenge is enabled by recent advances in solar sail propulsion technology, which promises to be able to carry instruments beyond the heliosphere in less than 15 years. Exploring to the very edge of the Sun s sphere of influence and beyond would represent mankind s first steps towards leaving our Solar System. This mission would be one of NASA s greatest challenges to date. 31

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33 Life and Society: Space Weather A Growing Priority: Major changes in the geospace environment generally follow severe solar events, resulting in rapid changes in the particle populations and the electrical currents flowing through interplanetary space and geospace. These storms often can be traced back to specific events on the Sun. Sometimes cause-and-effect chains can be easily recognized, such as the ionizing effects of flare emissions on the Earth s atmosphere. At other times, the connections are more complicated and subtle. For example, the aurora is a hallmark of disturbed space weather, but auroral displays do not always follow a known solar event. The radiation effects experienced by satellites in orbit may depend as much on the location of the orbit as on the level of solar activity. Currently our overall capability to forecast such events is poor, akin to the accuracy of weather forecasting 50 years ago. The meteorological problem was solved by the deployment of a network of surface weather stations and, most importantly, meteorological satellites that provide the comprehensive data to track the approach and development of weather systems. These data are being used to build more accurate models of the Earth s weather patterns, making 7-day forecasts feasible. Prediction: How can we improve space weather forecasting? First, we do not understand all the physical processes and how they interact. Also, we do not have the required continuous observations of the entire Sun or the changes in the solar wind before it strikes the Earth. These measurements must be made continuously over a complete solar cycle at least, so that the appropriate interconnections can be identified. Changes in the Sun s radiant-energy output also must be measured over the entire electromagnetic spectrum to predict changes in the Earth s atmosphere. Gathering data relevant to space weather is becoming more important. In the near future, the number of active satellites in Earth orbit will increase and we will have a permanent human presence on the International Space Station. As society becomes more dependent on space for communications, defense, and environmental and Earth-resource monitoring, reliable space weather forecasting will be a requirement. It is a priority to understand the basic physical processes involved so that we can use them to eventually be able to model and predict space weather. 33

34 Meeting the Challenge The SEC domain is an interactive system of vast complexity, where causes and effects are connected through a myriad of processes that are presently poorly understood and difficult even to describe. To achieve the goal of understanding this system, innovative observations must be made simultaneously from many vantage points, together with breakthrough methods of data analysis and visualization, all integrated via theoretical interpretation. The challenges that must be met in order to attain this goal are both daunting and at the forefront of science. This roadmap describes a scientific and technological pathway to the achievement of the SEC goals. Working through science groups within the SEC community, the important scientific and supporting technology issues were identified and a logical plan for future space missions was developed to address these issues. The SEC Roadmap presents an overview of the Sun-Earth system, our strategy for studying the SEC system, the tactics used in pursuit of our strategy, the SEC program's advanced technology thrusts, and The SEC education and public outreach plan. The individual missions designed to answer this challenge are described in detail in Appendix A. 34

35 Recent Achievements Reconnecting magnetic flux tubes observed in the solar corona (TRACE). Site of the magnetic dynamo region in the deep solar interior imaged (SOHO). Precursors to solar eruptive events such as coronal mass ejections identified (Yohkoh). The location in the Earth s magnetic tail where reconnection occurs during substorms discovered (Geotail). Global images of energetic ion injection into the Earth s radiation belts (Polar). High-speed solar wind flow found to be emanating from the edges of honeycomb magnetic field structures near the solar polar regions (SOHO). Ganymede s magnetosphere discovered (Galileo). Energetic ion signatures at Jupiter similar to terrestrial substorm particle injections measured (Galileo). Distance to the solar wind termination shock inferred from anomalous cosmic ray observations (Voyager). Energetic neutral atoms emanating from the termination shock observed (SOHO). Space weather event predicted successfully following initial detection of a coronal mass ejection (SOHO). Dominance of high-speed solar wind at high latitudes demonstrated (Ulysses). 35

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38 .. QUESTS & CAMPAIGNS 9057/007B _007B 23

39 QUESTS, CAMPAIGNS, AND MISSIONS Quests: The SEC theme is made up of four primary Quests. A quest is long-term search that directly contributes to achieving our primary objective, namely, to Understand Our Changing Sun and Its Effects on the Solar System, Life, and Society. The quests are stated in the form of four questions: I. Why Does the Sun Vary? II. III. IV. How Do the Planets Respond to Solar Variability? How Do the Sun and Galaxy Interact? How Does Solar Variatiability Affect Life and Society? To succeed in these quests, fundamental scientific questions have to be answered, defined in the SEC Campaigns. Campaigns Lead to a Higher Level of Understanding: A Campaign is a 25-year plan to reach a new level of understanding that will help reach closure on the Quest. The fundamental scientific questions associated with each campaign reflect gaps in our current understanding, demonstrated by recent scientific advances. The six SEC Campaigns are designed to understand: 1. The origins of solar variability 2. The effects of solar variability on the corona and solar wind 3. The geospace environment 4. Comparative planetary space environments 5. The heliospheric boundary and nearby galactic environment 6. Space weather 39

40 Missions Answer Specific Scientific Questions: To answer each scientific question, a set of specific measurements must be made. A mission has been defined to obtain the required measurements. The missions are prioritized according to their scientific contribution to the Quest, synergy with the other simultaneous SEC missions, and their technological readiness. Because of the interlinked nature of the SEC theme, some of the missions can address more than one Campaign or Quest. Strategy: The SEC community has adopted the strategy of pursuing a larger number of modest, synergistic missions rather than fewer large missions. The SEC domain is an interconnected system that spans large distances, timescales, and wavelength ranges, requiring extended observations using different observational techniques from vantage points distributed widely in space. The Current SEC Program: The previous SEC Roadmap defined a new series of six missions called the Solar Terrestrial Probes (STP). STEREO will investigate the eruption and propagation of those fields from the Sun to the Earth and the associated changes in the local plasma and particle environment. The other four STP missions were designed to measure the effect of the resulting perturbation of the solar wind on Geospace. In situ measurements of the outer magnetosphere will be provided by Magnetospheric Multiscale (MMS) and Magnetotail Constellation (MagCon) TIMED and the Geospace Electrodynamic Connections (GEC) measure the response of the ITM region. Solar Probe, an Outer Planets Mission, will make the first in situ measurements of the solar atmosphere. These missions provide the next logical step from the ISTP and GGS programs. Solar B is designed to observe the evolution of the surface magnetic fields on the Sun. 40

41 The Next-Generation SEC Program: This new roadmap builds on the foundation of knowledge expected to be obtained by the current SEC program. The SEC community has developed an exciting series of four new STPs and two Frontier Probe (FP) missions in an unprioritized queue. Inner Magnetospheric Constellation 1 (IMC) is the natural extension of the MMS and Magnetotail Constellation missions to make similarly distributed measurements but in the critical Van Allen belts. (STP class) Interstellar Probe 1 will explore to the edge of the Sun s domain and beyond into the interstellar medium. (FP class) ITM Waves 1 fills in our knowledge of energy redistribution in the Earth s atmosphere by waves, which will be a significant advance after the TIMED and GEC missions. (STP class) Reconnection and Microscale Probe 1 (RAM) is a high-resolution telescope to look at the interactions of magnetic fields in the solar corona and will build on the successful SOHO, Yohkoh, TRACE, and Solar B missions. (STP class) Solar Polar Imager 1 (SPI) will observe the source region of the solar wind and see the reversal of the solar magnetic field at the Sun s pole; it is the next logical step after Solar Probe. (FP class) SONAR 1 builds of the results from SOHO to help us understand how active regions develop by using helioseismology techniques to detect their subsurface origins and coronal observations to determine how they evolve in a global context. (STP class) Most importantly, these new SEC missions will be coordinated with each other and with the existing SEC missions to make a Space Weather Network to enable our overall goal of understanding the Sun-Earth system. Campaign 6, Space Weather, apart from having its own distinct scientific goals, acts in an integrating and coordinating role for SEC, bringing together the diverse measurements in the various SEC disciplines. It is only when we can use the physical intuition developed as a result of the accurate predic- 1 See Appendix A for details of specific missions 41

42 tive capability of the SEC that we can claim to have discovered and quantified the driving factors in determining the Earth s response to the solar input. The Long-Term SEC Program: Each campaign has defined a complete series of missions through 2025 that will enable us to gain the comprehensive understanding required to be able to model the complex connections, interfaces, and boundaries created by the variable outflow of energy from the Sun. They are prioritized according to scientific and technological readiness and scope. 42

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44 QUEST I: WHY DOES THE SUN VARY? Overview The Sun provides the energy that sustains life on Earth. The energy comes from nuclear fusion of hydrogen into helium in the Sun's core. A combination of radiative and convective processes transports the energy outwards to the visible surface, where it is ultimately radiated into space. Most of the energy is radiated as light, but the solar wind carries material and magnetic fields throughout the heliosphere. The small fraction of the Sun s energy that reaches the Earth is the principal driver of all of Earth s atmospheric phenomena. It powers weather patterns, aurorae, and the space weather environment of energetic particles at the altitudes of orbiting satellites and manned space flight. Convective motions and nonuniform rotation in the outer third of the Sun generate intense magnetic fields that erupt through the surface to produce areas of strong magnetic field, the active regions. These dynamic fields act to cool the surface in sunspots and heat the Sun s entire outer atmosphere to millions of degrees, trigger coronal mass ejections, and accelerate particles in explosive flares. They also drive the solar wind that fills the interplanetary medium to the outer frontier formed by the heliopause. Changes in complex, strong fields frequently lead to short-circuiting in the solar atmosphere; the results of this range from explosive flares that emit large amounts of highly energetic radiation and particles to enormous, sudden ejections of mass from the Sun into interplanetary space. The surface fields modulate the energy emitted from the Sun s surface on timescales from milliseconds to millions of years. The heating of the outer atmosphere varies dramatically throughout the cycle, even in nonflaring conditions: over the 22-year solar activity cycle, changes up to a factor of 100 are seen in typical levels of radio, UV, and X-ray signals. Short-term solar variations can be as large as a factor of 10 6 in X- ray brightness during flares. The total solar power output changes on the timescale of the 11-year sunspot cycle by a few parts in a thousand, something that over time is enough to cause noticeable climatic changes on Earth. 44

45 We know a great deal about solar activity. We believe that the source of the activity lies near the bottom of the envelope in which gas convects solar energy towards the surface. We know many of the properties of the active-region population as it emerges onto the solar surface. We can effectively calculate the dispersal of the magnetic field over the surface. We have many tantalizing clues to how the field heats the outer atmosphere, how eruptive destabilizations deform the field or force it open, and how outbursts propagate away from the Sun, sometime toward the Earth. But answers to many questions are still ambiguous or escape our understanding altogether. Campaign 1: Understand the origins of solar variability. Campaign 2: Understand the effects of the solar activity on the corona and solar wind (i.e., the entire heliosphere). These Campaigns require a series of fundamental steps that must be taken to achieve their respective goals. Associated with these steps are specific measurements that define a coordinated mission suite, as outlined in the Campaign descriptions. The unifying theme behind Quest I is the search to understand the interaction of solar magnetic fields and matter in widely different physical environments. We have identified two Campaigns to address the most puzzling of these questions: 45

46 CAMPAIGN 1 ROADMAP Understand the Origins of Solar Variability Global Properties of the Sun and Solar Wind The Internal Dynamics of the Sun Small-Scale Magnetic Structures 9057/007B 10 Solar B SONAR Solar Polar Imager Farside Observer Inner Heliospheric Constellation SISP 46

47 CAMPAIGN 1 MISSIONS Farside Observer: How do active regions evolve? SONAR: How do active regions form? Solar Polar Imager: What is the nature of the solar polar regions? Inner Heliospheric Constellation: What are the global properties of the Sun? 9057/007B 11 47

48 Campaign 1: Understand the Origins of Solar Variability Introduction To understand the origins of solar variability, we need to know the physics of two key elements: The origins of the solar cycle: The solar magnetic field is generated deep beneath the surface of the Sun. How this field is generated and transported intact to the solar surface is key to understanding the reason why solar activity varies in the way it does. Observations of the internal structure of the convection zone will provide this necessary information. The dynamic interaction of magnetic structures and flows in the solar photosphere: Sunspots and smaller magnetic structures form an intricate pattern on the surface of the Sun. These moving fields interact chaotically but result in evolving large-scale patterns, including the reversing polar fields. The interaction of fields with convection heats the solar atmosphere and powers the solar wind outflow from the Sun. To reach this understanding, we have to successfully answer a series of fundamental scientific questions which, in turn, will require specific measurements using new techniques from new vantage points. Once we know how a stellar dynamo operates, we can begin to understand the role of magnetic activity in the origin and development of life, including the formation of planets. For example: Is angular momentum stored in a planetary system or shed through early magnetic activity? How important is energetic radiation in early phases of high stellar activity to the generation of, e.g., nucleic acids? How are planets affected by mode switching in the stellar dynamo process as activity declines? 48

49 How Do Active Regions Form? From its source regions near the bottom of the convective envelope, magnetic field emerges onto the surface of the Sun at all latitudes. The field emerges on a wide range of size scales: small regions emerge very frequently and almost uniformly over the entire Sun, while larger concentrations emerge much less frequently and occur at the mid-latitudes. All scales are important for determining the total flux on the Sun and the field patterns we see on the surface. The question of how solar magnetic fields are created and transported is key to understanding why the Sun varies. It can be answered, in part, by measuring the changes in the fields as they emerge and evolve on the surface of the Sun. This is the objective of the nearterm mission Solar B and the long-term mission HRSOT. However, the exciting possibility of actually looking beneath the surface of the Sun and seeing how the field is transported through the body of the Sun is now within reach by using the maturing science of helioseismology. Our understanding of the internal structure of the Sun has increased tremendously during the past two decades because of the development of helioseismology. This technique has enabled the measurement of the dynamic properties throughout the convective envelope of the Sun. Helioseismology has also demonstrated that although the Sun rotates differentially through much of its volume, the radiative interior rotates essentially as a solid body. In the overlying convective envelope, the equatorial zone rotates faster than the polar regions. The transition layer between the core and envelope (the tachocline) is now known to be relatively thin, although its precise characteristics throughut the solar cycle are not yet resolved. A slow meridional flow from equator to pole is seen in the top layers of the envelope, but the return flow in the deeper layers has not yet been observed. The large-scale transport mechanisms in the Sun turn out to be very important to human society since they generate a cyclic magnetic field. This field constantly modifies the solar atmosphere and affects the total solar irradiance on timescales from minutes to centuries - the latter being the most important for climate change. Solar cycles do not repeat with the same strength or length. In fact, the Sun's activity has been strongly 49

50 suppressed or enhanced irregularly in the past, sometimes for centuries. Such periods are correlated with substantial changes in the Earth's climate patterns: for example, low activity persisting for several decades coincided with uncommonly cold European winters in the latter half of the 17th Century - the Little Ice Age. Recently, the Sun has been very active, and it is a matter of speculation that recent climate change may, at least in part, be due to solar effects. One of the most puzzling questions is how the magnetic field avoids being shredded as it traverses the zone of convection. The field is strong enough initially to resist bending by convection, but that strength ought to lead to a rapid expansion and weakening just prior to emergence, when the confining presence of the surrounding plasma is greatly reduced. However, the field does not expand, remaining concentrated in strong bundles (i.e., sunspots). Now a new method is reaching maturity: local-area helioseismology. This tool promises to detect the presence of magnetic fields even before they emerge on the surface by the perturbations they cause in the subsurface density and/or temperature. We expect to see fields below the surface, much like we can see babies by a sonography before they are born. SOHO has demonstrated the potential of this method, but the next generation of instruments is needed to properly see below the solar surface. The SONAR mission concept has been developed to address problems associated with the small-scale fields and the internal dynamics of the Sun in the layers just below and above the surface, building on the recent SOHO results and those expected from Solar B. What Is the Nature of the Solar Polar Regions? Helioseismology has given us our first direct insight into the internal structure of a star. It indicates that the solar polar regions have some unique properties in terms of subsurface flows. Moreover, the polar regions are the only places where the small-scale fields underlying coronal-hole fields can be studied without contamination by or confusion with the activeregion fields. Every 11 years or so, the solar magnetic polarity reverses, defining a 22-year magnetic cycle on the Sun. That reversal is clearly seen in the polar zones, which 50

51 are covered by nearly unipolar fields most of the time. Observing the reversal process may be key to predicting the nature and timing of the following cycle. During most of the solar cycle, the field of the polar coronal holes dominates the structure of the heliosphere. Except near solar maximum, the bulk of the heliospheric magnetic flux originates in the open magnetic field lines of the polar coronal holes. To understand the transport of particles in the solar wind which cause space weather effects at Earth, the modulation of cosmic rays and the interaction of the solar wind with the interstellar medium, we need to quantify the magnetic field strength and its geometry at all latitudes. Unfortunately, the solar polar regions are not clearly visible from our ecliptic perspective owing to foreshortening. The only way to address these issues is to send a mission to image the polar regions of the Sun; hence, we have developed the concept for a Solar Polar Imager to make the needed observations. Exploring the solar polar regions addresses the nature of small-scale fields and the internal dynamics of the Sun. It is the first phase, with SONAR and STEREO, of getting a global view of the Sun. It also provides a technology challenge, since it would be an excellent demonstration mission for the concept of solar sails, although alternative propulsion systems may work. How Do Active Regions Evolve? Active-region fields are moved about in an interaction with convection, being shredded and buffeted on scales of tens of kilometers and dispersed by flows so large that they cover much of the Sun. The smallestscale interactions need ultra-high-resolution magnetic measurements, as performed by HRSOT. Bold new space missions will give us unprecedented views of the Sun from different perspectives that will enable us to address new problems. Active regions and their residual fields persist for months. We do not yet understand how active regions emerge or disperse. SOHO has demonstrated the value of continuous observations of the magnetic evolution of active regions. SONAR will further increase our three-dimensional understanding of active regions. However, even SOHO and SONAR see less than half of the evolution of such regions because of solar rotation and perspective distortion. 51

52 A single perspective also limits our ability to probe deep into the dynamic interior of the Sun. By placing a solar observatory on the far side of the Sun, we can make new measurements of the tachocline, where the dynamo operates, as well as extend our coverage of the solar activity cycle to a global perspective. Hence, we have developed the concept of the Solar Farside Observer. long-term evolution of the Sun is likely to be. This will be accomplished through observations of the internal structure and activity patterns of other Sun-like stars. These will determine how typical the Sun is compared to other cool stars. We envision being able to image the surfaces of other stars like the Sun through the development of a stellar interferometer (SISP). How Does the Sun Function as a System? Ultimately, we need to study the entire Sun as a system, building a full 4π-steradian picture of the generation, propagation, and dissipation of the solar magnetic field. These properties will have to be followed for at least an entire solar cycle to see how they are modulated by it. Hence, the concept of an Inner Heliospheric Constellation has been developed. This mission will give us new insights into how the Sun functions, and it will allow valuable forecasting capabilities for space weather driven by our very own, lifesustaining star. Campaign 1 seeks to give us a comprehensive understanding of the origins of solar variability. Its ultimate goal is to be able to answer the question of what the 52

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54 CAMPAIGN 2 Understand the Effects of Solar Variability on the Solar Wind & Heliosphere Global Dynamics of the Solar Wind Small-Scale Coronal Structures Origin of Eruptive Events 9057/007B 12 STEREO Solar Probe RAM PASO Solar Flotilla IHC 54

55 CAMPAIGN 2 MISSIONS Solar Probe: How is the solar wind accelerated? Why is the solar corona heated? Reconnection & Microscale Probe: What is the origin of flares and CMEs? Particle Acceleration Solar Observatory: How do solar eruptions accelerate particles? Inner Heliospheric Constellation: What are the global properties of the Sun? 9057/007B 18 55

56 Campaign 2: Understand the Effects of Solar Variability on the Corona and Solar Wind The effects of magnetic activity on the solar atmosphere and solar wind (i.e., the inner heliosphere) are complex and varied. To understand this problem fully, we need to take the following steps: Understand the dynamics of the solar atmosphere: The solar chromosphere and corona are dynamic and changing environments on every spatial and temporal scale that we can sample. It is in this complex environment that magnetic fields are redistributed and dispersed, heating the atmosphere in the process of reconnecting and interacting with waves. Discover the origin of eruptive events: The solar magnetic field stores energy and catastrophically releases it in many different forms, primarily as radiation and mass motions. These eruptive events directly impact the conditions in geospace; hence, we need to understand their nature and origins. Understand what drives the solar wind and the propagation of heliospheric disturbances: Somehow a rather uniform solar wind is accelerated into the heliosphere towards the planets. This steady wind is interrupted by small-scale perturbations and by major events, such as coronal mass ejections (CMEs) and flares. Once a CME, a wave packet, or a chargedparticle beam has been launched from the Sun, it moves through the heliosphere and interacts with it. By the time it reaches the Earth, the solar wind has changed its nature in ways that depend on its velocity, density, and residual magnetic fields. To complete this campaign we need to answer the scientific questions that address these challenges. What Are the Origins of Flares and Coronal Mass Ejections? The magnetic field generated in the deep interior of the Sun emerges to form arcs of strong field, temporarily anchored in the interior, that reach high above the surface. Large concentrations of flux form sun- 56

57 spots that are surrounded by smaller concentrations in the magnetic plage. Sunspots are strong enough to resist the action of convection for a substantial period, but convective flows are strong enough to move smaller concentrations of magnetic field. This force balance changes rapidly with height. In the solar atmosphere above the surface of the Sun, the plasma is so tenuous that the magnetic field dominates: material is forced to move with the field as it in turn responds to the moving sources on the surface. Higher, in the solar wind, matter dominates the field once again, accelerating segments of it away from the Sun. This changing force balance determines the characteristic properties of the solar atmosphere. The domain where the magnetic field dominates the plasma is characterized by very fine filamentation, seen as loops in the corona, because material can move freely along but not perpendicular to the field. As a result, a large ensemble of different atmospheres exist in the corona in close proximity. These density, temperature, and compositional contrasts persist far out into the solar wind. The magnetic field in the solar atmosphere and heliosphere is continually restructuring as surface sources appear, evolve, and disappear. These motions, and the multitude of waves coupling to the field, heat the solar corona to millions of degrees. Whereas we know that the magnetic field plays an essential role in this heating, we do not know what kind of energy is most readily transported and dissipated. Waves, electric currents, or perhaps both are thought to be instrumental in the atmospheric heating, but it is not clear which dominates or even if one process does dominate throughout the outer atmosphere. The primary difficulty in understanding this problem is the range of scales involved: dissipation is likely to occur primarily on scales of kilometers or less, yet the local field is determined by the field evolution over a large fraction of the solar surface. Overcoming this problem requires simultaneous imaging of the entire Sun combined with a high-resolution view of the small scales. It may be that chromospheric and coronal effects are intimately tied together, requiring data from a wide range of wavelengths to be accessible simultaneously. Moreover, there are several rival heating theories that can be distinguished only by the results of detailed, high-resolution observations. Thus, we have developed a mission concept, the Reconnection and Microscale Probe (RAM), that will provide 57

58 observations with a resolution 100 times higher than is typically possible currently. These data will complement the results that we expect from STEREO, which will provide the larger-scale view of the corona and the onset of CMEs. How Does the Sun Accelerate High-Energy Particles? SOHO, Yohkoh, and TRACE have advanced our understanding of the solar atmosphere tremendously: the high cadence and spatial resolution combined with spectroscopic tools have shown how the field and the matter trapped in it evolve. The free energy stored in the magnetic field can be released rapidly in substantial processes such as flares, filament eruptions, and CMEs. However, the bulk of the energy is deposited in very small-scale processes, leading to heating, with few side effects observable by current instrumentation. The mixture of thermal energy, energy of bulk mass motions, and energy in beams of rapidly moving electrons or ions differs from case to case. Ultrarelativistic particles are injected into the heliosphere sporadically in solar flares and CMEs by mechanisms that are only poorly understood. The mechanisms of particle acceleration during impulsive flares remain a mystery: how can the dissipation of electric currents cause ions to be accelerated to velocities near the speed of light? The Particle Acceleration Solar Observatory (PASO) mission is designed to address this question. What Is the Physics of the Solar Wind? Part of the hot corona evaporates off the Sun as the solar wind. Material starts out rather slowly near the surface but accelerates rapidly to supersonic speeds within a few solar radii. There are two types of solar wind. The high-speed solar wind originates primarily from unipolar areas, which are largely open to the solar wind. The low-speed solar wind comes from the edges of the coronal holes or boils off from the dynamic mixed-polarity regions and active regions, where the field opens and closes on a short timescale. In addition, magnetic field is seen to open up towards the heliosphere in major eruptions, such as CMEs, with some fraction of the field being torn away permanently. Many fundamental questions about wind acceleration, stream-stream interactions, flows, mass ejections, waves, and shocks are still unanswered. 58

59 The changing magnetic fields and fine structures in the corona result in large variations in solar wind conditions. The most dramatic are associated with CMEs, but there is a spectrum of inhomogeneities down to the smallest scales observed. How these highly contrasting coronal features smooth out in the accelerating solar wind is unclear. Nor do we understand in sufficient detail how solar wind structures evolve as they propagate from near the Sun into the heliosphere. Various components of the solar wind have different bulk properties and anisotropies, e.g., the temperature and bulk speed of protons, electrons, and ions differ at the same location and from structure to structure. The solar wind parameters are highly variable and not currently predictable on short timescales, particularly in the nonspiral directions. The internal state of the solar wind is greatly affected by many kinds of waves whose origins are uncertain. The solar wind provides an ideal laboratory for exploring the generation of turbulence in plasmas. Many competing models exist to explain the structure and composition of the solar wind. Particles are accelerated to high and ultrahigh energies not only in the Sun but also in the wind. We need to understand more about the structure of the shocks that develop in the wind where fast and slow streams interact. We plan to address the fundamental issues of the solar wind with the STEREO and Solar Probe missions. However, they leave open the issue of the global properties of the solar wind. Solar Flotilla will provide a network of in situ instruments to determine the spatial and temporal scales that characterize the solar wind structure and its variations. This mission would complement and enhance the Inner Heliospheric Constellation (IHC) and would be a prime space weather asset. At the orbit of the Earth and beyond, the solar wind is mixed with the neutral atoms from the interstellar medium that manage to penetrate deep into the heliosphere because of the low collision frequencies in the very tenuous wind. Particles evaporated from grains of material that penetrate even closer to the Sun appear to be another source of unusual material that mixes with the wind well within the Earth s orbit. The data available (mostly from Ulysses) do not allow us to identify this inner source of pickup ions uniquely. The material may be true interstellar material, coming into the Solar System as dust, or it may be recycled 59

60 solar wind, which was caught by distant grains of Solar-System material and subsequently released as that material drifted toward the Sun. Inner-heliosphere missions (e.g., Solar Polar Imager, PASO, and Solar Farside Observer) would be particularly suitable to explore this by observing the ion composition of the solar wind. 60

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62 QUEST II: HOW DO THE PLANETS RESPOND TO SOLAR VARIABILITY? Overview The aim of this quest is to understand how the plasma environments and upper atmospheres of the planets are modified as a result of changes in the Sun s output of electromagnetic radiation, solar energetic particles, and, especially, the solar wind plasma with its embedded magnetic field. Progress in this area requires not only learning how and why individual regions respond (e.g., the magnetospheric cusps or the tropical ionosphere), but also the coupling mechanisms which link them tightly into a single vast system. At the Earth, four very basic questions cut across essentially all of our geospace scientific endeavors: How do mass and energy enter geospace? How is electromagnetic energy converted into charged-particle kinetic and thermal energy? What are the sinks for mass and energy? The same questions apply to the environments of the other planets, with each planet possessing unique characteristics that test our understanding of the physical processes. Complete answers to these questions will not only entail major advances in our understanding of basic physical processes, which will benefit the broader astrophysics and plasma physics communities, but will also enable the development of the predictive space weather systems as described in Quest IV. How are mass, momentum, and energy transported within magnetospheres and upper atmospheres? 62

63 Two campaigns have been developed to answer these over-arching questions and fulfill the quest. They are: Campaign 3: Understand the Geospace Environment Campaign 4: Understand Comparative Planetary Space Environments Below we identify the gaps in our scientific knowledge, the measurements which will be required to fill them, the mission concepts leading to the collection of the required measurements, and a roadmap for the implementation of both campaigns. 63

64 CAMPAIGN 3 Understand the Geospace Environment Geospace System Response Regional Dynamics Coupling and Boundary Process 9057/007B 13 MMS GEC MagCon ITM Waves Inner MagCon Tropical ITM DBC GSRI 64

65 CAMPAIGN 3 MISSIONS Dayside Boundary Constellation: How is the solar wind input to the geospace environment affected at the boundary layers? ITM Waves: How do waves redistribute energy in the upper layers of the Earth s atmosphere? Inner Magnetospheric Constellation: What are the dynamics of global magnetospheric structures? Geospace System Response Imager: What is the 3-D dynamic response of the magnetosphere to changes in the solar wind? Tropical ITM Coupler: How is energy transported by mass motions in the Earth s atmosphere? 9057/007B 19 65

66 Campaign 3: Understand the Geospace Environment Introduction The goal of Campaign 3 is to understand the dynamic response of the geospace environment to solar variability. The geospace environment has traditionally been divided into the magnetosphere and the ionosphere, thermosphere, and mesosphere (ITM) regions. These regions are very complex and rich in physical phenomena. However, they are also tightly coupled by poorly understood mechanisms that must be elucidated before the global response of geospace to solar variability can be adequately described and modeled. The magnetosphere has been studied most recently by the highly successful ISTP program with satellites located in the principal regions of the magnetosphere. ISTP is continuing to add significantly to our understanding of the global configuration of the magnetosphere. With its solar monitor and satellites located in the magnetotail, over the poles, and in the inner magnetosphere, many aspects of the system responses to variations in the solar input are now understood. The last NASA mission to take measurements in the ITM region was Dynamics Explorer, flown in 1981 to This mission demonstrated the great importance of coupling between the ionospheric plasma and neutral gas in the thermosphere and shed much new light on the coupling between the ionosphere and magnetosphere. ITM researchers have concluded that the ITM regions are much more highly coupled than was previously realized. To further explore this region, the TIMED mission has been developed. Following its launch in mid- 2000, it will collect measurements that will enable the total energy budget for the mesosphere and lower thermosphere to be computed and will allow us to determine how the energy input from the magnetosphere is redistributed by radiative, chemical, and dynamic processes. This campaign has been designed to address the knowledge gaps in both magnetospheric and ITM dynamics that cannot be addressed by existing missions. The additional steps needed to achieve the goal of un- 66

67 derstanding the global response are outlined on the Campaign Roadmap Chart. Understand coupling and boundary processes: The most critical plasma processes regulating mass transport and energy conversion take place in the thin electric current layers at the boundaries between major regions of geospace (e.g., the magnetopause and ionosphere). A mature model of the coupling between regions and the global response of geospace to solar variations is not possible until such small-scale boundary processes as reconnection, particle acceleration, turbulence, and current closure are well resolved observationally and adequately addressed by theory. Determination of these processes requires high-time-resolution measurements recorded simultaneously from multiple satellites and global kinetic scale simulations. Understand regional dynamics: The different regions of geospace participating in collective dynamic behavior, such as geomagnetic storms, range in altitude from the mesosphere at ~60 km to the middle-tail at more than 250,000 km. These regions are interconnected by electric and magnetic fields and possess plasma populations whose basic properties are still not sufficiently well known. An understanding of the dynamics of individual regions must be achieved before the system-wide coupling and feedback mechanisms can be grasped. Understand the geospace system response: Among the most challenging experimental and theoretical aspects of the geospace research enterprise are the close linkages that exist between the different regions. Magnetospheric substorms initiated by the formation of a neutral line in the tail ~150,000 km downstream of the Earth are known to produce, within minutes of their onset, large electrical currents in the ionosphere and greatly enhanced energetic-particle fluxes in the outer radiation belts. Moreover, conditions in the ionosphere, and other regions, are believed to feed back to the tail and damp or enhance the local rate of reconnection depending upon the ability of the entire system to accept these massive energy releases. Understanding the full global response is the ultimate goal of the campaign. To address these issues, we have designed missions focused on answering specific scientific questions. 67

68 How Do Microscale Processes Regulate the Transfer of Energy and Mass in Geospace? A major knowledge gap that cannot be sufficiently addressed by the widely spaced ISTP satellites is in the understanding of the microscale processes operating in the magnetospheric boundaries, such as reconnection, particle acceleration, and turbulence. To be able to make the measurements necessary to test competing theories in these areas, we require closely spaced clusters of satellites. This will be the primary focus of the Magnetospheric Multiscale mission (MMS) and the ESA/NASA Cluster Mission. Their measurements will reveal the microscale processes operating at the magnetopause, the magnetotail, and the cusp, as well as how they regulate the transfer of mass and energy from the solar wind to the magnetosphere and its release in the tail and transfer to the radiation belts and the upper atmosphere. How Is Energy Generated and Coupled within the ITM System? The electromagnetic coupling between the magnetosphere and the ITM system is poorly understood yet critically important in determining the geospace response to solar variability. The electrically conducting ITM region interacts with the magnetosphere to form a geospace electrical system that responds to variations in the solar wind. These responses are manifested in the ITM region by large-scale currents, enhanced plasma convection, heating, particle precipitation, and wave generation. The electrical coupling of the ITM region with the magnetosphere will be addressed by the ITM probe, the Geospace Electrodynamic Connections (GEC) mission. This multispacecraft mission will map the electrodynamic processes unique to this region and the coupling with the magnetosphere. How Does the Magnetosphere Evolve during Geomagnetic Disturbances? Another area that cannot be addressed by the ISTP missions is that of the large-scale variations in the dynamic magnetosphere. A single measurement in the magnetotail, for example, will not clarify how the whole magnetotail reconfigures during a substorm. The Magnetotail Constellation (MagCon) and Inner Magnetospheric Constellation (IMC) missions will complete our knowledge of the dynamics of these re- 68

69 gions of the magnetosphere. These missions will employ large numbers of microsats (<100 kg) and nanosats (~10 20 kg) to map the large-scale timedependent structure of the magnetosphere from the inner radiation belts to the magnetopause and the middle-tail. The availability of simultaneous, multipoint measurements from MagCon and IMC will also make it possible to construct the first highfidelity images of the regional structure of the magnetosphere from the in situ measurements they will return. The final constellation mission in the sequence is the Dayside Boundary Constellation. This mission will show the location and global extent of reconnection at the dayside magnetopause and how it evolves during geomagnetic disturbances. What Factors Influence the Dynamics of the ITM Regions? The state of the ITM system is also strongly influenced by tidal and gravity wave propagation and dissipation from a variety of sources. Wave dissipation is a significant energy and momentum source for the global ITM circulation, thermal state, and evolution. However, this energy source is poorly determined and yet is considered fundamental to the development of the ITM region. For this reason, the ITM Waves mission has been developed and included in the Campaign 3 Roadmap. The way in which these upperatmosphere waves are generated, propagated, and dissipated and their role in the redistribution of energy and momentum within the ITM region will be determined through modeling and analysis of the measurements returned by this mission. Processes at low latitudes within the ITM region are distinctly different and demand a focused mission. Ion-neutral interactions, horizontal magnetic fields, internal dynamo processes, and explosive instability processes unique to this region demonstrate significant longitudinal variability. Therefore, a lowinclination multispacecraft mission has been designed to appropriately address the longitudinally dependent plasma-neutral behavior within the region. The Tropical ITM Coupler mission will be equipped to measure the neutral and plasma state whose measurements will provide extremely useful information on equatorial ITM behavior as well as for atmospheric drag on lowlatitude spacecraft, such as the International Space Station. 69

70 How Do Global Magnetospheric Disturbances Evolve? The final step in the Campaign is to understand the full global response of the magnetosphere to solar variability. Global magnetospheric disturbances cannot be understood and modeled without obtaining synoptic images of the key regions with sufficient temporal resolution to capture the most critical developments in the sequence of events which constitute, for example, a magnetic storm or substorm. The constellation missions are one method of obtaining these images. However, because they will not all fly simultaneously, they are not sufficient to reveal the full global response of the magnetosphere. Thus, SEC is pursuing a parallel path: imaging the magnetosphere. First, IMAGE, a medium-class Explorer mission, will be launched in early 2000 to use newly developed remote-sensing technologies to view global changes in the various regions of the magnetosphere during storms and substorms. The final mission of the campaign will be the Geospace System Response Imagers (GSRI) mission, which will use a combination of a stationary spacecraft positioned over the poles combined with polar-elliptical orbiting satellites to provide multiple views of the magnetospheric plasma populations. Using tomographic techniques, this will allow imaging of the 3-D dynamic response of the full magnetosphere to variations in the solar wind and interplanetary magnetic field. Because understanding the full system response is the ultimate goal of Campaign 3, it is highly desirable to overlap the ITM and magnetospheric missions to the maximum extent possible. Such an overlap has been built into the Campaign 3 flight scenario. Overlapping MMS and Magnetotail Constellation with GEC and ITM Waves, for example, is beneficial to both programs while also supporting the space weather concerns discussed in Quest IV. This broad synergism with the other Quests and Campaigns is an overarching theme within SEC. 70

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72 CAMPAIGN 4 Jupiter Mars Neptune Understand Other Planetary Environments Large Magnetic Dipole Tilt Mercury No Magnetic Shielding Venus Rapid Rotation and Internal Plasma Sources No Ionosphere 9057/007B 14 MESSENGER Jupiter Polar Orbiter Mars Aeronomy Neptune Orbiter Io Electrodynamics Venus Aeronomy 72

73 CAMPAIGN 4 MISSIONS Messenger: How does the lack of an ionosphere affect the response of a magnetosphere to solar variability? Jupiter Polar Orbiter: What processes are involved in driving Jupiter s magnetosphere and ionosphere? Venus/Mars Aeronomy: How is the upper atmosphere of an Earth-like planet affected by the lack of a global magnetic field Neptune Orbiter: How does a planet with a large axis tilt interact with the solar wind? Io Electrodynamics: What energy conversion processes are involved in Io s extreme environment? 9057/007B 20 73

74 Campaign 4: Understand Comparative Planetary Space Environments Introduction The opportunities to compare and contrast the many different planetary environments are among the most exciting in all of space science. Within the SEC theme, the primary focus remains the understanding and predictive modeling of geospace. However, terrestrial studies are limited to certain ranges of physical parameters that are locally available. From studying Earth s magnetosphere and upper atmosphere, we know that the planetary plasma environments and their dynamic properties depend on 1. their intrinsic magnetic field parameters, 2. the solar wind and interplanetary magnetic field conditions found at that distance from the Sun, 3. the properties of the planets upper atmospheres and ionospheres, and 4. the presence of a natural satellite that might as a gas or plasma source. The Solar System contains a variety of examples in which these different components dominate, allowing us to isolate each piece and determine its parametric role in the solar wind-magnetosphere-upper atmosphere system. By exploring and characterizing other planetary environments, we will extend and deepen the knowledge gained from Earth-based studies and subject our predictive models to challenging new tests that will greatly strengthen our capabilities. The Campaign 4 Roadmap has four intermediate steps that lead to a mature understanding of planetary magnetospheres and ionospheres. Although the underlying physics is complex, these steps are labeled by the planetary properties that give rise to the notable differences between their environments and that of the Earth: Understanding planets with no ionosphere Understanding planets with high rotation rates and large internal plasma sources Understanding planets with no magnetic shielding Understanding planets with large magnetic dipole tilt angles 74

75 What Is the Role of Planetary Ionospheres in the Response of Their Magnetospheres to Solar Variabity? As described in Campaign 3, measurements at the Earth have shown the ionosphere and magnetosphere to form a tightly coupled system. The magnetic fields threading the magnetosphere nearly all have at least one end anchored in the ionosphere. Stress is very rapidly transferred along these field lines as Alfven waves and field-aligned currents. Hence, when the rate of plasma transport in the magnetosphere at altitudes of ~100,000 km, for example, becomes greatly enhanced during a substorm, the speed at which ionospheric plasma and, via collisional coupling, the neutral atmosphere circulate soon becomes similarly enhanced due to the momentum transfer from the magnetosphere. However, the situation is quite complicated at the Earth and other planets with ionospheres, because the charged particles carrying much of the electrical current between the ionosphere and magnetosphere also produce additional ionization when they impact the upper atmosphere. Hence, the electrical conductivity of the ionosphere is increased at certain local times and latitudes in response to magnetospheric activity. These temporal changes in ionospheric conductivity greatly alter the coupling constants between the ionosphere and magnetosphere and are communicated to the magnetosphere by Alfven waves and field-aligned electrical currents to create a feedback loop. The available theoretical models describing this coupled system are complex and frequently differ from one another regarding the magnitude of the effect of the ionosphere on magnetospheric dynamics. For example, some models indicate that the feedback involving rapid increases in ionospheric conductivity and magnetospheric plasma circulation is a necessary condition to generate the explosive release of energy which takes place in the tail during the early stages of substorms. To fill these gaps in our knowledge of magnetospheric dynamics as a function of the electrical conductivity of the region in which the magnetospheric field lines rooted are rooted, we are very fortunate to have the planet Mercury. It has an intrinsic magnetic field but no ionosphere. Furthermore, the small but very valuable data set returned by Mariner 10 s three fly-bys strongly suggests that this planet exhibits terrestrialstyle substorm activity and that it is a very efficient 75

76 accelerator of charged particles. A recent winner in the Discovery program competitive selection process was a Mercury orbiter mission named MESSENGER. This mission will explore the planet Mercury and its magnetosphere with special emphasis on magnetosphere dynamics in the absence of an ionosphere. What Effect Do Rapid Planetary Rotation and Large Internal Sources of Plasma Have on Magnetospheric Dynamics? The outer planets, like Earth, possess large intrinsic magnetic fields and upper atmospheres but have rapid rotation rates and, in some cases, natural satellites which are strong plasma sources. The most extreme example is Jupiter, where the dynamics of the magnetosphere is dominated by the effects of planetary rotation and the torus of neutral gas and plasma emanating from Io. The result is an immense magnetosphere containing extremely high-energy and highintensity radiation belts that are a major source of radio emissions. At the Earth, the magnetosphere is a major energy and momentum source for the ionosphere and upper atmosphere; however, the opposite is true at Jupiter. Much of the magnetosphere is dragged into near corotation with the planet and its ionosphere as a result of upward energy and momentum transport along magnetic field lines by Alfven waves and field-aligned currents. Much of this net outward flux of energy goes into the acceleration and heating of newly created ions derived from neutral gas originating from Io. In this case, measurements from a Jupiter Polar Orbiter and an Io Electrodynamics mission are required to fill the gaps in our understanding of how planetary rotation-dominated magnetospheres operate and couple to their ionospheres, especially in the presence of mass from natural satellite plasma sources such as Io. Recent results indicate that Jupiter has energetic particle injection events and auroral zone emissions resembling those produced by magnetospheric substorms at the Earth; this strengthens the case for the benefits to be derived from comparative studies of Earth, Jupiter, and Io. 76

77 How Do the Plasma Environments and Upper Atmospheres of Planets with Little or No Intrinsic Magnetic Field Respond to Solar Variability? Venus and Mars have atmospheres and terrestrial-type ionospheres but little or no intrinsic magnetic field. The observations returned by previous survey missions to both of these planets indicate that a very complicated interaction with the solar wind ensues. The draping of interplanetary magnetic field lines about their dayside ionospheres results in the buildup of magnetic barriers which, to some extent, mimic the intrinsic field magnetospheres of the other planets including the formation of long magnetic tails. However, these induced magnetospheres have only modest ability to shield the upper atmospheres of these planets from solar wind plasma and solar energetic particles. In addition, they do not appear to have the ability to store large amounts of solar windderived energy in the tail magnetic fields for later release as magnetic storms and substorms. Finally, the more extensive measurements available on the interaction of Venus with the solar wind have revealed strong solar cycle effects with large changes in the extent of the interaction region and the rates at which volatiles from the upper atmosphere are scavenged. The Campaign 4 Roadmap includes the Mars and Venus Aeronomy Probes. They will provide definitive information on the evolution of the upper atmospheres of these bodies in response to solar variability and the nature of the coupling processes in the absence of an intrinsic magnetic field. How Does the Planetary Magnetic Dipole Tilt Angle Affect the Response of the Planetary Magnetospheres to Solar Variability? It has been well established that the relative orientation between the IMF and the magnetic field intrinsic to a given planet is usually the single most important factor regulating the transfer of energy from the solar wind into the magnetosphere. This comes about because of the strong dependence of the local rate of reconnection between these two classes of field lines on their relative orientations. There are competing theories that make somewhat disparate predictions that are difficult to resolve over the limited range of angles typically observed at the Earth. 77

78 In addition, the poles in the planetary magnetic fields, of which there are usually two because of the dominance of the dipole component of the planetary magnetic field, function to some extent as holes in the magnetic shields of these planets. At high altitudes the two magnetic poles widen to become the cusps of the magnetosphere, which resemble opposing magnetic funnels emanating from the sunward edges of the north and south auroral ovals. These cusps funnel solar wind plasma and some more energetic particle species down to the upper atmosphere. Overall, the Earth s magnetosphere provides only limited opportunities for gathering the measurements which are necessary to fill the many gaps in our knowledge of the effects of the direction of the planetary dipole magnetic field relative to the IMF and the solar wind velocity vector. However, the Solar System has one planet that is ideal for such purposes, and that is Neptune. The reason is that Neptune, unlike any other planet, has a rotation axis that is largely normal to the plane of the ecliptic and a dipolar magnetic field that makes a large angle to rotation axis. Hence, during the course of a single planetary rotation, nearly the full range of angular combinations is achieved between the solar wind, the IMF, and the planetary magnetic field. For this reason, particles and fields measurements from a Neptune orbiter are an essential element of Campaign 4. Because the Jupiter Polar Orbiter is focused on the magnetosphere-ionosphere interaction, a critical component of the geospace response, we have recommended this as the highest-priority planetary mission. This is followed by the Mars Aeronomy Probe, because understanding the evolution of the atmosphere in an environment with little or no magnetic field will clarify the role our own magnetic field played in evolving our life-sustaining atmosphere. Because the planetary environments are unique, the order in which these missions are executed is not critical. The Comparative Planetary Environments campaign is key to understanding the origin and evolution of planetary systems, both around the Sun and around other stars. In addition, it is critical to answering questions about the origins and evolution of planetary and satellite magnetic fields, the effects of surfaceplasma interactions, and the formation and evolution of planetary atmospheres. These answers will ultimately help us understand how planetary environments lead to the development and sustenance of life. 78

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80 QUEST III: HOW DO THE SUN AND GALAXY INTERACT? Overview Sending a spacecraft beyond the heliopause to nearby interstellar space ranks as one of the last great frontiers in space exploration and one of the grand scientific enterprises of the next century. The expanding solar atmosphere - the solar wind - forms a bubble called the heliosphere that shields the Solar System from the plasma, magnetic fields, and most of the cosmic rays and dust that make up our local galactic neighborhood. To explore this remote region and understand how the interstellar medium interacts with the Solar System, we must send a spacecraft through the surface of this bubble and directly sample the galactic environment beyond. Our Sun and its heliosphere is one of many stellar systems with similar astrospheres, but it is the only one that we can examine directly. The primary goals of Quest III are as follows: To determine the nature of the boundary regions separating the heliosphere from the local interstellar medium To directly sample the properties of the interstellar medium as an initial step in exploring the nearby Galaxy This highly focused quest requires a single campaign: Campaign 5: Understand the heliospheric boundary and the nearby galactic environment As described below, this Campaign provides a Roadmap for the exploration of the boundaries of the heliosphere and initiation of the era of exploring the space between the stars. 80

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82 CAMPAIGN 5 ROADMAP Understand the Heliospheric Boundary and Nearby Galactic Environment Explore Local Galactic Neighborhoods Determine the Properties and Composition of Interstellar Medium Explore Heliospheric Boundaries, Structure, and Dynamics Oort Cloud 9057/007B 15 Interstellar Probe Heliosphere Imager and Galactic Gas Sampler Outer Heliosphere Radio Imager Interstellar Trailblazer 82

83 CAMPAIGN 5 MISSION Outer Heliosphere Radio Mapper: How does the heliosphere respond to solar variations? Interstellar Probe: What are the nature of the interstellar medium and the boundaries of the heliosphere? Interstellar Trailblazer: Is there structure in the local interstellar medium? Heliosphere Imager and Galactic Gas Sampler: What is the 3-D structure of the heliosphere and the composition of neutral interstellar gas? 9057/007B 21 83

84 Campaign 5: Understand the Heliospheric Boundary and Nearby Galactic Environment Introduction As the solar wind flows out through the Solar System, it pushes against the plasma and fields of the interstellar medium, forming a large bubble called the heliosphere. On the inside of this bubble is the interplanetary medium, within which spacecraft have now ventured from ~0.3 AU to beyond 75 AU, including passage over the poles of the Sun. On the outside of this bubble is a new, unexplored region - the interstellar medium (ISM) - about which we know very little. Although high-energy cosmic rays, neutral interstellar gas, and large interstellar dust grains are able to enter the heliosphere, the Solar System is effectively shielded from the interstellar plasma, magnetic fields, low-energy cosmic rays, and small dust grains that make up the bulk of the energy density of the local ISM. There are three steps in the Campaign 5 roadmap: Exploring the Structure and Dynamics of the Heliospheric Boundaries: The actual size of the heliosphere is determined by a balance of pressure between the solar wind and the largely unknown contributions of pressure from the interstellar magnetic field, interstellar gas, and low-energy cosmic rays. It is generally believed that the solar wind suddenly undergoes a shock transition (the solar wind termination shock) once it can no longer hold off the pressure of the ISM. Although our knowledge of the termination shock is only indirect, there is a general consensus that it is presently located between ~80 and ~100 AU from the Sun, in which case the heliopause (the boundary between solar wind and interstellar plasmas) is expected to be somewhere between ~120 and ~150 AU. It is anticipated that Voyager-1 will cross the termination shock within the next few years, thereby establishing the scale size of the heliosphere. The boundaries of the heliosphere provide an accessible laboratory for studying the interaction of a star 84

85 with its environment. As the solar wind pressure varies over the solar cycle, the termination shock and heliopause are expected to move in and out by 20 to 30 AU. The heliosphere also responds on shorter timescales to large interplanetary shocks created by violent outbursts of solar activity. The Voyagers have discovered intense radio emission from the direction of the nose of the heliosphere, occurring approximately a year after the largest episodes of solar activity. Determining the Properties and Composition of the Interstellar Medium: The nearby interstellar medium includes species that are predominantly ionized (e.g., C, S, and Si), those that are predominantly neutral (e.g., H, He, N, O, Ne, and A), and others that are mainly locked up in grains (e.g., Al, Ca, and Fe). The neutral component of the gas is able to penetrate the heliosphere. Some of these atoms become ionized to become "pickup ions," which are picked up by the solar wind and convected into the outer heliosphere, where some of them are accelerated to energies as high as a GeV (presumably at the termination shock) to become the "anomalous cosmic rays." Although pickup ions and anomalous cosmic rays provide information about those few species that are predominantly neutral in the ISM, we presently have no information about the elemental and isotopic composition of elements that are mostly ionized, nor do we know to what extent refractory species like Si, Ca, and Fe have condensed into grains. In addition, we have almost no knowledge of the direction and strength of the interstellar magnetic field. Exploring the Local Galactic Neighborhood: As the Sun journeys around the Galaxy, it encounters a wide range of interstellar conditions. At present, the Solar System is apparently located at the border of a great void in nearby interstellar matter known as the local bubble, where it is immersed in a low-density cloud. However, very little is known about the scale size of any structure in the immediate local neighborhood. Technology is now finally within reach to undertake a historic journey through the boundaries of the heliosphere into the unexplored interstellar medium, thereby making it possible to address longstanding questions like those below. 85

86 What Is the Nature of the Boundaries of the Heliosphere and How Do They Respond to Solar Variations? Studies of global heliospheric structure and dynamics are best carried out by a combination of in situ and remote-sensing observations. Although the Voyagers will make key discoveries about the nature of the heliosphere, a new mission will be required to carry out detailed studies of the heliospheric boundaries and to begin the exploration of the nearby ISM; this mission (Interstellar Probe) will carry modern instrumentation specifically designed for that purpose. Interstellar Probe would study shock acceleration processes in situ from kev to GeV energies and determine the shock structure in detail (is the termination a gasdynamic or a cosmic-ray-mediated shock?). Interstellar Probe would also explore the "hydrogen wall" beyond the heliopause that results from charge exchange between ionized and neutral hydrogen, investigate the origin of the mysterious radio bursts from this direction, and determine whether the heliosphere creates a bow-shock in the ISM. Energetic neutral atoms (ENAs), which result from the charge exchange of accelerated anomalous cosmic rays with neutral interstellar hydrogen, were recently detected, thereby demonstrating a promising approach to studying the boundaries of the heliosphere remotely. Charge exchange processes involving shockheated solar wind will produce somewhat lowerenergy ENAs which carry information about the nature of the termination shock. It is also possible to image the size, shape, and dynamics of the heliosphere with EUV radiation resonantly scattered from singly charged interstellar oxygen ions as they are diverted around the heliopause. What Are the Properties of the Local Interstellar Medium? Once beyond the heliopause, Interstellar Probe would begin exploring the local galactic environment, addressing key questions about the plasma, neutral atoms, magnetic field, and energetic-particle populations that combine to control the size of the heliosphere. What are the direction, intensity, and turbulence spectrum of the interstellar magnetic field? What are the properties of the interstellar gas and the spectrum of low-energy cosmic rays that are excluded from the heliosphere? With modern instrumentation, it is also possible to determine the elemental and iso- 86

87 topic composition of interstellar plasma, which is of key interest to galactic chemical evolution studies, and the composition of interstellar dust grains that are excluded from the heliosphere. What Effect Does the Galaxy Have on the Solar System? A pressure balance between the solar wind and the ISM determines the present size of the heliosphere. Interstellar densities ranging from 10-5 to 10 5 are seen in our galactic neighborhood. MHD simulations indicate that if the local density increased to that of a typical diffuse cloud (~10 cm -3 ), the dimensions of the heliosphere would shrink by nearly an order of magnitude, which would undoubtedly have significant effects on the interplanetary environment at 1 AU. By targeting an Interstellar Probe in the direction upstream of the Sun s motion, we can explore the future environment of the Solar System over the coming decades. complemented by remote-sensing images from within the heliosphere (Heliospheric Imager & Galactic Gas Sampler and Outer Heliosphere Radio Imager), is to determine the structure and dynamics of the global heliosphere. The second objective is to obtain in situ measurements of the composition of interstellar matter, including the neutral gas that penetrates into the inner heliosphere; the plasma, dust, and low-energy particle populations in the local ISM; and organic matter in the outer Solar System and local ISM. The third, longer-term objective is to explore the nature and properties of the local ISM to great distances in order to observe the scale size of structure and variations in the local galactic environment, including, perhaps, the edge of our local cloud (Interstellar Trailblazer). These exploratory studies will undoubtedly lead to a wide range of other discoveries about the outer Solar System, the boundaries of the heliosphere, and the nature of the ISM, by analogy to the era of discovery that occurred when spacecraft first ventured outside the magnetosphere into interplanetary space. In summary, this Campaign has three main objectives that are expected to lead to major advances in our knowledge. The first objective, to be addressed by a combination of in situ studies (Interstellar Probe) 87

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90 EFFECTS ON LIFE & SOCIETY From 9057_004A 9057/007B 9057/007A 9 9

91 QUEST IV: HOW DOES SOLAR VARIABILITY AFFECT LIFE AND SOCIETY? Overview The Sun provides the energy which makes life possible here on Earth; however, it also immerses the whole of the Solar System in streams of electrified plasma and radiation that can be harmful to life. The fundamental questions to be addressed by Quest IV are as folows: What are the impacts of space weather? How can space weather hazards be predicted? How does the changing Sun affect planetary climates? How have (living) conditions evolved in the Solar System as a result of evolution of the Sun? To exist and operate in this environment, we need to: 1. Understand the dynamics of geospace and be able to predict its effects. The attainment of this goal is key to our ability to a) build and operate reliable, cost-effective spacebased technological systems b) ensure the safe exploration of space as we start to travel beyond the protective magnetic and atmospheric shields of the Earth. 2. Understand the long-term changes in the Sun and their potential effects on climate (timescales of decades to millennia). Whether the global warming trend recently measured is dominated by anthropogenic effects or has a significant solar component is not yet understood. Solving this important problem is the joint charge of SEC and Earth Science programs. 3. Understand the conditions that determine whether life is viable on planets orbiting other stars. There is great interest in finding planets orbiting other stars, but even if we can observe them directly, it is not yet possible to tell if they are conducive to supporting life as we know it. Studying other Sun- 91

92 like stars in the context of the SEC program will give us such knowledge. We believe that understanding and predicting space weather has special urgency. It is critical, as we establish a permanent human presence in geospace and contemplate human exploration of other planets, to understand the space environment and to be able to predict the extreme conditions that we will encounter. Long-Term Goals The Sun-Earth system remains our best model for understanding how life may have evolved elsewhere in the Universe. Solar variations and the solar connections studied here govern the ability of a planet to develop and sustain life (e.g., atmospheric water content is key to understanding how life can evolve; the presence or absence of a magnetic field influences solar wind access to atmospheres). Input to these efforts include, for example, paleoclimatic records such as ice cores and tree rings and the studies of stars and planetary systems at different stages of existence. The Roadmap has identified three missions that pertain to the long-term goals of Quest IV: 1 Sun-Earth Energy Connector (SEEC), which will address the problem of radiative energy transfer from the Sun across the electromagnetic spectrum directly to the terrestrial ITM regions. 2 Global Mesospheric Water Cycle Probe is a first step toward quantifying the effectiveness of water transport from the troposphere through geospace and hence measures the rate of planetaryscale loss of water. 3 Stellar Imager and Seismic Probe (SISP) will look directly at the activity cycles on other stars and compare them to the Sun to see if our star is typical or in some way especially conducive to the creation and evolution of life. These missions will address questions that must be answered to understand the effects of long-term solar variability on planetary atmospheres and climate, as well as the origins and evolution of life on Earth. Answering these fundamental questions will require knowledge accumulated over multiple solar cycles. In addition, Quest IV considers interdisciplinary investigations critical to integrating data from multiple missions. Furthermore, the SEC system level problems require significantly more cross-fertilization 92

93 between and support from Quests I, II, and III and the other NASA science programs. The establishment of specific research environments (e.g., analysis, simulation, and theory programs) to accommodate scientists, as well as mission data flow and model development, is suggested as a crucial component to the existing discipline orientated environment. Such a research environment would also act as catalyst for cooperation between NASA-OSS themes and other government agencies (e.g., NSF, NOAA, DOD, and DOE). Solar Variability, Technology, and Human Space Flight We are embarking on a new era of continuous human presence in space. Astronauts and the space hardware on which they depend are subject to risks from highly variable particle radiation from several sources, as well as other hazards also driven by the Sun. As human exploration extends to other planets, the hazards will change depending on interplanetary space and on the planet's space environment. Campaign 6 will develop the knowledge to make it safer for humans to live in space and the tools to predict the impacts of space weather on our technological systems. As human society relies more on technology, spacebased communications, and navigation, the impacts from the space environment will increase. Groundbased technological systems, such as electric power grids and long-distance pipelines, are also impacted. The space weather effects include, but are not limited to, radiation damage, software and command upsets, communication disruptions and induced currents. Determining the extremes of the space environment and even monitoring and categorizing events will allow engineers to improve satellite and payload designs, develop appropriate technologies, and build more cost effective systems that can withstand space weather impacts. To provide a systems-integration approach to achieving the SEC goals, Campaign 6 is structured differently from the other SEC Campaigns. The approach to accomplish Campaign 6 requires the synergistic combination of SEC missions drawn from the other campaigns plus some campaign-specific missions or missions of opportunity. Interagency cooperation is also critical and is presently being coordinated through the AFSPC/NASA/NRO partnership, the National Security Space Architect s Office, and the National Space Weather Program. 93

94 LIVING WITH A STAR Solar Polar Orbiter North Pole Sitter L 4 Solar Sentinel Solar Dynamics Platform Ionospheric Platforms L 3 Solar Sentinel L 1 Geostorm Radiation Belt Mappers L 2 Night-Side Geospace Imaging L 5 Solar Sentinel South Pole Sitter A distributed network of spacecraft will provide continuous observations of Sun-Earth system. 9057/007B 25

95 Campaign 6: Space Weather Introduction The goal of the SEC Space Weather campaign is to provide the scientific context and understanding that will lead to a capability to accurately predict solar activity and its effect on the space environment. Initially the main application of such knowledge is to geospace, but as mankind starts to explore the Solar System, the requirement will be extended to interplanetary space and other planets, specifically Mars. Campaign 6 seeks solutions to a broad class of problems associated with the dynamic effects of solar, interplanetary, magnetospheric, and upper-atmospheric phenomena that have an impact on humans. In particular, it is focused on the impact of these phenomena on modern technology and on the safety of humans as they travel beyond the Earth. To achieve this goal, we have to make global measurements of solar activity and output into the heliosphere, contiguous measurements of the interplanetary space between the Earth and the Sun, global measurements of geospace and the upper layers of the Earth s atmosphere. These measurements have to be taken in a coordinated fashion over an extended period, at least a solar cycle. The Space Weather Network (SWN) would provide these critical measurements from a series of specific vantage points distributed around the Sun and Earth. The results would then be brought together and analyzed in a coordinated fashion to discover the essential knowledge, to provide warning of specific events that will affect our space assets, and to relieve effects on our increasingly technology-reliant society. The SWN concept developed for Campaign 6 draws heavily upon missions developed by other Quests, although their implementation may be modified if they are applied solely to space weather investigations. The ultimate output of this campaign would be the obser- 95

96 vational specifications for an operational space weather system and the models to apply to the data to produce accurate and reliable forecasts over the timescales required to be beneficial to humanity s space endeavors. A Global View of the Sun The first part of SWN program is to obtain the required measurements of the Sun, the driver of the system. The output of particles and fields in the form of the solar wind and radiation across the whole electromagnetic spectrum can affect our environment in many different and specific ways. It is vital to observe the entire Sun, including the far side, which is not visible from Earth. For mediumterm (days) prediction, it is important to know whether an active region that is about to rotate onto the solar disk has grown or decayed while on the far side of the Sun. It is then possible to better assess its likelihood of producing a major flare or coronal mass ejection (CME). Events such as CMEs on the far side of the Sun can affect geospace weather. Also, events on the far side of the Sun can affect other planets that we are studying such as Mars, and we would be unaware of what caused any perturbations observed. For longer-term prediction (weeks), it is important to be able to see how the subsurface magnetic field is evolving before it erupts into new sunspot groups. This is now possible due to the recent developments in helioseismology. Predictions of the next solar cycle (years) require continuous observations of the Sun s polar regions, where the reversal of the global dipole field first becomes evident. Also, precise measurements of the solar irradiance as a function of wavelength is required to determine the solar input to the Earth and planets. Similarly, measurements of the amount of energy lost by the Earth across the spectrum are equally vital. The specific measurements we need to obtain a highfidelity view of the Sun are as follows: Remote sensing of the internal dynamics of the Sun from a geosynchronous vantage point, which provides a capability of high data rate. This mission could be combined with the irradiance measurements of the Sun and Earth (i.e., an extended version of SONAR). 96

97 Remote sensing of solar activity from key vantage points around the ecliptic (i.e., a next-generation STEREO mission including a Solar Farside Observer component). Remote sensing of the solar polar regions (i.e., a version of the Solar Polar Imager mission) Such a group of Sentinel missions would produce the data we require individually, but operating together they would provide us with a powerful predictive tool for space weather. Assuming that they were designed in a coordinated way, they could also make true tomographic (3-D) images of solar events. While such measurements would characterize solar activity on all the required timescales in a coordinated fashion for the first time, we also need to know the effects that our ever-changing Sun has on the inner heliosphere and understand how those perturbations propagate out from the Sun towards the Earth. Transit of the Solar Wind The second stage of the SWN program is to see how solar disturbances propagate towards the Earth. Their passage through the interplanetary medium dominated by the solar wind changes their nature and effect on the planets they encounter. It is vital that we use both in situ and remote-sensing techniques to sample their progress and evolution. Such measurements also give a short-term alert (hours) to the approach of a solar disturbance, such as a CME. The required measurements consist typically of particle, field, and plasma wave instruments that characterize the composition, velocity, and density of the solar wind as well as the strength and direction of the embedded magnetic field. This vector information determines the geoeffectiveness of a given event. The CME mass will be tracked by remote-sensing techniques (e.g., STEREO). Such measurements should be made from the solar Sentinel missions discussed above. A small group of such sensors is needed in the solar wind stream that will impact the Earth. The L1 point has been the ideal location for such a group of instruments to character- 97

98 ize the global as well as the local properties of the solar wind disturbances that may cause strong geomagnetic storms. The Global Properties of Geospace The previous two parts of the SWN program provide warning and characterization of the events as they approach the Earth. The last and most complex part of the puzzle consists of determining how a given event will impact geospace. To do this, we must understand how the energy leaks through our magnetospheric shield, and how it is redistributed and dissipated. These are global phenomena that are often controlled by local microphysical processes. Hence, we have to use a combination of remote sensing to sample a broad range of the macroscale phenomena and widely distributed in situ measurements similar to those used in the heliosphere to understand the microscale processes. The measurements we need to make are Remote sensing of the Earth s polar regions and night-side to see auroral development (i.e., an extension of the Pole Sitter concept to include both poles and L2). In situ plasma and field measurements of the Earth s radiation belts to see how they are affected by such events (i.e., IMC). A combination of remote sensing and in situ sampling of the Earth's upper atmospheric layers to see how the effects propagate down and affect the Earth itself (i.e., a combination of GEC and ITM waves). A Coordinated Approach This exciting program would be the first step in creating a comprehensive space weather forecasting capability. However, it also requires that the data be brought together in a systematic and coordinated fashion so we can study the Sun-Earth connection as a system. A new breed of interdisciplinary scientist must be encouraged to approach the space weather problem in much the same way as we solved the problem of inaccurate short-term meteorological forecasts 25 years ago. 98

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100 TECHNOLOGY REQUIREMENTS Introduction Implementation of the SEC strategic plan requires a prudent and timely investment in four broad technology areas: Advanced Propulsion (e.g., solar sails) Spacecraft Technology (e.g., microsats, highdata-rate communications, autonomous spacecraft, and robust long-lived spacecraft) Scientific Instrumentation (e.g., advanced imaging and miniaturized in situ instruments) Information Architecture (e.g., data synthesis, modeling, and visualization). All of these technology areas are driven by the scientific objectives of carrying out new measurements in new places to make new discoveries, to forward our knowledge and understanding of the Sun and Earth as a connected system. These measurements are derived from all of the SEC Roadmap missions addressed in the Campaigns in support of the four Quests of the SEC theme. Advanced Propulsion There are three broad areas to be considered for advanced propulsion technology: 1. In the near term, missions to probe further down into the upper atmosphere require propulsion systems of low total mass operating at high thrust, enabling dipping into the atmosphere to depths at which drag is significant. To provide the required measurements from multiple platforms, less fuel mass per spacecraft than is currently feasible is required. 2. In the medium-term, miniaturized systems and base-deployment development are required to determine feasible means of deploying tens of satellites or more into orbits where constellations of satellites are needed, flying in formation, for multipoint measurements. 3. In the long term, many SEC missions are enabled only with advanced propulsion technologies that 100

101 can deliver velocity changes (δv) of greater than ~50 km/s in a cost-effective, high-performance system. Such performance is not possible with chemical propulsion. Trade studies suggest that Solar Electric Propulsion (SEP) system performance is significantly reduced at δv 15 km/s due to the mass and cost of (projected) solar arrays. Only Solar Sail and Nuclear Propulsion appear to offer the promise of providing the required performance, and only sails appear to offer this performance for overall low system mass. To implement the identified missions, near-term technology development, including technology demonstration and validation missions, is required to provide timely implementation of a variety of heliospheric and solar missions, in particular the Interstellar Probe and Solar Polar Imager. This development can also favorably impact various missions in the Solar System Exploration theme. Solar Sails Recent technology advances have given new promise to the application of solar sail propulsion. Of the more than 20 SEC Roadmap missions, nine are considered enabled by sail technology. Three metrics help define solar sail technology advances: sail size areal density thermal characteristics. Solar sail size (radius) and areal density (sail mass to sail area ratio) affect structure, deployment, packaging, material, and control technologies. The thermal characteristics affect the closest approach of the spacecraft to the Sun, affecting sail material, structure, control, and navigation technologies. Examples of mission concepts for the nine SEC Roadmap sailenabled missions illustrate the breadth of application of this technology to SEC science goals (see following table). 101

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103 Preliminary trade studies of alternative propulsion have been conducted for most of the above missions. Solar sail technology has been found to be enabling because of the enormous velocity change (δv) required to meet mission requirements (e.g., reasonable flight times to measurement locations). The attraction of solar sail propulsion is that it does not require any propellant. Payloads can be delivered to previously inaccessible regions of space in reasonable flight times. Access to the entire heliosphere and beyond is available with solar sail technology. Four regions of space that can be reached via solar sail are of particular interest to SEC science investigators: Sail technology advances are occurring in a number of parallel areas, e.g., in materials, structures, deployment, packaging, control, and navigation technologies. The SEC Roadmap requires that solar sail technology evolve in these technology areas and enables missions as the integrated set of solar sail technologies is validated. The solar sail flight validation roadmap illustrates a sail technology development strategy that combines science and technology demonstration missions. Far-distant targets (e.g., outer planets, galactic interface, and interstellar medium) High solar latitudes from highly inclined orbits (e.g., solar polar exploration and solar storm evolution) Non-Keplerian orbits (e.g., hovering observational orbits) Inner planets (low-cost delivery, frequent access) 103

104 SOLAR SAIL FLIGHT VALIDATION ROADMAP Interstellar Probe Mission 200 m Deployment Demo 50 m Advanced Validation 100 m 1 g/m µm Films 200 AU in <15 years Russian Znamya 1 10 m (radius) g/m 2 (?) 5 µm Films Zero-g Deployment GeoStorm 16 g/m g/m 2 1 µm Films Zero-g Deployment Stability & Control 1-2 g/m µm High Tech Films Zero-g Deployment Stability Validation Control Experiment Navigation Science Gathering Solar Polar Imager-SEC Particle Acceleration Solar Orbiter-SEC Titan Explorer-SSE Saturn Ring Rendezvous-SSE Fast Outer Planet Missions-SEC/SSE Space Weather Sentinel (Sub L1)-SEC High-Inclination Comet Sample Returns-SSE Interstellar Probe (above) SEC Pluto Orbiter-SSE Outer Planet Satellite Sample Returns-SSE Most Deep Space Missions 9057/007B 32

105 Spacecraft Technology Advances in spacecraft design and performance are needed to achieve many of the SEC scientific goals cost effectively. Significant advances in SEC science require multiple measurements from many satellites flying in a loose formation that is time-synchronized. To implement these measurements with affordable launch vehicles, the unit spacecraft mass, power, and cost must be significantly reduced. These reductions require miniaturizing all spacecraft subsystems as well as relevant scientific instrumentation while maintaining science measurement requirements. These resource reductions require timely infusion of new technology, primarily in specialized highperformance electronics that are resistant to radiation. Microsats (100 kg > mass S/C > 10 kg) will be enhanced with these developments, while nanosats (10 kg > mass S/C > 1 kg) are enabled by such technology. Picosats, envisioned in the previous Roadmap as spacecraft with masses less than 1 kg, will probably require several paradigm shifts on a variety of levels, which will become clear only with a phased development of nanosat technologies, including demonstration spaceflight validation missions. The latter are required to phase out deployment, orbit injection and formation maintenance, and mission operations and data management. Nanosat technology is also required to match up with the low-thrust characteristics for solar sail propulsion, as indicated in long-term missions such as Inner Heliospheric Constellation. Other spacecraft technologies that are required include 1. High-data-rate communications (burst mode from near-earth constellations as well as continuous imaging from deep-space) 2. Spacecraft autonomy, in order to manage missions in a cost-efficient manner 105

106 MICROSATS AND NANOSATS Mission Number of Spacecraft Mass (kg) Begin Phase C/D Orbit Technology Challenges Cluster II (ESA) (launch) 4 x 20 Re Magnetospheric Multiscale Apogees from 12 to 127 Re Variable cluster Near Geospace Electrodynamic Connections x 2000 km Dipping satellites Mag Constellation Re Dispenser ship, miniaturization Mid Inner Mag Constellation Re Dispenser ship, radiation tolerance Dayside Boundary Constellation Re Multiple inclination Solar Flotilla Heliocentric (perihelion ~0.2 AU), various inclinations Solar sails, deep-space microsats, near-solar communications Far Inner Heliospheric Heliocentric (perihelion ~0.2 AU), various inclinations Solar sails, deep-space microsats, near-solar communications Outer Heliospheric Radio Imager 16 (+ 1 mother ship) AU Interferometric RF measurements among 16 spacecraft; ~autonomous formation flying (~1000-km spacing) in deep space 9057/007B 29

107 3. Robust, long-lived (sometimes called immortal ) spacecraft to enable long-design life missions, as well as missions into harsh environments such as near the Sun, deep into the upper atmosphere of the Earth, and through multiple passes of terrestrial and planetary radiation belts. The associated technology developments are required for both single-spacecraft and constellation missions. Microsats and Nanosats In the near term, multispacecraft missions will generally involve a handful of highly capable spacecraft that will fly in loose formation. Variation of the spacing of the spacecraft will enable resolution of unresolved issues of the magnetosphere (MMS) and ITM (GEC). These missions will consist of a handful of medium-size spacecraft (hundreds of kilograms), often with substantial mass devoted to propellant to enable the variation of the formation spacing and orbital location needed to achieve the science objectives. While there will certainly be challenges in the building and operation of constellations of four or more spacecraft, the technology needed is primarily enhancing and thus represents an evolution of technology used on past SEC missions. The next level of understanding of geospace will require simultaneous in situ measurements that span the entire system under study. This suggests the need for 100 spacecraft to study the spatial-temporal dynamics of the magnetosphere (Magnetotail Constellation [MagCon]). Although constellations of spacecraft are now commonplace for telecommunications and global positioning, MagCon present at least an order-ofmagnitude increase in the number of spacecraft for a space science mission. There will be many technical challenges in making the leap from MMS (4 spacecraft) to MagCon (~100). Dispensing 100 spacecraft into orbits where the science return of their measurements is maximized will probably require a low-mass dispenser spacecraft or propulsion-capable spacecraft. Mechanisms for dispensing nanosats will be needed. 107

108 LARGER SCALE SEC MISSIONS Mission Type Mission Objective Frontier Probe Discovery Program Outer Planets Program Interstellar Probe Solar Polar Imager MESSENGER Solar Probe Explore the interaction of the heliosphere with the local interstellar medium Determine the nature of the solar polar fields where the solar wind and activity cycle seem to originate Determine the response of an Earth-like magnetosphere to solar variability in the absence of an ionosphere Discover the coronal heating mechanism(s) and the acceleration process for the solar wind 9057/007B 34

109 The number of discrete spacecraft and available launch vehicles suggests the need for nanosats outfitted with a few key instruments, for example, a plasma analyzer, an energetic-particle spectrometer, and a magnetometer. One instrument alone on previous SEC spacecraft may have weighed 10 Kg or more. Instruments compatible with nanosats will have to be low-mass, low-volume, and low-power in nature. They will have to be inexpensive and readily manufactured in numbers up to 100. SEC missions will probably meet their low-mass requirements by use of structures that serve multiple functions such as thermal and power. Multifunctional structures that incorporate the spacecraft battery or thermal control devices will enable significant mass reductions. Systems for spacecraft power, energy storage, attitude and thermal control will have to be developed to meet nanosat cost and manufacturing constraints. Constellations exploring the magnetosphere will be constantly flying through the radiation belts. Spacecraft electronics will have to be radiation-tolerant, as the number of spacecraft will necessitate highly autonomous spacecraft able to routinely operate independently of ground operators. Communication limits will probably require smart management of the downlink bandwidth and adaptive data management. Nanosat autonomy will thus be needed not only for system health, maintenance, and fault correction but also for adaptive control of instruments. Using existing architectures, data flowing from a 100- spacecraft constellation will be cumbersome and unwieldy. New synthesis methods will be needed for the near-real-time incorporation of data into models and visualization tools. The SEC Roadmap suggests that in the long-term, substantial qualitative improvements in the capability of nano- and microsats will be needed. Dipping (temporary excursions into the high-atmospheric-drag region at <150 km) microsats will study the ITM regions (e.g., Tropical ITM Coupler). These microsats will require highly aerodynamic, low-drag structures and booms, as well as mass-efficient propulsion systems to enable sustained dipping campaigns into the ITM. Solar Flotilla will require deep-space flying microsats, integrated with solar sail-equipped dispensing craft. 109

110 These microsats will also have to cope with the severe thermal and radiation environment encountered in near-solar orbits (~0.2 AU). Communications with microsats in deep space will be complicated by the proximity of the Sun, a problem that may require interspacecraft communications or even a near-solar relay network. The addition of solar imaging (envisioned for Inner Heliospheric Constellation) will require three-axis-stabilized microsats. Although the proximity to the Sun will produce some gains in sensitivity and resolution, lightweight optics for Sunobserving microsats will be needed. High-Data-Rate Communications The new SEC Roadmap missions will pose several challenges to the existing state of the art in spacecraft communications. Quest III spacecraft exploring interstellar space will require communication links with Earth from distances of many hundreds or even thousands of AU. Communication with near-solar spacecraft is complicated by solar RF emission and frequent conjunction with the Sun. Lastly, constellations in the geospace environment will require communications compatible with nanosats. Interstellar Probe is slated to reach 200 AU distance from Earth in less than 15 years of flight time, 2.5 times the distance from Earth of the Voyager 1 spacecraft in January Its suite of instruments will have significantly greater downlink requirements than the Voyager Interstellar Mission (~160 bps) spacecraft. Ka-Band, or possibly optical communications is expected to replace X-Band as the preferred method of communicating with spacecraft in interstellar space. Communication with near-solar spacecraft is problematic and subject to frequent interruption due to solar conjunction. Future SEC solar missions such as PASO, Solar Polar Imager, Solar Farside Observer, Solar Flotilla, and Inner Heliospheric Constellation may provide critical support to interplanetary manned missions with real-time solar monitoring. Substantial on-board storage, as well as autonomous, on-board processing will be needed for such missions. Innovations that involve interspacecraft relay networks will be required. Microsats will pose a substantial challenge for communications technology. Geospace constellations will have to balance downlink data with nanosat power, mass, and volume con- 110

111 straints. A miniature, low-voltage, high-efficiency, X- Band transmitter will have to be developed for use on high-perigee nanosats. General communication technology needs are Autonomous on-board processing Onboard data storage Large, lightweight deployable antennae Lightweight, high-density power sources Deep-space/near-solar communications Optical communications Ground stations (e.g., improved antennae, receivers, and processors) Autonomous Spacecraft In August 1999, there were 15 operating spacecraft in the SEC Theme. By 2011, it is anticipated that an additional 120 discrete spacecraft will have been launched. Constellation missions in the SEC Roadmap conservatively suggest an increase of 10 spacecraft/year after Given that operations costs as a fraction of mission costs have fallen and are expected to continue to decline with improved technology, future SEC missions will have to have much more spacecraft autonomy. Constellation spacecraft in very-high-perigee orbits will be out of communications range for nearly a week at a time and will fly through radiation belts known to cause upsets. Faults that require intervention from ground controllers could result in loss of data and in degradation of a constellation s science return. Spacecraft in deep space (near-solar or interstellar space) will have to manage science return given limits of bandwidth. Long-lifetime missions will require autonomous management of degrading subsystems. Autonomous spacecraft that employ technologies like onboard software agents and automated reasoning are necessary to detect, diagnose, and recover from faults. These must also interact intelligently with the payload to allow autonomous operation and management of the mission s science return. Testing and flight validation of autonomous agents will be challenging but necessary. Routine autonomous operation, data col- 111

112 lection, and data synthesis are required to make mission operations manageable and cost-effective. Robust, Long-Lived Spacecraft SEC spacecraft will go where no other man-made objects have gone, and they will return groundbreaking scientific data. In the future, they will pass blazingly close to the Sun (Solar Probe), explore the farthest reaches of the heliosphere, and even probe interstellar space. They will dip into the upper atmosphere of the Earth and other planets and will measure the trapped radiation of the Van Allen belts. To ensure successful missions, they will have to withstand these severe environments and, in some instances, have mission lifetimes measured in decades. All of this will be achieved at a cost equal to or less than that of previous comparable NASA missions. In some instances, the substantial reductions in mission cost are vital enabling factors. While all SEC missions will benefit from anticipated advances in low-cost, high-performance avionics, the impact of the radiation environment will constrain the incorporation of new information technology. Seven missions in the SEC Roadmap anticipate flying through the Earth s (or Jovian) radiation belts. Radtolerant avionics systems will be required for many of these missions (e.g., Jupiter Polar Orbiter and Io Electrodynamics). Thermal management for the near-solar environment will be an issue since eight missions will pass within 0.5 AU of the Sun. Some of these will be for brief perihelion encounters, but others will orbit within 0.2 AU of the Sun and thus will require high-temperature solar arrays. Thermal control structures, materials, capillary-pumped loops, diamond substrates, and advanced packaging will be needed for nanosats and microsats. Measurement of the ITM will require spacecraft capable of sustained dipping into the upper atmosphere. These spacecraft will require mass-efficient, aerodynamic structures and booms. They will also require advanced coatings to withstand atomic oxygen erosion and the thermal environment induced by atmospheric heating. Advances in propulsion are urgently needed, since this is a life-limiting factor for all dipping spacecraft. Long-lifetime cryocoolers will enable long-duration study of the mesosphere in the infrared and thus contribute to an understanding of the 112

113 planet s water cycle (knowledge with possibly profound implications for life on Earth and Mars). Quest III missions will pose significant challenges. They must be especially long-lived spacecraft; Interstellar Probe has a minimum lifetime of 15 years, and so this is a minimum requirement for spacecraft probing interstellar space. New missions must achieve this with quality approaches and programs that are in keeping with present-day financial realities. They will be designed to cope with the extreme heat of velocity-boosting perihelion approaches at 0.25 AU and to withstand the cold of interstellar space. Advanced radioisotope power sources (ARPS) will be needed to provide power for 30 years or more and must meet evolving requirements for system safety. Scientific Instrumentation The SEC roadmap requires advanced imaging and miniaturized in situ instrumentation technologies that further divide structurally into electronics, mechanisms, detector heads (including collimators, guiding fields, and stray light rejection), and detectors (including defection physics as well as focal-plane conditions and operational constraints). These structuralelement technologies are all candidates for miniaturization, reduction of mass, power and volume consistent with achieving science goals while enabling deployment on nanosat constellations or microsats with low-thrust solar sails. All identified instrumentation can benefit, in some instances in enabling ways, from miniaturization (to integrated circuit chips and/or bore-die- chip on board mounting) that reduces mass, and more importantly in many cases, required power. Improved performance, in the form of lower mass while maintaining or improving measurement characteristics, tends to be limited by the physics of detectors and detector head structures. These comments apply to the entire spectrum of identified in situ and remote-sensing instrumentation. In a functional sense, technology infusion is required so that the instrumentation, as well as spacecraft subsystems, can enable spacecraft autonomy. The instrumentation must itself be "smart" to be able to deal with knowledge downlink versus data downlink as driven by both communications bandwidth and autonomy. Technology tradeoffs in hardware versus software are required. 113

114 OPTICS TECHNOLOGY New solar science that will be enabled by the development of precision optics for the study of: - Structure and evolution of atmospheric features - Resolution and detection of magnetic activity in other stars - Research on physical processes occurring in the Sun s magnetized atmosphere Existing Capability Future Investigations 9057/007B 27

115 Finally, the development of various advanced instrument components is a required mission enabler for most of the new measurements. Low-mass, lowpower instruments will be realized by such technology investments. These components include backups for many performance requirements that allow for robust exit strategies for some of the more straight toward technology development approaches to miniaturization. Advanced Imaging Instruments Optical remote sensing will require several enhancement technologies: High-spatial-resolution imaging (~0.1 arcsec) Rapid imaging and spectroscopy Energy-resolving detectors Polarization capability The technologies required to obtain our observational goals can be summarized as follows: 1. Optics: The angular resolution as a function of energy for SEC missions is summarized in the Optics Roadmap figure. Hence, large (meter class), lightweight optics are needed to achieve the required resolution and flux levels. Surface quality (figure and mid-frequency errors) must achieve diffraction limited quality. Microroughness must be reduced to improve image contrast (scattered light). High reflectivity must be available from X-rays through the visible range. RAM and HRSOT would greatly benefit from this technology. 2. Detectors: Current detectors generally are CCDs or some other Cartesian devices that have the capability of measuring the number of photons falling on arrays of 1Kx1K to 9Kx9K pixels. The integration times and readout times of these devices are typically on the order of 5 s. A primary desire would be devices capable of 1 s or less time resolution. SONAR, RAM, and HRSOT would benefit most from this technology. Miniaturized In Situ Instruments Addressing the SEC Quests involves a series of measurement strategies that flow from the SEC Campaigns 115

116 require a combination of imaging instruments (photons as well as neutral particles) and in situ instruments for making measurements of particles and fields in the immediate vicinity of the spacecraft. These measurements provide information on both local and remote processes relevant to the Quests. Historically, the term in situ has referred to electric and magnetic fields on the one hand and charged particles on the other. Neutral-atom imagers, a newer technology beginning to provide important new observations, have aspects of each type of instrumentation. Required tasks include the following: 1. Measuring 3-D distribution functions of charged particles, sorted by mass and charge state, up to energies characteristic of the processes being studied (typically up to ~10s of MeV and sometimes higher), with the measurements made on timescales characteristic of the processes being studied (i.e., at the subsecond level), 2. Measuring both magnetic and electric fields at the spacecraft with clear separation of the fields produced by the spacecraft itself, including both the DC and wave (rapidly varying in time) components up through radio frequencies, 3. Measuring remotely produced neutral atoms that are diagnostic of plasma and energetic particle processes, 4. Measuring the properties of dust grains diagnostic of interstellar and interplanetary processes, including physical properties and composition, as well as electrical charge state, and 5. Measuring infrared radiation diagnostics of processes in the upper atmospheres of the Earth and other planets. In all cases, the instrumentation consists of a detector head, a sensing element, and the appropriate electronics for control, power, and translation of the measured signal into an appropriate digital form. This captured data is then processed onboard the spacecraft, on the ground, or a combination of the two. The greatest challenge facing the making of these required in situ measurements for future SEC missions is the miniaturizing instrument types that currently exist while maintaining or increasing signal-to-noise ratios. At the same time, as spacecraft themselves decrease in size, one must still eliminate any contamination of the measured data by the presence of the spacecraft itself. 116

117 For example, booms have traditionally been used to move magnetometers away from current-carrying elements of a spacecraft, but increasing sensitivity by using longer booms increases the mass and structural concerns for implementation of nanosats. Technology advances are required to minimize the mass and power requirements for all of these instrument types while also increasing their ability to deal with data in an autonomous fashion whether flying on a satellite in a constellation near the Earth or solo in deep space. Information Architecture In a cost-constrained environment, operation of both autonomous single spacecraft as well as fleets require technology investment in data interpretation infrastructure. This is broadly defined to include general development of autonomy in operation, onboard processing, compression, and downlink (i.e., knowledge downlink versus data downlink) and the communications and ground data systems to handle such information simultaneously from hundreds of sensors. On the ground, information architecture must be develop and infrastructure established to 1. Infuse these data, including any required intermediate modeling steps, e.g. 3-D inversion of incomplete or non uniform tomographic data, 2. Synthesize these data, including incorporation with theoretical and phenomenological models, and 3. Visualize the analysis results new knowledge for transmittal both to the scientific community and to the public at large. Phased, timely, and appropriate investment in these technology areas will ensure that the SEC mission and its applications to pure and applied human knowledge will continue. 117

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120 Internet Webcasts and Science Museum Events Total solar eclipses used as a hook to highlight SEC science High Visibility Live@The Exploratorium Webcasts National participation of museums Extensive Media Coverage Interactions between SEC scientists and the public 9057/007A 2

121 EDUCATION AND PUBLIC OUTREACH Education and Public Outreach (EPO) is well integrated throughout all elements of the SEC theme. The SEC Education Forum and a set of regional Broker/Facilitator institutions help create partnerships between SEC scientists and EPO communities, and provide national coordination of activities. High Leverage for EPO Efforts Educators and the general public welcome interactions with scientists who provide role models for investigation and scientific inquiry. It is critical for EPO efforts to be highly leveraged and amplified through partnerships, existing educational networks, and dissemination channels. Additionally, it is important that SEC EPO products and programs support NASA s overall education effort and address the National Science Education Standards. High visibility for SEC EPO efforts is achieved by building on existing programs, institutions, and networks and by coordinating activities within NASA and other institutions. Partnerships with EPO Networks By partnering with existing educational structures, SEC missions can prevent reinvention of the wheel and amplify their limited EPO resources. The work of SEC missions can be disseminated by partnering with science museums in the production of planetarium shows, curriculum guides, and professional development programs for teachers. Collaboration with experienced EPO institutions can also ensure that materials and programs are carefully evaluated for impact on the user communities. Through partnerships with educators, science museums, amateur astronomers, the media, etc., the SEC community can effectively share information and ideas through resources that are appropriate for broad audiences and available in a variety of formats. The SEC community is well positioned to contribute to an effective and highly leveraged EPO program. There are many examples of successful products and programs highlighting SEC discoveries. Future missions and research efforts offer unique opportunities to share the excitement of SEC discoveries, as well as the relevancy of our research to society, with educators, students, and the public. 121

122 High Leverage for EPO Efforts Through Planetarium Shows Collaboration with Lawrence Hall of Science provides national distribution of Northern Lights planetarium show Activity Guide with every Starlab portable planetarium sold by commercial partner. SEC scientists contribute science review, NASA SEC images, and the latest research results for planetarium show. 9057/007A 3

123 Sun-Earth Connection Education Forum The Sun-Earth Connection Education Forum (SE- CEF) serves as a national coordination and support structure for the SEC theme. A partnership between NASA s Goddard Space Flight Center and UC Berkeley s Space Sciences Laboratory, SECEF is chartered to Facilitate the involvement of SEC scientists in education and outreach Help identify high-leverage opportunities Coordinate nationally and synthesize the education and outreach programs undertaken by SEC flight missions and individual researchers Arrange for the widest possible dissemination and long-term sustainability of SEC education and outreach programs and products, and Identify and disseminate best practices in education and public outreach. Working with the other OSS themes, the U.S. Department of Education, and other national efforts, SE- CEF is developing an on-line resource directory to provide a single point of access for educators and members of the public to SEC EPO resources. SECEF is supporting a coordinated presence at national education and science conferences, such as the National Science Teachers Association, the National Council of Teachers of Mathematics, and the American Geophysical Union. SECEF is creating an inventory of current and planned EPO activities of missions and research programs to promote collaboration and minimize duplication of effort. SECEF is supporting programs that target underserved and underutilized groups, evaluating activities for quality and impact, and sharing best practices with researchers. Highvisibility public events (e.g., Live@The Exploratorium) provide opportunities for SEC scientists to showcase and discuss their research and share with the public the excitement of scientific inquiry. By pursuing a systemic and coordinated approach, the impact of a modest investment in education and outreach by the SEC community can be enormously amplified, thereby enabling us to make a significant and long-lasting contribution to education and the public understanding of science in the United States. 123

124 Use of the Media for SEC Outreach Progress into 21st Century on Cable TV Voyager/Ulysses Project Outreach Program aired in 6 Los Angeles Counties Award-Winning Space Web Site for Kids Passport to Knowledge - Live from the Sun Electronic field trip - broadcast TV, videotape, Web chats, , teachers guides 250 PBS stations and NASA-TV Estimated reach: 1.5 to 2 million people SEC mission participation: ISTP, SoHO, ACE 9057/007A 4

125 Examples of Future SEC EPO Opportunities The robust SEC mission and research programs outlined in the SEC Roadmap provide rich opportunities for developing future EPO efforts for the benefit of educators, students, and the public. Potential opportunities include Adopt a Constellation Spacecraft: For multisatellite constellations, assign ownership of each spacecraft to specific schools whose students could monitor/analyze its data. Ownership could be determined by a national competition with the winning schools given the privilege of naming the individual satellites. Auroral Alert: Establish an Auroral Alert network based on SEC satellites that monitor CMEs and image the polar aurora. Alerts can be sent via to people at locations where auroras are visible. Space Weather Reports: Provide space weather information to schools and the public. Conditions in geospace and around other planets can be disseminated in real time to increase awareness of the Sun-Earth Connection. Voyage to the Sun: Provide a virtual voyage to the Sun through a variety of media, highlighting the data and discoveries of various missions. Using venues provided by science museum networks across the country and Internet communication technologies, provide an opportunity for the public to come along for the ride on a voyage of understanding of the active Sun and its effects on Earth, other planets, life, and society. 125

126 9057/007A 5 Sharing Discoveries Through Printed Resources Storms from the Sun Tormentas Solares Posters in English and in Spanish 60,000+ distributed at national education conferences Available through existing NASA dissemination channels Included in Live from the Sun teacher kit Available with movies on the web Spectra Teacher Workshops National reach Workshops for teacher leaders in science curriculum development & teacher training Responsive to constructivist learning and National Science Education Standards ISTP scientists partner with educators Participants conduct additional workshops in their home states and districts

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128 SEC PROGRAM ELEMENTS Programs Program Elements Definition Basic Research and Technology Flight Programs Ongoing Mission Support R&A Program Space Physics Theory Program Suborbital Program Explorer Program Discovery Program Solar Terrestrial Probe Program Frontier Probes Mission Operations and Data Analysis Basic research and analysis, instrument development Theory and modeling Competitively selected rocket and balloonborne experiments Competitively selected space science missions Competitively selected planetary missions Strategic SEC missions (<$250M) Strategic missions requiring advanced technology for breakthrough science (>$250M) Supports ongoing SEC missions and the processing, analysis and archiving of science data 9057/007B 33

129 IMPLEMENTATION PLAN Program Elements As evidenced by the nature and range of the scientific objectives set forth in the SEC Roadmap, a single mission will generally contribute to more than one Campaign and often to more than one Quest. A carefully designed and deliberate approach to missions is required to achieve the scientific objectives of the SEC program with the greatest efficiency, costeffectiveness, and scientific yield. This goal can be achieved by a well-considered mix of Solar- Terrestrial Probes (<$250M) and Frontier Probes (>$250M); the ongoing SEC program, including the suborbital program; theory/modeling programs; and participation in the Explorer, Discovery, Mars Program, and Outer Planets Program. Program Requirements The implementation plan described below has four recommended actions at its core and four primary recommendations: Provide the STP Program with sufficient resources to reduce the interval between new mission launches to 1.5 years. Initiate formulation and technology development for four new STP missions - IMC 2, ITM Waves 1, RAM 1, and SONAR 1. Initiate formulation and technology development for two new Frontier missions - Interstellar Probe 1 and Solar Polar Imager 1. Maintain support for ongoing missions which are still returning high-priority measurements for reasonable costs. Below we address each of the implementation issues in somewhat greater detail. 2 For details, see Appendix A 129

130 Mission Objective Comments Current STP Program SOLAR TERRESTRIAL PROBES TIMED Solar B STEREO Magnetospheric Multiscale Geospace Electrodynamic Connection Magnetotail Constellation SONAR Medium-term STP Program Reconnection and Microscale Probe Inner Magnetospheric Constellation ITM Waves Investigate the response of ITM to solar variability and forcing from below Study solar magnetic field evolution in the photosphere and lower corona Study CMEs and solar energetic particles from their origins on the Sun to their arrival at Earth orbit Investigate role of turbulence and reconnection in plasma entry and substorms Study plasma and electrodynamic coupling in the Earth s upper atmosphere/ionosphere Produce a 3-D dynamic image of the outer magnetosphere Observe the propagation of magnetic field beneath the surface of the Sun Investigate the interaction of magnetic fields in the corona and inner heliosphere Measure the dynamics of the Earth s radiation belt Map the redistribution of energy in the ITM region caused by wave propagation Launch 2000 ISAS/NASA mission, launch 2004 First stereoscopic imaging of the Sun. Launch 2004 STD report in preparation STD report in preparation STD report in preparation; first Constellation Class mission Quest I and IV Mission Quest I and IV Mission Quest II and IV Mission Quest II and IV Mission 9057/007B 30

131 Rationale for Accelerating the STP Line An interval of 1.5 years between the launches of successive solar terrestrial probes was recommended by the SEC 1997 Roadmap Team on the grounds that it would provide significant overlap between the primary phases of adjacent missions. Such overlaps provide essential opportunities to observe the coupling between the Sun, the solar wind, and the different regions of geospace for specific solar terrestrial events. The statistical analysis of ensembles of events collected within the various regions during different epochs is still expected to be the primary approach to investigating the coupled response of this system to solar variability in the near-term and mid-term. However, it is extremely important that the effects of some individual events be followed from the Sun through the inner heliosphere to the magnetosphere and, finally, into the upper atmosphere. These end-to-end measurements are vital for calibrating and validating our statistical models as well as our theoretical space weather simulations of the system s response to solar transients. The present 2.5-year gap between successive STP missions is too long to provide any significant overlap between the primary mission phases. Hence, the opportunity exists to greatly enhance the return-oninvestment for the STP program by providing sufficient funding to accelerate the pace until it can support the 1.5-year launch cadence. STP Mission Queue The majority of the candidate missions described in the SEC 2000 Roadmap would be implemented under NASA s STP program. The STP missions are strategic in nature (much like the Mars Surveyor line) and form the backbone of the SEC flight program. STP is a sequence of flexible, cost-capped missions designed for the systematic study of SEC science. The strategy embodied in the STP mission line is to use a creative blend of in situ and remote-sensing observations, employing innovative approaches to achieve highpriority science measurements with a modest budget. 131

132 LARGER SCALE SEC MISSIONS Mission Type Mission Objective Frontier Probe Discovery Program Outer Planets Program Interstellar Probe Solar Polar Imager MESSENGER Solar Probe Explore the interaction of the heliosphere with the local interstellar medium Determine the nature of the solar polar fields where the solar wind and activity cycle seem to originate Determine the response of an Earth-like magnetosphere to solar variability in the absence of an ionosphere Discover the coronal heating mechanism(s) and the acceleration process for the solar wind 9057/007B 34

133 SEC MISSION SUPPORT MULTIPLE CAMPAIGNS Campaign 1. Solar Variability 2. Inner Heliosphere 3. Geospace Environment 4. Comparative Planetary Environments 5. Outer Heliosphere and ISM 6. Space Weather Current SEC Missions Timed Solar B STEREO MMS GEC Mag Con Solar Probe Medium-term SEC Missions SONAR RAM Solar Polar Imager Interstellar Probe IMC ITM Waves Primary Science Supporting Science 9057/007B 31

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135 Dayside Boundary Constellation Fundamental Question: How do processes at the magnetopause and bow shock modulate the flow of solar wind mass, energy, and momentum into the magnetosphere? Science Objectives: Define the size, shape, motion, and occurrence rate of the magnetopause boundary phenomena which regulate the flow of solar wind energy through the magnetosphere, and thereby determine the significance of these phenomena to the solar wind-magnetosphere interaction. Establish the causal relationship(s) between boundary phenomena and corresponding solar wind, foreshock, and magnetosheath drivers Mission Description: An array of 36 polar orbiting spacecraft can map out the reconnection sites at all latitudes on the dayidemagnetopause. Three equatorial spacecraft monitor upstream conditions. Technology Requirements: Miniaturized field and simplified plasma instrumentation Miniaturized spinning spacecraft and subsystems injected into orbits covering a wide range of latitudes and longitudes A network of 36 small spacecraft, separated by ~ 1 RE, skim both sides of the dayside magnetopause to provide simultaneous comprehensive observations of boundary phenomena over a wide range of latitudes and local times. Three spacecraft hover near apogee outside the bow shock to monitor the foreshock preconditioned solar wind input Measurement Strategy: Vector magnetic field and plasma flow measurements Synthesis into a continuous series of synoptic maps

136 Geospace System Response Imagers (GSRI) Fundamental Question: What is the 3-D dynamic response of the global magnetosphere to changes in the solar wind and interplanetary magnetic field? Science Objectives: Determine how the global topology of the magnetosphere responds to external forcing and internal instabilities Obtain closure between the physical processes determined to be operating by earlier missions within localized regions and both the dynamical global topology and 3-D structure of the magnetosphere determined by remote sensing Mission Description: Understanding how the global magnetosphere responds to forcing will provide insights into magnetospheric dynamics. Technology Requirements: Solar Sail with density of 0.5 gm/m2 and area of 0.4 km2 Energetic neutral-atom, 30.4-nm, and auroral imagers with resolutions and sensitivities 5 times better than those presently available One spacecraft in a pole-sitting" stationary position on the night-side at a latitude of 60 degrees north and a radial distance of ~50 Earth radii to provide continuous global imaging of magnetospheric and auroral responses and monitors interplanetary inputs. At least four small spacecraft within two separate, polar-elliptic orbits to provide multiple views of the hot and cold plasma populations. Measurement Strategy: Pole-Sitter Energetic neutral-atom, 30.4-nm helium ion, and auroral imagers In situ magnetometer and solar wind monitor Orbiters Energetic neutral-atom and 30.4-nm helium ion imagers In situ hot and warm plasma sensors and magnetometer

137 Global Mesospheric Water Cycle Fundamental Question: How do planets lose water? Science Objectives: Measure globally the ultimate destruction rate of water vapor in the mesosphere Study the dynamics of vertical and horizontal transport of water vapor and its chemical partners through the atmosphere Determine the influence of polar mesospheric clouds in moderating water vapor destruction Analyze global change through measurement of odd oxygen, odd hydrogen, methane, water vapor, and temperature Measure the loss of hydrogen from Earth s upper atmosphere Mission Description: Ground-based image of a noctilucent cloud 6-year mission duration Polar orbiting satellite Measurements from stratosphere to thermosphere Technical Requirements: High reliability for long duration Long-life, miniaturized mechanical cryogenic coolers Advanced, on-board radiofrequency and digital signal processing Low-power, miniaturized UV, infrared, and sub-millimeter Measurement Strategy: Single, polar orbiting satellite Remote sensing of winds, temperature, aerosols, and composition utilizing both optical and sub-millimeter techniques Systematic coverage in the altitude, geographic, and local time domains Utilization of correlative ground-based measurements Long duration (>6-year) mission

138 Heliosphere Imager and Galactic Gas Sampler (HIGGS) Fundamental Question: How does the Sun interact with the local galactic environment? Science Objectives: Diagram of the large scale structure of the heliosphere, including the termination shock, heliopause, and possible bow shock. Technology Requirements: Advanced instrumentation for measurement of low-speed neutral atoms Low-mass, high-sensitivity pickup ion spectrometers High-sensitivity, low-noise diffuse radiation spectrometer Low-mass instruments for measuring charge states of energetic ions Highly autonomous spacecraft Establish the 3-D structure of the interaction region between the heliosphere and the local galactic environment Determine the elemental and isotopic composition of neutral atoms in a present-day sample of the galaxy and explore the implications for Big Bang cosmology, galactic evolution, stellar nucleosynthesis, and the birthplace of the Sun Determine the shape of the heliosphere Measure precisely the cosmologically important abundances of 2H and 3He in local interstellar material Map the location and establish the characteristics of the extended inner source of neutral atoms in the heliosphere Mission Description: Heliocentric, low-inclination, ecliptic orbit, 1 by 4 AU Highly autonomous, Sun-pointing, spinning, solar-powered spacecraft with conventional propulsion Measurement Strategy: Image the heliopause and the termination shock by using global sky maps of both 83.4 nm O+ and energetic hydrogen atoms Measure precisely the isotopic and elemental composition of the neutral portion of the interstellar gas and of the anomalous cosmic rays Determine the flow direction, speed, and temperature of interstellar atoms Establish the composition and radial profiles of the extended inner-source pickup ions

139 High-Resolution Solar Optical Telescope Fundamental Question: What are the dynamics of the flux tubes that drive atmospheric heating? Science Objectives: Understand the internal structure, heating, and evolution of the Sun s magnetic flux tubes Understand the relationships between fine-scale photospheric magnetic activity and overlying regions Understand the changes in magnetic energy, structure, and helicity in active region magnetic fields Mission Description: Sun-synchronous, Earth-orbiting satellite Measurement Strategy: Very-high-angular-resolution observations of intensity, velocity, and vector magnetic field EUV images of chromospheric and coronal structures Technology Requirements Understanding flux tube characteristics provides insights about the Sun s magnetic field. High-data-rate communication Large-aperture optics and/or interferometers

140 Inner Magnetosphere Constellation Fundamental Question: How are the radiation belts created? Science Objectives: Discover the origin and dynamics of inner magnetospheric particle populations Derive the global, large-scale magnetic and electric fields Determine the development and evolution of magnetic storms Create time dependent maps of the inner magnetosphere and near-earth tail Mission Description: TA constellation of spacecraft situated in six different low-inclination orbits can map the build-up and decay of trapped particles while monitoring the more distant source regions in much the same way as weather stations track storm systems across the Earth s surface. Technical Requirements: Microsat technology Miniaturized instrumentation Three inner "petal" orbits (2x6.5 Re) with 5 to 10 satellites each Three outer "petal" orbits (2x12 Re) with four satellites each Instruments: Magnetometer, plasma analyzer, energetic-particle analyzer (with maximum-ion-composition information) Measurement Strategy: Direct measurement of equatorial magnetic field Independent measurement of magnetic field using energetic particle phases space density contours Determination of large-scale electric field by using the ExB drift of lower-energy particles, with conservation of invariants along drift paths Direct measurement of the dynamics of the ring current, radiation belt, and plasmasphere particles

141 Interstellar Probe Fundamental Question: What is the nature of the interstellar medium and its interaction with the solar system? Science Objectives: Explore the interstellar medium and determine the properties of plasma, neutral atoms, dust, magnetic fields, and cosmic rays Determine the structure and dynamics of the heliosphere as an example of the interaction of a star with its environment Study, in situ, the structure of the solar wind termination shock and the acceleration of pickup ions and other species Investigate the origin and distribution of solar system matter beyond the orbit of Neptune Mission Description: Interstellar Probe would pass through the boundaries of the heliosphere and begin exploring nearby interstellar space. Technology Requirements: Solar sail propulsion Low-mass/power optimized instrumentation Advanced Ka-band telecommunications Lightweight, low-cost spacecraft Integral design of structure and electronics Send a spacecraft to 200 AU in 15 years with solar sail propulsion Use sail to decelerate, swing by the Sun at 0.25 AU, and then accelerate the spacecraft towards the nose of the heliosphere Jettison the sail at ~5 AU and coast to >200 AU, exploring the Kuiper Belt, heliospheric boundaries, and interstellar medium Measurement Strategy: Measure in situ, the properties and composition of interstellar plasma, neutrals, dust, and low-energy cosmic rays Determine heliospheric structure and dynamics by in situ measurements and global imaging Map IR emission of the zodiacal dust cloud and measure the distribution of interplanetary dust and small Kuiper Belt objects

142 Interstellar Trailblazer Fundamental Question: What is the scale size of variations in composition, density, temperature, ionization state, and dust content in our local cloud? Science Objectives: Determine the nucleosynthetic state of matter in our local cloud Catalog the identities and abundances of organic and inorganic molecules in the interstellar medium and outer solar system Determine the detailed composition of interstellar dust Measure the complete charge-state distribution of elements in the interstellar medium Search for predicted sources of low-energy cosmic-ray antiprotons and positrons from black holes and dark matter annihilation Explore the nature of the galactic environment that our solar system will occupy over the coming centuries Solar sail trajectory that passes within 0.1 AU of the Sun and then accelerates to ~67 AU/year. Technology Requirement: Advanced solar sail (0.1 g/m2; 600-m radius) High-temperature sail materials High-resolution spectrometers Miniaturized, durable instrumentation Advanced power and telecommunications systems Highly autonomous spacecraft Mission Description: Send a well-instrumented spacecraft to 2000 AU in ~30 years by using advanced solar sail propulsion Sail to ~0.1 AU, accelerate to 67 AU/year, jettison sail at ~10 AU, and then coast through our local interstellar cloud Measurement Strategy: Carry a payload of advanced, high-resolution spectrometers to ~2000 AU to explore the distribution of matter in our local cloud Measure the elemental, isotopic, and molecular composition of interstellar plasma, neutrals, low-energy cosmic rays, and dust

143 Io Electrodynamics Fundamental Question: How does a strong internal plasma source couple to a rotating magnetosphere and affect the magnetospheric dynamics? Science Objectives: Investigate the energy conversion processes in a magnetized plasma Understand mass transport in a rapidly rotating magnetosphere Determine how intense parallel electric fields are generated in a magnetized plasma Determine how momentum is transferred through field-aligned current systems Determine the role of Io on radio wave generation at Jupiter Mission Description: Magnetic field lines and flow stream lines near Io. Technology Requirements: Radiation-hardened electronics Advanced propulsion Lightweight, low-power transmitter Lightweight instrumentation Radiation-insensitive mass memory Frontier probe Equatorial orbit (5.9 by 70 Jovian radii, two-month orbit) Duration: 3 years at Jupiter Measurement Strategy: One year gravity assisted orbit adjustment Multiple returns to Io in 2-month-long orbits High-resolution particle and field snapshots during flyby stored in mass memory and downlinked over rest of orbit Different science emphasis for each of 12 encounters Orbit adjusted through gravity assists with additional orbit adjustment through advanced propulsion system to optimize encounter aim points

144 ITM Waves Probe Fundamental Question: How are atmospheric waves generated, propagated, and dissipated and how do these waves act to redistribute energy throughout the ITM region? Science Objectives: Explore global wave source regions, from the troposphere to the upper atmosphere, known to impact the ITM region Discover the sinks of wave energy in the ITM region and their effects on energy, momentum, and constituent transport Understand wave-wave, wave-mean flow, and wave-turbulence interactions Relate these findings to other planetary atmospheres known to be strongly influenced by atmospheric waves, such as Mars and Venus Ichematic view of gravity wave effects in the atmosphere and ionosphere. Technology Requirements: High-resolution visible and IR nadir imaging Improved IR sensors Miniaturized and lightweight instrumentation Mission Description: Four sun-synchronous satellites 600-km altitude Measurement Strategy: Imaging of small-scale structure within the ITM region and of wave source regions outside the ITM region Measurement of the neutral and plasma state parameters via a combination of remote-sensing and in situ measurements Measurement of concentrations of transportable minor species Assimilated theory and data analysis program involving numerical models combined with spacecraft and ground-based measurement program

145 Jupiter Polar Orbiter Fundamental Question: What processes are involved in the interaction between Jupiter s rotation-driven magnetosphere and its ionosphere and thermosphere, and how are these similar to or different from magnetosphere-ionosphere coupling processes at Earth? Science Objectives: Determine the relative contributions of planetary rotation and of the interaction with the interplanetary medium to Jovian magnetospheric dynamics Determine how global electric and magnetic fields regulate the processes that produce the radiation belts, plasma sheet, and aurora Identify the particles responsible for the generation of the Jovian aurora and determine their magnetospheric source regions Mission Description: The Jupiter Polar Orbiter will compare Jupiter s magnetosphere, ionosphere, and thermosphere with Earth s. Technology Requirements: Miniaturized instrumentation Solar array/power system development Aerobraking Radiation hardening * A Jupiter Polar Orbiter mission can be implemented with present-day technology; however, the technologies indicated here would allow for enhanced mission flexibility. Delta launch Elliptical polar orbit with perijove at 1.1 Rj and apojove at 15 Rj or 40 Rj Three-axis spin-stabilized spacecraft Frontier probe Measurement Strategy: Measure particles and fields in situ in the auroral acceleration region, along L shells, and in the conjugate magnetospheric source regions Image the aurora at visible and UV wavelengths Measure the magnitude and configuration of the near-planet magnetic field and map the 3-D structure of the radiation belts

146 Mars Aeronomy Probe Fundamental Question: How are the upper atmospheres of planets affected by solar variability in the absence of a global magnetic field? Science Objectives: Map upper-atmosphere composition, thermal profile, and global circulation Determine the properties of the ionosphere, its sources and sinks, dynamic coupling to the neutral atmosphere including dust storms and gravity waves, and its electrodynamic response to the solar wind Observe the response of the upper atmosphere to solar variability and model the effects of space weather on satellite drag and aerocapture The Mars Aeronomy Probe will not only enhance our knowledge of the upper atmospheres of terrestrial-type planets, but also will provide atmospheric models for future manned Mars missions. Technology Requirements: Aerobraking Miniaturized instrumentation Mission Description: Delta launch Low-altitude polar orbit Measurement Strategy: Measure neutral species escape rates, isotopic ratios, densities, temperatures, winds, and composition Measure thermal plasmas (ions and electrons), pickup ions, energetic particles, and magnetic and electric fields Integrate theory and data analysis programs by using numerical models of high-altitude solar wind interaction, ionospheric electrodynamics, and upper-atmosphere dynamics

147 Neptune Orbiter Fundamental Question: How do extreme variations in internal magnetic dipole tilt affect the structure and dynamics of a planetary magnetosphere and its response to solar variability? Science Objectives: The Neptune Orbiter will study the affect of extreme variations in internal magnetic dipole tile. Technology Requirement Advanced propulsion to reduce flight time and enhance science payload Advanced power to supply needs at 30 AU from the Sun Advanced communications to return data to Earth from 30 AU Radiation hard electronics Miniaturized instrumentation Measurement Strategy: Thermal plasmas, energetic particles, magnetic and electric fields, plasma waves, and auroral measurements (including UV spectral imaging of Neptune and Triton) Integrated theory and data analysis program involving numerical simulations processes, and energetic-particle acceleration under a variety of planetary magnetic-dipole orientations Map Neptune's highly asymmetric magnetic field Determine the magnetospheric structure as the highly oblique and offset magnetic field rotates with the planet Determine the densities, compositions, and temperatures of magnetospheric plasma populations, and their distributions throughout the magnetosphere Measure the plasma flows associated with the dynamics of the magnetosphere driven by the planet's rotation and by the solar wind Determine whether Triton has an intrinsic magnetic field, and characterize the plasma interaction with Triton and its atmosphere Compare the magnetosphere of Neptune with other planetary magnetospheres, and compare the Triton-magnetosphere interaction with the Galilean satellites of Jupiter and with the role of Titan in Saturn's magnetosphere Mission Description: Moderate-inclination, highly eccentric orbit with an apoapsis of 20 to 30 planetary radii on the nightside Mission duration of 2 years to provide measurements of magnetospheric response to a wide range of solar wind conditions under a variety of planetary magnetic dipole orientations

148 Outer Heliosphere Radio Imager (OHRI) Fundamental Question: How do the boundaries of the heliosphere respond to solar variations? Science Objectives: Determine the large scale structure of the heliospheric boundary Map the 2-D shape of the heliospheric boundary, including the dynamic response to solar disturbances and to the solar cycle Mission Description: Illustration of a possible radio-interferometry image of the 2- to 3-kHz radiation coming from the nose of the heliosphere. Technology Requirement Propulsion system (e.g., solar sail propulsion) Interspacecraft communication and tracking Onboard data processing Long-lifetime radio receiver and power sources 16-subsatellite radio interferometer plus mother spacecraft, each with a sensitive radio receiver and crossed-dipole antenna Solar orbit at 20 to 30 AU in the direction of the nose of the heliosphere. After reaching orbit, subsatellites are dispersed into an Unwin sphere configuration, spaced ~1000 km apart, where they drift about a central position shepherded by the mother spacecraft Mother spacecraft performs station keeping and image processing; measures and maintains satellite positions; receives radio data from subsatellites; and does cross-correlation computation to produce 2-D images at frequencies from 1-5 khz Measurement Strategy: Sensitive radio receivers of array elements measure radio waves from 1 to 5 khz and transmit signals to the mother spacecraft Cross-correlation computations performed on signals from array elements to yield a 2-D radio image at each frequency 2-D radio images telemetered to Earth receiving stations

149 Particle Acceleration Solar Orbiter (PASO) Fundamental Question: How are particles accelerated to high energies by the Sun? Science Objectives: Understand particle acceleration mechanisms in flares and CMEs Analyze location and nature of energy release Study active-region evolution Explore the inner heliosphere Mission Description: PASO will provide the first systematic exploration of the inner heliosphere. Its measurements near the Sun will be particularly important for studying the newly discovered inner-heliosphere source of pick-up ions. Technology Requirement: Solar sail propulsion Thermal control system for near-sun orbit Communication and data compression Delta-class launch vehicle with solar sail Heliosynchronous orbit at 0.16 to 0.2 AU for continuous viewing of active regions and CME source regions Spin-stabilized Sun-pointing spacecraft for hard X-ray and gamma-ray signal modulation and in situ particle and field observations Mission around time of solar activity maximum Measurement Strategy: High spectral, spatial, and temporal resolution, hard X-ray and gamma-ray imaging spectroscopy and polarization Gamma-ray line and neutron spectroscopy Detailed energetic-particle, plasma, and field observations Soft X-ray and EUV context imaging

150 Reconnection and Microscale (RAM) Probe Fundamental Question: How are coronal plasmas heated during dynamic events? Science Objectives: Study the microscale instabilities that lead to global effects Examine the mechanisms contributing to the coronal energy balance Determine the conditions leading to flares and CMEs Measure the reconnection regions and their topology Mission Description: The RAM Probe will explore and measure the dynamic heating of coronal plasmas. Technology Requirement: Large-format cryogenic imaging detectors Diffraction-limited XUV optics Large-format, fast-read CCDs Onboard AI event processing Continuous broadband solar observations from L1 or geostationary orbit Complementary high-resolution and full-disk imaging STP-class mission Measurement Strategy: Ultra-high resolution (0.02 arcsec) coronal imaging High-resolution imaging (0.5 arcsec) spectroscopy (4 ev) from 0.25 to 50 kev High-resolution EUV spectroscopy Full-Sun EUV and white-light context images at 1 arcsec High time resolution in all instruments Mutual benefit from overlap with, e.g., Solar B and STEREO

151 Solar Farside Observer Fundamental Question: What is the 3-D structure of the Sun s magnetic field in its interior and in the entire atmosphere? Science Objectives: Probe 3-D structures deep inside the Sun Measure the Sun s global magnetic field Follow the evolution of active regions Determine coronal magnetic fields Study coronal mass ejection origin and development Mission Description: Inclined orbit at 1 AU on the far side of the Sun Venus gravity assist for orbit insertion Measurement Strategy: The Solar Farside Observer will observe the full evolution of solar phenomena by tracing their activity on the far side of the Sun. Full-disk magnetic and velocity field observations X and Ka band Faraday rotation to sound the corona EUV images of coronal structures In situ particles and fields Technology Requirements: High-data-rate interplanetary communication Low-mass advanced propulsion

152 Solar Flotilla Fundamental Question: How are particles and fields transported from the solar corona, and how do they evolve in space? Science Objectives: Multiple microsatellites in solar elliptic orbits will enable a greater understanding of how particles and fields are transported from the solar corona. Technology Requirement: Autonomous operation and onboard event recognition Solar electric propulsion system Microsatellite technology Advanced data retrieval system processes Miniaturized lightweight optimized instruments Lightweight low-cost spacecraft Interspacecraft communication Thermal control and survivability Integrated systems and instruments Understand the physics of shocks and shock particle acceleration Utilize spatial and temporal scales for energy dissipation and transfer in the solar wind Study the magnetic structure of the inner heliosphere Visualize the dynamics of the inner heliosphere Analyze magnetic reconnection in coronal mass ejections (CMEs) Determine temporal and spatial variations of global magnetic helicity and flux ejection from the Sun Study global variations of galactic cosmic rays and high-fip pickup ions Make improved predictions of shocks, CMEs, and high-speed streams Study the physics of heat flux dropouts in solar wind Develop spatial and temporal profiles of solar wind density, temperature, and speed Understand the genesis and structure of stream-stream interaction regions Mission Description: Multiple autonomous microsatellites in three principal solar elliptic orbits at 0.2 to 0.4 AU (two to six microsatellites per orbit) Small identical focused particles and fields payloads on each microsatellite Microsatellite orbital injection at Mercury rendezvous A 10-day cluster mission followed by the primary global mission Measurement Strategy: Magnetic field measurements with variable temporal resolution determined by dynamics Solar wind electron and ion (p, alpha, O minimum) measurements with variable time and energy resolution Energetic ion measurements with variable time and energy resolution Spinning microsatellites with at least the solar direction determined Data storage and relay in bursts Earth telemetry from either solar quadrature (over limb) or from master satellite

153 Solar Near-Surface Active-Region Rendering (SONAR) Fundamental Question: How do active regions develop in the Sun? Science Objectives: Determine why sunspots and solar active regions occur Predict how magnetic regions emerge, evolve, and decay Estimate when flares and mass ejections will occur Determine how activity, solar convection, and irradiance interact Determine the links between the dynamics of the interior and corona Predict what the next solar cycle will be like Mission Description: Local helioseismology shows that the sound speed beneath a sunspot increases several hours before the active region emerges. Technology Requirement: Large-format fast-readout CCD detectors Fast spacecraft data compression hardware Continuous high-rate telemetry coverage Spacecraft AI for self-operation Data handling and analysis facilities Continuous solar observations from geosynchronous orbit Full-disk solar and coronal imaging at multiple wavelengths Helioseismology and spectroscopy to follow the life cycle of active regions Measurement Strategy: High spatial and temporal resolution full-disk imaging Photospheric 1 arcsec velocity and vector magnetic fields Local-area helioseismology to determine interior conditions Magnetograms to reveal helicity and 3-D structure near the surface EUV spectroscopy for atmospheric structure and dynamics Tracking of interior and atmospheric features of developing active region across disk through solar cycle High-frequency EUV imaging to allow coronal seismology Microarcsecond astrometry of solar shape and radius changes

154 Solar Polar Imager Fundamental Question: How do the polar regions of the Sun affect the dynamics of the global corona and reveal the secrets of the solar cycle? Science Objectives: The first observations of the Sun from above the poles will provide valuable information concerning the solar cycle, solar activity, the 3-D structure of the dynamic solar corona and solar wind, and even space weather. Technology Requirement: Solar sail propulsion Lightweight subsystems and instruments High-rate telemetry from deep space AI event selection and spacecraft autonomy Examine solar and coronal structures from a revealing new polar perspective Image global effects of dynamic events on a full 3-D structure of the corona Track the complete life cycle of active regions and coronal holes Link variations in the high-latitude heliosphere to surface conditions Make pioneering measurements of the Sun's evolving polar magnetic field Refine solar dynamo theory by using measurements of subsurface polar motions Measure angular momentum loss in the solar wind Mission Description: Circular 0.5-AU 90 solar polar orbit in 3:1 resonance with Earth 30 to 150 separation from Earth to complement space weather program Solar array-powered three-axis or spin-stabilized platform Lightweight spacecraft with solar sail propulsion Minimum 2 years in final orbit, spanning the time of solar polar field reversal Measurement Strategy: Image corona and inner heliosphere from over the poles Reconstruct 3-D structure of coronal mass ejections (CMEs) from the Sun to 1 AU Measure high-latitude magnetic fields and coronal holes Determine surface velocity for local helioseismology Gather in situ particle and field measurements Measure solar irradiance from a new perspective

155 Stellar Imager Seismic Probe (SISP) Fundamental Question: What are the possible patterns of activity in a star like the Sun? Science Objectives: Determine the possible states of activity in the Sun, from Maunder minimum states to periods of enhanced activity Understand how stellar rotation modifies the butterfly activity diagram Determine the time scales for magnetic field evolution Study what flares and filaments are like on stars Determine the surface differential rotation and meriodional flows on Sun-like stars of different levels of magnetic activity Mission Description: The SISP mission will create an acceptance model for the Sun s dynamo and a database for stellar comparisons as well as provide a stepping stone t owards planetary interferometers. Technology Requirement: Long-lasting, low-mass propulsion Interferometer baseline of approximately 400 m to achieve a resolution of 40,000 km on a star at 4 parsec at 1500 A (there are 72 star systems within 6.5 parsec), equivalent to 1000 resolution elements on a distant Sun. Measurement Strategy: Perform photometry in multiple passbands to study stellar irradiance variations for each resolution element Map the evolution and rotation of stellar spots and active regions by observing continuously over at least a stellar rotation Perform asteroseismology with sufficient resolution to measure internal differential rotation; i.e., covering at least 2 weeks

156 Sun-Earth Energy Connector (SEEC) Fundamental Question: How do solar irradiance variations affect geospace? Science Objectives: Studying the plasmasphere is one aspect of tracing the flow of radiant EUV energy from the Sun to determine its effect on the Earth. Technology Requirement: Ionospheric 911Å imaging system Simultaneous Sun and Earth viewing at >3RE Optics-free photoelectron spectrometer Quantify the relationships between solar radiation and space weather on local and planetary scales by: Specifying solar EUV radiation variability and its source mechanisms Simultaneously mapping the neutral and plasma near-earth space environments Establishing instantaneous relationships among solar radiation, precipitating energetic particles, and the space environment Mission Description: Simultaneous imaging of the Sun s outer atmosphere and Earth s neutral atmosphere, day-night ionosphere, and plasmasphere Orbit at >3RE, ~50 inclination MIDEX or STP class mission Measurement Strategy: Simultaneous global images of the Sun and Earth High-angular-resolution images to observe local thermosphere, ionosphere, and plasmasphere weather Simultaneous high-accuracy solar EUV irradiance spectrum made with order-free spectrometer Development of new versions of neutral density and plasmaspheric-ionospheric models

157 Tropical ITM Coupler Fundamental Question: How do neutral and plasma motions distribute energy among and between the Earth's low latitude mesosphere, thermosphere, ionosphere, and inner plasmasphere? Science Objectives: Spread-F turbulence over Peru. Courtesy R. Woodman. Technology Requirement: Enhanced power systems optimal for eclipse measurements Improved propulsion systems High-resolution gravity wave imaging Low-cost flight computers Understand how large-scale neutral winds, gravity waves, and ion drifts are coupled in the low latitude upper atmosphere and how they respond to solar variations and to variable influences from the lower and middle atmosphere Discover the cause of planetary-scale plasma upwellings at low latitudes, and to investigate the effect of unstable flux tubes on inner plasmasphere dynamics Understand the chaotic and explosive transfer of energy between irregularity scale lengths ranging from 1000 km to 1 cm which occurs in the low latitude ionosphere at night Determine the extent and significance that tropical storms in the troposphere produce localized electric fields and neutral gas motions in the ionosphere Mission Description: 3 satellites: 2 with elliptical orbits of 150 km x 1500 km (nominal), one with a circular orbit of 600 km Inclinations will be < 20 Measurement Strategy: Elliptical orbit satellites include dipping to altitudes of 150 km or below Circular orbit satellite includes in-situ measurements and imaging of gravity wave and neutral winds Conjunctions of the perigees and apogees of the 2 elliptical satellites with each other and the circular satellite for unprecedented investigations of vertical coupling Measurements of electrodynamics and neutral and plasma gas properties Imaging of gravity waves, airglow, and neutral winds Tropical storm and lightning monitors and ground-based radar observations

158 Venus Aeronomy Probe Fundamental Question: How are the upper atmospheres of terrestrial planets influenced by the solar wind in the absence of a global magnetic field? Science Objectives: Determine the mechanisms for energy transfer from the solar wind to the ionosphere and upper atmosphere Measure the charged particles responsible for auroral-type emissions and infer their acceleration mechanisms Determine the formation processes for ionospheric magnetic flux ropes, ionospheric holes on the nightside, and the loss of ionospheric plasma in the form of streamers, rays, and clouds Mission Description: Diagnosing nonthermal plasma interactions, such as those planned with the Venus Aeronomy Probe, is a key component in understanding the influence of the solar wind on planetary atmospheres. Technology Requirement: Miniaturized, autonomous, intelligent instruments Nondisruptive floating potential neutralization spacecraft to see the bulk of escaping plasma in the planetary wake region Electrostatically clean spacecraft with floating potential neutralization and spin stabilization in a cartwheel fashion High-inclination elliptical orbit (150 km to 1 RV) 1-year lifetime to allow a survey of the ionosphere and upper atmosphere at all local times Measurement Strategy: In situ plasma, magnetic and electric fields, and plasma and radio wave measurements In situ neutral-gas composition, density, temperature, and wind measurements Remote observations by a UV imager, Fabry-Perot Interferometer, energetic-neutral-atom imager, and ionospheric sounder