Pathways for Venus Exploration

Transcription

1 Pathways for Venus Exploration Venus Exploration Analysis Group (VEXAG) September 2009 VEXAG is NASA s community-based forum that provides science and technical assessment of Venus exploration for the next few decades. VEXAG is chartered by NASA Headquarters Science Mission Directorate s Planetary Science Division and reports its findings to both the division and to the Planetary Science Subcommittee of the NASA Advisory Council. VEXAG, which is open to all interested scientists and engineers, regularly evaluates Venus exploration goals, objectives, investigations, and priorities on the basis of the widest possible community outreach.

2 Front cover is a collage showing Venus at radar wavelength, the Magellan spacecraft, and artists concepts for a Venus Balloon, the Venus In situ Explorer, and the Venus Mobile Explorer. (Collage prepared by Tibor Balint) Pathways for Venus Exploration Venus Exploration Analysis Group (VEXAG) September 30, 2009 VEXAG Executive Committee: VEXAG Co-chairs: Sanjay Limaye, University of Wisconsin, Madison, Wisconsin (sanjayl@ssec.wisc.edu) and Suzanne Smrekar, Jet Propulsion Laboratory (JPL), California Institute of Technology, Pasadena, California (Suzanne.E.Smrekar@jpl.nasa.gov) Mark Allen, VEXAG Focus Group Lead for Laboratory Measurements, JPL, Pasadena, California (Mark.A.Allen@jpl.nasa.gov) Kevin Baines, Focus Group Lead for Atmospheric Evolution, JPL, Pasadena, California (blueskies4321@yahoo.com) James Cutts, Focus Group Lead for Venus Exploration Technologies, JPL, Pasadena, California (James.A.Cutts@jpl.nasa.gov) David Grinspoon, VEXAG Focus Group Lead for Venus-Earth Climate Connections, Denver Museum of Nature and Science, Denver, Colorado (david.grinspoon@dmns.org) Lori Glaze, Focus Group Lead for Planetary Formation and Evolution, Goddard Space Flight Center, Greenbelt, Maryland (lori.s.glaze@nasa.gov) Adriana Ocampo, Ex Officio, Venus Program Executive, NASA Headquarters, Washington D.C. (adriana.c.ocampo@nasa.gov) Supporting members of the VEXAG Executive Committee: Tibor Balint, JPL, Pasadena, California (tibor.balint@jpl.nasa.gov) Mark Bullock, Southwest Research Institute, Boulder, Colorado (bullock@boulder.swri.edu) Larry Esposito, Laboratory for Atmospheric and Space Physics, University of Colorado (larry.esposito@lasp.colorado.edu) Jim Garvin, Goddard Space Flight Center, Greenbelt, Maryland (james.b.garvin@nasa.gov) Ronna Hurd, Lunar and Planetary Institute, Houston, Texas (hurd@lpi.usra.edu) Natasha Johnson, Goddard Space Flight Center, Greenbelt, Maryland (natasha.m.johnson@nasa.gov) David Senske, JPL, Pasadena, California (david.senske@jpl.nasa.gov) Tommy Thompson, JPL, Pasadena, California (thomas.w.thompson@jpl.nasa.gov) Allan Treiman, Lunar and Planetary Institute, Houston, Texas (treiman@lpi.usra.edu) Past VEXAG Co-Chairs (in chronological order): Janet Luhmann, University of California, Berkeley, California (jgluhmann@ssl.berkeley.edu); Sushil Atreya, University of Michigan, Ann Arbor, Michigan (atreya@umich.edu); Ellen Stofan, Proxemy, Inc. (ellen@proxemy.com) Steve Mackwell served as Focus Group Lead for Planetary Formation and Evolution since VEXAG was formed in 2005 until spring Janet Luhmann, and Sushil Atreya, served as VEXAG Co-Chairs since VEXAG was formed in 2005 until November Ellen Stofan served as VEXAG Chair from November 2007 until spring 2009.

3 TABLE OF CONTENTS Foreword... iii Findings and Proposed Actions... v Venus New Frontiers and Discovery Missions... v Venus Science Laboratory Measurements... vi Venus as a Future Earth/Comparative Planetology... vii Technology Development... viii Technology Development for a Venus Flagship Mission... ix 1. Context for Venus Exploration Key Themes and Questions for Exploring Venus The Role of VEXAG Background: Recent Reports Addressing Venus Exploration Current Status of NASA s Support of Venus Research Fifty Years of Venus Exploration Venus Exploration Missions Discovery, New Frontiers, and Flagship Missions Venus Flagship-Class Missions Traceability of VEXAG Science Objectives to Future Flagship Missions ESA Cosmic Vision European Venus Explorer Russian Space Agency Venera-D Venus Laboratory Measurements References and White Papers for Next Decadal Survey Acronyms and Abbreviations Appendix A. Venus Goals, Objectives, and Investigations Appendix B. Comparative Climatology Overview Appendix C. Enhancing and Enabling Technologies for Venus Exploration NASA's Venus Flagship Mission Fact Sheet Vignette 1: Magellan...14 Vignette 2: Venus Express: Revealing the Mysteries of a Neighboring World...16 Vignette 3: Recent Venus Express VIRTIS Results Vignette 4: Lessons Learned from Pioneer Venus Orbiter and Huygens...22 Vignette 5: Experiencing Venus by Air: The Advantages of Balloon-Borne In Situ Exploration...24 Figure 2-1. Artist s Concept of Elements of the Venus Design Reference Mission...26 Figure 2-2. Overviews of Venus Missions Endorsed by Solar System Exploration Roadmap...28 Table 1-1. Summary of Past, Present, and Future Venus Missions...19 Table 2-1. Traceability Matrix of Objectives Met with Venus Flagship Missions...31 Table 3-1. New Laboratory Studies to Support Future Venus Missions...34 Recommended bibliographic citation: VEXAG (2009), Pathways for Venus Exploration i

4 VEXAG Charter. The Venus Exploration Analysis Group is NASA's community based forum designed to provide scientific input and technology development plans for planning and prioritizing the exploration of Venus over the next several decades, including a Venus surface sample return. VEXAG is chartered by NASA's Solar System Exploration Division and reports its findings to NASA. Open to all interested scientists, VEXAG regularly evaluates Venus exploration goals, scientific objectives, investigations, and critical measurement requirements, including especially recommendations in the NRC Decadal Survey and the Solar System Exploration Strategic Roadmap. Perspective view of Ishtar Terra, one of two main highland regions on Venus. The smaller of the two, Ishtar Terra, is located near the north pole and rises over 11 km above the mean surface level. Courtesy NASA/JPL Caltech. ii

5 FOREWORD Since the previous release of the VEXAG report in May 2008, several events have occurred that necessitate an update to Venus exploration goals, objectives, investigations, and priorities (now this document, Pathways for Venus Exploration). NASA Headquarters has accomplished some of the findings and proposed actions that were originally formulated at the February 2007 VEXAG meeting. A significant accomplishment was the formation of a Venus Science and Technology Definition Team (STDT), which was established in January 2007 to develop a credible Venus flagship mission in the 2020s that addressed the VEXAG goals, objectives, and investigations. The Venus STDT completed its final report in April 2009, with a presentation to NASA Headquarters on April 6, In addition, the European Space Agency (ESA) Venus Express Mission, which arrived in April 2006, has continued to observe Venus on a daily basis, providing key information about the Venus atmosphere, surface, and near-space environment. Also, the Japanese Aerospace Exploration Agency (JAXA) is on schedule for its 2010 launch of the Venus Climate Orbiter, a multiyear mission to study the clouds in winds of Venus in unprecedented detail. In parallel with this, the National Research Council (NRC) and NASA initiated a new Planetary Sciences Decadal Survey in early 2009 to reexamine NASA s planetary missions as a follow-on to the 2003 Decadal Survey. To support the 2009 Decadal Survey, there are a number of Venus community white papers, which are posted on the VEXAG web site. Through its interactions with the community, VEXAG developed an overarching goal Understanding Venus and the Implications for the Formation of Habitable Worlds supported by a set of three scientific goals: Origin and Evolution: How did Venus originate and evolve, and what are the implications for the characteristic lifetimes and conditions of habitable environments on Venus and similar extrasolar systems? Venus as a Terrestrial Planet: What are the processes that have shaped and still shape the planet? Climate Change and the Future of Earth: What does Venus tell us about the fate of Earth s environment? VEXAG findings and proposed actions, which were originally the outcome of the January 2007 VEXAG meeting, have been updated to reflect current circumstances and are presented below as an executive summary. Section 1 provides a context for Venus exploration with vignettes providing additional information on Magellan, Venus Express, recent Venus Express VIRTIS results, and lessons learned from Pioneer Venus Orbiter and Huygens. Possible missions to accomplish these goals are discussed in Section 2, with a vignette providing additional information on balloon-borne in situ exploration. New laboratory measurements needed to maximize the science return from current and future Venus missions are identified in Section 3. The appendices are brief overviews of white papers submitted to the Planetary Sciences Decadal Survey: Appendix A. Venus Goals, Objectives, and Investigations; Appendix B. Comparative Climatology Overview; and Appendix C. Enhancing and Enabling Technologies for Venus Exploration. The fact sheet for NASA s Flagship Mission to Venus follows the appendices. iii

6 Artist s concept of Mariner 2, the first spacecraft to visit Venus (1962) Artist concept of Magellan spacecraft at Venus ( ) iv

7 FINDINGS AND PROPOSED ACTIONS As noted above, the first set of VEXAG findings and proposed actions was developed at the January 2007 VEXAG meeting and remained unchanged until the February 2009 meeting. NASA has acted on some of the proposed actions, particularly the formation of a Venus STDT in January The current set of VEXAG findings and proposed actions, discussed at the February 2009 meeting, is presented here. Key unanswered questions about Venus relevant to our understanding of the Earth as well as other terrestrial planet systems include the following: Was there ever an ocean on Venus and, if so, when did it exist and how did it disappear? Was Venus ever habitable? Was the early Venus atmosphere like the early atmosphere of Earth, and at what point did it diverge in character so greatly and why? Why does Venus rotate so slowly and is the lack of a planetary dynamo a consequence? What was the impact on the evolution of Venus? Why does the Venus atmosphere rotate 60-times faster than its solid body? How are atmospheric heat and momentum transferred from equator to poles? What caused the extensive resurfacing of Venus during the last 500 million to one billion years? Is Venus still an active planet? Are the resurfacing and climate change somehow related? To address these questions and the recommendations of recent reports described in Section 1, VEXAG, through interaction with the community, developed an overarching goal Understanding Venus and the Implications for the Formation of Habitable Worlds supported by a set of three overarching scientific goals: Origin and Evolution: How did Venus originate and evolve, and what are the implications for the characteristic lifetimes and conditions of habitable environments on Venus and similar extrasolar systems? Venus as a Terrestrial Planet: What are the processes that have shaped and still shape the planet? Climate Change and the Future of Earth: What does Venus tell us about the fate of Earth s environment? A prioritized set of objectives and investigations to support these goals is given in Appendix A. VEXAG discussions and deliberations to date, together with these Venus goals, lead to the following findings and proposed actions for the next steps toward Venus exploration. VEXAG strongly suggests that the outstanding proposed actions be enacted as soon as possible. Venus New Frontiers and Discovery Missions The 2003 NRC Decadal Survey endorsed the Venus In Situ Explorer (VISE) as one of four New Frontiers mission candidates. In the 2009 New Frontiers AO, NASA identified a number of key science objectives and solicited a mission that would address all or a subset of these. Specifically, a New Frontiers Venus mission should be designed to: v

8 Understand the physics and chemistry of Venus atmosphere, especially the abundances of its trace gases, sulfur, light stable isotopes, and noble gas isotopes. Constrain the coupling of thermochemical, photochemical, and dynamic processes in Venus atmosphere and between the surface and atmosphere to understand radiative balance, climate, dynamics, and chemical cycles. Understand the physics and chemistry of Venus crust. Understand the properties of Venus atmosphere down to the surface and improve our understanding of Venus zonal cloud-level winds. Understand the weathering environment of the crust of Venus in the context of the dynamics of the atmosphere and the composition and texture of its surface materials. Search for planetary scale evidence of past hydrological cycles, oceans, and life and for constraints on the evolution of the atmosphere of Venus. Finding: VEXAG considers Venus In Situ Explorer (VISE) to be a vital New Frontiers mission as it has extremely high science value in the exploration of Venus. The 2003 NRC Decadal Survey recommended VISE as one of four 2003 New Frontiers AO mission candidates. The 2009 New Frontiers AO has included VISE as one of eight endorsed missions. Proposed Action: NASA should make Venus a priority for a future New Frontiers mission. The Discovery program, which began in the early 1990s, consists of PI-led missions that provide opportunities for targeted investigations with relatively rapid flight missions. Ten full missions and four missions of opportunity (instruments and investigations flown on a non-nasa spacecraft as well as extended missions for NASA spacecraft) have been selected. The Discovery program is open to proposals for scientific investigations that address any area embraced by NASA s Solar System Exploration program, including the search for planetary systems around other stars. Finding: The Discovery program provides an excellent means for tapping the creativity of the planetary science community for Venus exploration. Although Venus missions have been proposed at every Discovery opportunity, none has been selected for implementation. Thus, VEXAG finds that Venus Discovery-class missions are viable as they address fundamental solar system exploration goals. Proposed Action: NASA should make Venus a priority for a future Discovery-class mission. Venus Science Laboratory Measurements As described in Section 3, new laboratory measurements are needed to maximize the science return from current and future Venus missions. These measurements would characterize fundamental Venus processes based on newly revealed Venus system variables for (1) the atmosphere above the clouds, in which the temperature and pressure conditions are similar to those in the terrestrial atmosphere; (2) the sulfuric-acid-laced cloud layer; (3) the atmosphere below the clouds, in which the temperature and pressure range is unique for solar system exploration; and (4) the super-heated surface. Many of these laboratory measurements could be vi

9 conducted in a Venus Environmental Test Facility, which would simulate pressure, temperature, and atmospheric composition as a function of altitude. This enables would enable insights into how elements behave in the Venus environment and would also enable development and testing of new instruments and subsystems to operate under relevant conditions. Findings: New laboratory measurements are needed to maximize the science return from current and future Venus missions. Proposed Actions: NASA should support the development of a Venus Test Chamber suitable for both scientific research and instrument testing and provide access to all interested parties as a community facility. NASA should develop new research opportunities for funding Venus laboratory measurements and field investigations that support future Venus missions. Venus as a Future Earth/Comparative Planetology An understanding of the evolutionary histories and current states of the Venus and Mars climates is directly relevant for studies of the past and future climates of Earth (Appendix B). Investigating global warming and climate change on Earth has raised consciousness about the potential instability of terrestrial climate systems and the value in understanding the Venus greenhouse for comparisons with Earth s changing climate. Also, a key finding from the 2006 Chapman Conference on Venus as a Terrestrial Planet is that Venus may have had an ocean and could have been habitable for much of its history. Venus provides climatologists with an opportunity to test state-of-the-art models simulating the mechanisms and processes that led to Venus extreme climatology. NASA and VEXAG are pursuing an increased dialogue between Earth and Venus science communities. The thick atmosphere of Venus with its long radiative time constants and incomplete knowledge of the global radiation balance poses computational challenges. Current numerical models are inadequate. Findings: The study of the Venus greenhouse effect is needed to better understand Earth s climate stability and change. There is much to be learned about both planets as well as extrasolar-terrestrial planets from the divergent evolutionary paths of Earth and Venus. A key question is whether the warming Earth ultimately will become a Venus. Also, the Venus Atmosphere General Circulation Models still lag behind the capabilities of the terrestrial climate models. Such modeling efforts should be supported by NASA to fully exploit the atmospheric circulation observations made from past, current, and future missions to Venus. Proposed Action: A research program, encouraging conferences and/or workshops, should be initiated that brings together Earth and Venus scientists for a focused study of the evolutionary aspects (past and future) of these terrestrial-planet twins. Areas of mutual interest could include extreme climate scenarios, the role of volcanism and tectonics, as well as the presence/absence of a planetary dynamo in determining the fate of a planet and its atmosphere. vii

10 Technology Development Just as landed and mobile in situ exploration of the Mars surface has answered many key scientific questions, major advances in Venus science will require short- and long-lived landers, eventually leading to mobile in situ surface and/or near-surface measurements, networks, and surface sample return. In addition, a long-lived seismic network is of high priority but is currently a technological challenge. The impediment has been the technical difficulty of operating at the extreme pressures and at the high temperatures near and on the surface of Venus. There are opportunities to leverage technologies already developed for operation in similar environments encountered in aerospace (jet and rocket engine) and deep drilling applications. Nevertheless, the hot, supercritical carbon dioxide conditions at the surface of Venus are significant challenges for operations. Many other considerations related to the environment are unknown due to the lack of a Venus Environmental Test Facility. There are credible technical approaches, leveraging from technologies already developed in industry to achieve extended operation in the Venus environment. High-temperature electronics can enable systems that could operate for extended periods in the corrosive, high-pressure on the Venus surface. Advanced radioisotope-power systems and active thermal-control systems could enable operation of conventional components such as microprocessors or imaging sensors for extended periods on the Venus surface. Further details on technology requirements to enable or enhance future Venus missions can be found in the white paper Technologies for Future Venus Exploration, submitted to the Planetary Sciences Decadal Survey, available on the VEXAG web site. Findings: Although further work on mission architectures will be needed to define specific performance goals, technology work can and should begin now. NASA s involvement is needed to apply industry experience to the specific needs of in situ and near-surface exploration of Venus. Proposed Action: NASA should initiate a program to develop technologies for operation in the extreme environment of Venus, reflecting the priorities identified by the Venus Flagship Mission Study. These technologies could be competed through an amendment to the ROSES NRA: Sample Acquisition and Handling System: To understand the resource needs and technology development steps needed to meet the Venus design reference mission (VDRM) objectives. Lander Design: For the rotating pressure vessel and rough terrain landing approach in order to accommodate diverse terrain. Long-lived Seismometry and Meteorology: To address questions concerning which technical approach will be most fruitful and what performance can be achieved. Humans-in-the-Loop Lander Missions: To quantify how much lifetime is required for different levels of interaction. Technological advances are needed to achieve the required lifetime, which must be long enough to accommodate meaningful humans-in-the-loop interactions. Near-surface Aerial Mobility: To assess both refrigerated and nonrefrigerated implementations. viii

11 Technology Development for a Venus Flagship Mission As described in Section 2, certain high-priority investigations are so challenging that they cannot be achieved within the constraints of the Discovery and New Frontiers programs. With costs significantly higher than those of New Frontiers missions, flagship missions represent major national investments that must be strategically selected and implemented. Examples include comprehensive studies of planetary bodies, such as those undertaken by Voyager, Galileo, Cassini, and the Mars rovers. Thus, flagship missions conduct in-depth studies of solar system bodies as well as sample return from planetary surfaces. These missions generally require large propulsion systems and launch vehicles. In addition, flagship missions often require significant, focused technology development prior to mission start, extended engineering developments, and extensive pre-decisional trade studies to determine the proper balance of cost, risk, and science return. Finding: As part of the Venus Flagship Study, the NASA-appointed Science and Technology Definition Team reviewed the science goals and priorities identified by the VEXAG community and, with the support from a JPL Engineering Team, recommended a mission that resulted in the highest science return. The study also identified technology development needs that require further assessments and refinements. Proposed Action: The Planetary Science Division should support a second phase of the Venus Flagship Study, which would assess: Key technologies, such as those for sample acquisition and handling. Instrument development for in situ exploration elements. Precursor scientific measurements and technology developments that might be implemented with prior Discovery and New Frontiers missions. Technology investments needed for a Venus flagship mission emphasizing the long-lead time technologies needing early investments. Requirements for a Venus Environmental Test Facility, enabling instrument and subsystem development and testing at relevant pressure and temperature conditions. Alternative mission architectures. Alternative mission architectures would assess a Venus near-surface mobile explorer, a longlived surface network, a lifetime extension of the VDRM, and VDRM modifications if some objectives were accomplished on a prior Discovery or New Frontiers mission. ix

12 1. CONTEXT FOR VENUS EXPLORATION The context for Venus exploration, presented here, includes overviews of Venus as Earth s twin; the role of VEXAG; recent reports that address Venus exploration (such as the 2003 NRC Decadal Survey, Solar System Roadmap, etc.); the current status of NASA s support of Venus research; and recounting fifty years of Venus exploration. Accompanying vignettes provide additional information on Magellan, Venus Express, recent Venus Express VIRTIS results, and lessons learned from the Pioneer Venus Orbiter and Huygens. 1.1 Key Themes and Questions for Exploring Venus Venus is a unique terrestrial planet as distinct from Earth, Mars, and Mercury as Titan and Io are from the other Galilean and Saturnian satellites. Reasons for the divergent nature of these orbiting bodies are as varied as the bodies themselves. However, Venus is particularly compelling because it is so like Earth in size and bulk composition. In addition, Venus and Earth orbits are similarly close to the Sun, as a mere 0.3 AU separates Venus from Earth in a solar system that is >30 AU in scale. Although called Earth s twin due to these similarities, Venus, rather surprisingly, is a far cry from the Earth in terms of surface habitability as well as in atmospheric composition, chemistry, composition, global circulation, and meteorology. Thus, Venus can provide valuable insights into our origins and our ongoing searches for and characterization of terrestrial planets in our galaxy. Although Mars may provide a more hospitable environment for humans and life, Venus provides insights into possible states of terrestrial planets as well as Earth s future evolution. As part of a science community s contribution to the 2003 NRC Decadal Survey [1], Crisp and co-authors [2] summarized what has been learned from previous missions to Venus, including the Soviet Venera lander and Vega balloon missions, the Pioneer Venus orbiter and probe, and Magellan radar missions. Crisp and co-authors suggested the following scientific themes and key knowledge areas for future research and exploration of Venus: Past: Origin of terrestrial planets in our solar system o Noble and trace gases as evidence of early history and evolution o Surface properties and age determination o The history of interior volatiles Present: What processes shape the terrestrial planets? o The Venus greenhouse mechanism o Atmospheric super-rotation o Lightning o Middle-atmosphere composition and dynamics o Thermospheric composition and dynamics o Ionospheric structure, composition, and dynamics Future: What does Venus tell us about the fate of the Earth s environment? o Venus runaway greenhouse and the future of the Earth o The limits of plate tectonics and future geologic processes on Earth Several fundamental issues need to be addressed in order to explore these themes: the nature of geologic and atmospheric processes that stabilize climate, the evolutionary effects of impacts, 10

13 and the ways in which surface composition, internal makeup, and geologic history can sustain habitable environments. Factors that contributed to the uniqueness of each of the terrestrial planets include their bulk compositions, distances from the Sun, internal structures, and impact histories as well as the histories of their water and other volatiles. The analysis of Venus surface in seven locations by the Soviet landers in the 1970s and the isotopic measurements of volatiles by these landers and the Pioneer Venus probes provide some but not all of the information for constraining Venus evolutionary history. The 2003 NRC Decadal Survey [1] and Crisp et al. [2] concluded that further research and analysis of existing data are also needed to understand how Venus operates as a system and how it arrived at its present state. A renewed program focusing on Venus was called for as an important target for NASA scientific exploration. Several Venus missions in all size ranges were suggested in order to address the key questions in a systematic and reasonable way. These missions included Small noble and trace gas explorer Small atmospheric-composition orbiter Small- to medium-class global geological-process mapper Medium atmospheric-dynamics explorer with an orbiter and balloons Large-class surface and interior explorer mission, including a small network of landers Sample-return mission A subsequent 2006 Solar System Roadmap [3] investigated Venus missions with goals that mirror those in the 2003 NRC Decadal Survey and the Crisp paper. Although Discovery-class missions are left undefined, this Solar System Roadmap endorsed a New Frontiers Venus mission to perform in situ sampling and analysis of the atmosphere and surface as well as a subsequent sample-return flagship mission. This mission sequence has surface and lower atmosphere remote sensing and upper atmosphere in situ measurements from orbit, followed by a visit to the surface including first measurements and sampling technology demonstrations which in turn is followed by a sample return mission. The 2006 NASA Science Plan [4], developed by a subgroup for the NASA Advisory Council, took inputs from the 2003 NRC Decadal Survey and Solar System Exploration Roadmap to synthesize a grand vision for NASA science missions and supporting programs as a whole. Habitability is the guiding theme for both the Solar System Roadmap and the 2006 NASA Science Plan. At a Chapman Conference on Venus as a Terrestrial Planet held in February 2006 [5], the concept was presented that Venus had an ocean and a relatively mild climate for the first few billion years of its history. This suggests that future research should focus on the possible existence of a past ocean and a search for fossil biosignatures. The LPI workshop on Venus Geochemistry: Progress, Prospects, and Future Missions [6] in February 2009 provided an assessment of the most crucial investigations for understanding the geochemistry of Venus. 1.2 The Role of VEXAG NASA s Science Mission Directorate established the community-based Venus Exploration Analysis Group (VEXAG) in July 2005 to provide scientific and technical assessments for the exploration of Venus. VEXAG reports its findings to NASA and to the Planetary Science 11

14 Subcommittee of the NASA Advisory Council. VEXAG is currently composed of two co-chairs and five focus groups for Laboratory Measurements, Atmospheric Evolution, Venus Exploration Technologies, Venus Earth Climate Connections, and Planetary Formation and Evolution. Each focus group includes scientists, technology experts, NASA representatives, international partner representatives, and the VEXAG chair. Other focus groups may be constituted, as needed. The Jet Propulsion Laboratory, operated for NASA by the California Institute of Technology, manages VEXAG logistics on behalf of NASA's Planetary Science Division. This Pathways for Venus Exploration and its predecessor, VEXAG Goals, Objectives, Investigations, and Priorities, were developed to provide information for Venus exploration needs. It is a living document, with revisions on an as-needed basis to capture the consensus community views of the Venus community. From the first edition in November 2007 through February 2009 (VEXAG Meetings 4 6), modest updates were made to the document. This edition, now titled Pathways for Venus Exploration: 2009, has updates based largely on the Venus STDT efforts and the addition of a section on laboratory measurements. 1.3 Background: Recent Reports Addressing Venus Exploration Major studies involving Venus exploration include the 2003 NRC Decadal Survey for Solar System Exploration [1], with the companion paper by Crisp [2]; the 2006 NASA Solar System Exploration Roadmap [3]; and the 2006 NASA Science Plan [4]. As these studies provide a foundation for the expectations for Venus exploration, their findings on Venus science and missions are summarized here New Frontiers in the Solar System: An Integrated Exploration Strategy (2003) The NRC Decadal Survey for Solar System Exploration The relevant section of the Venus exploration 2003 NRC Decadal Survey is Chapter 2, Inner Solar System: Key to Habitable Worlds. Unifying themes for studies of the inner planets were identified as: The past: Where did we come from? What led to the uniqueness of our home planet? The present: What is going on now? What common processes shape Earth-like planets? The future: Where are we going? What fate awaits Earth s environment and that of the other terrestrial planets? Measurements to address these themes include: High-resolution imaging of the surface and radar probing of the subsurface. Surface mineralogical and chemical weathering investigations. Seismicity, heat flow, and other probing of the interior. Abundances of noble gases and their isotopes. Trace gas and atmosphere composition, density, temperature, and dynamics measurements from the upper atmosphere (including the ionosphere) to the surface, with a wide range of spatial and temporal sampling. Detection of radiation fields within the atmosphere and on the surface. In situ and remote imaging of the cloud layers and their dynamics (including winds) and variability. 12

15 Lightning detection by electromagnetic and/or optical means. Ionospheric and exospheric observations pertaining to atmosphere escape, and the contextual information to interpret them. To accomplish these measurements, the inner-planets panel of the 2003 NRC Decadal Survey for Solar System Exploration endorsed Venus In situ Explorer (VISE) as the next Venus New Frontiers class mission. VISE would have measurement objectives to determine: Atmosphere composition, including trace gases and isotopes. Noble gas isotope abundances. Meteorological information, including cloud-level winds. Near-infrared surface images at 10 km and closer ranges. Composition and mineralogy of a core sample. Information on surface weathering. These measurement objectives would be accomplished by multiple in-situ elements, including an aeroshell entry, passive insulation, and a rapid sample-acquisition system. Suggested instrumentation included a neutral-mass spectrometer, a meteorological package, radio tracking of balloon(s) for wind measurement, and a landed package with a near-infrared camera, a surface composition probe, imaging microscope, and a mineralogy analyzer. The technologies developed for VISE would be vital to a subsequent Venus Surface Sample Return (VSSR) mission, as rock ages, isotope ratios, and trace-element abundances can be obtained only with sophisticated Earth-based laboratory analyses of Venus return samples NASA s 2006 Solar System Exploration Roadmap Subsequent to the NRC Decadal Survey, NASA commissioned a new Solar System Roadmap Study [3] to establish planetary mission planning and priorities over the next 25 years. While revisions to these NASA roadmaps occur from time to time in order to update the science priorities and to build upon new discoveries and technologies, they are used as an official guide in targeting technology development and selections of flight investigations. Planetary exploration is carried out using both strategic missions, endorsed by these roadmaps, as well as by the Principal Investigator led Discovery and New Frontiers missions. The lower-cost Discovery program solicits proposals of mission concepts with any targeted planetary science focus, while the New Frontiers program solicits mission proposals addressing one of several specific high-priority science goals endorsed by the 2003 NRC Decadal Survey. Missions endorsed by the Solar System Roadmap are enabled by investments in both Science Definition Teams as well as technology developments tailored to their measurement goals and architectures. NASA s 2006 Solar System Roadmap [3] had planetary habitability as its guiding theme. The main science questions for a Venus mission were identified as: 1. How did the Sun s family of planets and minor bodies originate? 2. How did the solar system evolve to its current diverse state? 3. What are the characteristics of the solar system that led to the origin of life? 4. How did life begin and evolve on Earth? Has it evolved elsewhere in the solar system? 13

16 Vignette 1: Magellan The Magellan spacecraft was launched May 4, 1989, and arrived at Venus on August 10, The Magellan synthetic aperture radar (SAR) mapped 98% of the surface of Venus, with a resolution of about 100 m. Global altimetry and radiometry observations also measured surface topography and electrical properties. A global-gravity map was obtained after Magellan s aerobraking to a circular orbit. This aerobraking paved the way for several future missions. The Magellan mission ended in October 1994 with a controlled entry into the Venusian atmosphere. Magellan SAR images confirmed that an Earth-like system of plate tectonics does not operate on Venus, most likely due to the lack of surface water. Volcanism characterizes the surface; more than 85% consists of volcanic plains. Two types of highland regions were identified: topographic rises with abundant volcanism interpreted to be the result of mantle plumes, and complexly deformed highland regions called tessera plateaus, hypothesized to have formed over mantle upwellings or downwellings. The gravity field is highly correlated with surface topography, with some highland regions apparently supported by isostatic compensation and others by mantle plumes. Erosion of the surface is not significant due to the lack of water, although some surface modification by wind streaks was seen. The biggest surprise revealed by the Magellan mission was the crater population of Venus, which is randomly distributed and largely unmodified. Although resurfacing in the last 500 million to one billion years has obscured the impact history of Venus (particularly when compared to the Moon, Mars, and Mercury), the mean surface age is estimated to be ~500 million to one billion years. A debate has ensued over whether the entire surface was resurfaced in a catastrophic event approximately 500 million years ago, or if it was resurfaced more slowly over time. Understanding the history of the surface is not only important for constraining the interior evolution of Venus, but also the evolution of the atmosphere. While Magellan unveiled Venus, the data returned did not answer the question of why Venus and Earth have followed such different evolutionary paths. However, Magellan data provide a basis for a new set of specific scientific investigations, which will help constrain how habitable planets evolve. Magellan Radar Mosaic. Blues and greens are the lower plains areas; whites are the rugged highlands. 14

17 The first question on how the planets and minor bodies originated can be addressed by comparative studies of the abundances and isotopic ratios of the noble gases. The second question on the evolution of the solar system can be addressed with comparative studies of climate evolution and Venus surface-atmosphere interaction as well as via the chemical and isotopic compositions of Venus surface and atmosphere. The characterization of surface rocks particularly granitic and/or sedimentary rocks, hydrated silicates, and oxidized iron can give immensely valuable clues to climate change, in particular, yielding insights into the existence of an ocean early in Venus history. The third and fourth questions regarding the origin and evolution of possible past life-forms could similarly be addressed with surface samples that might contain isotopic, chemical, or structural signatures of biological specimens or processes. The Solar System Roadmap noted that the history of water and climate on Venus, including the timing and fate of a possible early ocean, should be investigated with in situ measurements prior to a sample return. In particular, it endorsed a VISE mission involving a brief visit to the surface to obtain samples, followed by sample analysis aloft in a balloon-borne robotic laboratory. A flagship Venus Mobile Explorer (VME) mission was proposed as the follow-on to VISE, possibly implemented via floating platforms rather than rovers. Whereas VISE would survive for only a few hours, VME would operate for days to weeks. VISE and VME would, in turn, enable a subsequent Venus sample return mission. The Solar System Roadmap recognized that both VISE and VME need technological developments in order to carry out their measurements at the high temperatures and pressures as well as the corrosive environment associated with Venus lower atmosphere and the surface. The Roadmap identified several enabling technologies, including: Radioisotope-power systems that can operate at the 460ºC near-surface temperatures, Thin metal balloons that would provide buoyancy and mobility and would survive under the harsh conditions, Thermal-control systems and pressure vessels to contain instruments and electronics, and High-temperature electronics and sample-acquisition mechanisms. Development of instrumentation for mineral and isotopic analyses that are sophisticated and accurate enough to produce answers to the key questions, and that can operate semiautonomously on a balloon platform, is also needed. The Solar System Roadmap noted that the technology developments on VISE would enable a subsequent VME mission. Thus, a New Frontiers VISE mission could be a technology demonstration mission as well as a science mission NASA Science Plan The 2006 NASA Science Plan [4], developed by a subgroup for the NASA Advisory Council, took inputs from the NRC Decadal Survey and Solar System Exploration Roadmap to synthesize a grand vision for NASA science missions and supporting programs as a whole. Reports from community advisory groups such as VEXAG were also used. As with the Solar System Roadmap, the guiding theme for the overall vision in this 2006 NASA Science Plan was habitability. This translated to five main science questions and four associated research objectives. 15

18 Vignette 2: Venus Express: Revealing the Mysteries of a Neighboring World Circling the planet once per Earth day since arriving in April 2006, ESA s Venus Express is the first mission to comprehensively explore the entire globe of our sister world from the ground up through the mesosphere, thermosphere, ionosphere, and into space. In particular, Venus Express is the first Venus orbiter to utilize the new tool of nighttime near-infrared spectroscopic imaging to regularly map the structure and movement of clouds and gases in the hostile depths of Venus below the obscuring upperlevel clouds, thereby obtaining new insights into the planet s enigmatic circulation, dynamic meteorology, and complex chemistry. This novel spectroscopic tool embodied on Venus Express as the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) maps both (1) the structure and movement of clouds at three different levels (~50-km altitude on the nightside, and 59- and 70-km altitude on the dayside), and (2) the abundances of a plethora of chemically reactive species, including water (H 2 O), sulfur dioxide (SO 2 ), carbon monoxide (CO), and OCS at a variety of altitudes in the deep atmosphere below the clouds. It also observes the hot (~740 K) surface of Venus near 1-micron wavelength, mapping thermal emissions from the ground, which can be used to constrain 1-micron surface emissivity and composition as well as to search for and characterize active volcanic processes, as evidenced by locally elevated thermal temperatures and enhanced trace-gas abundances. Further information from the surface comes from a bistatic-radar experiment that utilizes the spacecraft s communication-radio system to reflect signals off the surface toward Earth. As one facet of the Venus Radio experiment (VeRa), these echoes of Venus are then intercepted by NASA s Deep Space Network (DSN) to reveal characteristics of Venus surface texture and emissivity at cm wavelengths. VeRa also utilizes radio-occultation techniques to measure the vertical profile of Venus temperature, density, and pressure down to ~36-km altitude over a large range of latitudes, thereby providing detailed information on the planet s 3-D temperature structure, thermal winds, and vertical wave properties. The Venus Monitoring Camera (VMC) images the upper-level clouds in the UV and near-ir at 0.36 and 0.94 µm wavelength, thus providing high-spatial resolution imagery (better than 1-km resolution) of the wave and cell structures of Venus s clouds, as well as providing detailed movies of their motions. Long exposures by this experiment of Venus night side can be used to search for lightning. Venus Express also scrutinizes the upper atmosphere of Venus above the clouds. Dual UV and near- IR spectrometers, SPICAV and SOIR, regularly observe the limb of the planet in solar occultation from close range (typically less than 1000 km), thereby producing high-resolution (~5-km) vertical profiles of a variety of light-absorbing species, including H 2 O, CO, and SO 2. VIRTIS observes nighttime emissions produced by the recombination of photochemically generated oxygen atoms into oxygen molecules, thereby revealing key day-to-night circulation flows near the 120-km level. Also, VIRTIS maps the nighttime temperatures of the atmosphere at 5-km vertical resolution from 60 to 90 km, providing constraints on the thermal winds in this region. Enigmatic polar features known as Polar Dipoles at the south and north poles, possible manifestations of the Hadley circulation, can also be mapped in detail and followed in time. Venus Express also investigates the planet s ionosphere and near-space environment. ASPERA measures the solar wind as it streams around Venus, assessing the number density and speed of protons ejected from the Sun. A magnetometer experiment (MAG) measures the local magnetic field produced by ionization of Venus upper atmosphere by both intense UV sunlight and solar wind. Joint measurements by ASPERA and MAG from a variety of positions around Venus then reveal how Venus interacts with the Sun s magnetosphere and solar wind. ASPERA also measures ionized atoms such as hydrogen and oxygen ejected from the planet s tenuous uppermost atmosphere by the solar wind, thus providing constraints on the loss of atmospheric elements responsible for the extremely dry state of Venus today. Venus Express has generated more than 1 Terabit of data to Earth in its first 500 days of operation. Recent Venus Express VIRTIS results are given in Vignette 3. 16

19 The science questions are: How did the Sun s family of planets and minor bodies originate? How did the solar system evolve to its current diverse state? What are the characteristics of the solar system that led to the origin of life? How did life begin and evolve on Earth and has it evolved elsewhere in the solar system? What are the hazards and resources in the solar-system environment that will affect the extension of human presence in space? The associated research objectives (some abridged) to address these questions are: Learn how the Sun s family of planets and minor bodies originated and evolved. Understand the processes that determine the history and future habitability in the solar system. Identify and investigate past and/or present habitable environments and determine if there is or ever has been life elsewhere in the solar system. Explore the space environment to discover potential hazards to humans and to search for resources. The expected similar yet disparate natures of present-day Venus and Earth were noted, with Venus being an excellent test bed for understanding the evolution of habitable planets. The first mission, VISE, would spend a short time on the surface and would provide some of the technological and scientific groundwork for sample return. A subsequent detailed surface exploration by a Venus Mobile Explorer (a strategic mission also endorsed by the Solar System Roadmap) would lead to a sample-return mission. The instrument developments for in situ Venus lower atmosphere and surface exploration are technical precursors for these future Venus missions. 1.4 Current Status of NASA s Support of Venus Research The Crisp paper [2], the adjunct to the 2003 NRC Decadal Survey [1], provides a summary of Venus science status prior to ESA s Venus Express Mission. Their assessment was that after the observations of the Pioneer Venus Orbiter (PVO) and Magellan, vital knowledge of the interior structure, surface composition, lower and middle atmosphere, and atmosphere-surface interactions is still minimal to missing. Although Magellan exposed the resurfacing enigma, we do not know why it happened, over what time period it occurred, and what the larger implications and consequences are. Similarly, PVO found possible evidence of active volcanism, but the results are only suggestive. In the interest of brevity, we refer the reader to the Crisp paper [2] for the details and focus here on programmatic issues related to our ability to expand the Venus knowledge base. More recently, NASA has supported more than a dozen science investigations as part of its Venus Express mission support. Some eighteen investigators distributed among three categories Participating Scientists, Interdisciplinary Scientists, and Instrument Scientists have been supported to help optimize the science return of the Venus Express Mission as well as to conduct focused investigations on the chemistry, dynamics, evolution, magnetospheric environment, and surface properties of Venus. As part of this effort, Venus Express data will be deposited in an 17

20 open European data archive that parallels the NASA Planetary Data system. These data are especially beneficial to atmospheric science investigators. In the past, Venus data analysis has benefited from targeted Venus Data Analysis Programs (VDAP) within NASA s research and analysis (R&A) initiatives. Such programs focus on selected topics of interest to NASA, such as exploiting new observations toward increasing knowledge needed for informed exploration planning. It is important to exploit the data from current, past, and future missions to answer the science questions posed above. The challenge is how these key Venus data analyses and interpretations can be supported within NASA s R&A program s budgets. Of the ~1000 NASA Planetary R&A investigations funded per year, about thirty are currently for Venus-focused investigations. Although a few of these are for data archiving activities, the majority are for science efforts that run the gamut from tectonism to climate change. In summary, NASA s investments in analysis of Venus Express results, continued study of Venus geology and geophysics, and understanding Venus atmosphere evolution are needed to understand Venus and to provide a foundation for future missions. 1.5 Fifty Years of Venus Exploration To complete the context for future Venus exploration, we examined the past and current Venus missions (Table 1-1), which have been carried out by the Russian, European, Japanese, and American space agencies. The Russian space program in 1961 initiated an extensive program for the exploration of Venus, which included atmospheric probes, landers, orbiters, and balloon missions. This produced many successful missions, which provided information on how to survive and conduct experiments in the Venus environment. The Venera 1 impactor was the first spacecraft to land on another planet. The Venera 13 lander survived on the surface for 127 minutes, which is still unmatched by any other spacecraft at Venus. The Vega balloons demonstrated the ability of balloons for aerial exploration. U.S. Venus exploration commenced in 1962 with the flyby of the Mariner 2 spacecraft. Following this, U.S. missions conducted an exploration of the atmosphere and the surface of Venus. In the late seventies, NASA conducted the orbiter/multiprobe Pioneer Venus mission, with the objective of understanding the atmosphere of the planet. Magellan in the early 1990s mapped 98% of the surface of the planet, as described in Vignette 1. Today, Europe s Venus Express orbiter is providing significant science contributions to the understanding of Earth s sister planet by measuring atmospheric dynamics and structure; composition and chemistry; cloud layers and hazes; radiative balance; the plasma environment and escape processes; and, to a certain extent, surface properties and geology through remote sensing, as described in vignettes 2 and 3. Another orbiter, Japan s Planet-C (Venus Climate Orbiter, VCO), is under development for a mid-2010 launch. VCO investigations include surface imaging with an infrared camera and experiments designed to detect possible lightning and present-surface volcanism. 18

21 Spacecraft Table 1 1. Summary of Past, Present, and Future Venus Missions. Launch Date Type of Mission Venera Impactor; spacecraft sealed and pressurized with nitrogen Mariner Flyby; first to fly by Venus (US) Zond Probe and main bus; entry capsule designed to withstand 60 to 80 C / 2 to 5 bars Venera 2 & Probe and main bus; entered the atmosphere of Venus; designed for 80 C / 5 bar Venera Stopped transmitting at 25 km; 93 minutes descent; first to descend through the atmosphere; designed for 300 C / 20 bar (Russia) Mariner Flyby (US) Venera Hard-lander; stopped transmitting at ~20 km (320 C / 27 bar); 53 min descent (Russia) Venera Hard-lander; stopped transmitting at ~20 km (320 C / 27 bar); 51 min descent (Russia) Venera First to soft land on surface; parachute failure, rough landing, landed on the side; 55 min descent / 23 min on surface (Russia) Venera Performed as designed; soft-lander; 55 min descent / 50 min on surface (Russia) Mariner Flyby en route to Mercury (US) Venera Orbiter (moves out of radio range); soft-lander; first to return photos of surface; min descent / 53 min on surface (Russia) Venera Orbiter (moves out of radio range); soft-lander; min descent / 65 min on surface (Russia) Pioneer-Venus Orbiter with radar altimeter; first detailed radar mapping of surface (US) Pioneer-Venus Four hard-landers (US) Venera Flyby, soft-lander; 60 min descent / 95 min on surface (Russia) Venera Flyby, soft-lander; 60 min descent / 110 min on surface (Russia) Venera Orbiter, soft-lander; first color images of surface; 55 min descent / 127 min on surface (Russia) Venera Orbiter, soft-lander; 55 min descent / 57 min on surface (Russia) Venera Orbiter with radar mapper (Russia) Venera Orbiter with radar mapper (Russia) Vega Flyby, atmospheric balloon probe (Russia / International) Vega Flyby, atmospheric balloon probe (Russia / International) Magellan 1989 Orbiter with radar mapper (mapped 98% of the surface); first high-resolution global map of Venus (US) Venus Express 2005 Orbiter ongoing mission (ESA) Planet-C (VCO) 2010 Venus Climate Orbiter Planet-C in development (JAXA) Venera-D 2016 Orbiter with lander and balloons (Russia) 19

22 Artist s concept of Venus Express spacecraft operating at Venus since Courtesy of ESA. Vignette 3: Recent Venus Express VIRTIS Results Surface Temperatures. (left) Black-body temperatures measured for the surface correlate well with topography (right), due to decreases of surface temperature with height. Slight variations in this correlation may indicate differences in the surface rock emissivities. Courtesy of ESA. 20

23 Vignette 3: Recent Venus Express VIRTIS Results (continued) Day and night images of the south pole of Venus. Daytime images (left side of each image) show high-altitude clouds of small particles near the 70-km level. Night images (right side of each image) show thick clouds of relatively large particles near the 50-km level. Clouds at night are seen in silhouette against the glow of Venus hot lower atmosphere, using near-infrared thermal radiation near 1.7-µm wavelength. Following the dark (cloudy) and bright (less cloudy) regions, as they move around the planet, yields measurements of Venus winds near the 55-km level. Comparison with 70-km altitude winds as measured by the movements of dayside clouds yields wind shears, providing clues to the processes powering Venus enigmatic system of super-rotating winds. Polar Vortex Phenomena. Venus Express confirmed that the Venusian south pole has a complex and variable vortex-like feature, sometimes taking the shape of a dipole, but at other times morphing into tripolar, quadrupolar, and amorphous, indistinct shapes. Temperatures near the 60-km level are shown in the nighttime portions of 5-µm images, revealing the dipole to be notably hotter than its surroundings, likely due to compression of descending air. (Bottom left image, taken in daytime conditions, is overexposed by the Sun). Right-hand, close-up image shows filamentary nature of the dipole, which changes shape constantly in the dynamically active atmosphere. The dipole is offset from the pole by several degrees of latitude and rotates with a period of about 2.4 days. 21

24 Vignette 4: Lessons Learned from Pioneer Venus Orbiter and Huygens Pioneer Venus Orbiter Venus orbiter with comprehensive payload for remote sensing and in situ aeronomy. 1. Showed that the greenhouse effect operates much more efficiently on Venus. Data from the four atmospheric probes led to a greenhouse model that closely matches the observed vertical temperature profile. 2. Measured long-term changes in atmospheric minor constituents above the clouds. These indicate forcings on decades-long timescales. Possible causes are volcanic activity and variable dynamics of the middle atmosphere. 3. Measured upper atmosphere s response to solar cycle. Pioneer Venus demonstrated the need to examine the long-term stability of the current climate and to probe all altitudes during an entire solar cycle. In addition, the nature of the middle and deep atmosphere remains to be examined via remotely sensed spectral signatures or long-duration in situ probes. Huygens Titan lander with cameras, spectrometers, and in situ atmospheric and surface science instruments. 1. Huygens provided vertical resolution and sensitivity impossible from remote sensing by the Cassini orbiter, thus providing direct measurements of wind and chemical profiles from >200 km altitude down to the surface and measurement of volatiles entrained within surface materials. 2. Huygens descent images, when combined with other remote observations, allowed identification of dune fields by their distinctive color. This, in turn, yielded the exact lander location and ground truth for remote sensing as well as provided regional context for the landing-site measurements. Also, radar identification of fields of linear dunes on Titan allowed comparisons to similar features on Earth, Venus, and Mars. Comparisons to Earth analogs in turn have increased understanding of surface processes on both bodies. Pioneer Venus Orbiter and Probes. Artist s Conception of Huygens Probe. Courtesy of ESA. 22

25 2. VENUS EXPLORATION MISSIONS In parallel with providing the context for Venus exploration, it is useful to examine past, current, and future Venus missions and to examine the Venus missions identified in the 2003 NRC Decadal Survey and Crisp paper [1, 2], the 2006 NASA Solar System Roadmap [3], the 2007 NASA Science Plan [4], and the 2008 Venus STDT study [7]. These reports also identify technologies that must be developed in order to accomplish the endorsed science measurements. These technologies, in turn, are closely linked to the proposed new missions and their implementations through various mission architectures. The relevant missions and their science traceability the mapping of the science goals and objectives against various proposed missions is discussed in this section. Vignette 5 provides additional information on balloonborne in situ exploration. 2.1 Discovery, New Frontiers, and Flagship Missions Venus exploration is discussed in the NRC Decadal Study [1] and in the NASA Solar System Exploration Roadmap [3], which endorsed missions to solar system bodies under three mission classes: The Discovery Program consists of PI-led smaller missions that provide opportunities for targeted investigations with relatively rapid flight missions. The New Frontiers Program consists of PI-led medium-class missions addressing specific strategic scientific investigations endorsed by the NRC Decadal Survey. Flagship missions address high-priority investigations so challenging that they must be implemented with resources significantly larger than those allocated to New Frontiers missions Discovery-Class Missions The Discovery Program, which began in the early 1990s, consists of PI-led missions that provide opportunities for targeted investigations with relatively rapid flight missions. Ten full missions and four missions of opportunity (instruments and investigations flown on a non-nasa spacecraft as well as extended missions for NASA spacecraft) have been selected. The Discovery program is open to proposals for scientific investigations that address any area embraced by NASA s Solar System Exploration program, including the search for planetary systems around other stars. This provides an excellent means for tapping the creativity of the planetary science community. Details on these past and current missions can be found on the Discovery Program web site at New Frontiers Missions The New Frontiers program comprises medium-class missions that address objectives identified by the NRC Decadal Survey [1]. In particular, the Venus In Situ Explorer (VISE) was endorsed by the NRC in its 2003 Decadal Survey and the NRC Committee for New Opportunities for Solar System Exploration (NOSSE) in 2007 [8]. Although exploration of the surface and lower atmosphere of Venus will be a significant technical challenge, it also will yield high scientific rewards. Venus is considered Earth s sister planet, and there is much to learn about Earth by studying Venus tectonics, volcanism, surface-atmospheric processes, atmospheric dynamics, and chemistry. Furthermore, technology demonstrations on VISE could 23

26 Vignette 5: Experiencing Venus by Air: The Advantages of Balloon-Borne In Situ Exploration Balloons provide unique, long-term platforms from which to address such fundamental issues as the origin, formation, evolution, chemistry, and dynamics of Venus and its dense atmosphere. As successfully and dramatically demonstrated by the USSR s twin Vega balloons in 1985, such aerial vehicles can uniquely measure Venus dynamic environment in three dimensions, as they ride the powerful, convective waves in Venus clouds near the 55-km level. Also, by sampling over an extended period, balloons can measure the abundances of a plethora of tell-tale chemical and noble gases, key to understanding Venus origin, evolution meteorology, and chemistry. While the Vega balloons successfully pioneered the use of aerial platforms to explore planets, weight restrictions prevented their measuring abundances of diagnostic chemicals or noble gases. The new, highly miniaturized instrument technologies of the 21 st century allow such measurements to be made. Our knowledge of the origin, formation, and evolution of all the planets including Venus relies primarily on knowledge of the bulk abundances and isotopic ratios of the noble gases helium, neon, argon, krypton, and xenon as well as on the isotopic distributions of light gases such as nitrogen. For example, xenon, with its nine tell-tale isotopes, along with krypton (Kr) and argon (Ar) and their isotopes, can together reveal a range of ancient cataclysms on Venus and other planets. These include the nature of (1) any global atmospheric blowoff by intense solar EUV radiation, and (2) any major impacts by large (>200-km diameter) comet-like planetesimals from the outer solar system. On the other terrestrial planets where xenon has been adequately measured Earth and Mars one or more such major cataclysmic events occurred early in their histories. Similar measurements for Venus would reveal whether cataclysmic events occurred on our sister planet as well. As these key tell-tale noble elements have no appreciable spectral signature, in situ sampling is the only means by which to measure them. Thus, to reach into the planet s past, one must sample Venus directly, with typical precisions of better than 5% for both isotopic ratios and bulk abundances. Such detailed and precise isotopic measurements can be more than adequately achieved by today s lightweight balloon-borne instrumentation suspended for several days in the middle atmosphere near an altitude of 55 km. Riding the strong winds of Venus near the Earth-like 297-K, 0.5-bar pressure level, hundreds of high-precision, mass-spectroscopy measurements can be acquired and transmitted during the balloon s two-day transit across the face of Venus as viewed from Earth, thus achieving the requisite tight constraints on isotopic abundances of all the noble gases and many light elements. In addition, vertical profiles of chemically active species can be obtained as the balloon rides the planet s dynamic array of gravity waves, planetary waves, and convective motions, thus providing unique insights into photochemical and thermochemical processes. Additionally, the planet s sulfur-based meteorology can be explored, for example, by measuring over time and altitude both cloud particles and their parent cloudforming gases, as well as lightning frequency and strength. As was done by the Vega balloons, both local dynamics and planet-scale atmospheric circulation can be investigated via radio-tracking of the balloon from Earth. Today s improved interferometric and Doppler tracking together with well-calibrated onboard pressure sensors can yield knowledge of all three components of balloon velocity an order of magnitude more accurately than achieved by Vega, that is, better than 10 cm/s on time scales of a minute in the vertical and an hour in the horizontal. Such accuracies can provide fundamental measurements of the amplitude and power of gravity waves and the latitude/longitude characteristics of zonal and meridional winds at known pressure levels. All of these are key to understanding the processes powering Venus super-rotating circulation. Beyond providing unique insights into the origin/evolution, dynamics, and chemistry of Venus, exploring Venus by balloon provides valuable experience for flying the skies of other worlds. Experiencing Venus for days and perhaps weeks by the first airborne rovers could well lead to a new era of aeroving the distant skies of Titan and the many gas giants of the outer solar system. 24

27 pave the way for a future flagship class mission to the surface and lower atmosphere of Venus, as well as for a subsequent Venus Surface Sample Return (VSSR) mission. In the 2009 New Frontiers AO, NASA identified a number of key science objectives and solicited a mission that would address all or a subset of these. Specifically, a New Frontiers Venus mission should be designed to: Understand the physics and chemistry of the Venus atmosphere, especially the abundances of its trace gases, sulfur, light stable isotopes, and noble gas isotopes. Constrain the coupling of thermochemical, photochemical, and dynamic processes in Venus atmosphere and between the surface and atmosphere to understand radiative balance, climate, dynamics, and chemical cycles. Understand the physics and chemistry of the Venus crust. Understand the properties of the Venus atmosphere down to the surface and improve our understanding of Venus zonal cloud-level winds. Understand the weathering environment of the Venus crust in the context of the dynamics of the atmosphere and the composition and texture of its surface materials. Search for planetary scale evidence of past hydrological cycles, oceans, and life and for constraints on the evolution of the Venus atmosphere. The 2009 New Frontiers AO identified eight potential medium-class missions, including the Venus In Situ Explorer (VISE). A New Frontiers mission will be selected and launched not later than the end of Venus Flagship-Class Missions Certain high-priority investigations are so challenging that they cannot be achieved within the constraints of the Discovery and New Frontiers programs. With costs significantly larger than those of New Frontiers missions, flagship missions represent major national investments that must be strategically selected and implemented. Examples include comprehensive studies of planetary bodies, such as those undertaken by Voyager, Galileo, Cassini, and the Mars rovers. Thus, flagship missions conduct in-depth studies of solar system bodies as well as sample return from planetary surfaces. These missions generally require large propulsion systems and launch vehicles. In addition, flagship missions often require significant focused technology development prior to mission start, extended engineering developments, and extensive pre-decisional trade studies to determine the proper balance of cost, risk, and science return Venus Flagship Design Reference Mission NASA Headquarters conducted a Venus flagship mission study in based on recommendations identified by the 2003 NRC Decadal Survey [1] and the NASA Solar System Exploration Roadmap [3], in parallel with a finding from VEXAG. This study was conducted by a NASA-appointed Venus STDT, an international group of scientists and engineers from France, Germany, Japan, the Netherlands, the Russian Federation, and the United States. JPL supported this study with a dedicated engineering team and the Advanced Project Design Team (Team X). The STDT assessed science goals and investigations, leading to the Venus Design Reference Mission (VDRM) which includes a notional instrument payload, subsystems, and technologies implemented using an orbiter, balloons, and landers (Figure 2-1). 25

28 Pathways for Venus Exploration: 2009 Figure 2 1. Artist s concept of Venus flagship orbiter, balloons, and landers elements of the Venus Design Reference Mission, developed by the Venus STDT in Artwork by Tibor Balint. 26

29 NASA guidelines for this study specified a launch between 2020 and 2025 with a cost of $3B to $4B. Although the study assumed no international contributions, it is expected that a future NASA Venus flagship mission would, in fact, be conducted with international collaboration. This mission would revolutionize our understanding of the climate of terrestrial planets (including the coupling between volcanism, tectonism, the interior, and the atmosphere); the habitability of planets; and the geologic history of Venus (including the existence of a past ocean). The mission would address top-level science questions: Is Venus geologically active today? How does the Venus atmospheric greenhouse work? What does the surface say about Venus geological history? How does the Venus atmospheric super-rotation work? How do the surface and atmosphere interact to affect their compositions? How are the clouds formed and maintained? How is sunlight absorbed in the Venus atmosphere? What atmospheric loss mechanisms are currently at work? What kind of basalts make up Venus lava flows? Are there evolved, continental-like rocks on Venus? How is heat transported in the mantle, and how thick is the thermal lithosphere? What happened on Venus to erase 80% of its geologic history? Did Venus ever have oceans and, if so, for how long? Did the early atmosphere of Venus experience catastrophic loss, either due to hydrodynamic escape or a large impact? Did Venus have a magnetic field, and does it have a remnant one now? These questions translate to 3 major themes: What Does the Venus Greenhouse Tell Us About Climate Change? Addressed by characterizing the dynamics, chemical cycles, and radiative balance of the Venus atmosphere and by placing constraints on the evolution of the Venus atmosphere. How Active is Venus? Addressed by identifying evidence for active tectonism and volcanism in order to place constraints on evolution of tectonic and volcanic styles, characterizing the structure and dynamics of the interior in order to place constraints on resurfacing, and by placing constraints on stratigraphy, resurfacing, and other geologic processes. When and Where Did the Water Go? Addressed by identifying evidence of past environmental conditions, including oceans, and characterizing geologic units in terms of chemical and mineralogical composition of the surface rocks in context of past and present environmental conditions. 27

30 Pathways for Venus Exploration: 2009 Figure 2 2. Overviews of Venus Missions Endorsed by the Solar System Exploration Roadmap 28

31 The flagship mission to address these questions, the Venus Design Reference Mission (VDRM), consists of two launched spacecraft, one being an orbiter and the other delivering two entry vehicles, where each entry vehicle carries dual landers and balloons (Figure 2-1). In this dual-launch configuration, two Atlas V launches are required to send these spacecraft to Venus. The first launch vehicle delivers the two landers and the two balloons to Venus on a Type-IV trajectory. The second launch vehicle delivers the orbiter on a Type-II trajectory to Venus. The orbiter arrives at Venus first, with sufficient time for checkout and orbit phasing before the landers and balloons arrive 3.5 months later. The orbiter supports two functions. First, it acts as a telecommunication relay to transmit data to/from the landers and balloons to Earth during the in situ observations. Once the landers and balloons complete their observations, the orbiter transitions from its telecom relay phase to an orbital science phase with a 2-year remote sensing mission. The landers are designed for a 1-hour atmospheric descent followed by 5 hours of operation on the surface. The balloons and their payloads are designed to operate for 1 month at an altitude of 55 km, circumnavigating the planet several times, while gradually drifting from mid latitudes towards the polar vortex. VDRM can be implemented with modest technology developments, such as those for sample acquisition and handling; aerial mobility; and high temperature tolerant components (e.g., sensors, electronics, mechanisms, instruments, and power storage). This mission lends itself to spinoffs, as various elements could be implemented as precursor Discovery or New Frontiers missions. Continuation of the flagship study would further refine science objectives, and technology development planning based on technology needs for this and other mission architectures requiring long-lived mission elements. The fact sheet for NASA s Flagship Mission to Venus follows the appendices Other Future Venus Flagship-Class Missions Flagship missions beyond the timeframe (such as those shown in Figure 2-2) will be defined and selected based upon the results of earlier missions. Other high-priority flagshipclass missions for Venus endorsed by the NRC Decadal Survey [1] and NASA Solar System Roadmap [3] include the following: Venus Mobile Explorer (VME) a long-range, long-duration air mobility platform would perform up to several months of extensive measurements at the Venus surface, including a search for granitic and sedimentary rocks. This would be accomplished by in situ analysis of the crust for meta-stable hydrated silicates and measurements of the oxidation and mineralogical state of iron. VME and VISE could determine how long ago an ocean may have existed on Venus and, therefore, how long Venus may have had to nurture life. Equipped with visual imaging and a targeted set of geochemical sensors, VME would use mobile scientific exploration to sample different surface sites. VME would have the advantages of mobility demonstrated by the Mars Exploration Rovers, as these rovers have accomplished extraordinary advances in the understanding of geochemistry and hence past climate conditions on Mars. A similar understanding for Venus would be enabled by VME. 29

32 A Venus Surface Sample Return (VSSR) mission would return a Venus surface sample to Earth for further analysis. This enables high-precision measurements of the isotopic composition of oxygen in surface rocks, as well as trace elements, in order to characterize the age of rocks and core-mantle formation. This mission requires significant technology development of sample acquisition and handling instrumentation, including a multi-stage ascent air-mobility system to lift the sample to launch altitude. In orbit, rendezvous expertise could be inherited from a Mars Sample Return mission. A Venus Geophysical Network mission would investigate the internal structure and seismic activity of the planet as well as monitor the circulation of the atmosphere. It would provide insight into the causes and effects of the apparent global climate change that Venus experienced in the distant past, as discussed at the Chapman Conference on Venus Terrestrial Planet [5]. Key technologies for this long-lived in situ mission include high-temperature telecom systems, actively cooled radioisotope power systems, and highly efficient thermal-management and pressure-mitigation systems. Another challenge is transmitting large data volumes back to Earth. For further details on the VME, VSSR, and Venus Geophysical Network missions, see their respective overviews (Figure 2-2). 2.3 Traceability of VEXAG Science Objectives to Future Flagship Missions Potential science returns from the future Venus missions described above are shown in a traceability matrix (Table 2-1), which maps the missions to the VEXAG science, goals, and objectives (Appendix A). Each objective is grouped into one of three main VEXAG goals, while missions are divided into the flagship mission classes. Green dots indicate that a mission can produce major contributions to meeting VEXAG science objectives, while light-blue triangles identify the missions that can produce contributory science to these objectives. Artist s concept of balloon explorers flying in the Venusian skies. Such mobile vehicles, riding the strong winds of Venus under Earth like temperature and pressure conditions, can explore the dynamics and active chemistry of Venus while also uncovering tell tale clues to Venus past locked in isotopic distributions of noble and light gases. 30

33 Table 2 1. Traceability Matrix of Objectives Met with Venus Flagship Missions Flagship Class Missions VDRM Mission Elements Enhanced VDRM Other Missions Objectives Venus Orbiter Mid-Altitude Balloon(s) Short Lived Lander(s) Enhanced Balloon(s) Enhanced Lander(s) VME VNET VSSR Goal I. Origin and Evolution Understand atmospheric evolution Seek evidence for past changes in interior dynamics Determine if Venus was ever habitable Goal II. Venus as a Terrestrial Planet Understand what the chemistry and mineralogy of the crust tell us about processes that shaped the surface of Venus over time Assess the current structure and dynamics of the interior Characterize the current rates and styles of volcanism and tectonism, and how have they varied over time Characterize current processes in the atmosphere Goal III. Climate Change and the Future of Earth Characterize the Venus Greenhouse Determine if there was ever liquid water on the surface of Venus Characterize how the interior, surface, and atmosphere interact Convention: Major Contribution Supporting Contributions VDRM Venus Design Reference Mission (Orbiter + 2 short lived landers + 2 balloons): Venus Orbiter Science & relay telecon orbiter Mid-Altitude Balloon(s) Superpressure balloons in the 52 km-to-70 km altitude range Short lived landers Descent science + 5 hours on the surface Enhanced VDRM: Enhanced Balloon(s) ASRG powered superpressure balloon, continuous operation Enhanced Lander(s) Long-lived lander, 90 days on the surface, humans-in-the-loop, seismic measurements, active cooling and radioactive power source. Enhanced VDRM Architectures: VME Venus Mobile Explorer near surface, using bellows; possibly periodic surface access; 90-day aerial traverse VNET Venus Network Explorer; seismic network with 4 or more landed elements VSSR Venus Surface Sample Return; multiple balloons, short surface stay 31

34 Artist s concept of lightening on Venus. Courtesy of ESA. The Venus surface observed by the Russian Venera lander showing a platey basaltic surface. 32

35 2.4 ESA Cosmic Vision European Venus Explorer The European Venus Explorer (EVE) mission was proposed to the European Space Agency (ESA) for launch in in response to 2007 ESA s Cosmic Vision AO. Although ESA s Venus Express mission will answer many questions about Venus, including those relating to the isotopic-ratio and cloud-chemistry objectives, other questions relating to Venus need to be addressed. The answers to these questions are key to understanding climate evolution on Venus. Consequently, the EVE mission focuses on understanding the evolution of Venus and its climate, with relevance to terrestrial planets. The proposed EVE mission consists of a balloon platform floating at an altitude of km; a short-lived lander provided by Russia; and an orbiter with a polar orbit, which would perform science observations as well as relay data from the balloon and short-lived lander. The balloon lifetime of 7 days enables one full transit around the planet. This is significantly longer than the 48 hours of data returned from Russia s Vega balloons. Earth-based VLBI and Doppler measurements would provide tracking information for the orbiter, allowing measurement of the variations in the planet s gravity field, while the balloon and short-lived lander will yield wind measurements in the lower atmosphere. The probe s descent through the atmosphere would last 60 minutes, followed by 30 minutes operation on the surface. The Japanese space agency (JAXA) also proposed to augment this mission with a small water-vaporinflated balloon, which would be deployed at 35-km altitude and then communicate directly to Earth. Thus, the EVE mission was proposed as an international project, with mission elements from Europe, Russia, and Japan. While it was not selected as the next medium-class Cosmic Vision mission, the EVE proposal was recognized for its high science value and resulted in a European investment for balloon technology. This development will greatly benefit EVE when proposed again as a potential subsequent Cosmic Vision mission. 2.5 Russian Space Agency Venera-D The Russians are contemplating a new Venus mission, Venera-D, with a target launch in 2016 on Soyuz-Fregat. This mission would have an orbiter, balloon, and lander for precise measurements of clouds, surface properties, and mineral composition. The orbiter is 600 kg with 50 kg for science instruments. The balloon and lander are 170 kg with 20 kg for science instruments. Lifetime of the lander would be 1 3 months using an internal evaporating water mass to provide temperatures. The balloon will be deployed to southern sub-polar regions, where the atmosphere is not that well understood and where the balloon could circumnavigate Venus a few times during the lifetime of the balloon. The lander, with a lifetime of 50 days, a mass of about 20 kg and silica-based electronics, would be inside a 0.2-meter spherical dewar, powered by batteries located outside the pressure vessel. Contemplated orbiter instruments are Fourier spectrometer, mapping spectrometer (like VIRTIS), radiometer, and magnetometer. Balloon instruments would be nephelometer, meteorological (pressure/temperature/winds), mass spectrometer, CCD camera, radiometer, acoustical sensor, electric/magnetic field sensor, and meteorological dropsondes. Lander instruments would be nephelometer, meteorological (pressure/temperature/winds, mass spectrometer, wide/narrow-angle camera, acoustical sensor, and electric/magnetic field sensor. 33

36 3. VENUS LABORATORY MEASUREMENTS In addition to the missions for future Venus exploration described in the previous section, new laboratory measurements are needed to maximize the science return from current and future Venus missions. These measurements, shown in Table 3-1, can be divided into two categories: Category 1 are laboratory data necessary for retrieving Venus system variables from calibrated instrument data, and Category 2 are laboratory data necessary for characterizing fundamental Venus processes based on newly revealed Venus system variables. There are four basic physical regimes for the new laboratory measurements: (1) the atmosphere above the clouds, in which the temperature and pressure conditions are similar to those in the terrestrial atmosphere; (2) the sulfuric-acid-laced cloud layer; (3) the atmosphere below the clouds, in which the temperature and pressure range is unique for solar system exploration; and (4) the super-heated surface. Many of these laboratory measurements could be conducted in a Venus Environmental Test Facility, which would simulate pressure, temperature, and atmospheric composition as a function of altitude. This would provide insights into how elements behave in the Venus environment and would also enable development and testing of new instruments and subsystems to operate under relevant conditions. Table 3 1. New Laboratory Studies to Support Future Venus Exploration Context Category 1 Measurements of Venus System Variables Category 2 Measurements of Venus System Processes Atmosphere above the clouds Cloud layer Trace constituent atmospheric sounding: mm/sub-mm spectral line pressure-broadening coefficients Molecular spectral parameters: frequency, transition strengths (cross sections) in IR, submm, etc. Cloud composition: optical properties of sulfuric acid aerosols under the conditions experienced in the clouds of Venus, especially at the lower temperatures of the upper clouds Cloud composition: effects of various likely impurities (i.e., sulfur allotropes and other photochemical byproducts) on the scattering and absorbing properties of these aerosols Excited atom/molecule-molecule reaction rates, for example, O* + CO 2 Reaction rate parameters for sulfur- and chlorine-containing species in a CO 2 dominated atmosphere Aerosol formation and properties Cloud microphysics: critical saturation for nucleation under Venus cloud conditions Cloud microphysics: charging properties of the cloud aerosols could be investigated in a manner similar to terrestrial aerosol charging 34

37 Context Atmosphere below the clouds Surface Technical issues Category 1 Measurements of Venus System Variables Atmospheric IR opacity: Very high-pressure, high-temperature CO 2 and H 2 O spectroscopy, isotopologues, O 3, O 2, H 2, etc. Near-surface atmospheric sounding: cm wavelength properties of CO 2 and OCS >30 bars Supercritical CO 2 in new temperature range at high pressures Chemical weathering of surface materials (basalts): reaction rates, decomposition rates Spectroscopic (visible, near-ir) characteristics of various ferric/ferrous, silicate, sulfate, and hydroxide under Venus conditions Surface conductivity sounding: dielectric loss properties at 750 K for various basalts and other major rock types Atmospheric IR opacity: Very high-pressure, high-temperature CO 2 and H 2 O spectroscopy, isotopologues, O 3, O 2, H 2, etc. Fundamental thermophysical data: specific heat, speed of sound, equation of state, thermal expansion coefficients Stability of spacecraft materials, and rates of reaction/corrosion with hot supercritical CO 2 - SO 2 gas Chemical transfer of elements from surface into atmosphere (and onto spacecraft windows?) Category 2 Measurements of Venus System Processes Molecular spectral parameters: frequency, transition strength (cross sections), line shape, pressure-induced absorption, particularly CO 2 and its isotopologues Scattering properties A Venus Environmental Test Facility would enable: Understanding the chemistry in the atmosphere above the cloud tops: There is a shortage of laboratory measurements under Venus atmospheric conditions that would enable accurate determinations of the atmospheric properties. In addition, for understanding what acquired measurements reveal about atmospheric processes, there is a shortage of laboratory measurements for key parameters of relevant reaction processes, particularly those unique to a sulfur-rich atmosphere. Understanding the physical and chemical properties of the sulfurous cloud layers: There is a shortage of laboratory measurements at Venus cloud conditions related to the optical properties of different candidate cloud aerosols. Thus, new laboratory measurements concerning aerosol formation and properties are required to understand the formation of these clouds. 35

38 Understanding the significance of the composition in the atmosphere below the clouds: A region of high temperature and pressure, new laboratory measurements on the optical properties of different molecular constituents, including sulfur compounds, are required. In addition, new laboratory studies under Venus surface conditions are required to obtain rates of chemical weathering of potential surface materials, spectroscopic parameters for possible Venus surface materials, measurements of conductivity of surface materials, and fundamental thermophysical data. Laboratory investigations and studies of analog environments on Earth will provide the necessary information to support future Venus measurements and their interpretation. Facilities for laboratory investigations at extreme Venus temperature and pressure conditions can be small and devoted to particular investigations. If they were made available, larger chambers for spacecraft and instrument testing under Venus conditions would enable the general scientific community to perform laboratory investigations. In summary, new laboratory measurements are needed to maximize the science return from current and future Venus missions. Diagram showing the possible atmospheric interactions taking place in the Venus lower atmosphere 36

39 4. REFERENCES AND WHITE PAPERS FOR NEXT DECADAL SURVEY [1] National Research Council New Frontiers in the Solar System: An Integrated Exploration Strategy (also known as the NRC Decadal Survey for Solar System Exploration) (2003): [2] Crisp, D., et al., Divergent Evolution Among Earth-like Planets: The Case for Venus Exploration, The Future of Solar System Exploration, , Community Contributions to the National Research Council (NRC) Solar System Exploration Survey (Mark Sykes, Ed.), ASP Conference Series, vol. 272, pp. 5 34, [3] NASA Solar System Exploration Roadmap (2006): [4] NASA Science Plan for NASA s Science Mission Directorate : [5] Exploring Venus as a Terrestrial Planet, Guest Editors: L. Esposito, E. R. Stofan, and T. E Cravens, Venus Chapman Conference Special Issue, Journal of Geophysical Research, Vol. 112, No. E4, [6] Treiman, A., et al., Report on the LPI Workshop: Venus Geochemistry: Progress, Prospects, and Future Missions, April 2009, [7] NASA s Flagship Mission to Venus: Final Report of the Venus Science and Technology Definition Team, April 2009, [8] Opening New Frontiers in Space: Choices for the Next New Frontiers Announcement of Opportunity, National Research Council Committee on New Opportunities in Solar System Exploration (NOSSE), Space Studies Board, The National Academies Press, Washington, D.C., Most of the these reports can be accessed via the Reports section of VEXAG website. Other references of interest are: Special Issue on Pioneer Venus Orbiter, Journal of Geophysical Research, Vol. 85, No. A13, December 30, VENUS, D. M. Hunten, L. Colin, T. M. Donahue, and V. I. Moroz (eds.), Space Science Series, The University of Arizona Press, Tucson, Arizona, 1143 pages, Magellan at Venus, Journal of Geophysical Research, Vol. 97, No. E8, August 25, 1992, Vol. 97, No. E10, October 25, 1992, The American Geophysical Union. J. G. Luhmann, J. B. Pollack, and L. Colin, The Pioneer Mission to Venus, Scientific American, pp , April VENUS II, Geology, Geophysics, Atmosphere, and Solar Wind Environment, S. W. Bougher, D. M. Hunten, and R. J. Phillips (eds.), The University of Arizona Press, Tucson, Arizona, 1376 pages, "Venus and Venus Express, Planetary and Space Science, F. W. Taylor (ed.), Volumes 54 and 55, 2006 and

40 Venus White Papers for the Planetary Sciences Decadal Survey 1. Venus Exploration Goals, Objectives, Investigations, and Priorities Sanjay Limaye, Suzanne Smrekar, and VEXAG Executive Committee 2. Venus Atmosphere: Major Questions and Required Observations Sanjay Limaye, Mark Allen, Sushil Atreya, Kevin H. Baines, Jean-Loup Bertaux, Gordon Bjoraker, Jacques Blamont, Mark Bullock, Eric Chassefiere, Gordon Chin, Curt Covey, David Grinspoon, Samuel Gulkis, Viktor Kerzhanovich, Stephen Lewis, Kevin McGouldrick, W. J. Markiewicz, Rosalyn A. Pertzborn, Christopher Rozoff, Giuseppe Piccioni, Gerald Schubert, Lawrence A. Sromovsky, Colin F. Wilson, Yuk Yung 3. Venus: Constraining Crustal Evolution from Orbit Via High-Resolution Geophysical and Geological Reconnaissance, James Garvin, Lori Glaze, Sushil Atreya, Bruce Campbell, Don Campbell, Peter Ford, Walter Kiefer, Frank Lemoine, Greg Neumann, Roger Phillips, Keith Raney 4. Comparative Planetary Climate Studies David Grinspoon, Mark Bullock, James Kasting, Janet Luhmann, Peter Read, Scot Rafkin, Sanjay Limaye, Kevin McGouldrick, Gordon Chin, Samuel Gulkis, Feng Tian, Eric Chassefiere, Hakan Svedhem, Kevin Baines 5. Venus Geochemistry: Progress, Prospects, and Future Missions Allan Treiman, David Draper, M. Darby Dyar 6. Previously Overlooked/Ignored Electronic Charge Carriers in Rocks Friedemann Freund 7. Mission Concept: Venus in situ Explorer (VISE) Larry W. Esposito and the SAGE Proposal Team 8. Venus Atmospheric Explorer New Frontiers Mission Concept Kevin Baines, Sushil Atreya, Tibor Balint, Mark Bullock, David Crisp, David Grinspoon, Jeffery Hall, Gary Hunter, Sanjay Limaye, Viktor Kerzhanovich, Paul Mahaffy, Christopher Russell, David Senske, Stuart Stephens, Chris Webster 9. The Venus Science and Technology Definition Team Flagship Mission Study Mark Bullock, David Senske, Tibor Balint, Alexis Benz, Bruce Campbell, Eric Chassefiere, Anthony Colaprete, Jim Cutts, Lori Glaze, Stephen Gorevan, David Grinspoon, Jeff Hall, George Hashimoto, Jim Head, Gary Hunter, Natasha Johnson, Viktor Kerzhanovich, Walter Kiefer, Elizabeth Kolawa, Tibor Kremic, Johnny Kwok, Sanjay Limaye, Steve Mackwell, Mikhail Marov, Adriana Ocampo, Gerald Schubert, Ellen Stofan, Hakan Svedhem, Dimitri Titov, Allen Treiman 38

41 10. Technologies for Future Venus Exploration Tibor Balint, James Cutts, Mark Bullock, James Garvin, Stephen Gorevan, Jeffery Hall, Peter Hughes, Gary Hunter, Satish Khanna, Elizabeth Kolawa, Viktor Kerzhanovich, Ethiraj Venkatapathy 11. Thermal Protection System Technologies for Enabling Future Venus Exploration Ethiraj Venkatapathy, Helen H. Hwang, Bernard Laub, Joseph L. Conley, James Arnold, Christine E. Szalai, Jim Tibaudo, Robert Knudsen, Andrew Chambers, David Atkinson, Sushil K. Atreva, Joseph M. Vellinga, William H. Willcockson, Janine M. Thornton, Nicholas G. Smith, Richard A. Hund, John Dec, Max L. Blosser, Michelle M. Munk, Robert Maddock, Prasun N. Desai, Walter Engelund, Stephen Sandford, David A. Gilman, Steven W. Gayle, John Kowal, Christopher B. Madden, Stan Bouslog, Brian J. Remark, Donald Curry, Scott Coughlin, Adam J. Amar, Kevin H. Baines, Tibor Balint, Bernard Bienstock, George T. Chen, James A. Cutts, Jeffery L. Hall, Samad A. Hayati, Pamela J. Hoffman, Linda Spilker, Romasso P. Rivellini, Robert Manning, Eric M. Slimko, Adam D. Steltzner, Thomas Spilker, Jeffrey Umland, Charles Kiskiras, Duane Baker, Thomas Foster, Dominic Calamito, James B. Garvin, Timothy A. Sauerwein, Sharon Seipel, Lori S. Glaze, Spencer Stolis, Mark Lippold, Francis Schwind, James Thompson, Raj Narayan, Thomas Andrews, Conley Thatcher, Edwin B. Curry, John McKinney, Robert Frampton, Todd Stever, Charley Bown, William Congdon, Jennifer Congdon, Daniel M. Empey, Joe Hartman, Dinesh Prabhu, Nancy L. Mangini, Kristina A. Skokova, Margaret M. Stackpoole, Tood White, Howard Goldstein, Melmoth Covington, Robin A. Beck, Carol W. Carroll, Charles A. Smith, Deepak Bose, Anthony Colaprete, David M. Driver, Edward Martinez, Donald T. Ellerby, Matthew J. Gasch, Aga M. Goodsell, James Reuther, Sylvia M. Johnson, Dean Kontinos, Mary Livingston, Michael J. Wright, Harry Partridge, George A. Raiche, Huy K. Tran, Kerry A. Trumble All of the these white Papers can be accessed via the White Papers section of VEXAG website. A composite of the hemispheric vortex on Venus left, a polar stereographic version of a Venus Express ultraviolet image) and Hurricane Frances, a tropical cyclone on Earth showing the remarkable similarities in the vortex structure. Given this similarity, it may become feasible to better understand the vortex structure on Venus from its terrestrial analog despite the difference in the energy source. 39

42 5. ACRONYMS AND ABBREVIATIONS AO Announcement of Opportunity ASPERA Venus Express fields and particles experiment ASRG Advanced Stirling Radioisotope Generator CCD charge-coupled device DSN Deep Space Network ESA European Space Agency EUV Extreme Ultraviolet EVE European Venus Explorer (Cosmic Vision proposal, 2007) JAXA Japanese Aerospace Exploration Agency JPL Jet Propulsion Laboratory LPI Lunar and Planetary Institute MAG Venus Express magnetometer experiment NASA National Aeronautics and Space Administration NOSSE NRC Committee for New Opportunities for Solar System Exploration NRA NASA Research Announcement PVO Pioneer Venus Orbiter R&A research and analysis ROSES Research Opportunities in Space and Earth Sciences STDT Science and Technology Definition Team USSR Union of Socialist Soviet Republics VCO Venus Climate Orbiter VDAP Venus Data Analysis Programs VDRM Venus Design Reference Mission Vega Russian Halley/Venus Lander and Orbiter Mission VeRa Venus Express radio science experiment VEXAG Venus Exploration Analysis Group VIRTIS Visible and Infrared Thermal Imaging Spectrometer VISE Venus In situ Explorer VMC Venus Monitoring Camera VLBI very long baseline interferometry VME Venus Mobile Explorer VSSR Venus Surface Sample Return 40

43 APPENDIX A. VENUS GOALS, OBJECTIVES, AND INVESTIGATIONS Excerpts from Venus White Paper: VEXAG Goals, Objectives, and Investigations Why Venus now? Venus proximity to Earth and its similarity in size and bulk density to Earth s have earned it the title of Earth s twin. As well, the lack of seasons and overall regular nature of the surface with no land/water contrasts to help generate weather nor large oceans to help transport heat and momentum seemingly renders Venus a relatively simple planet to understand. Yet we understand very little about this very alien world next door. Indeed, the contrast between Venus hellish 450 C surface temperature, sulfuric acid clouds, and its divergent geologic evolution has challenged our fundamental understanding of how terrestrial planets, including Earth, work. The absence of plate tectonics on Venus helped move models away from an emphasis on buoyancy to an understanding of the function of lithospheric strength, convective vigor, and the role of volatile history in controlling these processes. Venus is the planet where the importance of the greenhouse effect was first realized, and where winds blow with hurricane force nearly everywhere across the planet, from the first km above the ground to above 100 km altitude and from the equator to the high polar region. What powers such global gales when the planet itself rotates at a speed slower than the average person can walk on Earth is unknown? The study of the links between surface, interior, and climatic processes on Venus has reinforced the idea that Venus could represent the fate of the Earth. The realization that two such similar planets could produce this extreme range of processes and conditions makes Venus an essential target for further exploration as we move out in the universe and discover Earth-like planets beyond our solar system. Recent results from Mars show that liquid ground water was limited to the first billion years of its evolution, during its geologically active period. Venus Express has provided new reasons to explore Venus now. Surface thermal emissivity observations suggest tantalizing evidence of more evolved crustal plateaus, suggesting past oceans. Observations of atmospheric cyclones show structure nearly identical to those on Earth. As climate evolution comes into sharp focus on Earth, we must resume exploration of the planet that serves as an extreme end member. Overarching Theme for Venus Exploration With the context provided by the 2003 NRC Decadal Survey [1, 2], the 2006 Solar System Roadmap [3], and the 2007 NASA Science Plan [4], VEXAG has adopted an overarching theme for Venus exploration: Venus and Implications for the Formation of Habitable Worlds. This theme is supported by three goals and prioritized objectives and investigations (Table 1-1). 1. Origin and Evolution: How did Venus originate and evolve, and what are the implications for the characteristic lifetimes and conditions of habitable environments on Venus and similar extrasolar systems? 2. Venus as a Terrestrial Planet: What are the processes that have shaped and still shape the planet? 3. Climate Change and the Future of Earth: What does Venus tell us about the fate of Earth s environment? 41

44 Table 1 1. Venus and Implications for the Formation of Habitable Worlds Goal Objective Investigation Origin and Evolution Venus as a Terrestrial Planet Understand atmospheric evolution Seek evidence for past changes in interior dynamics Determine if Venus was ever habitable Understand what the chemistry and mineralogy of the crust tell us about processes that shaped the surface of Venus over time Assess the current structure and dynamics of the interior Characterize elemental composition and isotopic ratios of noble gases in the Venus atmosphere, especially Xe, Kr, 40 Ar, 36 Ar, Ne, 4 He, 3 He, to constrain origin and sources and sinks driving evolution of the atmosphere. Determine isotopic ratios of H/D, 15 N/ 14 N, 17 O/ 16 O, 18 O/ 16 O, 34 S/ 32 S and 13 C/ 12 C in the atmosphere to constrain paleochemical disequilibria, atmospheric loss rates, the history of water, and paleobiosignatures. Characterize the structure, dynamics, and history of the interior of Venus, including possible evolution from plate tectonics to stagnant-lid tectonics. Characterize the nature of surface deformation over the planet's history, particularly evidence for significant horizontal surface movement. Characterize radiogenic 4 He, 40 Ar and Xe isotopic mixing ratios generated through radioactive decay to determine the mean rate of interior outgassing over Venus history. At the surface, identify major and minor elemental compositions (including H), petrology, and minerals in which those elements are sited (for example, hydrous minerals to place constraints on past habitable environments). Characterize gases trapped in rocks for evidence of past atmospheric conditions. Characterize geologic units in terms of major, minor, and selected trace elements (including those that are important for understanding bulk volatile composition, conditions of core formation, heat production, and surface emissivity variations), minerals in which those elements are sited, & isotopes. Characterize the chemical compositions of materials near Venus surface as a function of depth (beyond weathering rind) to search for evidence of paleochemical disequilibria and characterize features of surface rocks that may indicate past climate or biogenic processes. Assess the petrography (shapes, sizes, & mineral grain relationships) & petrology (formation characteristics) of surface rocks to aid in interpretation of chemical and mineralogical characterization. Determine the physical properties and mineralogy of rocks located in a variety of geologic settings, including meteoritic and crater ejecta, volcanic flows, aeolian deposits, and trace metals in the high radar reflectivity highlands. Characterize surface exposure ages through measurements of weathering rinds. Characterize the current structure and evolutionary history of the core. Place constraints on the mechanisms and rates of recent resurfacing and volatile release from the interior. Determine the structure of the crust, as it varies both spatially and with depth, through measurements of topography and gravity to high resolution. Measure heat flow and surface temperature to constrain the thermal structure of the interior. Measure the magnetic field below the ionosphere and characterize magnetic signature of rocks in multiple locations. Characterize subsurface layering and geologic contacts to depths up to several km. Determine the moment of inertia and characterize spin-axis variations over time. 42

45 Table 1 1. Venus and Implications for the Formation of Habitable Worlds Goal Objective Investigation Venus as a Terrestrial Planet Climate Change and the Future of Earth Characterize the current rates and styles of volcanism and tectonism, and how have they varied over time Characterize current processes in the atmosphere Characterize the Venus Greenhouse Determine if there was ever liquid water on the surface of Venus Characterize how the interior, surface, and atmosphere interact Characterize active-volcanic processes such as ground deformation, flow emplacement, or thermal signatures to constrain sources and sinks of gases affecting atmospheric evolution. Characterize active-tectonic processes through seismic, ground motion, or detailed image analysis. Characterize the materials emitted from volcanoes, including lava and gases, in terms of chemical compositions, chemical species, and mass flux over time. Characterize stratigraphy of surface units through detailed topography and images. Assess geomorphological, geochemical, and geophysical evidence of evolution in volcanic styles. Characterize the sulfur cycle through measurements of abundances within the Venus clouds of relevant gaseous and liquid/solid aerosol components such as SO 2, H 2 O, OCS, CO, and sulfuric acid aerosols (H 2 SO 4 ). Determine the mechanisms behind atmospheric loss to space, the current rate, and its variability with solar activity. Characterize local vertical winds and turbulence associated with convection and cloud-formation processes in the middle cloud region, at multiple locations. Characterize superrotation through measurements of global-horizontal winds over several Venus days at multiple-vertical levels (day and night) from surface to thermosphere. Investigate the chemical mechanisms for stability of the atmosphere against photochemical destruction of CO 2. Characterize local and planetary-scale waves, especially gravity waves generated by underlying topography. Measure the frequencies and strengths of lightning and determine role of lightning in generating chemically-active species (e.g., NO x ). Search for and characterize biogenic elements, especially in the clouds. Determine radiative balance as a function of altitude, latitude, and longitude. Measure deposition of solar energy in the atmosphere globally. Determine the size, distribution, shapes, composition, and UV, visible, and IR spectra, of aerosols through vertical profiles at several locations. Determine vertical-atmospheric temperature profiles and characterize variability. Determine isotopic ratios of H/D, 15 N/ 14 N, 17 O/ 16 O, 18 O/ 16 O, 34 S/ 32 S 13 C/ 12 C in solid samples to place constraints on past habitable environments (including oceans). Identify and characterize any areas that reflect formation in a geological or climatological environment significantly different from present day. Determine abundances and height profiles of reactive atmospheric species (OCS, H 2 S, SO 2, SO 3, H 2 SO 4, S n, HCl, HF, SO 3, ClO 2 and Cl 2 ), greenhouse gases, H 2 O, and other condensibles, in order to characterize sources of chemical disequilibrium in the atmosphere. Determine rates of gas exchange between the interior, surface and atmosphere. 43

46 Goal 1. Origin and Evolution: How did Venus originate and evolve, and what are the implications for the characteristic lifetimes and conditions of habitable environments on Venus and similar extrasolar systems? Goal 1 involves understanding the origin and evolution of Venus, from its formation to today. Like Earth and Mars, the atmosphere of Venus today seems to have substantially evolved from its original composition. Whether the major processes that shaped the atmospheres of Earth and Mars such as impacts of large bolides and significant solar wind erosion also occurred on Venus is largely unknown. Detailed-chemical measurements of the composition of the atmosphere (in particular, the noble gases and their isotopes) will provide fundamental insight into the origin and evolution of Venus. The surface of Venus appears to have been shaped, for the most part, within the geologically recent past, likely within the past 500 million to one billion years. Venus surface may contain evidence of the planet s earlier history and origin (which may be accessible through a more complete characterization of the surface than previously accomplished), as well as a deeper understanding of the nature and evolution of the interior dynamics. In addition, detailed-chemical measurements of the composition of the atmosphere (in particular, the noble gases and their isotopes) provide additional information about the origin and evolution of Venus. Of particular interest is the possibility that Venus, early in its history, had long-lived oceans and a climate amenable to the development and evolution of life possibilities that are not excluded by current knowledge. The objectives of Goal 1 are to: (1) understand the sources of materials that formed Venus and their relationship to the materials that formed the other terrestrial planets, (2) understand the processes that subsequently modified the secondary (or original) atmosphere, leading to the current inventory of atmospheric gases (which is so unlike those present on Earth), and (3) determine whether Venus was ever habitable. Goal 2. Venus as a Terrestrial Planet: What are the processes that have shaped and still shape the planet? Although Earth and Venus are twin planets in size and mass, Venus surface at this time is clearly hostile to carbon-water-based organisms. Venus atmosphere, which is far denser than Earth s, is composed mostly of carbon dioxide with abundant sulfur oxides and a significant deficit of hydrogen. Venus atmosphere moves (everywhere except within a few hundred meters of the surface) with hurricane-force velocities reaching 60 times planetary rotation speed near the cloud tops. How a planet that revolves more slowly than a normal walking speed can generate such winds globally is an enigma. Venus surface is composed mostly of Earth-like igneous rocks (basalt) at an average temperature of ~460 ºC, precluding the presence of liquid water. Venus highlands are mantled by deposits of an electrically-conductive or semiconductive material. Venus geologic processes are also largely dissimilar from those on Earth, aside from volcanic eruptions. The surface of Venus appears to have been resurfaced within the past

47 million to one billion years, obscuring possible signatures of earlier geological episodes. The nature and duration of this resurfacing remain enigmatic. Subsequent to resurfacing, styles of tectonism and volcanism evolved as the planet cooled, such that the thermal/dynamic regime of the planet is now thought to be a convection under a stagnant or sluggish lid. There is no manifestation of the global-plate tectonic processes like those on Earth. Analyses of gravity and topography data suggest that Venus has a comparable number of active large mantle plumes as Earth, as well many hundreds of smaller scale plumes that may also be active. Although there is little information on current levels of volcanic or tectonic activity, some atmospheric data suggest that Venus is still volcanically active. Exploring and characterizing processes on and in Venus will help us understand dynamical, chemical, and geologic processes on other planets throughout our galaxy. The objectives of Goal 2 are to: (1) understand what the chemistry and mineralogy of the crust tell us about processes that shaped the surface of Venus over time, (2) assess the current structure and dynamics of the interior, and (3) characterize the current rates and styles of volcanism and tectonism, and how they have varied over time, and (4) characterize current processes in the atmosphere. Goal 3. Climate Change and the Future of Earth: What does Venus tell us about the fate of Earth s environment? Although the terrestrial planets formed at about the same time within the inner solar system, from similar chemical and isotopic reservoirs, they have followed very different evolutionary paths. In particular, Venus and Earth, which formed at similar distances from the Sun with nearly identical masses and densities, currently have vastly different atmospheres, surface environments, and tectonic styles. It has been suggested that Venus may have been more Earthlike earlier in its history and then evolved to its current state, and that Earth may ultimately transform to a hot, dry, inhospitable planet like Venus. Thus, understanding the interior dynamics and atmospheric evolution of Venus provides insight into the ultimate fate of Earth. Objectives within Goal 3 are to: (1) characterize the present-day greenhouse of Venus, (2) determine if liquid water ever existed on the surface of Venus, and (3) characterize how the Venus interior, atmosphere, and surface are interacting. It has become clear that, as on Earth, the climate balance of Venus reflects a dynamic balance between geologic and atmospheric processes. 45

48 Courtesy NASA/JPL Caltech Courtesy of National Oceanic and Atmospheric Administration 46

49 APPENDIX B. COMPARATIVE CLIMATOLOGY OVERVIEW Investigating global warming and climate change on Earth has raised consciousness about the potential instability of terrestrial climate systems and the value of understanding the Venus greenhouse. A key finding from the 2006 Chapman Conference [5] is that Venus may have had an ocean and could have been habitable for much of its history. Thus, Venus provides climatologists with an opportunity to test state-of-the-art models simulating the mechanisms and processes that led to Venus extreme climatology. A new comparative-climatology initiative cosponsored by NASA S Earth and planetary science programs would motivate and encourage work in this increasingly relevant area. Venus is Earth s closest planetary neighbor, and a near twin in terms of bulk properties such as mass and size. Their densities and inventories of carbon and nitrogen are similar, suggesting similar primordial origins. Mars, Earth s next nearest neighbor, also has a wide range of meteorological and geological phenomena that are recognizable as variations on familiar terrestrial processes. Current understanding of planetary formation, volatile accretion, and the well-preserved ancient geological record of Mars all suggest that these three planets started out with comparable surface environments, geological processes, and atmospheric compositions. Yet, despite their close proximity and similar origins, they have evolved into very different states. Today s rotation state, magnetic field, surface temperature and pressure, atmospheric inventories of radiatively active gasses, total water inventory, polar deposits, and global patterns of geological activity are among the properties that differ so dramatically. An understanding of the evolutionary histories and current states of the Venus and Mars climates is directly relevant for studies of the past and future climates of Earth. As extreme examples of very different climate on otherwise similar, nearby planets, Venus and Mars provide opportunities to improve and validate our knowledge of planetary climate modeling. For example, Venus can provide a test bed for an extreme case of global warming where nonlinear effects have evidently played an important and irreversible role in climate evolution. Mars has a climate history where Milanković cycles on steroids have resulted in a history of extreme climate change. This synergism between Venus, Earth, and Mars goes both ways: Our understanding of Venus and Mars would benefit from use of the best Earth models and the expertise of the larger community of Earth climatologists. A much deeper understanding of these very different global climate systems should be possible, given the techniques developed to understand climate change on Earth. At the same time, these extreme cases can help to validate the crucial ability of terrestrial models to correctly predict variations from the current atmospheric composition and climate conditions of Earth, increase the ability of Earth modelers to work with unforeseen climate feedbacks, and expose potential weaknesses or limitations in our current Earth climate models. Although Venus and Mars represent very different evolutionary paths for terrestrial planets, they provide our closest analogs for many important processes and planetary mechanisms operating on Earth. This unique combination of similar initial conditions and bulk properties, with radically divergent evolutionary outcomes, makes Venus-Earth-Mars comparative studies a uniquely fruitful area for expanding and testing our knowledge of planetary science and global climate change. 47

50 APPENDIX C. ENHANCING AND ENABLING TECHNOLOGIES FOR VENUS EXPLORATION Excerpts from Venus Technologies White Paper [a], submitted to the NRC Decadal Survey Inner Planets Sub panel This appendix provides an overview of technologies required for future Venus exploration missions. These technologies will focus on mission-enabling and -enhancing capabilities for in situ missions, because most orbiter-related subsystems are considered heritage technologies. This appendix draws heavily on the Venus Flagship Mission study [b] that identified key technologies required to implement its Design Reference Mission (DRM). These technologies include surface sample acquisition and handling; mechanical implementation of a rotating pressure vessel; and a rugged terrain landing system. Also, a large-scale environmental test chamber is needed to validate these technologies under relevant Venus like conditions. Other longer term Venus flagship missions will require additional new capabilities; namely, a Venus specific radioisotope power system, active refrigeration, high-temperature electronics, and advanced thermal insulation. The chosen mission architectures whether large flagship, medium New Frontiers, or small Discovery-class missions are primary drivers for Venus technologies. The Venus Flagship Mission study [b] recommends a multi element mission architecture of an orbiter, two cloud level balloons, and two short lived landers, which have been successfully used for past Venus exploration missions. In addition, the Venus flagship DRM used heritage technologies and, in turn, minimized the number of new technologies required for this mission s implementation. This multi element architecture also allows designers to utilize appropriate technologies for smaller (New Frontiers or Discovery-class) missions, which would use similar mission elements. However, NASA s SSE Roadmap identified other missions, including the near-surface Venus Mobile Explorer, a seismic network, a New Frontiers class VISE, and Discovery-class balloon missions ultimately leading to a Venus Surface Sample Return mission. Discovery and New Frontiers missions are not expected to include a significant amount of new technologies and could be designed without them; although they could benefit from new technologies if they were made available as part of a technology development program for a future flagship mission. Table C-1 summarizes enabling and enhancing technologies for potential future Venus missions, with emphases on in situ elements. Further information can be found in the Technologies for Future Venus Exploration White Paper [a] and in the Venus Flagship Mission study final report [b]. Appendix C References a. Balint, T., Cutts, J., et al., Technologies for Future Venus Exploration, VEXAG White Paper to the NRC Decadal Survey Inner Planets Sub-Panel, September 9, b. Hall, J.L., Bullock, M., Senske, D.A., Cutts, J.A., Grammie, R., Venus Flagship Mission Study: Report of the Venus Science and Technology Definition Team, National Aeronautics and Space Administration, Jet Propulsion Laboratory, California Institute of Technology, Task Order NM , April

51 Legend: Bold italic Bold Italic Roman Table C 1. Technologies for Future Venus Exploration The highest priority technology items those that would enable the mission to survive for 5 hours on the surface as recommended by the Venus Science and Technology Definition Team Technologies that would enhance the DRM by extending its lifetime up to a day are in italics with light red shading New technologies that would extend the lifetime to up to several months are in regular text with light green shading Technologies that would further enhance future Venus exploration missions Capability Surface sample acquisition and handling (VDRM) Rotating pressure vessel (VDRM) Rugged terrain landing (VDRM) Testing facility (VDRM) Current state of the art (TRL) TRL 2 3 Heritage Soviet derived systems are not available off the shelf, but they demonstrate a feasible approach. TRL 2 Rotating pressure vessel concept is powerful but technologically immature. TRL 2 Russian landers provide proof of concept, however, these landed at benign surfaces and used a drag plate instead of parachutes. TRL 2-6 Two small Venus environment test chambers are operational at JPL; A small Venus test chamber setup is underway at GSFC; Proof of concept Technology development needs to enable Venus missions Surface sample acquisition system at high temperature and pressure conditions; Vacuum driven sample transfer is demonstrated on Venera, but requires development for NASA. Full scale design and testing of a rotating pressure vessel with a driver motor and mounted sampling system. Design and test a landing system that can account for a large variety of unknown landing hazards using parachutes. Large test chamber doesn t exist; Develop large Venus test chamber for full scale in situ elements (probe/lander) testing; Simulate transient atmospheric conditions; composition. Benefits to future Venus missions Drilling, sample collection and sample handling are enabling for the Venus Flagship Mission. It minimizes the external components, such as drill arms, actuators, motors, sampling systems; and the heat leakage from the outside through the number of windows required for panoramic imaging. Tessera and other rugged areas on Venus cannot be reliably accessed unless a properly engineered rugged terrain landing system is developed and tested. The 12.5 km anomaly on the Pioneer Venus mission demonstrates the critical need for an environmental chamber using relevant atmospheric composition and conditions; It can test spacecraft 49

52 Capability Advanced passive thermal control (enhancement to VDRM) High T and Medium T components, sensors, and electronics (new capabilities) Power generation (new capabilities) Current state of the art (TRL) from Russian test chamber (decommissioned). TRL 3 9 Venera and PV era insulation and phase change materials are mostly available. TRL 2 4 Geophones could operate up to 260 C; High-temperature pressure, temperature, anemometers used on Venera/VEGA and Pioneer Venus; Silicon based high T components are designed for up to 350 C for the automotive and oil drilling industry; Limited number of components and integrated circuit capability demonstrated for SiC at 500 C; Limited electronics packaging at 500 C; Data storage, ADC, power converters, and other needed components never demonstrated. TRL 4 Demonstrated single Stirling convertor operation for 300 hours Technology development needs to enable Venus missions Alternate insulation and phase change material technologies are needed to increase lander lifetimes beyond 2 5 hour operation. High temperature MEMS technology for seismometers could operate at surface temperatures; SiC and GaN high temperature sensors and electronics require development to operate at surface temperatures; Development of data acquisition, processing and storage capability, and packaging; Development of high T power management; Demonstration of reliability and long life. Cold side temperature must be raised from 90 C to 480 C with high conversion efficiency preserved (e.g., Benefits to future Venus missions components; validate and calibrate science instruments; test operating scenarios under realistic conditions. Achievement of 12 to 24 hour lander lifetimes would enable humans in the loop operation by ground controllers; Improved thermal insulation will decrease refrigeration requirements for truly long term lander missions. Long life on the surface is desirable (especially, for meteorology, seismometry); Sensors, actuators, instruments directly interfacing with the environment cannot be sufficiently protected, and therefore, high temperature components can enable operations and science measurements (e.g., long lived meteorology, seismometry) that otherwise cannot be achieved; High temperature data processing and storage, and power electronics results in a drastic reduction in refrigeration requirements, even at moderately high temperatures (>250 C); Low power dissipation at 300 C and long life reduces environmental tolerance requirements for components. Required for long life operation; Venus specific RPS with active cooling could enable 50

53 Capability Active refrigeration (new capabilities) Pressure control Thermal control (passive) Current state of the art (TRL) with a 850 C hot side temperature and 90 C cold side, 38% efficiency and 88 W power output with heat input equivalent to 1 GPHS module. TRL 4 Cryocoolers are space qualified, but high temperature operation is not demonstrated at the system level. TRL 4 9 Titanium pressure vessel is space qualified; New lightweight materials need development. TRL 4 9 Aerogels, MLI, PCM are space qualified, but not for high g load entries and high temperatures. Power storage TRL 4 Demonstrated LiAl FeS2, Na S, and Na metal chloride secondary batteries with specific energy in Technology development needs to enable Venus missions maintaining T through increased hot end temperature, which would required materials or design development); Material testing, system development and validation for reliable operation in Venus surface environment. Adopt Stirling conversion based coolers for Venus surface conditions; High efficiency duplex Stirling system must be produced that integrates the heat engine and refrigerator functions into a high efficiency and high reliability device; Refrigeration system should be coupled with the power source; Low mass and low vibration is desirable. Advanced materials (e.g., beryllium, honeycomb structures) could reduce structural mass. High performance thermal insulation for Venus environment is required for mission lifetimes beyond Venera demonstrated lifetimes. Adapt high temperature cell and battery designs for space applications; Address stability of seals and terminals; Minimize the corrosion of Benefits to future Venus missions long lived missions, operating for months; Low mass version could power near surface aerial mobility systems; It could power long lived seismometers and meteorology stations on the surface (117 days minimum). Almost every long duration (~25 hrs+) in situ platform will require some amount of refrigeration to survive; Focus should be on radioisotope based duplex systems that produce both refrigeration and electrical power; Low mass version would allow for near surface aerial mobility (metallic bellows); Low vibration version would enable a seismic network (on multiple landers) (117 days minimum); Extended mission life allows humans in the loop. Mass saving translates to higher payload mass fraction for the same entry mass. Improvements in passive thermal control could extend mission lifetime from ~2 hours to 5 hours or maybe more. (Beyond that active refrigeration and a power source is required.) High temperature batteries operating at Venus surface temperatures would make it possible to keep the power storage outside of the pressure vessel, thus 51

54 Capability Instruments (in situ) for the Venus Flagship Mission Upper atmosphere Balloons Near surface balloons Descent probes and sondes High T Telecom Current state of the art (TRL) the Wh/kg range; Short lived missions could use high TRL primary batteries. TRL 2 9 Descent probe instrument heritage from Pioneer Venus; New in situ contact instrument need development. TRL 5 7 Russian VEGA balloons successfully operated for 48 hrs over 20 year ago; Large super pressure balloon have been built and tested at JPL and at CNES; Development for a mid altitude balloon is underway at JAXA. TRL 2 3 Metallic bellows proof of concept was built at JPL and tested at high temperatures. TRL 2 9 Pioneer Venus probe heritage for large probes Microprobes have been designed but not yet tested. TRL 2 Demonstrated 2 GHz operation at 275 C using SiC; SiC and vacuum tube based oscillator Technology development needs to enable Venus missions current collectors at high temperatures; Optimize the electrolyte composition to improve performance and reliability. Several Venus Flagship Mission instruments, e.g., heat flux plate, XRD/XRF are at medium TRL; High T seismometry and high T meteorology are at low TRL; G load tolerance during atmospheric entry should also be addressed. Cloud level balloons are considered mature, but further development, testing, verification and validation are required to address lifetime and reliability issues for a 30 day mission; Materials must tolerate high temperatures, corrosive environment (sulfuric acid droplets in clouds). Development is needed to build and test a metallic bellows system and test it under Venus surface pressure and temperature conditions; Near surface operation must address altitude change and surface access. Develop small drop sondes that could be released from a balloon platform (also work as ballast). Development efforts should address SiC based RF components for transmitters; Miniaturized vacuum tube technology for power amplifiers; Benefits to future Venus missions reducing volume and thermal requirements for the pressure vessel. In situ instruments are key drivers for Venus missions and are required for mission success. The Venus Flagship Mission balloons are designed for 30 days operation; An ASRG powered balloon mission could operate for months, circumnavigating the planet and continuously measure dynamics and atmospheric composition. A near surface mobile platform could traverse hundreds of kilometers over a 90 day mission, image the surface at high resolution and periodically access the surface for sampling. Drop sondes can enhance science by providing vertical slice measurements to complement balloon constant altitude measurements of the atmosphere. High temperature telecom on the surface would drastically reduce cooling requirements; It would enable long lifetime (117 days minimum); 52

55 Capability Orbiter instruments and telecom Atmospheric entry Current state of the art (TRL) demonstrated at ~500 C. TRL 3 9 Magellan, Venus Express, Pioneer Venus heritage; Venus Flagship Mission InSAR needs development. TRL 5-9 Carbon-Phenolic (CP) used on Pioneer Venus and Galileo probe; Provides heritage for use in steep entry flight path angle (EFPA) missions; Special rayon needed to make heritage CP; This rayon is out of production; Current arc jet capabilities are limited; Mars and Titan TPS, lower density, could be useful for lower EFPA. Autonomy TRL 4 6 Autonomous operation have been tested in previous missions (e.g., Pioneer Venus probes), but at a lower complexity than required for a Venus flagship mission. Cross cutting See above technologies Technology development needs to enable Venus missions SiC based RF components for transmitters. Development is required for InSAR; passive infrared and millimeter spectroscopic techniques; and cloud LIDAR 1. Re-establish test capabilities; 2. Periodic verification of Industry capability to remanufacture heritage CP; 3. Establish alternate to heritage CP TPS, since heritage rayon is not made anywhere, anymore and current supply in hand is limited; 4. Assessment of lower density TPS be performed for shallow EFPA missions. Develop and test reliable autonomous operation for a Venus surface mission, including control of the rotating pressure vessel; drill site selection; sample acquisition; instrument operations; reliable telecom. TPS; pressure vessel materials; passive thermal control (insulation; phase change materials). Benefits to future Venus missions High data rate (~4.5 kbps) would support seismic operations; However, high temperature data storage at Venus surface temperature may represent a significant technology challenge. InSAR is a key instruments on the Venus Flagship Mission; Ultra fine resolution radar mapping and cloud LIDAR could provide high resolution science data on the surface and clouds, and highly desirable by science. TPS is essential and enabler; High entry flight path angle (EFPA) entries result in high heat flux, pressure and g- loads; Limited supply of heritage CP enables unrestricted access to the planet; Lower density TPS can provide significant mass savings, but constrain the EFPA and thus the mission architecture. Short lived missions (up to 5 hours) does not support humans in the loop; Autonomous operation is required for all science measurements and subsystem control. These technologies can benefit a number of planetary missions, e.g., probes to Venus and deep probes to the Giant Planets. 53

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