Extended Missions: Engines of Heliophysics System Science

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1 Extended Missions: Engines of Heliophysics System Science J. G. Luhmann, J.B. Blake, J.L. Burch, J.B. Gurman, J.T. Karpen, J.W. Leibacher, D. J. McComas, C. T. Russell, R. J. Strangeway, A.J. Tylka, T. T. von Rosenvinge While the successful planning, building, launching and commissioning of spacecraft constitutes a remarkable technical feat, the motivation for and end goal of these eyes, ears and hands in space is the science that results from these missions. Level 1 science requirements are developed during the years of formulation and implementation that precede missions. These goals are consistent with those of long-term National Academy Decadal Surveys and NASA Mission Roadmaps that synthesize and prioritize among the many knowledge goals of heliophysics and the other disciplines within the SMD. However, by their very nature, Level 1 Science Requirements are the minimum set that a mission must satisfy in order to achieve its pre-launch objectives, and are dictated in part by budget caps, not simply science objectives. They are focused on what can be achieved during the prime mission, the period of guaranteed operation. They are not the optimal science that can be achieved, nor even the bulk of the science that is ultimately achieved by most missions. In particular, Level 1 Science Requirements cannot cover what can be achieved by extending (or in some cases modifying) the operation of the spacecraft and its instruments, and by combining the observations with those from other spacecraft. Assumptions made about the state of solar activity or other conditions during the prime mission, and even our prior knowledge, may prove incorrect. In addition, unforeseen opportunities can and do arise. The history of Heliophysics has demonstrated that maintaining the operation of these probes beyond their prime missions invariably provides significant new scientific results and much deeper understanding. A major consideration is their synergistic contributions to the Heliophysics System Observatory (HSO), a complementary multisensor, multipoint study of the heliosphere. The marginal cost of this science is small compared to the cost of the original missions, or of the suite of new missions that would be required to achieve these objectives. A recent example of creative extended mission exploitation is the THEMIS mission s redirection of two of its satellites to form ARTEMIS, a lunar plasma interaction mission, when it was found that these two spacecraft would have been lost to long eclipses as their original orbits evolved. A recent example of the synergy enabled by extended missions is the use of ACE and Wind particles and fields measurements upstream of the Earth, and SOHO s enduring work horse LASCO coronagraph, to support the SDO mission. This combination, along with STEREO (in extended mission), also provides a more global heliospheric record of the coronal activity during the intriguing, muchdelayed rise of solar cycle 24. Most important, the three imagers combine to give unprecedented complete 1

2 imaging of the Sun including the lower corona in EUV, the mid corona to 30 solar radii and the heliosphere beyond with the heliospheric imagers. SOHO by itself demonstrates well the knowledge that can be garnered during an extended mission. The varying internal structure of the Sun, a major need for progress in understanding the solar dynamo, was unknown when SOHO was conceived, constructed, and launched. Observations by the GOLF and MDI instruments during the extended mission gave us measurements of the time-varying meridional flows that are believed to play a role in generating the solar magnetic field. Similarly, local helioseismology observations of the sub-surface structures of the Sun were unknown when SOHO was conceived, and have now become essential tools for the diagnostics of magnetic active region, while imaging of the farside of the Sun was unknown at the launch of SOHO, and has now become an essential space-weather forecasting tool. Some other important SOHO extended mission results include the discovery of coronal loop oscillations associated with CME passage; comprehensive solar observations of the major 2003 "Halloween" events, including the most intense solar flare of the last 30 years; demonstration of solar energetic particle event forecasting based on relativistic electron precursors; discovery of an acceleration of the solar convection zone meridional flow after the last solar maximum which may explain the marked decrease in solar polar magnetic flux compared with previous cycles. But the Heliophysics System Observatory is not only solar-focused; it encompasses Sun-Earth connections and their consequences in key ways. The TWINS Mission-of-Opportunity continues to make stereo ENA images of the magnetospheric response to this increasing solar (and hence geomagnetic) activity. In the last year of its life the Ulysses extended mission established the whole-heliosphere existence of the unusual interplanetary conditions of the solar cycle 23 minimum, providing further impetus to the observations of the geospace responses to the 30% lower solar wind mass flux and magnetic field strength. The FAST mission was able to study the evolving magnetosphere-ionosphere coupling as the Sun s activity wound down. While Polar was decommissioned prior to solar minimum, its extended mission allowed the exploration of the southern polar magnetosphere and provided complementary data for THEMIS studies of substorms. Extended mission components of the HSO also probe Earth s ionosphere and thermosphere (CINDI, TIMED), as well as the mesosphere (AIM, TIMED), providing information both useful for science and relevant to national priorities such as climate change research, security, navigation systems, and communications. For example, SOHO and TIMED together provided solar EUV flux trends used to investigate the origin of the unusually low upper atmosphere densities that have influenced satellite operations in Earth orbit. 2

3 Beyond the Sun and the Sun-Earth connection, Voyager finally breached the boundaries of the heliosphere with in-situ observations to complement and provide ground truth for the global picture now remotely observed in ENAs by the Interstellar Boundary Explorer (IBEX) -which itself passes into extended mission later in FY11. Meanwhile, SOHO provided new measurements of the interstellar magnetic field, and SOHO and STEREO continue to be primary resources for comet discoveries and interplanetary dust studies. To exploit the outstanding scientific opportunity presented by the long survival of well-built operating spacecraft that continue to produce valuable information for heliophysics researchers, NASA developed the Senior Review process, which provides orderly, peer-review assessments to aid decisions as to whether to continue funding each mission. This biennial event serves both to encourage long term science planning and operations strategizing by the NASA Heliophysics managers, and to provide the opportunity to determine what missions will continue to produce and which will be allowed to disappear from the Heliophysics System Observatory. As a result, both the community and NASA leaders gain further insight into the missions and their contributions, but this the Senior Review itself is faced with growing challenges related to increasingly unworkable budgetary constraints. This challenge demands special consideration, especially in light of the growing value and use of multispacecraft investigations in heliophysics and the growing interest in whole-sun, whole magnetosphere, whole heliosphere, and Sun-Earth connection observations and science. Only with the full HSO can we follow both quiescent and explosive activity from the Sun through the heliosphere and Earth s magnetosphere to the upper atmosphere, an unprecedented opportunity to attain the long-sought goal of understanding the heliosphere as a system. For example the extension of the STEREO mission now provides nearly whole-sun images, allowing knowledge of the far side activity to be used for understanding Earth-perspective large scale solar phenomena as well as characterizing interplanetary conditions in other parts of the solar system. Simultaneously, extended mission observations from the two TWINS spacecraft provide nearly continuous imaging of the inner magnetosphere with frequent stereo viewing. The extended RHESSI mission is currently our only window on the highest energy X-rays and gamma rays generated by solar eruptions, providing unique information that complements Hinode, STEREO, and SDO observations of the same activity and constitutes a vital contextual link to HSO observations at Earth. For the first time solar energetic particle events can be routinely observed at 1 AU at several separated heliolongitudes while ACE and Wind continue to provide critical upstream measurements of the solar wind plasma, field, and particles that are about to impact the Earth. In addition, 3

4 corotating high speed streams and stream interaction regions can be anticipated to provide opportunities for special campaigns of geospace observations or space weather forecasts. The need for these capabilities is particularly acute now that the Sun appears to be waking up from its unusually prolonged minimum. IBEX, viewing the edge of the heliosphere, benefits from the solar cycle-dependent 3D solar wind structure models validated with multipoint in-situ data provided by the Heliophysics System Observatory constellation, while the synergy between IBEX and the Voyagers at the edge of the heliosphere provides an irreplaceable observatory of these distant boundary regions, where the vast majority of galactic cosmic radiation is shielded from our solar system. Heliophysics researchers have become well-versed in accessing and using these multi-platform, multi-perspective, and multi-technique data sets and apply them routinely in constraining their theories and interpretations. The great change that has occurred on the Sun in the past decade is another important reason to maintain our current constellation of Heliophysics missions. The photospheric magnetic field strength has dropped by a factor of two and has shown only weak signs of recovery. We have no precedent for this in the space age, although historical sunspot observations indicate a similar phenomenon in the early 1800s. If we are experiencing a repeat of this solar behavior, the Sun may take several cycles to recover its field strength and return to what we call normal activity as defined by cycles 21and 22. We need to keep measuring and analyzing this potentially paradigm-changing behavior and its planetary, terrestrial, and global heliospheric consequences with as much of the Heliophysics System Observatory as we can maintain. Since at least the mid-1990s the NASA extended missions have been hampered by severely constrained resources for the PI teams that built and operate the instruments, and who know them and their data best. To perform any scientific analysis beyond the minimum necessary to validate the data flows, the PI team members and Co-Investigators now compete for analysis funding in the Guest Investigator, SR&T, TR&T, and Theory programs. Recent, devastating cuts in two of those programs have endangered our ability to continue to produce meaningful, new science that the novel and unique, spacecraft locations and the unusual solar activity make possible. Some of those cuts have been driven by "taxes" generated within NASA for initiatives outside Heliophysics, and others by the overall decrease in Heliophysics Mission Operations and Data Analysis (MO&DA) funding in the Administration budget. We need to restore the MO & DA level of effort and at a minimum, shield its most valuable assets, which include the extended missions within the HSO. The 2010 Senior Review differed from the last two Senior Reviews in important ways. In the previous Senior Reviews the mission teams were asked to submit both optimal and in-guide budgets. The 4

5 former allowed comparisons of the funding that would optimize the potential scientific impact of the missions against budgets adhering to the very tight fiscal constraints that NASA faces. Although the MO&DA budgets have never been sufficient to support all missions at the optimal level, it was the task of the Senior Review Panel to identify the missions that made the most compelling scientific cases for continuing operation and data analysis. However, in the 2010 Senior Review, mission teams were instructed to present only minimal science budgets. Moreover, the Senior Review Panel was informed of the need to cut the prospective MO&DA minimal science budget from $59.5M to $54.7M in FY11 and from $57.9M to $51.8M in FY12 to cover other areas of budgetary shortfall. The need for these reductions forced the Panel to undertake a line-by-line review of each mission s proposed budget, looking for places where funding could be cut even though the mission teams had already aggressively constrained their submitted cost projections. This process necessarily involved the Panel s judgments, generally on an instrument by instrument basis a subjective exercise lacking in rigor for recommendations of such importance. The Panel noted that while terminating satellites and/or instruments made obsolete by newer missions, such as SDO s replacement of TRACE and selected instruments on SOHO, made sense, the remaining missions in the Heliospheric System Observatory are complementary, not duplicative. Each mission occupies a unique vantage point, in terms of either its instruments and/or orbits. For example, the three spacecraft at L1 - SOHO, Wind, and ACE - carry distinct payloads. All of the HSO spacecraft and nearly all of the instruments are capable of returning high-quality data during the coming decade. Yet mature missions, especially those well into their extended phase, are targets for cuts since these missions already have a large database in hand. Such a viewpoint overlooks the new discoveries made possible by the synergies between old and new missions. As mentioned above, these give new combinations of diagnostics from multiperspective, multiwavelength images and coordinated imager and in-situ observations, together with the ability to investigate phenomena with both large and small spatial scales on a range of timescales. The decision making process also does not make allowances for discovery class results and those that feed into major Heliophysics programs such as LWS and other areas of climate studies, astrophysics, planetary research, space weather forecasting enterprises in NOAA and DoD, and NASA s humans in space activities. In summary, the Heliophysics System Observatory, including the extended missions, is the product of many years of effort and billions of dollars in investment poised to make new breakthroughs. But its existence and productivity depends on its support. The current Heliophysics Science Division budget allots only $55M out of $600M for operation of existing missions in 2011, with projections leaving them 5

6 chronically undefunded by at least ~$5M/yr. While the need for and value of new missions such as Solar Orbiter and Solar Probe cannot be denied, $60M/yr for the entire suite of HSO missions (including those in extended phase) is a modest expenditure for what has become the primary engine of Heliophysics system science. The existing and extended missions together provide data critical for understanding the physics of the Sun and heliosphere, and the past, current and future conditions to which Earth and all the planets are exposed. The coincidence that the Sun has entered a period that is unprecedented, and that we are at the same time serendipitously endowed with a remarkable Heliophysics System Observatory begs to be exploited. The Heliophysics Discipline must strategize to find a way to maintain the operation, data collection and validation, and scientific data analysis of all spacecraft that are still sufficiently productive as determined by the Senior Review process. Adequate allowance must be planned into the discipline budget for the next decade for this purpose, and ways to minimize ongoing operations and data archiving costs investigated and enabled. Extended missions are demonstrably Heliophysics best long term investment, with the greatest scientific return per dollar. 6