2
Enabling Exploration of the Sun-Heliosphere-Planetary System

NASA’s Sun-Earth Connection (SEC) program is both an integral element of exploration of the solar system and beyond (discussed in Chapter 1 above) and an enabler of that exploration. The latter, more applied role is the topic of this chapter.

The objectives of NASA’s vision for space exploration1 include (among others):

  • Implement a sustained and affordable human and robotic program to explore the solar system and beyond;

  • Extend a human presence across the solar system starting with the human return to the Moon by the year 2020, in preparation for human exploration of Mars and other destinations;

  • Conduct robotic exploration of Mars to prepare for future human exploration;

  • Explore Jupiter’s moons; and

  • Understand the history of the solar system.

Among the key ways that science will be expected to enable exploration, the Aldridge Commission report cited “monitoring and interpretation of space weather as relevant to consequence and predictability.”2

To implement a sustained human presence in space, either near Earth or elsewhere in the solar system, requires a comprehensive understanding of the heliospheric system and the effects of solar activity on the environment encountered by exploring humans. This chapter summarizes the approach to achieving this understanding by discussing (1) space weather hazards, (2) overarching themes in space physics that affect our ability to develop a predictive capability, and (3) the SEC’s existing programs and how they would function together to support NASA’s space exploration vision. Finally, Tables 2.1 and 2.2 presented toward the end of the chapter outline specific details of missions that are required to achieve success in support of the exploration vision, information that is augmented in Appendix B with one-page descriptions of the missions and their relevance to enabling exploration.

1  

National Aeronautics and Space Administration, The Vision for Space Exploration, NP-2004-01-334-HQ, NASA, Washington, D.C., 2004.

2  

A Journey to Inspire, Innovate, and Discover: Report of the President’s Commission on Implementation of United States Space Exploration Policy, p. 38, ISBN 0-16-073075-9, U.S. Government Printing Office, Washington, D.C., 2004.



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Solar and Space Physics and Its Role in Space Exploration 2 Enabling Exploration of the Sun-Heliosphere-Planetary System NASA’s Sun-Earth Connection (SEC) program is both an integral element of exploration of the solar system and beyond (discussed in Chapter 1 above) and an enabler of that exploration. The latter, more applied role is the topic of this chapter. The objectives of NASA’s vision for space exploration1 include (among others): Implement a sustained and affordable human and robotic program to explore the solar system and beyond; Extend a human presence across the solar system starting with the human return to the Moon by the year 2020, in preparation for human exploration of Mars and other destinations; Conduct robotic exploration of Mars to prepare for future human exploration; Explore Jupiter’s moons; and Understand the history of the solar system. Among the key ways that science will be expected to enable exploration, the Aldridge Commission report cited “monitoring and interpretation of space weather as relevant to consequence and predictability.”2 To implement a sustained human presence in space, either near Earth or elsewhere in the solar system, requires a comprehensive understanding of the heliospheric system and the effects of solar activity on the environment encountered by exploring humans. This chapter summarizes the approach to achieving this understanding by discussing (1) space weather hazards, (2) overarching themes in space physics that affect our ability to develop a predictive capability, and (3) the SEC’s existing programs and how they would function together to support NASA’s space exploration vision. Finally, Tables 2.1 and 2.2 presented toward the end of the chapter outline specific details of missions that are required to achieve success in support of the exploration vision, information that is augmented in Appendix B with one-page descriptions of the missions and their relevance to enabling exploration. 1   National Aeronautics and Space Administration, The Vision for Space Exploration, NP-2004-01-334-HQ, NASA, Washington, D.C., 2004. 2   A Journey to Inspire, Innovate, and Discover: Report of the President’s Commission on Implementation of United States Space Exploration Policy, p. 38, ISBN 0-16-073075-9, U.S. Government Printing Office, Washington, D.C., 2004.

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Solar and Space Physics and Its Role in Space Exploration SPACE WEATHER HAZARDS To achieve the space exploration vision objectives to “implement a human and robotic program to explore the solar system” and “extend human presence across the solar system,” we need the ability to make both short-term and long-term predictions of space weather across significant portions of the solar system. This is akin to knowing both the “travel” weather conditions and the average weather conditions at a destination. However, the stakes in space are much higher. Being unprepared for local weather conditions means getting wet or being too cold or too hot. In contrast, not having short- and long-term predictions of space weather adds to the challenge of protecting the health and perhaps even the lives of the human explorers.3 Understanding the fundamental physics that allows short- and long-term predictions of space conditions is a primary goal of the SEC program. Space radiation is among the top biological concerns for explorers beyond low Earth orbit (LEO), and it is also highly damaging to electronics, including critical spacecraft systems. Astronauts and their spacecraft will be exposed to penetrating particle radiation from three sources: terrestrial, solar, and galactic. The terrestrial source is Earth’s radiation belts (the Van Allen belts). Because they reach energies that penetrate matter to significant depths, ions in the inner belt and electrons in the outer belt pose the greatest hazards to astronauts and space hardware in the near-Earth phases of missions to the Moon or Mars. The risk of Earth’s radiation belts to astronauts depends strongly on the implementation scenarios developed for future missions and even more strongly on the nature of the missions that must be flown during the development of the systems that will eventually fly to the Moon and Mars. For example, Earth’s radiation belts do have substantial access to the relatively high inclination orbit occupied by the International Space Station. For the particular scenario of a near-equatorial launch with only minimal staging within low-inclination, low-altitude orbits, Earth’s radiation belts pose a relatively minor hazard because the astronauts spend very little time traversing them. Radiation from the Sun is of much greater concern over both the short and the long term. Intense penetrating radiation from the Sun takes the form of solar particle events (SPEs), which typically last several days to a week. SPEs are composed mainly of protons generated by solar storms, so they share the statistical properties of these storms. They exhibit a quasi-11-year cycle loosely synchronized with the solar activity cycle as represented by sunspot numbers. The geomagnetic field shields low-latitude LEO satellites from SPEs. Shielding ceases, however, at high latitudes and/or at altitudes above about 4 Earth radii (1 Earth radius, or Re, = 6,370 km) or less than one-tenth the distance to the Moon. Roughly, the dose accumulated by an astronaut in a spacesuit from one large SPE is equivalent to a dose accumulated over about 6 months by an astronaut inside the International Space Station.4 During a solar cycle, there are approximately 20 such SPEs, mainly clustered around solar maximum. We do not know the underlying physics well enough to predict when these SPEs will occur, how intense they will be, or how they will couple to Earth’s radiation environment. Galactic cosmic rays (GCRs) present a low-level, continuous source of highly penetrating radiation. They are partially shielded by the geomagnetic field so that on average a spacecraft in LEO receives about one third of the radiation dose of spacecraft in interplanetary space. In terms of total dose, the GCR component is roughly comparable to the SPE dose, and up to energies of a few GeV it is modulated by solar activity. Space travel beyond LEO will require prediction and mitigation of all three major radiation sources (see Box 1.1 in Chapter 1). Prediction involves understanding how solar events form, evolve, and couple with a planet’s space environment. This prediction goes beyond estimates of total dose because the damage from radiation depends strongly on energy, which in turn depends strongly on how the radiation is produced. The fundamental physics of predicting solar events and their evolution and coupling with Earth and planetary environments is a prime focus of both the Solar Terrestrial Probes (STP) and Living With a Star (LWS) mission lines. The state of space weather prediction today resembles the state of terrestrial weather prediction in the mid-20th century, because current space weather observations and modeling capabilities are quite limited. Coronographs on research satellites can warn of possible CMEs, but the arrival times and 3   See Safe on Mars, NRC, 2002; Safe Passage: Astronaut Care for Exploration Missions, Institute of Medicine, 2001; The Human Exploration of Space, NRC, 1997; Radiation Hazards to Crews of Interplanetary Missions, NRC, 1996 (The National Academies Press, Washington, D.C.). 4   National Research Council, Radiation and the International Space Station. Recommendations to Reduce Risk, National Academy Press, Washington, D.C., 2000.

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Solar and Space Physics and Its Role in Space Exploration consequences of CMEs can only be estimated roughly. Similarly, while we can monitor the development of active regions on the Sun, we are unable to predict when an active region will erupt or if hazardous levels of solar energetic particles will be created. Significant advances in prediction abilities are needed before adequate safety can be assured on long-duration interplanetary travel and during long-term habitation on other solar system bodies. These advances will only occur, as with terrestrial weather prediction, through a long-term research effort involving coordinated observations and modeling. There are numerous examples from the atmospheric sciences discipline of where research advances have led to improved operational capabilities.5 For example, the use of balloon-borne experiments in the 1930s to better understand Rossby waves in the atmosphere led to an improved description of large-scale atmospheric flow and contributed importantly to the development of numerical weather prediction. Early numerical simulations of the three-dimensional structure of thunderstorms have let to an improved understanding of severe storm dynamics. And recent advances in data-assimilative modeling have increased the accuracy of our weather prediction. Capabilities in terrestrial weather prediction have evolved over the past century through steady advances in observational capabilities, in numerical modeling techniques, and in understanding of the underlying physical processes. A similar approach will need to be taken to advance capabilities in space weather prediction. Space weather forecasters today rely on a variety of statistical relationships, some empirical and physics-based models, and qualitative assessments to predict important disturbances such as geomagnetic storms, radiation belt enhancements, and solar particle events. Although the availability of new data and scientific understanding have been improving forecast accuracy, the capabilities today do not yet provide the lead time or accuracy needed to ensure safe human travel through interplanetary space or habitation on unshielded planets and moons. For example, the extensive impact of the giant “Halloween Storm” of 2003 occurred with little warning. From solar and interplanetary observations forecasters knew that large solar storms would impact Earth, but they had only rough estimates of the timing and of the extent of the disruption of the terrestrial space environment that the Halloween events would cause. Through SEC missions such as SDO and STEREO, advances in helioseismology and in understanding the initiation and propagation of coronal mass ejections (CMEs) will give us greater capabilities to predict where active regions will develop, when they will erupt, and if they are likely to be major sources of energetic particles. Missions such as Magnetospheric Multiscale (MMS), Geospace Network, and Geospace Electrodynamic Connections (GEC) will improve our understanding of the resulting disturbances in planetary magnetospheres, ionospheres, and atmospheres. Data from these missions, coupled with data/results from the SR&T programs, will yield the quantitative, predictive models needed for space exploration. In the near term (1 to 5 years), the ever-improving models of the three-dimensional heliosphere and planetary environments should be used to model the transport of energetic particles throughout the solar system. This capability would allow us to assess the flux levels that would be experienced during a mission if a solar eruption occurred at any given location on the Sun. In the medium term (5 to 10 years), knowledge gained through techniques such as helioseismology, advanced imaging and image processing, and improved understanding of fundamental processes such as magnetic reconnection and shock acceleration will sharpen our ability to predict the location, evolution, and consequences of solar activity. In the long term, data-assimilative models that incorporate real-time data will be needed to obtain the most accurate predictions based on a given state of the space environment. SOLAR SYSTEM SPACE PHYSICS One of the major lessons from more than 40 years of solar and space physics research has been that making practical predictions of the space environment will require a broad, system-wide understanding of the fundamental physical processes in the Sun-heliosphere-planet system. Figures 2.1 through 2.3 illustrate the point that four key elements of that system—(1) the Sun as the driving energy source, (2) energy and mass transport interactions in the heliosphere, and (3, 4) the consequences at Earth and other planets—are all linked via a set of universal physical processes. Figure 2.1 also 5   See National Research Council, The Atmospheric Sciences: Entering the Twenty-First Century, Board on Atmospheric Sciences and Climate, National Academy Press, Washington, D.C., 1998.

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Solar and Space Physics and Its Role in Space Exploration FIGURE 2.1 Understanding of the interconnected system of the heliospheric system allows prediction and mitigation of hazards in the space environment. indicates that investigation of these processes and components leads naturally to enabling prediction and mitigation. Figures 2.2 and 2.3 give details of important cause-and-effect relationships and of the tools that should be developed in order to further increase our understanding of the four major components. The discussion below expands on these ideas. Solar Drivers The Sun drives the majority of dynamic interactions in the solar system. These arise both from its long-term variability on time scales of the solar cycle (11 years), and from short-term variability on time scales of minutes to days. Long-term variation in solar radiative output is a main source of “climate” in the target exploration environments. Short-term variability—or equivalently “weather”—includes impulsive events such as solar flares, coronal mass ejections, and acceleration of high-energy solar particles. Complete understanding of these critical sources of variability requires a balanced, long-term program that observes both solar evolution and dynamics, measures solar properties from the solar interior outward through the extended solar atmosphere, and develops validated models. Heliospheric Interactions The dynamic extension of the solar atmosphere is the solar wind, and its domain is the heliosphere, a region that encompasses all the solar system and extends more than three times the average distance to Pluto. Dynamic solar phenomena propagate outward through and are modulated by the ambient solar wind. For example, coronal mass ejections, high-speed solar wind streams, and

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Solar and Space Physics and Its Role in Space Exploration FIGURE 2.2 Tools necessary for understanding the heliospheric system and the impact of the environment on humans and technology in space. energetic particles may evolve as they propagate through the interplanetary medium. Similarly, the propagation of galactic cosmic rays is affected by magnetic shielding produced by CMEs as they propagate through interplanetary space. Understanding these interactions requires understanding first the ambient background by drawing, in part, on long-term databases of solar and heliospheric variability, along with models. One can then combine this information with observations of the propagating disturbances to develop quantitative models of the evolution of dynamic structures through the heliosphere. Earth Consequences Dynamic structures in the heliosphere affect Earth in a variety of ways. Long-term solar variability causes changes in Earth’s atmosphere and climate. Short-time-scale space weather can lead to magnetospheric storms, ionospheric disturbances, atmospheric heating, changes in atmospheric chemistry, and winds. To understand the full potential ramifications of these disturbances, observations (both from the ground and from space) and modeling are required of the magnetosphere, ionosphere, and atmosphere. Our own terrestrial magnetosphere-ionosphere system is a laboratory in which to investigate the basic phenomena that drive the environments of other solar system locations and to test our predictive capabilities.

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Solar and Space Physics and Its Role in Space Exploration FIGURE 2.3 Missions throughout the solar system form a space physics observatory, with each mission addressing components of the heliospheric system. Planetary Comparisons The space environment of a planet is affected by several factors, including the relative importance of the planetary magnetic field, the planet’s rotation rate, and any internal sources of plasma for the system. One learns the most by pushing a physical model of the environment to a “breaking point” and then discovering what changes in the assumptions of the underlying physics are needed to “fix” it to match observations. Thus, by comparing different planetary environments, one can test current understanding of universal processes under very different conditions. In the case of the rapidly rotating Jupiter, for example, comparisons of auroral processes with those at Earth test our theories of coupling between the solar wind, and the magnetosphere and ionosphere, of particle acceleration and the electrical currents that link the magnetosphere to the planet’s rotation. In the case of Mars, it is important to determine the extent to which the solar wind and cosmic rays penetrate the martian atmosphere or are deflected by patches of strong crustal magnetization. Continuous, long-term investigation of the Sun-Earth system, together with observations of the magnetospheres, ionospheres, and atmospheres of other planets, will enable critical estimates to be made of the likely range in conditions that instrumentation and exploring astronauts will need to withstand.

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Solar and Space Physics and Its Role in Space Exploration Universal Processes The disparate regimes discussed above (i.e., the Sun, interplanetary medium, Earth, and other planets) share in common the fact that they are the sites of a few universal physical processes.6 For example, the ability of global-scale magnetic fields to reconnect, releasing large amounts of magnetic energy in the process, may be responsible for the acceleration of high-energy particles at the Sun, throughout the solar system, and in the distant universe. Solar flares and coronal mass ejections, as well as magnetospheric substorms, are believed to originate in such reconnection events. Similarly, signatures of shocks and turbulence have been observed at the Sun, upstream of planetary magnetospheres, and at the outer boundary of the heliosphere. Shocks are also an important source of energetic particles throughout the universe. An understanding of these fundamental processes is essential to progress in understanding the behavior of the space environment. Theoretical models, computational simulations, laboratory experiments, and (whenever possible) direct observations are necessary tools in developing this understanding. Prediction and Mitigation As we embark on the exploration of new worlds, decisions will have to be made on issues such as the entry of orbiting (human and robotic) space vehicles into ionospheres and atmospheres, communication within and through planetary ionospheres, and survivability in the radiation environments of interplanetary space and within planetary magnetospheres. By combining observations from the various solar system regimes with physical analyses of the universal processes that unite them, steps may be taken to mitigate the effects of space climate and weather on humans, instrumentation, and communications and spacecraft systems. To that end, input from space physics observations and analysis will help in modeling and developing predictive capabilities for the extreme disturbances that occur, quantifying the long-term variability, and understanding the effects on humans and spacecraft systems. This information can then be incorporated in prediction software development, system design, materials testing, technology innovations, and physiology studies. UNDERSTANDING THE INTEGRATED HELIOSPHERIC SYSTEM Figure 2.3 illustrates some of the main connections between NASA missions and the four major components of the Sun-heliosphere-planet system. This coherent set of interrelated missions may be considered collectively as a “Great Observatory” for the field of solar and space physics. Missions exploring Earth’s space environment provide an up-close laboratory in which to observe solar system plasmas, providing insights and understanding that can be applied to more-distant areas of the heliosphere. Solar system plasmas are complex systems. Their complexity arises from nonlinear coupling, both within a single system, such as the solar drivers in Figure 2.1, and between two or more systems such as the solar drivers and heliospheric interactions. These plasma systems interact across a multiplicity of spatial and temporal scales. The physical processes by which they interact determine the evolution of the systems through the creation of both large- and small-scale structures. Examples of such cross-scale coupling are magnetic reconnection and plasma turbulence, which involve the nonlinear interaction of large-scale, relatively slow behavior and small-scale, very rapid processes. Finally, distinct regions are coupled across relatively thin boundaries in a highly nonlinear, dynamic fashion. Processes at the outer boundaries of planetary magnetospheres, where the solar wind and the planets’ magnetic fields interact, are examples of this coupling.7 6   See National Research Council, Plasma Physics of the Local Cosmos, The National Academies Press, Washington, D.C., 2004. 7   For a more detailed discussion, see National Research Council, Plasma Physics of the Local Cosmos, National Academies Press, Washington, D.C., 2004.

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Solar and Space Physics and Its Role in Space Exploration The study of the coupled system as defined in the decadal survey report8 and as depicted in Figure 2.1 requires the overlap of specific missions in key regions. For example, the study of solar drivers requires coordination with measurements of effects in Earth’s magnetosphere such as radiation belt creation and modification. Similarly, observations of the high-altitude radiation belts in equatorial regions and of consequences at lower ionospheric altitudes needs mission overlap. Other studies do not require overlap, but do require synergy among missions. For example, the results from the study of the fundamental process of reconnection by MMS will provide important comparison with reconnection processes on the Sun observed by SDO. Two missions can be singled out for their particular importance to both planetary science and space physics. These two planetary missions, Mars Aeronomy Probe (MAP) and Jupiter Polar Mission (JPM), are in the Solar System Exploration roadmap9 but are mentioned here because they offer significant advances in space physics through comparison of planetary environments. The goal of exploration of Mars elevates the significance of the MAP mission. From a purely scientific perspective, a mission of this type was cited in New Frontiers in the Solar System: An Integrated Exploration Strategy, the NRC’s recent decadal survey for solar system exploration,10 as a priority for Mars flight missions. Furthermore, the entry, descent, and landing requirements for complex payloads to Mars are sensitive to the density of the martian upper atmosphere, which in turn varies according to inputs from both the Sun and the lower atmosphere. A comprehensive understanding of the behavior of the martian upper atmosphere will therefore be required for extensive robotic and human exploration of Mars. Moreover, the interaction of the solar wind with Mars’s crustal magnetic field and upper atmosphere results in substantial atmospheric escape and hence may have played a critical role in Mars’s climate evolution and, hence, habitability. The objective to explore Jupiter’s moons and understand the history of the solar system11 makes JPM particularly important. A Jupiter Polar Mission also addresses goals (in the Aldridge Commission report under the “origins” and “evolution” themes12) of understanding the interior structure and composition of this archetypical giant planet; plus, JPM provides estimates of the angular momentum loss (thought to be an important process in the evolution of stars and giant planets) through the planet’s coupling to the magnetosphere. From a space physics perspective, Jupiter is an excellent test bed of fundamental magnetospheric processes (plasma transport, auroral emissions, particle acceleration, wave generation, and so on) under conditions very different from those experienced at Earth. Furthermore, Jupiter’s moons are major sources of magnetospheric plasma and are electrodynamically coupled to the planet, triggering radio emissions and auroras in Jupiter’s polar regions. THE NASA SUN-EARTH CONNECTION PROGRAM As is the case with all of NASA’s science programs, the SEC program depends critically on having a properly balanced portfolio of spaceflight missions, which are developed and phased strategically to address the objectives of the program, and of supporting programs and infrastructure, which provide the resources and capability to capitalize on the results from spaceflight missions, translate their results into scientific progress, and lay the scientific and technological foundation for the next steps in the program. For the SEC program, this portfolio is very much like the proverbial three-legged stool. There are two strategic mission lines—Living With a Star (LWS) and Solar Terrestrial Probes (STP)—and a coordinated set of supporting programs. LWS missions focus on observing the solar activity, from short-term dynamics to long-term evolution, that can affect Earth, as well as astronauts working and living in the near-Earth space environment. Solar Terrestrial Probes are focused on exploring the fundamental 8   National Research Council, The Sun to the Earth—and Beyond: A Decadal Research Strategy in Solar and Space Physics, The National Academies Press, Washington, D.C., 2003. 9   National Aeronautics and Space Administration, Roadmap for Solar System Exploration, NASA, Washington, D.C., 2002. 10   National Research Council, New Frontiers in the Solar System: An Integrated Exploration Strategy, The National Academies Press, Washington, D.C., 2003. 11   NASA, The Vision for Space Exploration, NP-2004-01-334-HQ, National Aeronautics and Space Administration, Washington, D.C., 2004. 12   A Journey to Inspire, Innovate, and Discover: Report of the President’s Commission on Implementation of United States Space Exploration Policy, ISBN 0-16-073075-9, U.S. Government Printing Office, Washington, D.C., 2004.

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Solar and Space Physics and Its Role in Space Exploration physical processes of plasma interactions in the solar system. A key assumption according to which the LWS program was designed was that the STP program would be in place to provide the basic research foundation from which the LWS program could draw to meet its more operationally oriented objectives. LWS relies heavily on other programs to either provide data such as that obtained with solar wind monitors and ground observatories, or use the data services as established by other programs, specifically the services that have been developed through NASA’s mission operations and data analysis (MO&DA) efforts. Furthermore, neither the STP nor LWS set of spaceflight missions can succeed without the third leg of the stool. That leg provides the means to (1) conduct regular small Explorer missions that can react quickly to new scientific issues, foster innovation, and accept higher technical risk; (2) operate active spacecraft and analyze the LWS and STP mission data; and (3) conduct ground-based and suborbital research and technology development in direct support of ongoing and future spaceflight missions.13 The SEC program plays a key national role by providing NASA’s contribution to the National Space Weather Program (NSWP). The NSWP is an interagency effort that also involves NSF and the Departments of Commerce, Defense, Energy, and Transportation and that is intended to provide timely, accurate, and reliable space environment observations, specifications, and forecasts to serve a variety of commercial and government activities. NASA and NSF, in particular, provide the research upon which new or improved capabilities depend, and DOD and NOAA have key responsibilities for translating that research into operational systems for modeling and predictions of space weather. Current SEC missions such as the Advanced Composition Explorer and SOHO are providing key data sets that are being used by NOAA and DOD forecasters. The LWS program, including both its spaceflight measurement missions and its theory, modeling, and data analysis components, is particularly important for meeting the future needs of DOD and NOAA. The Explorer Program The Explorer program contributes vital elements that are not covered by the mainline STP and LWS missions. Explorers fill critical science gaps in areas that are not addressed by strategic missions, they support the rapid implementation of attacks on very focused topics, and they provide for innovation and the use of new approaches that are difficult to incorporate into the long planning cycles needed to get a mission into the strategic mission queues. The Explorer program can also provide opportunities to respond rapidly to specific needs of human exploration. The Explorers also provide a particularly substantial means to engage and train science and engineering students in the full life cycle of space research projects. Consequently, a robust SEC science program requires a robust Explorer program. Because the full benefits of the SEC program accrue when the heliospheric system is understood as a unified system, it is vital to have a mechanism for filling critical gaps that are left open by the strategic STP and LWS missions. For example, the multi-spacecraft International Solar-Terrestrial Program (ISTP) in the 1990s identified a major uncertainty in understanding geomagnetic storms in the nightside of Earth’s magnetosphere: whether magnetic reconnection is a cause of dynamic behavior of the middle magnetosphere or is a consequence of such dynamics. The Explorer program will allow the THEMIS (Time History of Events and Macroscale Interactions during Substorms) mission to answer this one outstanding critical question. THEMIS also will complement the larger MMS mission by providing data on fundamental processes in space plasma physics at longer time and spatial scales than MMS will be able to sample. Mission Operations and Data Analysis No mission can achieve its research objectives until it is launched, delivered to its operating orbit or mission location, operated to collect the necessary scientific data, and the data delivered for processing and scientific analysis. Hence, the MO&DA phase constitutes the final critical step for a mission. All missions are transferred from a development phase to an MO&DA phase after 13   For a full discussion of the roles and relationships of spaceflight missions to supporting research and technology programs, see National Research Council, Supporting Research and Data Analysis in NASA’s Science Programs, National Academy Press, Washington, D.C., 1998.

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Solar and Space Physics and Its Role in Space Exploration commissioning (typically a few months or less after launch). The duration of the MO&DA phase varies. There may be an interplanetary cruise phase, or the mission may immediately enter a prime mission lasting one to several years. A mission extension may last many more years, often at a cost that is a small fraction of the initial mission development cost. Prime mission funding is provided under the mission budget, while extended mission funding is competed through periodic review of all ongoing missions. The objectives of mission operations and data analysis are to support: All postlaunch mission operations, Prime mission data analysis, Verification and validation of flight data sets, Data archiving, and Participation by a more significant number of researchers. MO&DA is the lifeblood of a mission because it constitutes the phase of the mission at which the investments in hardware development and launch are translated into scientific results. Optimum science return from missions often comes from extending the most productive science missions beyond their prime mission lifetimes.14 Missions are extended to create synergy with other missions or overlap with new missions. The senior review process15 is one mechanism for determining the value of extending an individual mission. The science during an extended mission is typically cutting-edge and new, providing measurements and synergy that would cost considerably more to produce in new mission concepts. For example, the extension of the Wind mission provided measurements of solar wind variability, while the Polar mission, which was launched later, measured the response of the magnetosphere to solar wind perturbations. Extension of the Voyager missions provided measurements of the outer heliosphere, including the exciting possibility of signatures of the heliospheric boundary. Part of the overall MO&DA budget often goes to a Guest Investigator program, which has the benefit of bringing a larger number of researchers to bear on the scientific utilization of ongoing SEC missions for a very small incremental cost. A Guest Investigator program provides the opportunity for both young and established scientists to participate in exciting, new science from ongoing missions. Fresh insight into the science is provided through the Guest Investigator program, enhancing the overall science return. Suborbital Program Suborbital sounding rocket flights and high-altitude scientific balloons can provide a wide range of basic science that is important to meeting SEC program objectives. For example, sounding rocket missions targeted at understanding specific solar phenomena and of the response of the upper atmosphere and ionosphere to those phenomena have potentially strong relevance. Missions in this category include high-time- and high-spatial-resolution imaging of the solar chromosphere, studies of ionospheric neutral winds and vortex structures, and measurements of noctilucent clouds that represent a near-Earth icy, dusty plasma. This science is cutting-edge, providing some of the highest-resolution measurements ever made and, in many cases, providing measurements that have never been made before. The Suborbital program serves several important roles, including: Conducting important scientific measurements in support of orbital spaceflight missions, Providing a mechanism to develop and test new techniques and new spaceflight instruments, and Training future scientists and engineers in effective space experimentation. 14   National Research Council, The Sun to the Earth—and Beyond: A Decadal Research Strategy in Solar and Space Physics, pp. 150-151, The National Academies Press, Washington, D.C., 2003. 15   For a fuller discussion of the senior review process, see National Research Council, Assessment of the Usefulness and Availability of Data from NASA’s Earth and Space Science Missions, The National Academies Press, Washington, D.C., 2002.

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Solar and Space Physics and Its Role in Space Exploration Development of new scientific techniques, scientific instrumentation, and spacecraft technology is a key component of the Suborbital program. Many of the instruments flying today on satellites were first developed on sounding rockets or balloons. For example, instruments on the SOHO and TRACE solar satellites were enabled by technology and experimental techniques developed in the Suborbital program. The low cost of sounding rocket access to space fosters innovation: instruments and technologies warrant further development before moving to satellite programs. Development of new instruments using the Suborbital program provides a cost-effective way of achieving high technical readiness levels with actual spaceflight heritage. The fact that any long-term commitment to space exploration will place a concomitant demand on the availability of a highly trained technical work force makes the training role of the Suborbital program especially important.16 For example, a 3-year sounding rocket mission at a university provides an excellent research opportunity for a student to carry a project through all of its stages—from conception to hardware design to flight to data analysis and, finally, to the publication of the results. This “hands on” approach provides the student with invaluable experience in understanding the spaceflight mission as a whole. Indeed, over 350 Ph.D.s have been awarded as part of NASA’s sounding rocket program.17 A significant fraction of these scientists have gone on to successfully define, propose, and manage bigger missions such as Explorer and even strategic missions. Supporting Research and Technology Programs Supporting research and technology (SR&T) programs are crucial for understanding basic physical processes that occur throughout the Sun-heliosphere-planet system, and for providing valuable support to exploration missions.18 The objectives of Supporting Research and Technology programs include: Synthesis and understanding of data gathered with spacecraft, Development of new instruments, Development of theoretical models and simulations, and Training of students at both graduate and undergraduate levels. SR&T programs support a wide range of research activities, including basic theory, numerical simulation and modeling, scientific analysis of spacecraft data, development of new instrument concepts and techniques, and laboratory measurements of relevant atomic and plasma parameters, all either as individual projects or, in the case of the SEC Theory program, via “critical mass” groups. These programs also are especially valuable for training students, at both the undergraduate and the graduate level, who will support and advance the NASA space exploration initiative. Theory and modeling, combined with data analysis, are vital for relating observations to basic physics.19 Numerical modeling can also be a valuable tool for mission planning. Insights obtained from theory and modeling studies provide a conceptual framework for organizing and understanding measurements and observations, particularly when measurements are sparse and when spatial-temporal ambiguities exist. For example, theories on radiation belt formation and dynamics of the plasmasphere during magnetic storms formed the essence of mission objectives for the IMAGE (Imager for 16   See National Research Council, The Sun to the Earth—and Beyond: Panel Reports, Chapter 5, The National Academies Press, Washington, D.C., 2003. 17   For a list of Ph.D. degrees awarded to students who worked on sounding rocket research projects, see http://rscience.gsfc.nasa.gov/education.html. 18   For a full discussion of the roles of supporting research and technology programs, see National Research Council, Supporting Research and Data Analysis in NASA’s Science Programs, National Academy Press, Washington, D.C., 1998. 19   For example, see National Research Council, The Sun to the Earth—and Beyond: A Decadal Research Strategy in Solar and Space Physics, p. 64, and The Sun to the Earth—and Beyond: Panel Reports, Chapter 4, The National Academies Press, Washington, D.C., 2003.

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Solar and Space Physics and Its Role in Space Exploration Magnetopause-to-Aurora for Global Exploration) mission, which subsequently confirmed, and in some cases led to modification of, theories. Theory and modeling will be especially important in the context of the space exploration initiative as exploration missions become more complex and the need for quantitative predictions becomes greater. Finding 3. To achieve the necessary global understanding, NASA needs a complement of missions in both the Living With a Star and the Solar Terrestrial Probes programs supported by robust programs for mission operations and data analysis, Explorers, suborbital flights, and supporting research and technology. Relevance of Specific SEC Missions to NASA’s Space Exploration Initiative Tables 2.1 and 2.2 present the science highlights of specific SEC missions and their relevance to the objectives of NASA’s space exploration initiative listed at the beginning of this chapter. Table 2.1 shows the exploration program benefits derived from these objectives and activities, the SEC contributions to exploration program success, and the SEC missions identified in the decadal survey report that are required to achieve these successes. Table 2.2 includes more detail on each mission. It identifies each mission that is listed in the right-hand column of Table 2.1, indicates the mission’s objectives, and outlines its relevance to the space exploration initiative. Finally, one-page descriptions of the missions and their relevance to the exploration initiative are included in Appendix B. TABLE 2.1 Contributions of Planned Solar and Space Physics Missions to Exploration Exploration Program Benefit SEC Contribution to Program Success SEC Missions Required Limit astronaut exposure to radiation Predictive models of CME formation and release, CME propagation, solar flare onset, radiation belt dynamics STEREO, SDO, MMS, RBSP, Solar Probe, Solar-B, MHM/Sentinels Avoid spacecraft hardware radiation damage/disruption Predictive models of SEP fluxes, radiation belt fluxes STEREO, SDO, Solar Orbiter, RBSP, MMS, MHM/Sentinels Maintain continuous, robust communication systems Predictive models of ionospheric dynamics, total electron content, solar flare x-rays GEC, ITSP, MAP, SDO Understand aerobraking and orbital stability at Earth, Mars, and beyond Predictive models of thermospheric structure and dynamics at Earth and Mars SDO, ITSP, MAP, GEC Understand past and future solar wind–planet and planetary–moon interactions Predictive models of Mars’s thermosphere/ ionosphere/exosphere structure, magnetosphere–moon interactions, loss of Jupiter’s angular momentum via coupling to the magnetosphere MAP, JPM

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Solar and Space Physics and Its Role in Space Exploration TABLE 2.2 Objectives and Relevance of Planned Solar and Space Physics Missions Mission Objective Relevance to Exploration Solar-B Understand the creation and annihilation of solar magnetic fields; understand the generation of energetic photons (EUV, x-ray); understand modulation of solar luminosity. By defining a quantitative relationship between the release of magnetic energy and the magnitude of the resulting flares, Solar-B will improve greatly our ability to forecast major eruptions that affect space weather. Solar-Terrestrial Relations Observatory (STEREO) Understand the fundamental origin, nature, and interplanetary propagation of coronal mass ejections (CMEs). Needed to understand and ultimately predict the arrival of CMEs, which are a primary cause of a range of hazardous space weather effects that impact all the planets. Solar Dynamics Observatory (SDO) Develop better understanding of the Sun’s influence on the planets by studying the solar atmosphere on small scales of space and time and in many wavelengths simultaneously. Needed to understand solar conditions that lead to flares and CMEs and the strong effects that these energetic phenomena produce throughout interplanetary space and the planetary environments. Magnetospheric Multiscale (MMS) Understand reconnection and the associated acceleration of energetic particles. Needed to provide the scientific foundation for the eventual development of a predictive capability for solar and planetary magnetic disturbances (flares, CMEs, auroral and magnetic storms). Geospace Network Understand the formation of radiation belts and the global solar-induced variability of the upper atmosphere and ionosphere. Understanding the formation and dynamics of radiation belts is crucial for the mitigation of hazards to astronauts and spacecraft systems. Understanding of the ionosphere/thermosphere system will lead to better application of aero-braking and communication systems to Mars missions. Geospace Electrodynamic Connections (GEC) Understand the electrodynamic processes in Earth’s lower ionosphere and its response to solar and magnetospheric inputs. Understanding of Earth’s ionosphere will include physical processes that are common to other planetary ionospheres, specifically to Mars. Solar Probe Understand how the solar wind is heated and accelerated. Understanding the source of the heliosphere is necessary for ultimate understanding of solar activity and how hazardous particles travel through the heliosphere. Multisatellite Heliosphere Mission (MHM/Sentinels) Determine how the global character of the inner heliosphere changes with time and how propagating solar disturbances (CMEs, shocks, co-rotating interaction regions) propagate and evolve. Needed for a better understanding of the role of interplanetary disturbances in modifying the radiation environment that poses dangers to the goals of NASA’s space exploration initiative. Solar Orbiter Identify the links between activity on the Sun’s surface and the resulting evolution of the corona and inner heliosphere. By combining high-resolution images of the sources of solar activity with in situ observations of the resulting inner heliospheric processes, Solar Orbiter will help characterize and ultimately predict the occurrence and effects of solar energetic particles and CMEs. Mars Aeronomy Probe (MAP) Understand how the upper atmosphere and ionosphere of Mars are affected by solar variability and energy inputs. Knowledge gained from MAP will provide important planetary comparison of atmospheric response to solar variability and will be crucial for the conduct of aero-capture and aero-braking maneuvers for Mars-bound spacecraft. Jupiter Polar Mission (JPM) Understand magnetospheric processes in the context of a rapidly rotating gaseous planet with embedded plasma sources. Provide a critical test of current understanding of fundamental auroral processes. Understanding of the space environment of Jupiter and its moons will be crucial for future exploration of this system.