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2 Integrated Research Strategy for Solar and Space Physics In developing a research strategy for solar and space physics for the coming decade, the committee was guided by several considerations. First, solar and space physics will achieve the greatest gains in understanding through coordinated investigations of its objects of study as interacting parts of complex systems. Second, to address the scientific challenges presented in Chapter 1, a combination of observational programs and complementary theory and modeling initiatives is needed, with the observational programs including both ground- and space-based elements. (The committee noted that many such efforts are already important components of planned or proposed agency programs.) Third, the vulnerability of society’s technological infrastructure to space weather necessitates a mix of basic, targeted basic, and applied research initiatives that will lead both to advances in fundamental scientific knowledge and to progress in the application of that knowledge to the mitigation of space weather effects on technology and society. The research strategy that the committee has developed is thus an integrated one, a strategy that provides for the coordinated investigation of solar system plasmas as complex, coupled systems and that seeks to maximize the synergy between observational and theoretical initiatives and between basic research and targeted research programs. A final, critical consideration was cost realism. Accordingly, the committee exercised great care to ensure that its recommended research strategy is consistent with the anticipated budgets of the various federal agencies. The programs and initiatives that constitute the committee’s recommended strategy for solar and space physics research during the decade 2003-2013 are described in the sections that follow. The discussion is organized in terms of the scientific challenges set forth in the preceding chapter and emphasizes the complementarity of the various recommended initiatives. The section “Roadmap to Understanding” describes the criteria that the committee used and the decision-making process that it followed in
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establishing priorities among the programs and initiatives recommended by the disciplinary study panels. Cost estimates are presented in tabular form, and costs and phasing for all recommended programs are illustrated graphically in three waterfall charts. THE SUN’S DYNAMIC INTERIOR AND CORONA Helioseismological studies of the solar interior have attained a high degree of sophistication through the ground- and space-based measurements of Doppler shifts by GONG and SOHO, from which images of the magnetic fields and flow systems below the solar surface are deduced. Similarly, imaging and spectral data from the solar corona and transition region provided by the SOHO and TRACE satellites have demonstrated the central role of the magnetic field in controlling coronal dynamics. However, the mechanisms by which the solar magnetic field is generated, including its reversals and temporal cycles, are still not completely understood. Solar B, a mission now in development by Japan’s Institute of Space and Astronautical Science (ISAS) and in which NASA is a participant, will measure how magnetic fields emerge onto the solar surface and reveal the details of the interaction between convective flows and magnetic fields. Also under development now is STEREO, which will measure the three-dimensional development and propagation of coronal mass ejections (CMEs) through the inner heliosphere. The next important scientific steps in solar physics are the following: (1) to refine and sharpen the probing of the solar interior; (2) to treat the outer layers of the Sun and its atmosphere as a single system; (3) to develop the science of coronal mapping for measurement of the structure and strength of the coronal magnetic field; and (4) to make precise spectral measurements of the solar atmosphere over a broad range to map velocity distributions and to determine what spectral bands have the strongest effects at Earth and how they vary over the solar cycle. Three new programs, working in concert, will take these steps: the Solar Dynamics Observatory (SDO), the Advanced Technology Solar Telescope (ATST), and the Frequency-Agile Solar Radiotelescope (FASR). SDO, which is part of the approved NASA Living With a Star program and is now in development, will explore the Sun from its center to the subsurface layers of the convection zone to the outer solar atmosphere, probing the subsurface origin of active regions with acoustic imaging of the convection zone and tracking their development in space and time. By virtue of the high data rate available from its geosynchronous orbit, SDO
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will make full-disk, high-resolution (in both space and time) maps of the Doppler velocities and magnetic fields of the Sun, making possible the exploration of the complete life cycle of active regions. SDO will also carry an ultraviolet (UV) spectrograph in order to understand the link between solar activity and solar spectral radiance. The ground-based ATST, which is currently undergoing a design study funded by the NSF, will be a 4-meter facility that employs adaptive optics to study the solar magnetic field, from the photosphere up through the corona. In the lower atmosphere the telescope will achieve a flux density sensitivity of a few gauss or smaller. It will provide observations of the solar atmosphere at a high temporal cadence and with better than 0.1-arcsecond resolution, which is sufficient to resolve the pressure scale height and the photon mean free path in the solar atmosphere. ATST will thus enable critical tests of models of solar plasma processes. An important ground-based element of the NSF-supported program recommended in this report is FASR (see Figure 2.1), which, like ATST, is now in a design study phase.1 FASR represents a significant advance beyond existing solar radio instruments yet is well within the reach of emerging technologies. A wide range of solar features from within a few hundred kilometers of the visible surface of the Sun to high up in the solar corona can be studied in detail with the unique diagnostics available in the radio regime. FASR capabilities will include measuring the properties of both thermal and nonthermal electrons accelerated in solar flares, measuring coronal magnetic field strengths in active regions, and mapping kinetic electron temperatures throughout the chromosphere and corona. Two of the major mysteries in solar physics are the fact that the Sun’s corona is several hundred times hotter than the underlying photosphere and the fact that the coronal gases are accelerated to supersonic velocities within a few solar radii of the surface to form the solar wind. Resolving these mysteries—understanding how the corona is heated and how the solar wind originates and evolves in the inner heliosphere—has been identified by the Panel on the Sun and Heliospheric Physics as its top science priority for the coming decade. To answer these questions requires measurements from a spacecraft that passes as close to the solar surface as possible. A Solar Probe mission will make in situ measurements of the plasma, energetic particles, magnetic field, and waves inward of ~0.3 AU to an altitude of 3 solar radii above the Sun’s surface. This region is one of the last unexplored frontiers in the solar system. Such measurements will locate the source and trace the flow of energy that heats the corona; determine the acceleration processes and find the source regions of the fast and
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FIGURE 2.1 Artist’s conception showing a portion of the Frequency-Agile Solar Radiotelescope’s ~100-dish antenna array. FASR, which is the committee’s highest-priority small initiative for solar physics, will produce high-resolution images of the Sun’s atmosphere from the chromosphere up into the mid-corona. Courtesy of D.E. Gary (New Jersey Institute of Technology). slow solar wind; identify the acceleration mechanisms and locate the source regions of solar energetic particles; and determine how the solar wind evolves with distance in the inner heliosphere. In addition, if suitable remote-sensing instruments are included, a Solar Probe mission can complement the in situ measurements with valuable close-up views of the Sun.2 Because of the profound importance of the scientific questions that a Solar Probe will address, the committee recommends that this mission be implemented as soon as possible.
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THE HELIOSPHERE AND ITS COMPONENTS The heliosphere begins in the outer solar corona and ends at its interface with the interstellar medium (see Chapter 1). As such, it encompasses the entire solar system and is the domain of solar plasmas, magnetic fields, and energetic particles as well as interstellar dust, neutral atoms, and pickup ions. The plasma continuously flowing from the Sun in fast and slow solar winds is highly dynamic and turbulent, and the embedded CMEs and interplanetary shocks cause the impulsive transfer of solar energy to the magnetospheres (whether intrinsic or induced) of planets and small bodies. The heliosphere contains the connective tissue of the Sun-Earth connection; however, little is known about its source or its destiny. The new frontiers of heliospheric research lie at its inner boundary in the solar corona and its outer boundary with the interstellar medium. A Solar Probe mission will investigate the innermost boundary of the heliosphere. Moving outward from the Sun, ESA’s Solar Orbiter mission will periodically corotate with the Sun in an elliptical orbit with perihelion of 45 solar radii. With its payload of imaging and in situ instruments, some of which will be contributed by the United States, Solar Orbiter will be poised to reveal the magnetic structure and evolution of the corona and the resulting effects on plasmas, fields, and energetic particles in the inner heliosphere. Participation in this mission will provide the United States with a highly leveraged means of investigating the structure and evolution of the inner heliosphere for the first time. STEREO will perform stereoscopic imaging and two-point, in situ measurement of CMEs in the inner heliosphere. The next important step in understanding the heliospheric propagation of CMEs will be accomplished with a Multispacecraft Heliospheric Mission (MHM).3 MHM will consist of four or more spacecraft separated in solar longitude and radius with at least one orbital perihelion at or within ~0.5 AU. Orbiting in and near the ecliptic plane, these spacecraft will make in situ measurements of plasmas, fields, waves, and energetic particles in the inner heliosphere, providing two-dimensional slices through propagating CMEs and the ambient solar wind. The boundary between the solar wind and the local interstellar medium (LISM) is one of the last unexplored regions of the heliosphere. Very little is currently known about this boundary or the nature of the LISM that lies beyond it. The outer boundary of the heliosphere will eventually be sampled directly by an Interstellar Probe mission. Advances in propulsion technology are expected to make such a mission feasible during the decade 2010-2020. Although it cannot yet be included in the program recommended by
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the committee, an Interstellar Probe is a high-priority future mission for which the required technology investments should begin as soon as possible. In the meantime, certain aspects of the heliospheric boundary and the LISM can be studied by a combination of remote sensing and in situ sampling techniques. This investigation could be accomplished by an Interstellar Sampler mission traveling to distances of several AU to measure the neutral atoms of the LISM that penetrate well into the heliosphere and to obtain energetic neutral atom images and extreme ultraviolet images of the heliospheric boundary. Such a mission is gauged to be feasible within the resources of the Explorer program and so is not prioritized separately in this report. SPACE ENVIRONMENTS OF EARTH AND OTHER SOLAR SYSTEM BODIES Earth’s magnetosphere and ionosphere formed the historical starting point for space physics research and remain an important focus for study because they constitute the human space environment and because they provide important prototypes for understanding the magnetospheres and ionospheres of other planets and small solar system bodies. In addition, the basic physical phenomena of space plasmas, which can be studied directly in Earth’s magnetosphere, occur in remote and therefore inaccessible locations in the universe. Having been the focus of numerous space- and ground-based investigations over the past four decades, the study of geospace has reached a level of maturity that brings the shortcomings of understanding into sharp focus. What specific physical processes transfer energy from the solar wind to geospace? What is the nature of the global response of Earth’s magnetosphere and ionosphere to the variable solar-wind input? These are the most basic and important questions that can be asked about geospace, but they have not received satisfactory answers. However, the maturity of the field now allows the interrogation of large databases, the development of sophisticated models, and the construction of new, definitive experiments both for Earth’s space environment and for that of other solar system bodies. Magnetic fields are continually being created by the solar dynamo but are also continually being annihilated by both small- and large-scale magnetic reconnection in the corona. Reconnection converts magnetic energy to particle kinetic energy and heat, and the results are heating of the corona and explosive outbursts of solar flares. Similarly at Earth, magnetic fields are continually being created by the internal dynamo and being annihilated
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by reconnection with solar wind magnetic field lines at the dayside magnetopause and reconnection of open field lines within the geomagnetic tail. As at the Sun, these processes result in the energization of charged particles. NASA’s Solar Terrestrial Probe (STP) mission Magnetospheric Multiscale (MMS) is designed to probe the reconnection process at the magnetopause and in the tail with a cluster of four spacecraft. MMS will benefit greatly from the groundbreaking research on magnetospheric and solar wind plasma dynamics that is being done with the European Cluster 2 mission. With its ability to adjust orbits and spacecraft separations, the MMS cluster will probe the boundary regions where reconnection is occurring and test directly theories of reconnection from the magnetohydrodynamic scale (thousands of kilometers) down to the ion and electron kinetic scales (kilometers). Earth’s ionosphere-thermosphere system is the site of complex electrodynamic processes that redistribute and dissipate energy delivered from the magnetosphere in the form of imposed electric fields and precipitating charged particles. Previous studies have revealed much about the composition and chemistry of this region and about its structure, energetics, and dynamics. However, a quantitative understanding has proved elusive because of the inability to distinguish between temporal and spatial variations, to resolve the variety of spatial and temporal scales on which key processes occur, and to establish the cross-scale relationships among small-, intermediate-, and large-scale phenomena. Geospace Electrodynamic Connections (GEC) (see Figure 2.2) is a multispacecraft STP mission that has been specifically designed to overcome these difficulties and to provide new physical insight into the coupling among the ionosphere, thermosphere, and magnetosphere. Sounding rockets are an important part of NASA’s Suborbital Program and have been a mainstay for the investigation of important small-scale physical processes in the ionosphere-thermosphere, for a wide range of magnetospheric studies, and for the development of new instruments for space physics. While the flight time of these rockets is small, their slow velocity through specific regions of space (nearly an order of magnitude less than that of orbiting vehicles) and their ability to sustain very high telemetry rates from multiple payloads launched from a single vehicle make them extremely useful for studying the fine structure of dynamic phenomena like the aurora. Moreover, some important regions of space are too low in altitude to be sampled by satellites (i.e., the mesosphere below 120 km), so sounding rockets are the only platforms from which direct in situ measurements can be carried out in these regions.
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FIGURE 2.2 The Geospace Electrodynamic Connections (GEC) mission is a multispacecraft Solar Terrestrial Probe mission designed to study the multiple spatial and temporal scales on which the ionosphere-thermosphere system receives electromagnetic energy from the magnetosphere and redistributes and dissipates it through ion-neutral interactions. During the 2-year mission, the spacecraft will perform several “deep dipping” excursions that will allow them to make in situ measurements down to altitudes as low as 130 kilometers. Courtesy of NASA Goddard Space Flight Center. The Advanced Modular Incoherent Scatter Radar (AMISR) is a planned NSF program that will bring the observing power of a modern multi-instrument, ground-based observatory to a variety of geophysical locations chosen to optimize the benefit of the observations to specific scientific inquiry (Figure 2.3). In addition to its incoherent scatter radar, AMISR will host a variety of ground-based diagnostics that together will address key science questions about atmosphere-ionosphere-magnetosphere (AIM) interactions
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FIGURE 2.3 The Advanced Modular Incoherent Scatter Radar (AMISR) is the committee’s top-ranked small initiative for ground-based geospace research. It combines a powerful state-of-the-art incoherent scatter radar with supporting optical and radio instrumentation in a transportable format. This flexibility enables the AMISR to study a wide range of ionospheric phenomena at polar, auroral, equatorial, and mid-latitudes and to act in close conjunction with other ground-based, suborbital, and satellite investigations of the geospace environment. This artist’s conception depicts the fast-steering, multibeam RAO probing the dynamic auroral environment at high latitudes. Courtesy of J. Kelly and C.J. Heinselman (SRI International). that can only be tackled with a detailed knowledge of evolving time and altitude variations in a specific region. A Small Instrument Distributed Ground-Based Network4 will combine state-of-the-art instrumentation with real-time communications technology to provide both broad coverage and fine-scale spatial and temporal resolution of upper atmospheric processes crucial to understanding the coupled AIM system. Placing a complement of instruments, including Global Posi-
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tioning System receivers and magnetometers, at educational institutions will provide a rich, hands-on environment for students, while instrument clusters at remote locations will contribute important global coverage. This flexible NSF initiative will provide the simultaneous real-time measurements needed for assimilation into physics-based models and to address the space weather processes and effects in the upper atmosphere. These detailed, distributed measurements will complement the capabilities at the larger ground-based facilities that host the incoherent scatter radars. Global magnetospheric imaging, currently available from the IMAGE mission, needs to be developed further, specifically with stereo imaging, which will be implemented for 1- to 30-keV neutral atoms with the Two Wide-Angle Imaging Neutral-Atom Spectrometers (TWINS) mission (launch dates in 2003 and 2004). Stereo imaging is essential because magnetospheric plasmas are optically thin. The Stereo Magnetospheric Imager (SMI), a proposed STP mission,5 will obtain EUV images of the plasmasphere and neutral atom images of the plasma sheet and ring current from two widely spaced spacecraft, thereby greatly improving the accuracy with which global ion images can be produced. In addition, SMI will provide an auroral imaging capability, which has become a standard tool for assessing the global activity of the magnetosphere. A large database of spacecraft magnetic field measurements has made it possible to construct good models of the average configuration of Earth’s magnetosphere for different levels of magnetic activity. However, the actual instantaneous configuration of the magnetosphere is not expected ever to resemble any of its average states. What is needed is a dynamic image of the magnetic fields and plasmas within the magnetosphere. Measurements by a large constellation of spacecraft carrying magnetometers and simple plasma instruments can yield dynamic “images” of large portions of the magnetosphere. Magnetospheric Constellation (MagCon) is an STP mission that is designed to investigate the dynamics and structure of Earth’s near magnetotail by means of a constellation of 50 to 100 spacecraft. The Explorer program has long provided the opportunity for targeted investigations, which can complement the larger initiatives recommended by the committee. However, the committee is concerned that the overall rate at which solar and space physics missions are undertaken is still rather low. A revitalized University-Class Explorer (UNEX) program would address this problem while allowing innovative small investigations to be conducted. However, the very existence of a UNEX program depends critically on low-cost access to space, which is discussed in Chapter 7. Jupiter has a giant magnetosphere that has gross similarities with Earth’s
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FIGURE 2.4 Electrical currents aligned with Jupiter’s strong magnetic field couple the moons Io, Ganymede, and Europa with Jupiter’s high-latitude ionosphere. Bright auroral emissions observed at the footpoints of the magnetic flux tubes linking the moons to the ionosphere (inset) are the signature of this coupling, the physics of which is only partially understood. (The letters superposed on the auroral image in the inset identify the emission features associated with the footpoints of Io, Ganymede, and Europa.) A probe to study the still unexplored polar regions of Jupiter’s magnetosphere will answer basic questions about the nature of electrodynamic coupling between the Jovian atmosphere and magnetosphere and about auroral acceleration in a magnetospheric environment much different from Earth’s. Hubble Space Telescope image courtesy of J.T. Clarke (Boston University) and NASA/Space Telescope Science Institute. Artist’s rendering of the Jovian inner magnetosphere courtesy of J.R. Spencer (Lowell Observatory). Reprinted by permission from Nature 415:997-999 and cover, copyright 2002, Macmillan Publishers Ltd.
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TABLE 2.1 Mapping of Missions and Facilities to Scientific Challenges Scientific Challenges Missions and Facilities The Dynamic Solar Interior and Corona The Heliosphere and Its Components Earth and Planetary Space Environments Fundamental Space Plasma Physics Space Weather Large Solar Probe X X X Moderate Magnetospheric Multiscale X X Geospace Network X X Jupiter Polar Mission X X Multispacecraft Heliospheric Mission X X Geospace Electrodynamic Connections X X X Suborbital Program X X X Magnetospheric Constellation X X X Solar Wind Sentinels X X Stereo Magnetospheric Imager X X Small Frequency-Agile Solar Radiotelescope X X X Advanced Modular Incoherent Scatter Radar X X L1 Monitor X Solar Orbiter X X Small Instrument Distributed Ground-Based Network X X University-Class Explorers X X X X Planned/approved initiatives Solar Dynamics Observatory X X Advanced Technology Solar Telescope X X X
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Recommendation: The committee recommends the approval and funding of the prioritized programs listed in Table 2.2. While all the programs in Table 2.2 are exceptionally meritorious, small discriminators emerged in the ranking process. The maturity of the study phase of the Magnetospheric Multiscale mission and its attack on the fundamental problems of magnetic reconnection are highly valued. So, too, are the fundamental science questions related to ionospheric variability and particle acceleration in the inner magnetosphere that will be addressed by the LWS Geospace Network missions. Together, these programs will significantly improve the nation’s ability to specify and predict the response of the geospace environment to solar activity. Similarly, the ability to image the Sun with rapid temporal and spatial resolution using the Frequency-Agile Solar Radiotelescope, an important science opportunity in its own right, greatly complements the science program associated with the Solar Dynamics Observatory. Finally, the AMISR will allow many fundamental parameters to be measured in regions important to understanding the response of the ionosphere and atmosphere to external energy inputs driven by the Sun. In addition to their importance for ground-based basic research in solar and space physics, the committee also notes that FASR and AMISR will contribute importantly to the national space weather effort—FASR by providing real-time and near-real-time solar data and AMISR through improved understanding of disturbances of the upper atmosphere and ionosphere associated with space weather events. Beyond these programs are others with great scientific merit and societal benefit that are directly related to an improved specification of how the geospace system responds to changes in inputs from the Sun and solar wind. An important element of this endeavor is the maintenance of an L1 solar-wind monitor, which the committee recommends be implemented by NOAA (cf. Chapter 5). The rankings set forth in Table 2.2 were combined with available cost estimates and considerations of technical readiness to arrive at a phasing of programs that could be conducted in the next decade and remain within a reasonable budget. Table 2.3 shows the costing and readiness factors that the committee used to construct the implementation schedule for the NASA initiatives shown in Figure 2.5. In each case the costs include Phases B through D only. MMS and Geospace Network take their place as the important first steps in the committee’s recommended program. These and the other flight programs are superposed on enhancements to the SR&T program and the Suborbital Program that reflect the high scientific produc-
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TABLE 2.2 Priority Order of the Recommended Programs in Solar and Space Physics Type of Program Rank Program Description Large 1 Solar Probe Spacecraft to study the heating and acceleration of the solar wind through in situ measurements and some remote-sensing observations during one or more passes through the innermost region of the heliosphere (from ~0.3 AU to as close as 3 solar radii above the Sun’s surface). Moderate 1 Magnetospheric Multiscale Four-spacecraft cluster to investigate magnetic reconnection, particle acceleration, and turbulence in magnetospheric boundary regions. 2 Geospace Network Two radiation-belt-mapping spacecraft and two ionospheric mapping spacecraft to determine the global response of geospace to solar storms. 3 Jupiter Polar Mission Polar-orbiting spacecraft to image the aurora, determine the electrodynamic properties of the Io flux tube, and identify magnetosphere-ionosphere coupling processes. 4 Multispacecraft Heliospheric Mission Four or more spacecraft with large separations in the ecliptic plane to determine the spatial structure and temporal evolution of coronal mass ejections (CMEs) and other solar-wind disturbances in the inner heliosphere. 5 Geospace Electrodynamic Connections Three to four spacecraft with propulsion for low-altitude excursions to investigate the coupling among the magnetosphere, the ionosphere, and the upper atmosphere. 6 Suborbital Program Sounding rockets, balloons, and aircraft to perform targeted studies of solar and space physics phenomena with advanced instrumentation. 7 Magnetospheric Constellation Fifty to a hundred nanosatellites to create dynamic images of magnetic fields and charged particles in the near magnetic tail of Earth. 8 Solar Wind Sentinels Three spacecraft with solar sails positioned at 0.98 AU to provide earlier warning than L1 monitors and to measure the spatial and temporal structure of CMEs, shocks, and solar-wind streams. 9 Magnetospheric Imager Stereo Two spacecraft providing stereo imaging of the plasmasphere, ring current, and radiation belts, along with multispectral imaging of the aurora. Small 1 Frequency-Agile Solar Radiotelescope Wide-frequency-range (0.3-30 GHz) radiotelescope for imaging of solar features from a few hundred kilometers above the visible surface to high in the corona.
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Type of Program Rank Program Description 2 Advanced Modular Incoherent Scatter Radar Movable incoherent scatter radar with supporting optical and other ground-based instruments for continuous measurements of magnetosphere-ionosphere interactions. 3 L1 Monitor Continuation of solar-wind and interplanetary magnetic field monitoring for support of Earth-orbiting space physics missions. Recommended for implementation by NOAA. 4 Solar Orbiter U.S. instrument contributions to European Space Agency spacecraft that periodically corotates with the Sun at 45 solar radii to investigate the magnetic structure and evolution of the solar corona. 5 Small Instrument Distributed Ground-Based Network NSF program to provide global-scale ionospheric and upper atmospheric measurements for input to global physics-based models. 6 University-Class Explorer Revitalization of University-Class Explorer program for more frequent access to space for focused research projects. Vitality 1 NASA Supporting Research and Technology NASA research and analysis program. 2 National Space Weather Program Multiagency program led by the NSF to support focused activities that will improve scientific understanding of geospace in order to provide better specifications and predictions. 3 Coupling Complexity NASA/NSF theory and modeling program to address multiprocess coupling, nonlinearity, and multiscale and multiregional feedback. 4 Solar and Space Physics Information System Multiagency program for integration of multiple data sets and models in a system accessible by the entire solar and space physics community. 5 Guest Investigator Program NASA program for broadening the participation of solar and space physicists in space missions. 6 Sun-Earth Connection Theory and LWS Data Analysis, Theory, and Modeling Programs NASA programs to provide long-term support to critical-mass groups involved in specific areas of basic and targeted basic research. 7 Virtual Sun Multiagency program to provide a systems-oriented approach to theory, modeling, and simulation that will ultimately provide continuous models from the solar interior to the outer heliosphere.
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TABLE 2.3 Cost Estimates for Phases B Through D and Technical Concern Levels for the Recommended Flight Missions and Ground-Based Facilities (million dollars) Program Cost (FY 2002) Technical Concern Solar Probe 650 Moderate-high Geospace Electrodynamic Connections 300 Low Geospace Network 400 Low Jupiter Polar Mission 350 Moderate Magnetospheric Constellation 325 High Magnetospheric Multiscale 350 Low Multi-Heliospheric Probes 300 Moderate Solar Wind Sentinels 300 Moderate Stereo Magnetospheric Imager 300 Low Suborbital Program 30/yr (2002)-60/yr (2012) Low Frequency-Agile Solar Radiotelescope 60 Low L1 Monitor 100 Low Relocatable Atmospheric Observatory 65 Low Small Instrument Distributed Ground-Based Network 5/yr Low Solar Orbiter 100 Moderate University-Class Explorer 35/yr Moderate NOTE: Cost estimates were obtained directly from agency estimates whenever possible. Large, medium, and small programs are grouped separately in alphabetical order. tivity of these efforts and the need to ensure that the overall science under-pinning the major missions does not fall short of its full potential. Because the committee believes that it is imperative to understand the three-dimensional development of energetic solar events such as CMEs as they propagate from the inner heliosphere to 1 AU and beyond, it has included a Multispacecraft Heliospheric Mission in its recommended program. The committee is aware that the different ways in which a mission of this type might be implemented present different technology challenges. For example, an inner heliospheric mission might best be implemented using solar sails. However, in view of the importance of the understanding to be gained through multipoint measurements in the inner heliosphere, the committee recommends the early implementation of an MHM that is consistent with existing technology. The committee emphasizes the scientific importance of investigating the complex space environments of other planets. Such investigations serve
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FIGURE 2.5 Recommended phasing of the highest-priority NASA missions, assuming an early implementation of a Solar Probe mission. Solar Probe was the Survey Committee’s highest priority in the large mission category, and the committee recommends its implementation as soon as possible. However, the projected cost of Solar Probe is too high to fit within plausible budget and mission profiles for NASA’s Sun-Earth Connection (SEC) Division. Thus, as shown in this figure, an early start for Solar Probe would require funding above the currently estimated SEC budget of $650 million per year for fiscal years 2006 and beyond. Note that mission operations and data analysis (MO&DA) costs for all missions are included in the MO&DA budget wedge. as rigorous tests of the ideas developed from the study of Earth’s own environment while extending the knowledge base to other solar-system bodies. The committee therefore strongly recommends a Jupiter Polar Mission, which will study energy transfer in a magnetosphere that is the largest object in the solar system and that, unlike Earth’s, is powered principally by planetary rotation. A Solar Probe is the only large mission considered by the committee for which the technical readiness is appropriate for implementation in the decade 2003-2013. The scientific merit of a Solar Probe mission (which was the top priority of the Panel on the Sun and Heliospheric Physics) is out-
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FIGURE 2.6 Recommended phasing of the highest-priority NASA missions if budget augmentation for Solar Probe is not obtained. MO&DA costs for all missions are included in the MO&DA budget wedge. standing, and the committee recommends its implementation as soon as possible. However, the projected cost of such a mission is too high to fit within either the LWS program or the STP program. Thus, for this important program, separate funding would be required, as is illustrated in Figure 2.5, in which the Solar Probe budget profile extends above the projected Sun-Earth Connection (SEC) baseline budget projection. In the event that funding augmentation for a Solar Probe mission cannot be secured, the recommended program can still be implemented but with Solar Probe having to start later, which would not be desirable or in keeping with its high scientific priority. Such an alternative sequencing is illustrated in Figure 2.6, which is based on a conservative estimate of the SEC budget. A summary of the expected NSF funding profile and the recommended phasing of major NSF initiatives is shown in Figure 2.7. An important aspect of the recommended program is the additional funding for facilities
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FIGURE 2.7 Recommended phasing of major new and enhanced NSF initiatives. The budget wedge for new facilities science refers to support for guest investigator and related programs that will maximize the science return of new ground facilities to the scientific community. Funding for new facilities science is budgeted at approximately 10 percent of the aggregate cost for new NSF facilities. science (“guest investigator”), which will allow the scientific community to reap the scientific results that the investment in new ground-based observatories will make possible. The new facilities science is budgeted at ~10 percent of the aggregate cost of the new NSF facilities. The cost estimate for the NSF Upper Atmosphere base program includes costs for the CEDAR, GEM, and SHINE research initiatives, which coordinate community research activity and encourage strong student participation, as well as for individual research support in the areas of aeronomy, magnetospheric physics, and solar-terrestrial relations. NSF projections are that this baseline will double within 5 years; the committee has included this projection, doubling funding for the Upper Atmosphere base, the NSWP, and new facilities every 5 years.
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TABLE 2.4 Deferred High-Priority Flight Missions (Listed Alphabetically) Mission Reason for Deferral Large Interstellar Probe Advanced propulsion technology needed Moderate Auroral Cluster Lower priority than moderate missions shown in Table 2.2 Dayside Boundary Constellation Next step after Magnetospheric Constellation Geospace System Response Imagers Advanced solar sail technology needed Io Electrodynamics Next step after Jupiter Polar Mission Mars Aeronomy Probe Not supported by existing SEC mission lines Reconnection and Microscale Probe Lower priority than moderate missions shown in Table 2.2 Venus Aeronomy Probe Not supported by existing SEC mission lines The budgets for the highly rated AMISR and FASR projects begin immediately (some funds are already being spent for AMISR), and the ongoing ATST budget is shown on the reasonable assumption that it will continue through to completion. Funding for the new program involving small arrays begins gradually and accelerates as the AMISR buildout is completed. DEFERRED HIGH-PRIORITY FLIGHT MISSIONS Several large and moderate missions suggested by the panels were given high priority by the committee but were not included in the recommended program because of the overall budget constraint, mission sequencing requirements, or technical readiness issues. These missions are listed alphabetically in Table 2.4. SUMMARY The committee based the foregoing national strategy for the next decade of solar and space physics research on a systems approach to understanding the physics of the coupled solar-heliospheric environment. The work of the study panels was essential to the committee’s deliberations and conclusions, as were all of the public outreach activities that were undertaken. The existence of ongoing NSF programs and facilities in solar and space physics, of two complementary mission lines in the NASA Sun-Earth Connection Division—Solar Terrestrial Probes (STP, basic research) and Living With a Star (LWS, targeted basic research)—and of applications and operations activities in NOAA and the DOD facilitated the development of an integrated research strategy.
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As a key first element of its systems-oriented strategy, the committee endorsed three approved NASA missions, Solar-B (STP), STEREO (STP), and the Solar Dynamics Observatory (LWS). Together with ongoing NSF-supported solar physics programs and facilities as well as the start of the Advanced Technology Solar Telescope (ATST), these missions constitute a synergistic approach to the study of the inner heliosphere. This approach will involve coordinated observations of the solar interior and atmosphere and of the formation, release, evolution, and propagation of CMEs toward Earth. Later in the decade covered by the study, an overlapping of the Solar Dynamics Observatory (LWS), the ATST, and the Magnetospheric Multiscale mission (STP), together with the start of the Frequency-Agile Solar Radiotelescope, will form the intellectual basis for a comprehensive investigation of magnetic reconnection in the dense plasma of the solar atmosphere and the tenuous plasmas of geospace. The committee’s ranking of the Geospace Electrodynamic Connections (STP) and Geospace Network (LWS) missions acknowledges the importance of studying Earth’s ionosphere and inner magnetosphere as a coupled system. Together with a ramping up of the launch opportunities in the Suborbital Program and the implementation of both the AMISR and the Small Instrument Distributed Ground-Based Network, these missions will provide a unique opportunity to study the local electrodynamics of the ionosphere down to altitudes where energy is transferred between the magnetosphere and the atmosphere, while simultaneously investigating the global dynamics of the ionosphere and radiation belts. The implementation of the L1 Monitor (NOAA) and of the Vitality programs will be essential to the success of this systems approach to basic research and targeted basic research. Later on in the committee’s recommended program, concurrent operations of a Multispacecraft Heliospheric Mission (LWS), Stereo Magnetospheric Imager (STP), and MagCon (STP) will provide opportunities for a coordinated approach to understanding the large-scale dynamics of the inner heliosphere and Earth’s magnetosphere (again with strong contributions from the ongoing and new NSF initiatives). To understand the genesis of the heliospheric system it is necessary to determine the mechanisms by which the solar corona is heated and the solar wind is accelerated and to understand how the solar wind evolves in the innermost heliosphere. These objectives will be addressed by a Solar Probe mission. Because of the importance of these objectives for the overall understanding of the solar-heliosphere system, as well as of other stellar systems, a Solar Probe mission should be implemented as soon as possible within the coming decade. Solar Probe measurements will be comple-
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mented by correlative observations from such initiatives as Solar Orbiter, the Solar Dynamics Observatory, the Advanced Technology Solar Telescope, and the Frequency-Agile Solar Radiotelescope. Similarly, because comparative magnetospheric studies are so important for advancing understanding of basic magnetospheric processes, the committee has assigned high priority to a space physics mission to study high-latitude electrodynamic coupling at Jupiter. Such a mission will provide both a means of testing and refining theoretical concepts developed largely in studies of the terrestrial magnetosphere and a means of studying in situ the electromagnetic redistribution of angular momentum in a rapidly rotating system, with results relevant to such astrophysical questions as the formation of protostars. NOTES 1. While both FASR and ATST are now in the design phase, ATST is the more mature of the two programs. (The FASR design study began only recently, after the Panel on the Sun and Heliospheric Physics had finalized its recommendations.) The committee and the panel therefore regarded ATST as an “approved initiative” and considered FASR to be a “new initiative” that was to be evaluated and ranked with other new initiatives. The committee considers both ATST and SDO to be essential elements of a baseline program on which the recommended new initiatives will build. It recommends continued funding for technology development in support of ATST (cf. Chapter 3 of this report). 2. As explained in note 1 in the Executive Summary, the Solar Probe mission recommended by the Panel on the Sun and Heliospheric Physics emphasizes in situ measurement of the solar wind and corona near the Sun. The panel does not consider remote sensing a top priority on a first mission to the near-Sun region, although it does allow as a possible secondary objective remote sensing of the photospheric magnetic field in the polar regions. While accepting the panel’s assessment of the critical importance of the in situ measurements for understanding coronal heating and solar wind acceleration, the committee does not wish to rule out the possibility that some additional remote-sensing capabilities, beyond the remote-sensing experiment to measure the polar photospheric magnetic field envisioned by the panel, can be accommodated on a Solar Probe within the cost cap set by the committee. 3. For more details on MHM, see the report of the Panel on the Sun and Heliospheric Physics in the companion volume to this report (2003, in press). 4. Cf. the report of the Panel on Atmosphere-Ionosphere-Magnetosphere Interactions in the companion volume to this report (2003, in press). 5. Described in the Sun-Earth Connection Roadmap: Strategic Planning for the Years 2000-2020, NASA Office of Space Science, 1997. 6. Cf. the report of the Panel on the Sun and Heliospheric Physics in the companion volume to this report ((2003, in press). 7. Cf. the report by the Panel on Theory, Modeling, and Data Exploration in the companion volume to this report ((2003, in press). 8. Described in the Sun-Earth Connection Roadmap: Strategic Planning for the Years 2000-2020, NASA Office of Space Science, 1997.
Representative terms from entire chapter: