Space Studies Board Annual Report 2004 (2005)

A Report of the Committee on the Assessment of Options for Extending the Life of the Hubble Space Telescope

The Hubble Space Telescope (HST) was launched from the space shuttle in 1990 and has operated continuously in orbit for the past 14 years. HST was designed to be serviced by astronauts, and a series of four shuttle servicing missions from 1993 to 2002 replaced nearly all the key components except the original telescope mirrors and support structure. Three of the four servicing missions added major new instrument observing capabilities. A fifth planned mission, designated SM-4 (servicing mission 4), was intended to replace aging spacecraft batteries, fine-guidance sensors, and gyroscopes and install two new science instruments on the telescope.

Following the loss of the space shuttle Columbia and its crew in February 2003, NASA suspended all shuttle flights until the cause of the accident could be determined and steps taken to reduce the risks of future shuttle flights. In mid-January 2004 NASA decided, on the basis of risk to the astronaut crew, not to pursue the HST SM-4 mission. This cancellation, together with the predicted resulting demise of Hubble in the 2007-2008 time frame, prompted strong objections from scientists and the public alike. NASA continued to investigate options other than a shuttle astronaut mission for extending Hubble’s science life and is currently in the early stages of developing an unmanned mission that would attempt to service Hubble robotically. NASA also plans to de-orbit HST by approximately 2013 by means of a robotic spacecraft.

This report assesses the options for extending the life of HST. In keeping with its statement of task (Appendix A), the Committee on the Assessment of Options for Extending the Life of the Hubble Space Telescope assessed the scientific value of continued HST operation, issues of safety in using the space shuttle for servicing HST with an astronaut crew, the feasibility of robotic servicing, the impacts of servicing options on HST’s science capability, and risk/benefit relationships between those servicing options deemed acceptable.

Approximately every decade the U.S. astronomical research community develops a decadal strategy for the field. A premise of the most recently developed strategy¹ was that the HST SM-4 mission was an integral part of NASA’s facility planning for the future of the field and that this servicing mission would occur as planned at the time necessary to prevent the demise of the telescope. The strategy’s advisory recommendations reflect this assumption, and the committee, which was neither asked nor constituted to address any possible changes in priorities for astronomical research or research facilities, assumed that NASA would follow the decadal survey advisory recommendations. If NASA concludes that it cannot move forward with portions of the decadal survey strategy, then NASA will have to carry out an in-depth examination of priorities for the research field. The committee does not endorse such a re-examination. The committee notes, however, that if a re-examination should occur it would have to be conducted in a very timely and very expeditious fashion in order to ensure the continued operation and integrity of Hubble.

The Hubble systems with the greatest likelihood of failing and thus ending or significantly degrading Hubble science operations are the gyroscopes, the batteries, and the fine-guidance sensor (FGS) units. In addition, the HST avionics system is vulnerable to the aging of the facility.

The telescope uses three gyroscopes to provide precision attitude control. There are currently four functional gyros on HST—three in operation plus one spare. It is likely that the HST system will be reduced to two operating gyros in the latter half of 2006. The HST engineering team is currently working on approaches to sustaining useful, though potentially degraded, astronomical operations with only two gyros, and NASA expects to have that capability by the time it becomes necessary. Eventually, without servicing, the telescope will be reduced to operation with a single gyro in mid to late 2007. The spacecraft can be held in a safe configuration with one or no operating gyros, but science operations will not be possible.

Battery failures are another likely cause of loss of science operations. HST now has six batteries, of which five are necessary for full operations. If battery levels fall too low, the temperature of the structural elements in the Optical Telescope Assembly will fall below permissible levels, causing permanent damage to the facility. Recovery of scientific operations from this state is not possible.

The FGS units (in combination with their electronics subsystems) are used for precision pointing of the observatory. Two operating FGS units are required to support the HST observing program, with a third to supply redundancy. Based on recent test and performance data, one of the three currently operating FGS units is projected to fail sometime between October 2007 and October 2009, and a second is expected to fail sometime between January 2010 and January 2012.

Based on its examination of data and numerous technical reports on Hubble component operations, as well as discussions held with Hubble project personnel, the committee developed the following findings predicated on an estimated SM-4 earliest launch date of July 2006 and a most likely robotic mission launch date of February 2010.

FINDING: The projected termination in mid to late 2007 of HST science operations due to gyroscope failure and the projected readiness in early 2010 to execute the planned NASA robotic mission result in a projected 29-month interruption of science operations. No interruption of science operations is projected for a realistically scheduled SM-4 shuttle mission.

FINDING: The planned NASA robotic mission is less capable than the previously planned SM-4 shuttle astronaut mission with respect to its responding to unexpected failures and its ability to perform proactive upgrades. Combined with the projected schedule for the two options, the mission risk² associated with achieving at least 3 years of successful post-servicing HST science operations is significantly higher for the robotic option, with the respective risk numbers at 3 years being approximately 30 percent for the SM-4 mission and 80 percent for the robotic mission.

Over its lifetime, HST has been an enormous scientific success, having earned extraordinary scientific and public recognition for its contributions to all areas of astronomy. Hubble is the most powerful space astronomical facility ever built, and it provides wavelength coverage and capabilities that are unmatched by any other optical telescope currently operating or planned.

The four key advantages that Hubble provides over most other optical astronomical facilities are unprecedented angular resolution over a large field, spectral coverage from the visible and the near infrared to the far ultraviolet, access to an extremely dark sky, and highly stable images that enable precision photometry. Hubble’s imaging fields of view are also considerable, permitting mapping of extended objects and significant regions of sky. In contrast, ground-based telescopes have a view that is blurred by the atmosphere,³ and they are completely blind in the ultraviolet and large portions of the near infrared. Hubble can see sharply and clearly at all wavelengths from the far ultraviolet to the near infrared. Hubble images are 5 to 20 times sharper than those obtained with standard ground-based telescopes, in effect bringing the universe that much “closer.” Image sharpness and the absence of light pollution in orbit help Hubble to see objects 10 times fainter than even the largest ground-based telescopes. Moreover, Hubble’s images are extremely stable, in contrast to those obtained with ground telescopes, whose view is continually distorted by changing atmospheric clarity and turbulence.

Singly, each of these advantages would represent a significant advance for science. Combined, they have made Hubble the most powerful optical astronomical facility in history. Hubble is a general-purpose national observatory that enables unique contributions to and insights concerning most astronomical problems of greatest current interest. Among the most profound contributions of Hubble have been the following:

• Direct observation of the universe as it existed 12 billion years ago,

• Measurements that helped to establish the size and age of the universe,

• Discovery of massive black holes at the center of many galaxies,

• Key evidence that the expansion of the universe is accelerating, which can be explained only by the existence of a fundamentally new type of energy, and therefore new physics, and

• Observation of proto-solar systems in the process of formation.

In addition to its impact on science, Hubble discoveries and images have generated intense public interest. Examples of Hubble data and images that have fascinated the public (and scientists) include the big “black eye” left by comet Shoemaker-Levy’s direct hit on Jupiter’s atmosphere, which alerted the public to the dangers of asteroids impacting Earth; a panoply of jewel-like planetary nebulas that illustrate the ultimate death of our Sun; portraits of planets in the solar system, including auroras on Jupiter and Saturn; and such astronomical spectacles as the “pillars of dust” in the Eagle nebula that appeared on nearly every front page in America and became iconic for Hubble itself. The Hubble Space Telescope has clearly been one of NASA’s most noticed science projects, garnering sustained public attention over its entire lifetime.

The four previous servicing missions to Hubble have added new observing modes and increased existing capabilities, typically by factors of between 10 and 100, since the telescope first flew in 1990. As a result, Hubble now produces more data per unit time than it did originally. The total rate of calibrated data has grown by a factor of 33 since launch.⁴ A further increase was expected with the installation of the two new science instruments, the Wide-field Camera 3 (WFC3) and the Cosmic Origins Spectrograph (COS), each of which would provide a greater

than 10-fold improvement in scientific efficiency and sensitivity compared with previous instruments. Both of these instruments are already built.

With the installation of WFC3 and COS, and the continued operation enabled by a fifth servicing mission, a broad range of new discoveries would be expected from Hubble. In fact, the committee concluded that Hubble’s promise for future discoveries following a fifth servicing mission would be comparable to the telescope’s promise when first launched. For example, an important new technique that Hubble would offer for finding planets could enable detection of as many as 1000 new planets in the Milky Way Galaxy in the years after servicing. In addition, a large number of new supernovas could be found for the study of dark energy, reducing uncertainties in its properties by a factor of two. A wealth of data would also be collected to explore the nature of stars in the Milky Way Galaxy and in neighboring galaxies. Hubble is just now beginning to image objects being found by sister NASA missions such as Chandra (an x-ray observatory), Galaxy Evolution Explorer (GALEX; an ultraviolet imager), and Spitzer (an infrared imager and spectrograph), which are currently in orbit. These satellites are relatively wide-field survey telescopes whose goal in part is to detect objects for Hubble follow-up observations. These detailed follow-ups take time because of Hubble’s smaller field of view; a large fraction of the scientific benefit of these other satellites will be lost if Hubble’s mission is cut short prematurely. And finally, a servicing mission is needed to allow an orderly completion of large, homogeneous data sets such as spectral libraries and imaging surveys of large areas of the Milky Way Galaxy that Hubble is now gathering. These data sets will be archived to serve astronomers for decades to come, given that there are no foreseeable plans to replace Hubble with a telescope of comparable size, wavelength coverage, and high resolution.

The key findings of the committee related to the benefits of future servicing of Hubble are as follows:

FINDING: The Hubble Space Telescope is a uniquely powerful observing platform in terms of its high angular optical resolution, broad wavelength coverage from the ultraviolet to the near infrared, low sky background, stable images, exquisite precision in flux determination, and significant field of view.

FINDING: Astronomical discoveries with Hubble from the solar system to the edge of the universe are among the most significant intellectual achievements of the space science program.

FINDING: The scientific power of Hubble has grown enormously as a result of previous servicing missions.

FINDING: The growth in the scientific power of Hubble would continue with the installation of the two new instruments, WFC3 and COS, planned for the SM-4 shuttle astronaut mission.

Because a robotic servicing mission does not involve risks to the safety of an astronaut crew, the principal concerns are the risk of failure to develop a robotic mission capability in time to service Hubble, and the risk of a mission failure that results in an inability to perform the needed servicing, or worse, critically damages Hubble during the mission. Both schedule risk and mission risk are composed of a large number of factors that were studied in considerable detail by the committee.

Some of the critical components of mission risk include lack of adequate development time to validate the hardware, level of software and system performance required to rendezvous with Hubble, failure to successfully grapple and dock with Hubble, failure to successfully execute the combination of complex autonomous and robotic activities required to actually accomplish HST revitalization and instrument replacement, and the risk of unforeseen Hubble failures prior to mission execution that the robotic mission will not have been designed to repair. One example of a mission risk that concerned the committee is the complicated docking maneuver required for a Hubble robotic servicing, which has never been performed autonomously or teleoperated with time delays. Specifically, the use of the grapple system to autonomously perform close-proximity maneuvers and the final capture of Hubble is a significant challenge and is one of the key technical aspects of a robotic servicing mission that has no precedent in the history of the space program.

The components of schedule risk examined by the committee included the readiness levels of such technologies as the sensors, software and control algorithms, and vision-based closed-loop support for autonomous docking

operations, as well as NASA’s relevant programmatic and technical expertise, resources, and specific development plans for a robotic servicing mission. From the risk mitigation viewpoint, the committee judged that the planned use of the mature International Space Station robotic arm and robotic operational ground system helps reduce both the schedule risk and the development risk for the robotic mission. In addition, the committee assessed the development schedule for the robotic servicing mission based on its experience with programs of similar complexity and the historical spacecraft development schedule data provided by both NASA and the Aerospace Corporation. The committee’s key findings regarding the question of the risk of robotic servicing are as follows:

FINDING: The technology required for the proposed HST robotic servicing mission involves a level of complexity, sophistication, and maturity that requires significant development, integration, and demonstration to reach flight readiness and has inherent risks that are inconsistent with the need to service Hubble as soon as possible.

FINDING: The Goddard Space Flight Center HST project has a long history of HST shuttle servicing experience but has little experience with autonomous rendezvous and docking or robotic technology development, or with the operations required for the baseline HST robotic servicing mission.

FINDING: The proposed HST robotic servicing mission involves a level of complexity that is inconsistent with the current 39-month development schedule and would require an unprecedented improvement in development performance compared with that of space missions of similar complexity. The likelihood of successful development of the HST robotic servicing mission within the baseline 39-month schedule is remote.

Based on extensive analysis, the committee concluded that the very aggressive schedule for development of a viable robotic servicing mission, the commitment to development of individual elements with incomplete systems engineering, the complexity of the mission design, the current low level of technology maturity, the magnitude of the risk-reduction efforts required, and the inability of a robotic servicing mission to respond to unforeseen failures that may well occur on Hubble between now and the mission, together make it highly unlikely that NASA will be able to extend the science life of HST through robotic servicing.

The risks that must be considered in making a decision to service Hubble with the shuttle are the risk to the safety of the crew and the shuttle, as well as the risk of failing to accomplish the servicing objectives. As part of its assessment of safety risk, the committee looked carefully at the findings and recommendations of the Columbia Accident Investigation Board (CAIB)⁵ and at NASA’s return-to-flight (RTF) requirements. Strong consideration was given to understanding differences in the safety risk factors between shuttle missions to the International Space Station (ISS)—to which NASA still plans to fly 25 to 30 missions—and a shuttle mission to Hubble. Technical considerations examined by the committee included comparisons of on-orbit inspection and repair capabilities at ISS and Hubble, various safe-haven and rescue options, and the likelihood of the shuttle being damaged by micro-meteoroid orbital debris (MMOD). With regard to mission risk, the committee considered both the known on-orbit operations required for Hubble servicing and past experience with Hubble shuttle astronaut servicing, including such factors as unforeseen on-orbit contingencies.

The committee developed a large number of findings based on the various analyses cited above. Some of the key findings relevant to the question of the risk of shuttle servicing of HST are as follows:

FINDING: Meeting the CAIB and NASA requirements (relative to inspection and repair, safe haven, shuttle rescue, MMOD, and risk to the public) for a shuttle servicing mission to HST is viable.

FINDING: The shuttle crew safety risks of a single mission to ISS and a single HST mission are similar and the relative risks are extremely small.

FINDING: Previous human servicing missions to HST have successfully carried out unforeseen repairs as well as executing both planned and proactive equipment and science upgrades. HST’s current excellent operational status is a product of these past efforts.

FINDING: Space shuttle crews, in conjunction with their ground-based mission control teams, have consistently developed innovative procedures and techniques to bring about desired mission success when encountering unplanned for or unexpected contingencies on-orbit.

FINDING: The risk in the mission phase of a shuttle HST servicing mission is low.

As noted above, the Hubble Space Telescope provides unique capabilities for astronomical research. These capabilities will not be replaced by any existing or currently planned astronomy facility in space or on Earth. Hubble’s continuing and extraordinary impact on human understanding of the physical universe has been internationally recognized by scientists and the public alike.

Upgrading Hubble to address the predictable decline in HST component performance over time and thus ensure system reliability requires a timely and successful servicing mission in order to minimize further degradation and prevent a significant gap in science data return. Although it considered other options for extending the life of Hubble, the committee focused on two approaches: robotic servicing and shuttle astronaut servicing.

The need for timely servicing of Hubble imposes difficult requirements on the development of a robotic servicing mission. The very aggressive schedule, the complexity of the mission design, the current low level of technology maturity, and the inability of a robotic servicing mission to respond to unforeseen failures that may well occur on Hubble between now and a servicing mission make it unlikely that the science life of HST will be extended through robotic servicing.

A shuttle astronaut servicing mission is the best option for extending the life of Hubble and preparing the observatory for eventual robotic de-orbit by, for example, attaching targets to Hubble. The committee believes that a shuttle HST servicing mission could occur as early as the seventh shuttle mission following return to flight, at which point critical shuttle missions required for maintaining ISS will have been accomplished. All important systems needed to keep Hubble functioning well through 2011 were included in the original SM-4 shuttle servicing plan. Replacement of batteries and gyros and one FGS is deemed essential. Any spacecraft is subject to unanticipated failures, but if the repairs planned for the SM-4 mission are carried out promptly, there is every prospect that Hubble can operate effectively for another 4 to 5 years after servicing.

The committee finds that the difference between the risk faced by the crew of a single shuttle mission to ISS—already accepted by NASA and the nation—and the risk faced by the crew of a single shuttle servicing mission to HST, is very small. Given the intrinsic value of a serviced Hubble, and the high likelihood of success for a shuttle servicing mission, the committee judges that such a mission is worth the risk.

1. The committee reiterates the recommendation from its interim report that NASA should commit to a servicing mission to the Hubble Space Telescope that accomplishes the objectives of the originally planned SM-4 mission.

2. The committee recommends that NASA pursue a shuttle servicing mission to HST that would accomplish the above stated goal. Strong consideration should be given to flying this mission as early as possible after return to flight.

3. A robotic mission approach should be pursued solely to de-orbit Hubble after the period of extended science operations enabled by a shuttle astronaut servicing mission, thus allowing time for the appropriate development of the necessary robotic technology.

A Report of the Committee on Solar and Space Physics

In May 2003 the Space Studies Board’s Committee on Solar and Space Physics held the Workshop on Exploration of the Outer Heliosphere to synthesize understanding of the physics of the outer heliosphere and the critical role played by the local interstellar medium (LISM)¹ and to identify directions for the further exploration of this challenging environment. What emerged was a palpable sense of excitement about the field’s progress in the past 8 to 10 years.

It was only in the mid-1990s that the fundamental role of neutral interstellar hydrogen in determining the global structure of the heliosphere was elucidated and the hydrogen wall predicted. With the later discovery of the hydrogen wall, and then, the discovery of hydrogen walls about other stars in our galactic neighborhood and the associated discovery of stellar winds from solar-like stars, the field of solar and space physics underwent dramatic change.

Coupled to the theoretical advances were the increasingly exciting observations being returned by the Voyager Interstellar Mission, Ulysses, ACE (Advanced Composition Explorer), and Wind—ranging from observations of cosmic rays signaling the approach to the termination shock, to the large- and small-scale magnetic fields responsible for guiding and scattering energetic particles, to name only two types. At the workshop, the greatest excitement was generated by the suggestion that the low-energy cosmic rays showed evidence that Voyager may have crossed the termination shock—completely unexpected observations illustrating Voyagers’ promise for returning results with a capacity to surprise and baffle for years to come.

To further the exploration of the outer heliosphere four strategic directions became clear in workshop discussions:

• Making use of existing assets. ACE, SOHO (Solar and Heliospheric Observatory), Wind, Ulysses, and the Voyagers are all currently furthering understanding of the outer heliosphere. In particular, the importance of the Voyagers cannot be overstated as Voyager 1 is capable of lasting another 16 years, allowing it to reach 150 AU. The Voyager Interstellar Mission is impossible to replace at its current location in the next 20 years, making it a uniquely valuable platform. The spacecraft are reasonably well instrumented for the mission, making the Voyagers the best and only near-term hope for exploring the heliospheric boundaries and interstellar medium in situ. The other vital mission is Ulysses, since it is currently the best-situated, best-instrumented mission that directly addresses the fundamental question of how the solar wind couples to the LISM. Scientific understanding of the physics of pickup ions, their relation to interstellar atoms and anomalous cosmic rays, and their influence on the solar wind has been advanced almost entirely by Ulysses (and to a lesser extent ACE), and it is the only spacecraft to directly measure neutral interstellar material. Workshop participants agreed that continued support and a long-term vision from NASA Headquarters, and the provision of continuing data coverage of the Voyagers and Ulysses missions from the Deep Space Network, are essential.

• Developing new outer heliosphere missions. New missions should be developed that can use current and moderately improved in situ and remote techniques to conduct heliospheric studies from 1 to 3 AU and beyond. The possibilities include in situ studies and remote observations. For example, the ability to image the region of the termination shock and heliosheath remotely is steadily increasing, with several laboratories now working on experiments in this area. Energetic neutral atom imaging is a promising avenue, with technology outstripping theory

at present. Other possibilities for remote observations involve the use of Lyman-alpha absorption and backscatter techniques; the former is possible at 1 AU with space-based spectroscopic telescopes, and the latter offers the possibility of monitoring the temporal response of interstellar gas to the solar cycle as it flows into the heliosphere. In situ studies within 1 to 4 AU will remain critical to furthering understanding of the fundamental coupling of LISM material and solar wind plasma. Such studies will require spacecraft with instrumentation that can study the inflowing neutral gas and dust, pickup ions, cosmic rays (anomalous and galactic), energetic particles, and magnetic field directly since the measurements of these variables are essential if we are to eventually probe both the LISM and the heliospheric boundaries with new spacecraft (and even remotely). Understanding of the critical microphysics will be advanced best by in situ measurements. It is now possible to build instruments that allow orders-of-magnitude more accurate measurements than those made by the instruments that currently fly on missions. Both in situ and remote measurement could be accomplished within the MIDEX (Medium-Class Explorer) program or perhaps the SMEX (Small Explorer) program. For the interim period, this approach would complement current Voyager and Ulysses activities well.

• Continuing support of theory and modeling. Continuing theoretical and modeling studies are essential to ensure progress in understanding the interaction of the solar wind and the LISM. Numerous questions raised by Voyager, Ulysses, and other spacecraft missions remain unanswered, and theoretical studies continue to lag observations. Optimal planning for a mission of the magnitude of Interstellar Probe requires a sufficient understanding of the physics of the remote outer heliosphere and local interstellar medium, which in turn requires far more elaborate modeling of the outer heliosphere, and incorporation of current and future in situ and remote sensing results. In particular, remote sensing techniques, because they are by nature integrated line-of-sight observations, produce results whose interpretation depends on theoretical models of the global heliosphere.

• Preparing for Interstellar Probe. Interstellar Probe, a mission characterized by both enormous scientific potential and technical challenge, will be one of the most exciting undertakings of NASA in the new millennium. For a mission as ambitious as Interstellar Probe, the technical requirements, the scientific payload, including instrument and communications requirements, and feasibility have to be addressed far in advance. Developing the required propulsion technology is the primary technical challenge of this mission. At least three approachesænuclear-electric propulsion, solar sail propulsion, and powered Sun-gravity assistæare well suited for and, in principle, capable of accelerating Interstellar Probe to the speeds needed to reach the heliopause within 15 years or less from launch.² However, as detailed in the text, none of these options are currently available and all present significant hurdles in their development.

Because Interstellar Probe will require only a rather straightforward trajectory with little need for precise navigation, it could be regarded as an ideal demonstration of nuclear-electric propulsion or solar sailing.

The development of a mission as scientifically and technologically far-reaching as Interstellar Probe will require considerable planning. The eventual scientific payload must be guided by current missions, Pathfinder missions, and theory. A crucial role will be played by Pathfinder missions, which may explore interstellar material such as pickup ions, neutral atoms, or anomalous cosmic rays directly, or explore the boundary regions using remote measuring techniques such as Lyman-alpha or energetic neutral atoms, or explore physical processes induced by the complex partially ionized plasma populations that make up the outer heliosphere beyond some 10 AU.

Sending a well-equipped spacecraft to the boundaries of the heliosphere to begin the exploration of our galactic neighborhood will be one of the great scientific enterprises of the new century—one that will capture the imagination of people everywhere. Significant questions about the outer heliosphere and the LISM still to be addressed include the following:

• What are the nature, structure, and temporal character of the termination shock, and is the termination shock the same in all directions?

• How do pickup ions and solar wind plasma evolve at the shock and in the heliosheath?

• What are the size and shape of the heliopause?

• Does reconnection between the solar and interstellar magnetic fields at the heliopause affect the structure and dynamics of the heliosphere?

• What are the physical state and the degree of ionization of the LISM?

• What is the elemental and isotopic composition of the LISM? What are the direction and magnitude of interstellar magnetic field?

• Is the interstellar wind subsonic or supersonic?

These are among the most fundamental of the questions that can be addressed by space and planetary physics in the next 20+ years, and the answers will have far-reaching implications, not only revealing the nature of the heliosphere but also informing theories on the evolution of our galaxy, and, indeed, the entire universe.

A Report of the Space Studies Board

The workshop on national space policy was organized to air perspectives on the question, What should be the principal purposes, goals, and priorities of U.S. civil space? Or to simplify, What should be our national space policy? The timing of this workshop coincides with a newly directed focus on the long-term direction of the U.S. civil space program. In the wake of the space shuttle Columbia tragedy, the Columbia Accident Investigation Board (CAIB) found that a contributing factor in NASA’s organizational decline was the lack of an agreed national vision for human spaceflight. Congress has held several hearings on this topic, the press is commenting on it, and the Bush Administration is developing a new space policy (see Chapter 2).

The workshop’s six sessions are summarized in the chapters that follow. Through the course of these sessions several matters were addressed that transcended the subject of any one session in particular, emerging as more general themes relevant to the workshop’s principal questions. These seven themes become apparent when one reads the session summaries as a whole and are presented in this summary chapter.

Many workshop participants (panelists and ASEB and SSB members alike; see Appendix B) accepted that U.S. space and Earth science programs are currently productive and progressing steadily, and they described them as being of continuing importance. Many commented during the workshop on the inspiration, success, and progress of the science programs,¹ and they elaborated in their contributed abstracts on the benefits of the approach taken by the science programs.² Much of the success of NASA’s science programs was attributed to having clear long-range goals and roadmaps that are framed by scientists and periodically reassessed by the science community in the light of new knowledge and capability.³ The comments on science were brief, largely because many participants saw the human exploration program as more problematic than the science programs, which were considered healthy and solid. For example, as discussed in Chapter 3, Logsdon challenged the participants to consider that “discussion about the future of the space program would really be discussion about the future of the human spaceflight program. The space and Earth science programs are part of the nation’s portfolio of basic research and are not controversial in principle, though budget levels of course are always a concern.”⁴

Participants who commented that the science programs were successful noted not just the “facts” of success, but the means by which the science programs achieved their successes. They identified the following attributes of the science programs that are the primary contributing factors for their success:

1. Participation from the scientific community. An external-to-NASA constituency that has some “ownership” in the program creates “constructive tension” that pushes the programs to excel.

2. Clear goals. The science programs set out explicit goals and utilize the interest of the scientific community to establish these goals (e.g., through the decadal-scale strategy surveys conducted by the NRC).

3. Strategic planning. The science programs lay out a strategy for achieving their goals.

4. A sequence of successes. The science programs progress via a series of individual steps that can accumulate successes that help measure progress and sustain momentum for the program.

A number of participants observed that many of these attributes from the science programs were missing in the human exploration program and saw the opportunity to apply them as lessons learned for the improvement of the human spaceflight program.

Through the course of the day-and-a-half workshop, no participant argued either (1) that we already have a clear human spaceflight goal or (2) that we do not need one. As Chapter 2 suggests, these two points seemed to be part of the context that set the stage for a debate over national space policy.

Many participants echoed the CAIB’s conclusion that a lack of an agreed vision for the human spaceflight program has had a negative impact on the health of that program in NASA. Those participants noted that without such a long-range goal the human spaceflight program’s reason for being is hard to articulate. This is true for the specific elements of the human spaceflight program, the space shuttle and the space station, as well as for the program in general. It is not clear to what end the International Space Station (ISS) contributes or what would be the next logical step after the ISS has served its purpose. This stands in contrast to other programs, like military and commercial space programs, which have more easily stated justifications. Wesley Huntress made a crucial point about why such a goal is necessary in our risk-averse society: Human spaceflight is dangerous and requires risk taking, and the public may support risk taking if there is a clear, understandable purpose. Risk cannot be eliminated, but risk due to poor management or lack of rigor should be minimized. A bold goal could enable breaking out of this programmatic drift, providing a transcendent purpose for the risk of human endeavors in space.

Lennard Fisk’s closing statement (Chapter 8) synthesized comments of several others in saying that we no longer need to demonstrate U.S. technological prowess as Apollo did, because there are many such demonstrations, but there is a need to demonstrate U.S. leadership and goodwill. Human spaceflight could provide the opportunity for leadership if the United States would openly invite others to participate in setting and steadily pursuing a shared long-range goal.

The nation originally sent humans to space to demonstrate U.S. technical prowess and political will. Why should we do it now? Many workshop participants emphasized two fundamental reasons:

1. Exploration can and does add to the acquisition of new knowledge, that is, knowledge of space as a place for human activity, and knowledge of the solar system, including Earth, from the vantage point of space.

2. Exploration is a basic human desire: people explore. Riccardo Giacconi called it a general impulse of human nature, and others concurred, suggesting that exploration should be the primary motivation of human spaceflight in order to fulfill an innate human need to explore.

As Robert Frosch said, exploration can be the first step of science. He referred to the oceanographic community, noting that scientists want to dive on the Alvin and look at the deep oceans because they see things and they can get from the experience something that they don’t get from remote presentations.⁵ Fisk picked up on this point, stating that exploration is a legitimate form of science, if properly conducted. There is a need to incorporate defendable, legitimate science into the human exploration endeavor.

If science can generally be understood as the process through which we acquire new knowledge, then the search for new knowledge may in many ways be akin to humans’ innate desire to explore. As such we may think of these two reasons together as “the human desire to know, to learn.” It was former astronaut Thomas Jones who most clearly articulated the tie that binds these reasons to the tangible benefits of human spaceflight: Only a human can experience what being in space feels like, and only a human can communicate this to others. Indeed, communication of the space experience is the foundation for the entire cultural aspect of the space program. Several participants

agreed with this statement, including Todd La Porte, who stated that the important cultural benefits from the human space program are not always well articulated for the general public to recognize and understand. Better communication of the space experience, therefore, is seen as necessary to maintain the space program’s political support among the general public. A strong human spaceflight program can help secure public ownership and involvement in the rest of the civil space program. Several participants enunciated this point and spoke of the need for “heroes” and of how people can have a sense of participation through the participation of these heroes.

This cultural aspect, the communication of the space experience, reveals the unique opportunity that space presents for international cooperation. Norman Neureiter was most eloquent in describing how human spaceflight can be a means to enable fruitful and healing international collaboration. Saying that there is a perception that some in the world may fear our power, Neureiter argued that space exploration can be a compelling instrument for building a global fabric of relationships that dispel that fear—relationships that will endure whatever other bad things may happen. In other words we can increase national security by increasing understanding and trust through cooperation.

Participants described a need for human space exploration because it speaks across cultures to some of our greatest natural characteristics and intellectual curiosity: our desire to learn, to extend our grasp with technology, to modernize, to enhance that which makes us human. They also discussed the need for the nation to set a target for our exploration—a goal or a destination for humans to arrive at (that is, beyond low Earth orbit) as a way to help focus the exploration effort. Whatever the goal, participants argued that it will be decided through the course of a national and international dialogue that should begin now.

Participants expressed the importance of making the goal or destination one that excites the imagination and speaks best to our curiosities. Many of the participants suggested that the goal that best meets these criteria is the eventual human exploration of Mars. Others suggested that a mission to the Moon as a precursor to a human visit to Mars could be valuable, while some even suggested that the eventual human exploration of planetary bodies farther out in the solar system should be considered. Whatever the nation may decide through the course of an open dialogue, what emerged as important considerations for achieving that goal is the subject of the next several themes.

Many participants argued that having a clear, agreed upon, long-term goal, such as the human exploration of Mars, is essential for the future success of the human spaceflight program. It was seen as premature, however, to set a firm date for or cost of that goal. What is possible is a first assessment of what has to be accomplished to reach that long-term goal, and the identification of intermediate, subsidiary goals that can be met as a means to enable the achievement of that long-term goal. In this context the human spaceflight program would be conducted as a series of smaller steps and would evolve at a pace that reflects a meaningful rate of learning. Speakers suggested that this approach requires a coherent architecture or roadmap, which would elucidate how each intermediate step could be accomplished through a sequence of smaller projects that are both technically feasible and acceptable in the political environment.

Several participants observed that a national decision to pursue an ambitious long-term goal would be a political decision, not a scientific one. Therefore such a decision would require political support, which in turn requires realistic costs and broad support. Regarding costs, several participants suggested that the response to a statement by Congressman Sherwood Boehlert that “any vision that assumes massive spending increases for NASA is doomed to fail”⁶ should be one in which the nation agrees to pursue a long-term goal with a “buy it by the yard” approach. The big challenge of attaining the goal would be broken into many small achievable challenges. Instead of a fixed deadline, the budget would fund only as many of the “small steps” as could be afforded. Participants talked about an exit strategy for the shuttle and the space station, and, if adopted, that strategy could free up funds.

On the issue of coalitions of support many participants recognized the need for a process different from that used to build support for the space shuttle and space station programs. Frosch was most clear on this point. Recalling his experience as NASA’s administrator, he noted that instead of promising something for everyone, we

must strive to establish a coalition that agrees on a specific space exploration goal. Even if different members of the coalition have different motivations for this goal, there must be agreement on the goal itself. Similarly, there was much discussion on the role of international partners in a coalition for support of a long-term goal. The smaller steps envisioned here offer many opportunities for partner governments to contribute and be involved as true stakeholders in the program. The successes, accumulated in many small steps, will help to build political support. That is, if projects are evaluated against the agreed goal, the workshop discussions envisioned that after many milestones are achieved, and numerous small, cumulative steps are taken, the long-term goal will become inevitable.

In the ultimate achievement of a long-term goal for human exploration, numerous participants made statements echoing the spirit of the remarks made by Congressman Ralph Hall, quoted in Chapter 2: “There should no longer be a question of robotic versus human exploration—clearly both will be needed…” Fink recalled his experience with the Augustine Committee,⁷ noting that in the early 1990s there was an unnecessary tension and debate on the subject of “manned versus unmanned” exploration. He noted that this debate has passed and that planning for exploration beyond low Earth orbit will have to consider how to best utilize both human and robotic assets. Other participants agreed, stating further that they believed the space program should move beyond complementarity and toward a synergy between robots and humans, as the concept of synergy best highlights the potential benefits associated with taking advantage of the strengths of each.

Exactly how best to realize this synergy is a matter that requires further discussion and can be dependent on what destination is chosen as the eventual goal for human exploration. In her prepared remarks, Newman articulated this point explicitly, noting that human-robotic missions could take the form of humans assisted by robotic explorers or robots/probes assisted by humans who are not co-located, depending on the location being explored. Frosch was even more detailed, discussing how robots and humans could be integrated if Mars were chosen as the human exploration goal; we could begin with teleoperations from Mars orbit and guided autonomy on the ground, after which we could move to the surface of Mars where humans can undertake tasks that robots cannot perform. Whatever the destination and whatever the specific means chosen, many participants stated that being guided by a principle of synergy between robots and humans provides the opportunity to explore the solar system in the most optimal manner.

The participants noted that there are additional benefits to the synergy of human and robotic assets. One is the fact that it provides the opportunity to communicate the space experience, as Jones expressed. Fink noted that this was a conclusion reached in the Augustine Report as well. Another is the opportunity that a human presence creates for unanticipated learning. Building on Fisk’s assertion that good science can be done with properly devised exploration efforts, Frosch again cited the desire for human participation in the exploration of the deep sea. Newman referred to this as humans enabling serendipity through the co-exploration of space with robots.

In summary, while a history of separation between human and robotic efforts is part of the context, many participants, notably including many scientists, seemed to believe that now is the time to put the dichotomy behind us and to find and exploit synergies between the two.

Many participants confirmed the context described in Chapter 2, i.e., that both the space shuttle and space station programs made too many promises to too many people and thus lost focus on any one technical mission. Yet if the human exploration program had a goal involving long-term human spaceflight, the station could have a very clear justification: to conduct microgravity and variable-gravity research and technology development to support the agreed goal. To many participants, this meant a higher priority for biological research in support of long-duration spaceflight. Indeed, participants argued that soundly based research on scientific and technical problems tied to human exploration beyond low Earth orbit should be the primary purpose of the ISS. The key to successful

experiments lies in investigating gravity as an independent variable, whereby biological and physical processes in the weightless environment can be quantified. In addition to the microgravity research conducted on the ISS, participants argued that this approach means an additional focus on experiments utilizing fractional gravity—experiments that may be possible only with a variable-gravity research centrifuge aboard the ISS.

Others noted that learning how to stage and construct large systems, e.g., a large telescope, at a space station and move it to its operational orbit would realize and demonstrate the synthesis of robotic and human activities. Similarly, a human exploration goal could well raise new missions for the ISS, and ultimately, the goal of extending human presence beyond Earth orbit could define the exit strategies for the space station program. The thrust of these comments was that, given a human exploration goal, the ISS program should be modified to focus on supporting that goal, which would mean completing construction of needed facilities and choosing the right experiments to fly on the station. In other words, there would be very clear criteria for setting priorities across the program.

As with space station, the state of the shuttle program is a relevant part of the context of which workshop participants were well aware. The CAIB referred to the original promises and compromises required to gain approval for the shuttle program. These ensured there would be pressure for the vehicle to deliver more than it could. Participants argued that the shuttle program is now at a crossroad and the nation is faced with difficult choices—try to fix and continue with the shuttle or develop another launch vehicle. Discussions focused on the idea that a new human exploration goal could not only provide criteria for this decision, but could also make it possible to define a general exit strategy for the shuttle.

In summary, participants appeared to view the following activities as essential elements along the path to a goal for human exploration: (1) the continued robotic exploration of our solar system followed by the development of capable human-machine interfaces and teleoperators, (2) research on the ISS focused on addressing the questions posed by human exploration away from low Earth orbit, and (3) development of a space transportation system to replace the shuttle, all directed toward facilitating the eventual human exploration of some destination beyond low Earth orbit.

These first six themes are cross-cutting concepts relevant to the nation’s future approach to civil space. The seventh theme collects the views offered by participants on needs and opportunities for successful implementation of future space policy.

Concerning the needs of all U.S. space activities, participants cited the Final Report of the Commission on the Future of the United States Aerospace Industry⁸ and pointed to the need for an “industrial base.” Critical cross-institutional or cross-sector activities—e.g., joint technology development, taking advantage of synergies, and better planning and development—are all dependent on the availability of a skilled industrial base. This base was viewed as being in decline.

Regarding the civil space program, workshop discussions primarily addressed two particular stakeholders in future civil space activities. They were (1) NASA, as the primary executive branch agency responsible for implementing space policy, and (2) the scientific community, one of NASA’s key constituents.

Workshop discussions focused on the following five aspects of NASA as an institution:

1. Lack of human spaceflight stakeholders. Participants were attracted to an intriguing observation about human spaceflight in comparison with the science program. In the science program scientists set the goals, e.g., scientific questions to be answered by desired missions, and the agency carries them out. In this way NASA and the scientists share the direction of the program. The scientists have a big stake in the agency program, but there is always tension between the scientists who want as much science as possible and who honor scientific values, and

the implementers who face the practicalities of resource limitations. Noel Hinners found this tension creative, resulting in better science, and noted the lack of similar independent stakeholders and creative tension in the current human spaceflight program. La Porte noted that his research on high-reliability organizations shows that they tend to have a strong presence of, and often active coordination with, outside stakeholder groups.

2. NASA’s changed role. Participants noted that at NASA’s beginning its job was to help make the United States a space-faring nation, but today the United States would be a space-faring nation even if NASA disappeared. Now, they suggested, the agency’s new role is to advance several space frontiers: science, human physiology, applications, technology, and human exploration.

3. Trust and honesty. Chapter 2 quotes Representative Boehlert, who has said that “we need to be honest about the purposes and challenges” of human spaceflight. Several participants cited less than forthright justifications for programs, from Apollo to the present. Several noted that more candid justifications of programs would help justify the risk of spaceflight; the public is not risk-averse for worthwhile programs. More openness would improve trust. In addition, Neureiter noted that failing to involve one’s partners at the very beginning of program decision making damages one’s credibility as a partner. Others agreed that NASA cannot afford to be seen as less than fully open and honest.

4. Management competence. The NASA ISS Management and Cost Evaluation (IMCE) Task Force report,⁹ part of the workshop’s context, found that the ISS program lacked the skills and tools to control costs and schedules. Noting the conclusions of the CAIB report, participants observed that in both the Challenger and Columbia accidents NASA management demonstrated failure to detect and remedy the early onset of failures that would threaten the safe operation of the space shuttle. Managers were not seen as learning across generations; they repeat mistakes. Participants also felt that NASA managers overpromised and got into trouble on the shuttle and then did the same thing 10 years later on the ISS.

5. Technical competence. Several participants commented that NASA tended to freeze old technology into human spaceflight programs. As a result, these programs may have trouble attracting good technical people who are at the cutting edge, or younger engineers and scientists.¹⁰ NASA was described as maintaining the shuttle and the station rather than developing new technology.

Fisk concluded the workshop by saying that he believed that this workshop could be a truly historic event if the scientific and technical communities, in the broadest sense, can say that as a group “we believe in a human spaceflight program, we believe this country should invest in it, and we will stand up and say how it can be done productively.” Participants saw this as a realistic possibility for several reasons. First, the timing seems good, because the robotic-versus-human dichotomy has begun to dissipate. Second, the tradition in space and Earth science, in which there exists a constructive tension between the agency and scientists who act as continuous stakeholders, was viewed by many as a model by which scientific exploration could strengthen human exploration. Third, participants seemed to agree that the science community could constructively help NASA identify and carry out the best science possible over the course of human exploration missions. Fourth, the discussions suggested that there is an important role for scientists to become involved as stakeholders in helping to integrate humans and robotics in the kind of synergistic way described above, thus producing the best experiments and missions possible and ensuring that bargains are kept across management generations. Indeed, this last point may represent one of the most important and hopeful ideas to emerge from the workshop.

A Report of the Committee on Solar and Space Physics

Earth’s neighborhood in space—the local cosmos—provides a uniquely accessible laboratory in which to study the behavior of space plasmas (ionized gases) in a wide range of environments. By taking advantage of our ability to closely scrutinize and directly sample the plasma environments of the Sun, Earth, the planets, and other solar system bodies, we can test our understanding of plasmas and extend this knowledge to the stars and galaxies that we can view only from afar.

Solar and space physics research explores a diverse range of plasma physical phenomena encountered at first hand in the solar system. Sunspots, solar flares, coronal mass ejections, the solar wind, collisionless shocks, magnetospheres, radiation belts, and auroras are just a few of the many phenomena that are unified by the common set of physical principles of plasma physics. These processes operate in other astrophysical systems as well, but because these systems can be examined only remotely, theoretical understanding of them depends to a significant degree on the knowledge gained in the studies of the local cosmos. This report, Plasma Physics of the Local Cosmos, by the Committee on Solar and Space Physics of the National Research Council’s Space Studies Board attempts to define and systematize these universal aspects of the field of solar and space physics, which are applicable elsewhere in the universe where the action is only indirectly perceived.

The plasmas of interest to solar and space physicists are magnetized—threaded through with magnetic fields that are often “frozen” in the plasma. In many cases, the magnetic field plays an essential role in organizing the plasma. An example is the structuring of the Sun’s corona by solar magnetic fields in a complex architecture of loops and arcades—as seen in the dramatic close-up views of the solar atmosphere provided by the Earth-orbiting TRACE observatory. In other cases, such as the Sun’s convection zone, the plasma organizes the magnetic field. Indeed, it is the twisting and folding of the magnetic field by the motions of the plasma in the solar convection zone that amplifies and maintains the Sun’s magnetic field. In all cases, however, the plasma and the magnetic field are intimately tied together and mutually affect each other. The theme of magnetic fields and their interaction with plasmas provides an overall framework for this report. An overview is presented in Chapter 1, introducing the chapters that follow, each of which treats a particular fundamental set of phenomena important for our understanding of solar system and astrophysical plasmas.

The question of how magnetic fields are generated, maintained, and amplified, together with the complementary question of how magnetic energy is dissipated in cosmic plasmas, is explored in the second chapter of this report, “Creation and Annihilation of Magnetic Fields.” The focus is on the dynamo and on magnetic reconnection. Chapter 2 discusses the current understanding of the workings of these processes in both solar and planetary settings and identifies several outstanding problems. For example, understanding how the differential rotation of the solar interior arises represents a significant challenge for solar dynamo theory. In the case of planetary dynamos, important open questions concern the role of physical processes other than the Coriolis force in determining the morphology and alignment of the magnetic field (e.g., of Uranus and Neptune) and the influence of effects such as fluid inertia and viscous stress on Earth’s dynamo. With respect to magnetic reconnection, a significant advance in our understanding has been achieved with the development of the kinetic picture of this process. However, what triggers and maintains the reconnection process is the subject of great debate. Moreover, how reconnection operates in three dimensions is not well understood.

Chapter 3, “Formation of Structures and Transients,” examines some of the important structures that are found in magnetized plasmas. These include collisionless shocks, which develop when the relative velocity between different plasma regimes causes them to interact, producing sharp transition regions, and current sheets, which separate plasma regions whose magnetic fields differ in orientation and/or magnitude. A transient structure that occurs in a number of different plasma environments (solar active regions, the corona, the solar wind, the

magnetotail) is the flux rope, a tube of twisted magnetic fields. Scientists have learned much about the plasma structures in our solar system but still have numerous questions. Studies of Earth’s bow shock have provided basic understanding of shock dissipation and shock acceleration in collisionless plasmas, but much work remains in extending this understanding to large astrophysical shocks. This will require understanding of strong interplanetary shocks in the outer heliosphere and, ultimately, direct observation of the termination shock. Flux ropes have also been extensively observed, but many unanswered questions remain: How are flux ropes formed and how do they evolve? What determines their size? How are they destroyed? What is their relation to magnetic reconnection?

Chapter 3 also examines magnetohydrodynamic turbulence, a phenomenon that is a classic example of the way in which magnetized plasmas couple strongly across multiple spatial and temporal scales. In turbulent coupling, energy is fed into the largest scales and then progressively flows down to smaller scales, eventually reaching the “dissipation scale,” where heating of the plasma occurs. Turbulence has been most completely studied in the solar wind, but questions remain concerning the detailed structure of heliospheric turbulence and how this structure affects energetic particle scattering and acceleration. Turbulent processes also occur in the Sun’s chromosphere as well as in Earth’s magnetopause and magnetotail. Outstanding problems include the role of turbulence in transport across boundary layers, the onset of turbulence in thin current sheets, and the coupling of micro-turbulence to large-scale disturbances.

Plasmas throughout the universe interact with solid bodies, gases, magnetic fields, electromagnetic radiation, and waves. These interactions can be very local or can take place over regions as large as the size of galaxies. Chapter 4 discusses four classes of plasma interaction. Electromagnetic interaction is exemplified by the coupling of a planetary ionosphere and magnetosphere by electrical currents aligned with the planet’s magnetic field. The aurora is a familiar and dramatic manifestation of the energy transfer that results from this coupling. Electromagnetic coupling is also believed to be important in stellar formation, through the redistribution of angular momentum between the protostar and the surrounding nebular material. Flow-object interactions refer to the processes that occur when plasma flows past either a magnetized or an unmagnetized object. Typical processes include reconnection, turbulent wakes, convective flows, and pickup ions. The third class of plasma interactions are those that involve the coupling of a plasma with a neutral gas, such as the exchange of charge between ions and neutral atoms or collisions between ions and neutrals in Earth’s auroral ionosphere, which drive strong thermospheric winds. The final category is radiation-plasma interactions, which is important for understanding the structure of the Sun’s corona: radiation-plasma interactions produce a monotonically decreasing temperature-altitude profile in the corona in great contrast to a falling-then-rising profile produced by the standard quasi-static models.

Chapter 5, “Explosive Energy Conversion,” treats the buildup of magnetic energy and its explosive release into heated and accelerated particles as observed in solar flares, coronal mass ejections, and magnetospheric substorms. Since the first observation of a solar flare in 1859 and the recognition that solar disturbances are associated with auroral displays and geomagnetic disturbances, magnetic energy release has been a central topic of solar-terrestrial studies. Because of their potentially disruptive influence on both ground-based and space-based technological systems, such explosive events are of practical concern as well as of great intrinsic scientific interest.

Both solar flares and coronal mass ejections (CMEs) result from the release of magnetic energy stored in the Sun’s corona. It is not understood, however, how energy builds up and is stored in the corona or how it is then converted into heating in flares or kinetic energy in CMEs. At Earth, magnetic energy stored in the magnetotail through the interaction of the solar wind and the magnetosphere is explosively released in substorms, periodic disturbances that convert this energy into particle kinetic energy. The details of how stored magnetic energy is transferred from the lobes of the magnetotail to the plasma sheet and ultimately dissipated remain subjects of intense debate. The storage and release of magnetic energy occur universally in astrophysical plasmas, as evidenced by the enormous flares from M-dwarfs and the stellar eruption observed in the young XZ-Tauri AB binary system. What is learned about the workings of magnetic storage-release mechanisms in our solar system is likely to contribute to our understanding of analogous processes in other, remote astrophysical systems as well.

The key mechanisms by which magnetized plasmas accelerate charged particles are reviewed in Chapter 6, “Energetic Particle Acceleration.” Shock acceleration occurs throughout the solar system, from shocks driven by solar flares and CMEs to planetary bow shocks and the termination shock near the boundary of the heliosphere. Particles are accelerated at shocks by a variety of mechanisms, and the resulting energies can be quite high, >100 MeV and even in the GeV range for solar energetic particles accelerated at CME-driven shocks. One topic of particular interest in current shock acceleration studies is the identity of the particles that form the seed population

for the shock-accelerated ions. What, for example, are the sources and composition of the pickup ions that are accelerated at the termination shock to form anomalous cosmic rays?

Coherent electric field acceleration arises from electric fields aligned either perpendicular or parallel to the local magnetic field. Induced electric fields perpendicular to the geomagnetic field play a role in the radial transport and energization of charged particles in Earth’s magnetosphere and contribute to the growth of the outer radiation belt during magnetic storms. Parallel electric fields accelerate auroral electrons and accelerate plasma from reconnection sites; they are also involved in the energization of solar flare particles. Stochastic acceleration results from randomly oriented electric field perturbations associated with magnetohydrodynamic waves or turbulence. It plays a role in the acceleration of particles in solar flares, in the acceleration of interstellar pickup ions in the heliosphere, and possibly in the acceleration of relativistic electrons during geomagnetic storms.

All of these acceleration mechanisms may occur simultaneously or at different times. For example, direct energization of particles by electric fields, interactions with ultralow-frequency waves, and localized, stochastic acceleration may all contribute to the storm-time enhancement of Earth’s radiation belt. However, in this case as in others, distinguishing among the various acceleration mechanisms as well as determining the role and relative importance of each poses challenges to both the observational and the theory and modeling communities.

Plasma Physics of the Local Cosmos examines the universal properties of solar system plasmas and identifies a number of open questions illustrative of the major scientific issues expected to drive future research in solar and space physics. Recommendations regarding specific future research initiatives designed to address some of these issues are offered in another recent National Research Council report, The Sun to the Earth—and Beyond: A Decadal Research Strategy for Solar and Space Physics, which was prepared by the Solar and Space Physics Survey Committee under the auspices of the Committee on Solar and Space Physics.¹ The two reports are thus complementary. The Survey Committee’s report presents a strategy for investigating plasma phenomena in a variety of solar system environments, from the Sun’s corona to Jupiter’s high-latitude magnetosphere, while Plasma Physics of the Local Cosmos describes the fundamental plasma physics common to all these environments and whose manifestations under differing boundary conditions are the focus of the observational, theoretical, and modeling initiatives recommended by the Survey Committee and its study panels.

A Report of the Committee on the Assessment of the Role of Solar and Space Physics in NASA’s Space Exploration Initiative

In 2003, the National Research Council published the first decadal survey for Solar and Space Physics, The Sun to the Earth—and Beyond: A Decadal Research Strategy in Solar and Space Physics (referred to here as the decadal survey report).¹ The survey report recommended a research program for NASA and the National Science Foundation (NSF) that would also address the operational needs of NOAA and DOD. The report included a recommended suite of NASA missions, which were ordered by priority, presented in an appropriate sequence, and selected to fit within the expected resource profile for the next decade. In early 2004, NASA adopted major new goals for human and robotic exploration of the solar system,² exploration that will depend, in part, on an ability to predict the space environment experienced by robotic and piloted exploring spacecraft. The purpose of this report is to consider solar and space physics priorities in light of the space exploration vision.

In June 2004 the President’s Commission on Implementation of United States Space Exploration Policy (also known as the Aldridge Commission) issued a report in which it described a broad role for science in the context of space exploration.³ The report treated science as being both an intrinsic element of exploration and an enabling element:

The commission also presented a notional science research agenda, that comprises the three broad themes of origins, evolution, and fate (see Appendix C). Research in solar and space physics appears centrally under the topic “temporal variations in solar output—monitoring and interpretation of space weather as relevant to consequence and predictability” as an element of the fate theme, and it contributes in key ways to many aspects of several components of the origins and evolution themes. In light of the commission’s findings, the Committee on the Assessment of the Role of Solar and Space Physics in NASA’s Space Exploration Initiative chose to interpret its charge in the broadest sense and to examine the fundamental role of solar and space physics research both in scientific exploration and in support of enabling future exploration of the solar system.

From a purely scientific perspective, it is notable that the solar system, and stellar systems in general, are rich in the dynamical behaviors of plasma, gas, and dust that are organized and affected by magnetic fields. These dynamical processes are ubiquitous in highly evolved stellar systems, such as our own, and they play important roles in their formation and evolution. Magnetic fields produced in rotating solid and gaseous planets in combination with ultraviolet and x-ray photons from the planetary system’s central stars create plasma environments called asterospheres, or in the Sun’s case, the heliosphere. In its present manifestation, the heliosphere is a fascinating corner of the universe, challenging our best scientific efforts to understand its diverse workings. Consequently this “local cosmos” is a laboratory for investigating the complex dynamics of active plasmas and fields that occur throughout the universe, from the smallest ionospheric scales to galactic scales.⁴ Close inspection and direct

samplings within the heliosphere are essential parts of the investigations that cannot be carried out by a priori theoretical efforts alone.

Finding 1. The field of solar and space physics is a vibrant area of scientific research. Solar and space physics research has broad importance to solar system exploration, astrophysics, and fundamental plasma physics and comprises key components of the Aldridge Commission’s main research themes of origins, evolution, and fate.

Interplanetary space is far from empty—a dynamic solar wind flows from the Sun through the solar system, forming the heliosphere, a region that encompasses all the solar system and extends more than three times the average distance to Pluto. Gusts of energetic particles race through this wind, arising from acceleration processes at the Sun, in interplanetary space, in planetary magnetospheres, and outside our solar system (galactic cosmic rays). It is these fast particles that pose a threat to exploring astronauts. The magnetic fields of planets provide some protection from these cosmic rays, but the protection is limited and variable, and outside the planetary magnetospheres there is no protection at all. Thus, all objects in space—spacecraft, instrumentation, and humans—are exposed to potentially hazardous penetrating radiation, both photons (e.g., x-rays) and particles (e.g., protons and electrons). Just as changing atmospheric conditions on Earth lead to weather that affects human activities on the ground, the changing conditions in the solar atmosphere lead to variations in the space environment—space weather—that affect activities in space.

The successful exploration of the solar system on the scale and scope envisioned in the new exploration vision will require a prediction capability sufficient to activate mitigation procedures during hazardous radiation events. The development of such a capability will require understanding of the global system of the Sun, interplanetary medium, and the planets. This is best achieved by a mixed program of applied space weather science and basic research. A balanced, integrated approach with a robust infrastructure that includes flight mission data analysis and research, supporting ground and suborbital research, and advanced technology development must be maintained. The strategy outlined in the solar and space physics decadal survey report was designed to accomplish these goals; the committee believes that NASA should retain a commitment to the achievement of the goals of the decadal survey. Indeed curtailing program elements that address the scientific building blocks of space weather research jeopardizes the goal of space weather prediction. However, in light of likely constraints on resources in future years, the committee offers findings and recommendations that address a realistic revision of mission timelines that will still permit a viable program.

Space weather conditions throughout the heliosphere are controlled primarily by the Sun and by the solar wind and its interaction with the magnetic fields and/or ionospheres of the planets. While simple statistical statements (analogous to “March tends to be colder than June”) can be made as a result of empirical, short-term studies, accurate predictions (analogous to “a cold front will bring wind and rain late tomorrow afternoon”) will require longer-term studies of the underlying processes as well as of how the whole heliospheric system responds. Both basic science and applied studies are necessary components of a viable program that facilitates space weather predictions.

Finding 2. Accurate, effective predictions of space weather throughout the solar system demand an understanding of the underlying physical processes that control the system. To enable exploration by robots and humans, we need to understand this global system through a balanced program of applied and basic science.

NASA’s Sun-Earth Connection program depends upon a balanced portfolio of spaceflight missions and of supporting programs and infrastructure, which 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 physical processes of plasma interactions in the solar system. A key assumption in the design of the LWS program 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. Neither set of missions alone can properly support the objectives of the exploration vision. Furthermore, neither 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.⁵

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 Probe programs supported by robust programs for mission operations and data analysis, Explorers, suborbital flights, and supporting research and technology.

The decadal survey report from the Solar and Space Physics Survey Committee recommended a carefully reasoned and prioritized program for addressing high-priority science issues within the constraints of what was understood to be an attainable timeline and budget plan (see Figure 3.1 (a) in Chapter 3 below).

The integrated research strategy presented in the decadal survey for the period 2003 to 2013 is based on several key principles. First, addressing the scientific challenges that were identified in the survey report requires an integrated set of ground- and space-based experimental programs along with complementary theory and modeling initiatives. Second, because of the complexity of the overall solar-heliospheric system, the greatest gains will be achieved by a coordinated approach that addresses the various components of the system, where possible, in combination. Third, a mix of basic, targeted basic,⁶ and applied research is important so that the advances in knowledge and the application of that knowledge to societal problems can progress together. Finally, containing cost is an important consideration because the recommended program must be affordable within the anticipated budgets of the various federal agencies.

Finding 4. The committee concurs with the principles that were employed for setting priorities in the decadal survey report and believes that those principles remain appropriate and relevant today.

With those principles in mind, the decadal survey report recommended a specific sequence of high-priority programs as a strategy for solar and space physics in the next decade. To accomplish this task, the survey report presented an assessment of candidate projects in terms of their potential scientific impact (both in their own subdisciplines and for the field as a whole) and potential societal benefit (i.e., with respect to space weather). The survey report also took into consideration the optimum affordable sequence of programs, what programs would benefit from being operational simultaneously, the technical maturity of missions in a planning phase, and what programs should have the highest priority in the event of budgetary limitations or other unforeseen circumstances that might limit the scope of the overall effort. The recommended sequence of missions was supported by a strong base of Explorer missions, mission operations and data analysis (MO&DA), suborbital activities, and supporting research and technology (SR&T) programs, which together provide the core strength of the Sun-Earth Connection (SEC) program research base.

Finding 5. The committee concludes that, for an SEC program that properly fulfills its dual role of scientific exploration and of enabling future exploration of the solar system, the prioritized sequence recommended in the decadal survey report remains important, timely, and appropriate.

Although the recommendations and schedule presented in the decadal survey report were formulated in 2002—before the adoption by NASA of the new exploration vision—the essential reasoning behind the conclusions of the survey report remains valid: to explore and characterize the solar system and to understand and predict the solar-planetary environment within which future exploration missions will take place requires a scientific approach that treats the environment as a complex, coupled system. The extension of exploration beyond the environment close to Earth will require accurate prediction of conditions that will be encountered. Without programs such as the STP mission line, which study the physical basis of space weather, the development of accurate predictive tools would be placed at serious risk.

A robust program of SEC research depends on four foundation programs—Explorers, MO&DA, the Suborbital program of flights, and SR&T—for basic research and for development of technologies and theoretical models. The vitality of the Explorer mission line depends on the orderly selection of a complement of Small Explorer (SMEX) and Medium-Class Explorer (MIDEX) missions.

In the event of a more constrained funding climate, the timing of near-term missions may need to be stretched out. The committee recognizes that there may be a need to re-evaluate the order and timing of far-term missions in light of the way the exploration initiative evolves while keeping in mind the full scientific context of the issues being addressed.

Even with an SEC program that preserves the priorities and sequence of recommended missions, there will be important consequences from delaying the pace at which missions are executed as a means of dealing with resource constraints. First, there will be losses of scientific synergy due to the fact that opportunities for simultaneous operation of complementary missions will be more difficult to achieve. Furthermore, a number of missions that were recommended in the decadal survey report will be deferred beyond the 10-year planning horizon. This could be the case for the Jupiter Polar Mission, Stereo Magnetospheric Imager, Magnetospheric Constellation, Solar Wind Sentinels, and Mars Aeronomy Probe. These issues will demand careful attention as NASA develops its overall plan for science in the exploration vision.

A Report of the Committee on Environmental Satellite Data Utilization

There is no doubt that environmental satellite data have grown to be the most important source of information for daily global weather forecasting. In addition, these data are now also used by innumerable professionals and laypersons in pursuits as varied as oceanic, atmospheric, terrestrial, and climate research; environmental monitoring; aviation safety; precollege science education; and rapid-response decision support for homeland security, to name just a few. Compounding the pressure put on NOAA and NASA by expanding user communities to provide high-quality data products around the clock is the precarious state of the underfunded satellite data utilization program, which is struggling to keep up with demand for currently available data and the rapidly increasing sophistication of user requirements. The planned next-generation operational satellite systems, comprising both polar-orbiting and geostationary platforms, are designed to meet the needs of user communities whose complex applications are rapidly evolving.

Although the focus of this report is the use of satellite data for civilian rather than defense or national security purposes, a dual-use approach is expected as military and civilian satellite systems converge. The new systems will continue the record of climate-quality observations, but the increase in raw data will be unprecedented—perhaps an order-of-magnitude increase every 2 to 3 years. Expected to develop as a result of this expanded Earth-observing capability are novel ways of using satellite data that will have an increasing impact on citizens’ daily lives. Thus satellite data providers will have to continuously evolve, revise, and in some cases radically redefine their role as well as plan for increased research, operations, and infrastructure. The high-level training required by such personnel and the continuing education of users are equally important and also must be planned and provided for.

Meeting the challenges posed by the imminent and unprecedented exponential increase in the volume of satellite-system data requires an end-to-end review of current practice, including characterization of process weaknesses, an assessment of resources and needs, and identification of critical factors that limit the optimal management of data, plus a strategic analysis of the optimal utilization of environmental satellite data.

In this report, the Committee on Environmental Satellite Data Utilization (CESDU) offers findings and recommendations aimed at defining specific approaches to resolving the potential overload faced by the two agencies—NOAA and NASA—responsible for satellite data (see the preface for the committee’s statement of task). The committee has focused on the end-to-end utilization of environmental satellite data by characterizing the links from the sources of raw data to the end requirements of various user groups, although, given its limited scope, the committee could not thoroughly examine every link in the chain. CESDU’s goal is to characterize and provide sensible recommendations in three areas, namely, (1) the value of and need for environmental satellite data, (2) the distribution of environmental satellite data, and (3) data access and utilization. The committee’s findings are based on its members’ knowledge of trends in technology; past lessons learned; users’ stated requirements; and other supporting information. The committee hopes that this report will help NOAA and NASA identify and avoid impediments to optimal utilization of environmental satellite data.

Over the course of meetings held to collect information for this report, the committee heard presentations from several key agencies and organizations reflecting a broad range of professional perspectives. From these it distilled four consistent and recurring themes that significantly shaped its final findings and recommendations:

• A growing and diverse spectrum of individuals, companies, and agencies routinely utilize and depend on environmental satellite data and information;

• Products that best serve the public, together with effective use of public funds, create an ongoing evolution of requirements for data imposed on and by operational users;

• Improvements in available flight and ground technologies are being made that meet these new requirements—as demonstrated by research satellite missions and aircraft flights; and

• NOAA is committed to the collection of data with improved quality, reliability, latency, and information content.

The value of environmental satellite data derives from the unique, near-real-time, continuous global coverage from space of Earth’s land and ocean surfaces and its atmosphere—value that increases significantly as we accumulate satellite records that provide a historical perspective. In addition, the committee believes that, in the near future, environmental satellite data will be employed by a much wider spectrum of users—from individuals with real-time weather data displays in their home, car, truck, boat, plane, business, or campsite, to a wide range of companies with value-added products developed from those data, to farmers, mariners, truckers, and aviators dependent on weather, to numerical modeling centers that provide weather, crop, fire, drought, flood, health, climate, and other predictions and alerts. Indeed, evidence presented to the committee strongly suggests that we should look to and prepare for a future in which cable TV, wireless networks, personal digital assistants, direct satellite broadcast, and the Internet enable continuous, uninterrupted access to environmental satellite data, information, and knowledge as an essential element of commerce, recreation, and the conduct of everyday life for the majority of people.

Thus it will not be sufficient merely to collect greater amounts of environmental satellite data, although the expected orders-of-magnitude increase in the volume of collected data will in itself pose special challenges. The committee heard testimony about increasing requirements to recover more of the information content in the data, and also about an anticipated increase in the number and diversity of environmental satellite data users who will demand instantaneous access to the particular data and information they want. To achieve improved utilization of environmental satellite data will therefore require that as much effort and planning be devoted to the ground systems serving this user community as to the flight systems that originally collect the data. To successfully realize the future outlined above, the agencies responsible for archiving and distributing environmental satellite data must develop the essential visions, plans, and systems. The following findings of the committee and the recommendations based on them are offered to help NASA and NOAA in that process.

Finding: Improved and continuous access to environmental satellite data is of the highest priority for an increasingly broad and diverse range of users. Their needs include real-time imagery for decision making in response to events such as forest fires, floods, and storms; real-time data for assimilation into numerical weather prediction models; recent imagery for assessment of crops and determination of impacts on the environment resulting from diverse human activities such as marine and land transportation; and data coverage spanning many years that allows assessment of patterns and long-term trends in variables, such as sea-surface temperature, land use, urbanization, and soil moisture. Users of environmental satellite data include individuals; federal government agencies; state and local managers, planners, and governments; commercial producers of added-value products; and Web, print, and TV/radio broadcasters.

Finding: The national and individual user requirements for multiyear climate system data sets from operational environmental satellites, as currently delineated in the Climate Change Science Program strategic plan,¹ are placing special demands on current and future data archiving and utilization systems. These demands include more stringent requirements for accurate cross-platform radiometric calibration, new combinations of multiple satellite and instrument data, and algorithms for generating advanced biophysical variables. Detecting climate change trends often involves evaluating data at the limits of measurement precision, and so periodic, absolutely consistent reprocessing of climate data records is a fundamental requirement.

Finding: NOAA has limited experience with land data sets because historically its mission has focused on the oceans and atmosphere. Major advances in land remote sensing have occurred in the last decade, fostered primarily by the Earth Observing System developed by NASA, that are not reflected in NPOESS planning. The committee found that NOAA has so far not effectively utilized current satellite technologies and data sets for vegetation science, management, or applications. For example, of 58 environmental data records (EDRs) defined for NPOESS, only 6 are specifically for land, and of these only 2 are vegetation oriented. For the 2012 flight of GOES-R, only 20 of the approximately 170 environmental observation requirements (EORs) are land-surface related; of these, only 4 are vegetation related.

Finding: The constellations of satellites now in space and planned for the future include platforms launched by several nations, and more complete and comprehensive coverage of environmental data fields can be achieved by combining the data from these different national efforts.

Finding: The Comprehensive Large Array-data Stewardship System is being designed by NOAA to catalog, archive, and disseminate all NOAA environmental satellite data produced after 2006. Given the magnitude of this effort—and considering the growing volume, types, and complexity of environmental satellite data; the increasingly large and diverse user base; and expectations for wider and more effective use of the data—the committee emphasizes the importance of NOAA’s (1) having a comprehensive understanding of the full scope of the technical requirements for data cataloging, archiving, and dissemination and (2) ensuring implementation based on that knowledge. Key to successful implementation of a strong system that will serve operational users and the nation well are detailed planning, proactive follow-through, and NOAA’s incorporation of lessons learned from previously developed, similarly scaled initiatives with similar systems requirements.

1. NOAA should conduct an immediate review of the entire Comprehensive Large Array-data Stewardship System (CLASS) program. This review should aggressively solicit and incorporate recommendations from the designers, builders, operators, and users of similar systems, particularly those systems comprised by the Earth Observing System Data and Information System.

2. CLASS should be designated and developed as NOAA’s primary data archive system for environmental satellite data and other related data sets. NOAA should ensure that CLASS is designed to adequately serve the full spectrum of potential environmental satellite data users. In addition to end users, CLASS should be designed to disseminate data to the broadest possible community of data brokers and value-added providers. The CLASS architecture should explicitly include the public programmatic (e.g., Web services) interfaces that these third parties require.

3. NOAA should plan for and identify resources required for an increased CLASS effort to fulfill the needs outlined in a and b above.

Finding: NOAA does not appear to be effectively leveraging the substantial and growing third-party resources available for creating, archiving, and distributing environmental satellite data products. In particular, the current CLASS effort appears to include end-user services (such as Web ordering, e-commerce, and product customization) that could just as easily be provided by third parties, while ignoring the lower-level programmatic interfaces that value-added providers require.

1. NOAA should consider both centralized and decentralized approaches to managing the generation and distribution of environmental satellite data products to ensure cost-effective and efficient utilization of existing human and institutional expertise and resources. Centralized handling should be provided for operationally critical core products and should include the acquisition, processing, distribution, archiving, and management of calibrated, navigated radiances and reflectances at the top and bottom (atmospherically corrected) of the atmosphere, as well as for selected key products and metadata. Specialized higher-level environmental data products could be handled (processed, reprocessed, and distributed) in a physically and organizationally distributed (and diverse) manner.

2. NOAA should take maximum advantage of the exponentially decreasing costs of computing resources and allow for distributed implementations by third parties.

3. NOAA should consider mutually beneficial partnerships and partnering models with the private sector (e.g., commercial value-added data and product services providers) that have the twin objectives of ensuring user-oriented open access to the data and providing the best value to end users.

Finding: Over the life of a project the cost of ownership of online (disk) storage is competitive with, and decreasing more rapidly than, that of offline (tape or optical) storage. The ability to store and process large volumes of satellite data online will thus become ubiquitous. More than any physical medium, Internet connections to these online data sources will prove a stable, economical, and widely available mechanism for data transfer.

1. NOAA’s default policy should be to maintain all public satellite data online, in archives that can be accessed (partitioned) to maximize throughput and replicated (mirrored) to ensure survivability.

2. NOAA should transition to exclusively online access to satellite data. Distribution on physical media should be provided as a custom service by third parties.

3. NOAA should plan for and identify resources to support handling of the anticipated increase in archival and dissemination requirements beyond 2010.

Finding: Data from diverse satellite platforms and for different environmental variables must often be retrieved from different sources, and these retrievals often yield data sets in different formats with different resolution and gridding. The multiple steps currently required to retrieve and manipulate environmental satellite data sets are an impediment to their use.

1. NOAA should improve access to its data by allowing users to focus searches by geographic region, dates, or environmental variables, thus helping provide the means to search from one user interface across all environmental satellite data held by U.S. agencies. Tailored subsets of data products should be made available for routine distribution and/or in response to a specific request.

2. Further, NOAA’s user interfaces should allow stored environmental satellite data sets and/or images to be retrieved in a common data format and with geolocated gridding selected from a list of options by the user. Subsetting and subsampling should be combined to provide a continuum of data products from broad-area, low/moderate-resolution products to regional, high-resolution products.

3. NOAA should concentrate on ensuring the commonality, ease, and transparency of access to environmental satellite data and providing no-cost data streams in a few standardized, user-friendly formats selected primarily to maximize ease of translation into community-specific formats.

4. NOAA should support the development of third-party format translation services and the adaptation of existing community-standard tools to NOAA-standard formats.

5. The data that NOAA provides to users should be accompanied by metadata that documents data quality, discusses possible sources of error, and includes a complete product “pedigree” (algorithm theoretical basis, sensor and calibration, ancillary data, processing path, and validation status and component uncertainties).

Finding: Some major segments of the user community currently do not have the resources to fully utilize all of the environmental satellite data available to them. The principal obstacles to expanded use have been inadequate and/or discontinuous funding for applied research as a part of data utilization programs, the lack of support for education and outreach programs, and the lack of trained professional brokers and facilitators available to work with the various bidirectional interfaces between users and providers within the environmental satellite data utilization system.

Finding: Early and ongoing cooperation with dialogue among users, developers of satellite remote sensing hardware and software, and U.S. and international research and operational satellite data providers is essential for the rapid and successful utilization of environmental satellite data. Active research and development is required to achieve operational sustainability—today’s research anticipates and underpins the satisfaction of tomorrow’s operational requirements. Many of the greatest environmental satellite data utilization success stories (see, e.g., the case study on the European Centre for Medium-range Weather Forecasts in Appendix D) have a common theme: the treatment of research and operations as a continuum, with a relentless team focus on excellence with the freedom to continuously improve and evolve.