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Assessment of Mission Size Trade-offs for NASA’s Earth and Space Science Missions 3 Summary and Recommendations Chapter 3 presents the ad hoc committee’s findings in response to the tasks set forth in the original charge and its recommendations to NASA based on the analyses in Chapters 1 and 2. In its deliberations the committee focused on the implications of FBC for the space programs’ tolerance for risk; the scope, diversity, and timeliness of the science investigated; the results and analytical products produced from space research missions; the availability and use of advanced technology; the training and educational opportunities for students; and the role of international cooperation in supporting the mix of mission sizes in NASA programs. The committee’s findings and recommendations reflect the importance of these factors in facilitating a balanced portfolio of mission sizes for achieving high-priority science for NASA’s Earth science and space science programs. In light of the myriad and complex considerations bearing on mission planning, the committee did not prescribe what the mix of mission sizes should be. THE CHARGE The request for this report originated from the Senate Appropriations Committee in its FY99 report; NASA commissioned the NRC to conduct the assessment. The charge to the committee sets three key tasks: Evaluate the general strengths and weaknesses of small, medium, and large missions in terms of their potential scientific productivity, responsiveness to evolving opportunities, ability to take advantage of technological progress, and other factors that may be identified during the study; Identify which elements of the SSB and NASA science strategies will require medium or large missions to accomplish high-priority science objectives; and Recommend general principles or criteria for evaluating the mix of mission sizes in Earth and space science programs. The factors to be considered will include not only scientific, technological, and cost trade-offs but also institutional and structural issues pertaining to the vigor of the research community, government-industry-university partnerships, graduate student training, and the like.
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Assessment of Mission Size Trade-offs for NASA’s Earth and Space Science Missions STRENGTHS AND WEAKNESSES OF SMALL AND LARGE MISSIONS Small Missions Small missions (defined by NASA as missions costing less than $150 million) play a key and compelling role in the space-based Earth and space science programs. They are responsible for decreasing the time to science, leading to scientific analyses that can be conducted within years rather than decades. Smaller programs tend to be flexible and responsive to new scientific opportunities. They also provide for answering the more focused questions that emerge from larger-scale research activities (e.g., the Great Observatories). Shorter development periods for small missions reduce their overall costs and provide additional degrees of budgetary freedom for NASA’s Earth and Space Science Enterprises. What stands out prominently is the professional vitality and community involvement small missions can offer. Researchers who might have waited a lifetime to analyze data are stimulated, freshened, and sharpened when given the opportunity to conduct high-priority, high-quality science in a shorter period. In turn, these programs afford undergraduate and graduate students opportunities to participate in and experience the complex and organic nature of science, from proposal to development, to analysis, to publication. The STEDI program is a case in point, and the desirability of its broadly educated “alumni” is borne out by industry’s strong demand for them. Small satellites are appropriate for highly focused and relatively limited scientific objectives. However, their flexibility, while opportunistic for science, poses challenges for strategic planning and meeting long-term science objectives. The ESSP and Explorer lines rely on open AOs. While these AOs result in excellent scientific proposals, they may not give the scientific community a sense of the overall planning and direction for the program. Moreover, they may make it more difficult for international partners to submit proposals individually or join a proposing team. The balance between planning and flexibility is a fine one. Nonetheless, the committee believes that efforts to provide appropriate planning for small missions will ensure that their scientific contributions enhance the overall Earth and space science programs and the community’s objectives. Large Missions Smaller missions are not replacements for the scientific scope that large (defined by NASA for this study as missions costing more than $350 million) platforms can accommodate. The strength of large missions lies in their ability to accommodate complex scientific objectives requiring long-term measurements, sophisticated instruments, large mass, and/or instrument and spacecraft redundancy. When technology development and instrument development were included in large-scale programs, as they often were, the programs brought forth a wealth of experience and instrumentation that benefited subsequent programs. The scientific output of missions such as Hubble, Galileo, Magellan, and UARS testifies to their value in terms of scientific achievement. Current priorities continue to demand large as well as medium and small missions. Long-term records of climate fluctuations, for example, are required before scientists can draw conclusions about global climate trends or predict future impacts. Such long-term observations necessitate spacecraft with sufficient power. They must often assemble a time series of observations spanning decades or more. These requirements may translate into high levels of mass and a large enough platform to accommodate robust subsystems. Mass and platform size are also critical elements for astronomical observations requiring large-aperture telescopes. Looking deeper into the universe or making more accurate spectroscopic assessments of planets around remote stars demands larger, more complex spacecraft systems. The discussion in Chapter 1 of the physical constraints on and principles of conducting space-based science articulates these issues. Missions that address complex science have required longer development periods, which automatically increases a program’s cost. Moreover, as noted in the technology discussion in Chapter 1, the prospect of sending a large, expensive spacecraft carrying several sophisticated instruments to the outer planets reduces tolerance for risk that might be inherent in newer, more capable technologies or leaner management. By the same token the larger size of such a spacecraft could accommodate redundant systems, which is an effective mechanism for managing risk on large spacecraft carrying numerous science payloads and traveling long distances. Thus, an
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Assessment of Mission Size Trade-offs for NASA’s Earth and Space Science Missions intelligent balancing of capabilities, perceived risk, and available resources will continue to be the principal challenge to NASA managers. RECOMMENDATIONS IN RESPONSE TO THE CHARGE Faster-Better-Cheaper Principles The committee’s findings begin with a recommendation on the broader implementation of faster-better-cheaper principles. The committee found that FBC methods of management, technology infusion, and implementation have produced useful improvements regardless of absolute mission size or cost. However, while improvements in administrative procedures have proven their worth in shortening the time to science, experience from mission losses (Mars Climate Observer and Lewis, for example) has shown that great care must be exercised in changing technical management techniques lest mission success be compromised. Recommendation 1: Transfer appropriate elements of the faster-better-cheaper management principles to the entire portfolio of space science and Earth science mission sizes and cost ranges and tailor the management approach of each project to the size, complexity, scientific value, and cost of its mission. Science Goals and Mission Size In the Earth sciences long-term climate measurements are needed, and many of NASA’s research programs will have to be more closely integrated with the nation’s operational programs. Operational missions such as those of NOAA require redundancy and continuity of a complex set of measurements. These requirements usually translate into medium-size or large spacecraft. Climate research, on the other hand, requires sustained, accurate, and calibrated measurements. These requirements often translate into a mix of mission sizes at any one time, but they, too, imply a commitment to a long-term measurement strategy. The operational and research measurement variables overlap, but not completely. For example, long-term weather forecasting and the development of climate computer models place more rigorous demands on the horizontal and vertical resolution for temperature and moisture atmospheric profiles. These data are gathered by infrared and microwave atmospheric sounders on polar-orbiting satellites. Models were satisfied only 10 years ago by data sampled at 4-km vertical intervals and a 250-km spatial grid. Now scientists need 1-km vertical resolution and a spatial grid of less than 20 km. In response, the number of frequency bands in the instruments has had to be increased by a factor of approximately four, and aperture sizes have been increased to attain the smaller grid size. In spite of advances in technology, the newer instruments are larger and more massive than their predecessors and require larger spacecraft. In the planetary sciences, high-priority questions requiring samples to be returned to Earth from Mars or the core of a comet, exploration to the solar system’s outer planets, and planetary or cometary landers would all require large-scale missions. In solar and space physics, SSB science strategies and NASA strategic plans call for a full portfolio of mission sizes to carry out the scientific objectives of the discipline. The SEC long-range strategy has identified the medium-size and large missions needed for its science plan. Medium-size missions include those with clusters of near-Earth-orbiting spacecraft and certain solar missions with more focused objectives. Large missions are needed where orbital requirements are very severe (such as missions to access and study interstellar space or the polar regions of the Sun), where a long, continuous time line of observations is required (such as to observe solar variations and sunspot cycle effects), and where planetary environments (such as the plasma electrodynamics at Jupiter and Io) are studied. The astronomy and astrophysics community has implemented large-scale missions and continues to call for several more: SIRTF, SIM, GLAST, TPF, Constellation X, NGST, and Laser Interferometer Space Antenna
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Assessment of Mission Size Trade-offs for NASA’s Earth and Space Science Missions (LISA). These missions respond to the scientific imperative to detect the range of a radiation emitted by both common and exotic sources, and it is this imperative that drives the technology. Typically, work at the frontier requires enhanced sensitivity and enhanced angular and spectral resolution, with the consequent need for large missions. For example, studies of galaxies near the time of their formation require sensitive, high-angular-resolution imaging capabilities in the near-infrared part of the spectrum, capabilities that will be offered by the Next Generation Space Telescope. The sheer size of the telescope aperture required, coupled with the low operating temperatures, necessitates a large mission platform. In considering the role of science goals in planning for a portfolio of mission sizes, the committee found the following: The nature of the phenomena to be observed and the technological means of executing such observations are constrained fundamentally by the laws of physics, such that some worthwhile science objectives cannot be met by small satellites. The strength and appeal of faster-better-cheaper is to promote efficiency in design and timely execution—shorter time to science—of space missions in comparison with what are perceived as less efficient or more costly traditional methods. A mixed portfolio of mission sizes is crucial in virtually all space and Earth science disciplines in order to accomplish a variety of significant research objectives. An emphasis on medium-size missions is currently precluding comprehensive payloads on planetary missions and has tended to discourage planning for large, extensive missions. Recommendation 2: Ensure that science objectives—and their relative importance in a given discipline—are the primary determinants of what missions are carried out and their sizes, and ensure that mission planning responds to (1) the link between science priorities and science payload, (2) timeliness in meeting science objectives, and (3) risks associated with the mission. Technology Development A further key point is that small missions (and their concomitant short development times) have depended on access to previously developed instruments and technologies. Without a source of new instruments, the missions using faster-better-cheaper principles cannot be sustained. Indeed, smaller missions are intended, to some extent, to tolerate more risk from new instruments and/or technologies. However, to date the selection processes for medium (defined by NASA for this study as $150 million to $350 million) programs such as Discovery have been surprisingly risk-averse. The committee considered the role of technology as it assessed mission size trade-offs for Earth and space science missions and found the following: Technology development is a cornerstone of first-rate Earth and space science programs. Advanced technology for instruments and spacecraft systems and its timely infusion into space research missions are essential for carrying out almost all space missions in each of the disciplines, irrespective of mission size. The fundamental goal of technology infusion is to obtain the highest performance at the lowest cost. The scientific program in Earth and space science missions conducted under the FBC approach has been critically dependent on instruments developed in the past. The ongoing development of new scientific instrumentation is essential for sustaining the FBC paradigm. Recommendation 3: Maintain a vigorous technology program for the development of advanced spacecraft hardware that will enable a portfolio of missions of varying sizes and complexities.
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Assessment of Mission Size Trade-offs for NASA’s Earth and Space Science Missions Recommendation 4: Develop scientific instrumentation enabling a portfolio of mission sizes, ensuring that funding for such development efforts is augmented and appropriately balanced with space mission line budgets. Cost of Access to Space In addition to trade-offs in the areas of management, scientific scope, and technology noted above, several other factors must be taken into account when deciding on mission-size mixes in NASA’s space program. Specifically, the committee found that access to space is a primary determinant of timeliness and cost in executing science missions: The high cost of access to space remains one of the principal impediments to using the best and most natural mix of small and large spacecraft. While smaller spacecraft might appear to be the right solution for addressing many scientific questions from orbit, present launch costs make them an unfavorable solution from an overall program budgetary standpoint. Moreover, larger missions, too, are plagued by the excessive costs per unit mass for present launch vehicles. The national space transportation policy requiring all U.S. government payloads to be launched on vehicles manufactured in the United States prevents taking advantage of low-cost access to space on foreign launch vehicles. Recommendation 5: Develop more affordable launch options for gaining access to space, including—possibly—foreign launch vehicles, so that a mixed portfolio of mission sizes becomes a viable approach. International Collaboration The committee found that international collaboration has proven to be a reliable and cost-effective means to enhance the scientific return from missions and broaden the portfolio of space missions. Nevertheless, it is sometimes considered, within NASA, to be detrimental, perhaps because it adds complexity and can bring delays to a mission. It is also perceived to give a mission an unfair advantage and, in part, to increase NASA’s financial risk. In the past NASA had within its budgets an international payload line, which was an extremely useful device for funding the planning, proposal preparation, and development and integration of peer-reviewed science instruments selected to fly on foreign-led missions. This line offered the U.S. scientific community highly leveraged access to important new international missions by providing investigators with additional opportunities to fly instruments and retrieve data, especially during long hiatuses between U.S. missions in a given discipline. Recommendation 6: Encourage international collaboration in all sizes and classes of missions, so that international missions will be able to fill key niches in NASA’s space and Earth science programs. Specifically, restore separate, peer-reviewed announcements of opportunity for enhancements to foreign-led space research missions. OTHER FINDINGS ON ISSUES AFFECTING MISSION SIZE MIX The committee’s deliberations and findings as reported in Chapters 1 and 2 and above provide the framework for establishing the right balance of small, medium, and large missions in NASA’s science enterprise. There is a clear need for a mixed portfolio of mission sizes and scopes; any decisions in this regard must of course be tempered by the budgetary and resource limitations operative at any given time. The committee examined four additional issues that are important in considering the trade-offs on mission size mix: (1) education, (2) assessment of risk, (3) data analysis, and (4) evaluating the science return from space missions.
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Assessment of Mission Size Trade-offs for NASA’s Earth and Space Science Missions Education The committee notes that the emphasis on education as part of the FBC approach is positive. However, it is not aware of any attempts to assess how the quantity or quality of educational activities varies with mission size. The committee believes it is important to optimize the quantity and quality of educational activities (in line with the class of the mission) associated with all space and Earth science missions (Chapter 1, section “Implementation,” subsection “Education”). Risk The committee found that risk associated with smaller, shorter-duration missions will generally be higher than risk associated with traditional programs. However, such risk can be handled effectively, provided sound management and lessons learned from past mission failures are applied. Risks can be minimized by ensuring that the level and quality of staffing is commensurate with the degree of complexity and risk associated with missions conducted under the FBC approach (Chapter 1, section “Risk”). Data Analysis The scientific outcomes of a mission include data, data analysis, scientific findings, and publications. The scientific value and return from missions must be considered when evaluating mission scope and scale and the balance of mission sizes. Specifically, the committee found the following: In the Earth sciences, research on climate requires data from long-term satellite observations in addition to data collected in situ to identify changes and trends. A mix of mission sizes—including shorter-duration, narrowly focused missions; larger operational platforms; and in situ sources versus remote data collection—intensifies the need for careful planning, coordination, calibration, and integration among data sets. Good sensor characterization and calibration, along with continuing data product validation, are essential attributes of space-based measurement systems. Smaller, shorter-duration missions sometimes provide insufficient calibration and validation, which compromises the science return. Space research missions are successful only if they extract the optimum scientific value from the data set generated. An appropriate allocation of the investment—between the space system and instrumentation elements; data calibration, characterization, and validation; and the subsequent data analysis effort—is essential to a logical evolution of mission sequences in a given field of Earth or space science. The committee believes it is important to develop an implementation plan for each science mission, regardless of size, that will support data integrity (characterization, calibration, and validation) and scientific analyses beyond the data-acquisition part of the mission (Chapter 1, sections “Fundamental Science Limits” and “Measuring and Enhancing the Scientific Return on the Investment”). Evaluating the Science Return The committee notes the following: Comparing small and large missions after they have achieved their objectives to assess the quality or cost-effectiveness of the science product is inherently complex and not amenable to simple formulas. Peer review that takes place in advance against a background of long-term vision and science planning to establish mission priorities is an effective way to evaluate the scientific potential of a mission and the appropriateness of its size. The success of a particular mission can be judged by comparing its accomplishments to the original goals, recognizing that there may be unexpected discoveries and that other benefits may be realized only later.
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