NASA operates a large number of space science missions, approximately three-quarters of which are currently in their extended operations phase. They represent not only a majority of operational space science missions but also a substantial national investment and vital national assets. They are tremendously scientifically productive, making many of the major discoveries that are reported in the media and that rewrite textbooks. For example, the Spitzer Space Telescope together with the Hubble identified a very distant galaxy where star formation proceeds much more rapidly than previously known in the early universe. The Aqua Earth observing spacecraft showed that the melting of the Greenland ice sheet in 2012 was the most extensive surface melting measured to date. The STEREO spacecraft obtained the first 360 degree images of the Sun. The Mars Exploration Rovers Spirit and Opportunity identified habitable hydrothermal environments on Mars. (These and many other scientific discoveries made by missions in their extended phase are discussed in Chapter 2.)
The NASA Authorization Act of 2005 established a requirement for NASA to conduct reviews of missions in extended phase every 2 years. After a decade of this requirement, in summer 2015 NASA asked the National Academies of Sciences, Engineering, and Medicine to conduct a study on its extended science missions. In response, the Academies created the Committee on NASA Science Mission Extensions, which met in person and via conference call several times starting in December 2015. The committee was asked to evaluate the following:
- The scientific benefits of mission extensions,
- The current process for extending missions,
- The current biennial requirement for mission extensions,
- The balance between starting new missions and extending operating missions, and
- Potential innovative cost-reduction proposals for extended missions.1
NASA currently operates approximately 60 space science missions, of which approximately 45 have finished their prime mission phase and have entered their extended phase.2 Extended missions provide a substantial return
2 Missions can consist of more than one spacecraft, and it is possible in some cases for one or more spacecraft that is/are part of a mission to be extended while other/s is/are not. For various reasons it is difficult to obtain exact numbers of NASA missions in prime and extended phases. This is due in part to how NASA counts its missions and the fact that some missions (e.g., WISE/NEOWISE) have changed status over time. Also, the numbers are always in flux as new spacecraft are launched or change status. Thus, the numbers in this report should be considered approximations and will have changed by publication.
on investment for NASA and U.S. taxpayers, considering the very high science productivity of these extended missions at relatively low cost.
Extended science missions have made major contributions to scientific discovery over many decades. They are valuable assets in NASA’s portfolio because they are already operating successfully and no longer require development or launch costs but still provide excellent science at low incremental cost, needing only funding to conduct their operations and collect, process, and analyze their data. Approximately 75 percent of NASA’s space science missions operate on approximately 12 percent of the space science budget (Figures S.1 and S.2).
Many extended science missions have made important discoveries via new destinations, observation types or targets, and/or data analysis methods. Moreover, continuous coverage, long-baseline data sets, and statistically significant observations of infrequent events require continuity of measurement over years or decades and are best provided through missions in extended phase. NASA’s extended missions commonly achieve science objectives identified by the decadal surveys while providing unique insights for determining priorities and approaches for future exploration. Based on its assessment, the committee concluded that extended-phase science missions are a vital part of NASA’s overall science effort.
The NASA Science Mission Directorate (SMD) undertakes a Senior Review process for astrophysics and planetary science missions in even-numbered years and Earth science and heliophysics missions in odd-numbered years. For spacecraft missions that continue to operate beyond their prime phase, the Senior Review is a valuable peer review process for recommending future support based on assessments of the scientific accomplishments
and future projections, as well as the practical utility in meeting national and related interagency needs. NASA uses Senior Review recommendations as a major consideration when deciding on mission extensions. However, given budget constraints and uncertainties, the Senior Review may need to recommend termination of otherwise highly productive missions, although it is likely to express support for continuation of such missions if additional resources can be identified and allocated. The committee noted that the current NASA approach provides some flexibility in how the agency ultimately implements recommendations for mission termination, which at times allows for additional recommended missions to be continued. For example, in rare instances, non-government support for continuing missions has been provided by universities.
The exact manner in which NASA conducts its Senior Reviews is based on the specific needs of each division. For example, NASA Earth Science Division missions and some Heliophysics Division missions have potential or realized non-research utility—meaning that they can be used to support other NASA or national needs. So in addition to the primary criterion of continued scientific productivity, evaluating the applied and operational use of NASA Earth science missions is a secondary factor in Earth Science Senior Review evaluation and extension decisions. In addition, the Astrophysics Division deems a few missions (currently the Hubble Space Telescope and Chandra X-ray Observatory) to be multipurpose observatories with broad scientific capabilities and has decided to review them separately from other missions in the division. Also, Planetary Science Division missions have variable transit times to their destinations, some taking many years before the beginning of the prime mission,
which requires that the Senior Review process be applied to such missions on a case-by-case basis. These differing needs of the divisions highlight the need to allow the divisions flexibility in how they conduct their Senior Reviews, and no single template can be effectively applied to all of the divisions.
Senior Review teams are established by NASA and consist of volunteers who issue their recommendations independent of the agency but rely on NASA to establish the timeline for conducting the review. At times, the Senior Review process has become too compressed, and NASA has allocated insufficient time for some of the stages that are essential for an effective Senior Review. In particular, it is essential that
- The Senior Review panels have adequate time to review the proposals,
- Adequate time is also allocated to formulate questions for the mission teams, and
- The proposal (mission) teams have sufficient time to respond to questions from the panels.
Although NASA is required to conduct Senior Reviews every 2 years, the timing for launch of missions and their major events does not always correspond to the regular schedule for Senior Reviews. As a result, flexibility in scheduling the Senior Reviews (e.g., the ability to change the timing of individual reviews to avoid mission-critical events) is valuable for NASA’s science divisions. NASA divisions have at times conducted off-year reviews for some missions, determined by individual mission needs, or extended missions beyond the next 2-year cycle if the spacecraft is expected to terminate after the following review (i.e., Cassini). The committee determined that such flexibility has been important for the success of missions.
Regular reviews of operating missions are essential to ensure that missions are productive and scientifically relevant and that the nation is obtaining value for its expenditure on these missions. However, the current 2-year cadence creates an excessive burden on NASA, mission teams, and the Senior Review panels. A 3-year cadence would ease this burden, while still enabling timely assessment of the quality of the data returned from these missions and their potential for continued productivity. The committee judged that a 4- or 5-year cadence might be too long, given potential science developments and also changes in a mission’s health or overall capabilities. The committee also determined that other changes, such as reducing the number of pages required for proposals, would have a negligible or even negative effect on reducing the burden on proposal teams and NASA.
An important component of this revised 3-year cadence is conducting regular assessments of the health of the spacecraft and instruments so that both the agency and proposers are aware of any potential issues that might result in shorter useful lifetimes. NASA’s science divisions already have provisions for doing this—for example, Earth sciences missions undergo annual technical health assessments. These assessments need only be moderate in scope, assessing changes since the last review, but the committee noted in its recommendation that a regular assessment is necessary in order to ensure confidence in the extension process.
The committee recognizes that NASA alone cannot change this cadence and that it ultimately requires a change of language in NASA authorization bills. The committee believes that NASA can work with Congress to seek a change in the authorization language to allow for a 3-year cadence and that this will have a significant impact on reducing the burden and improving the overall efficiency of NASA’s mission extension process.
In some divisions, there is greater prioritization of new or ground-breaking science, whereas in other divisions continuity of observations may be emphasized. Once again, the committee concluded that flexibility was important for NASA to maximize the efficiency and effectiveness of its mission extension process and obtain the maximum return for its investment.
Overall, the committee was impressed with the way NASA SMD conducts its mission-extension review process and how much the four SMD divisions communicate amongst themselves regarding the reviews. With respect to the membership of the Senior Review panels, the committee concluded that there are several criteria that SMD can implement and standardize across the divisions.
As the divisions have performed more Senior Reviews, the details of the process have become more stable from cycle to cycle. Stability includes consistency of information requested, proposal format, timing for the various stages, and so on. Maintaining best practices through regular interactions and feedback between NASA Headquarters, the mission teams, and review panels will help to ensure that this consistency is maintained while also providing opportunities for incremental improvements to the process.
The committee was charged with evaluating the balance between prime and extended missions. Even though there is no formal definition for “optimal” balance, the committee concluded that the current balance between prime and extended missions is excellent, particularly with the high-quality science being returned at relatively modest cost for the extended missions. Extended missions represent only approximately 12 percent of the NASA SMD budget and provide a very high scientific return.
The committee’s task also asked for an assessment of generally applicable current, and as yet unidentified, cost reductions that NASA could implement. In general, the committee concluded that many cost reduction options are already identified and implemented by both prime and extended missions. For example, colocating mission operations centers to a greater extent than is already done might provide added efficiency (and cost savings) in some cases. However, as the committee was told, the location and responsibilities of the science team are also important factors, and there might be added efficiencies and synergies when science and operations centers are colocated, so flexibility is required regarding sites for science and operations centers. Many extended missions have adopted innovative planning and operations approaches that translate to good or best practices (e.g., early awareness of the potential for extended missions while developing ground system and flight procedures, generating staffing plans, and preparing for reduced budgets during the extended phase) that may be applicable to other missions. Each mission has unique features, so no single approach will be optimal for all.
The committee notes that repurposing extended missions to perform new science observations and missions is an extremely cost-effective approach for addressing new scientific opportunities and national interests.
With the expectation that most missions will be eligible for extension, investment in the development of standard procedures and templates during the prime phase can be a highly effective way to control long-term operations costs and limit the risks introduced by implementing new procedures specifically developed for extended operations. Some NASA divisions permit missions entering into or already in extended phase to accept increased risk, which is an inevitable consequence for aging spacecraft and science instruments and at least for some divisions, an acceptable option in the context of reduced budgets. The committee supports NASA’s current approach to establishing requirements and designs for prime phase and budgeting for extended missions, finding that it has many positive attributes and provides a very high return on investment.
Experience and knowledge gained during the prime phase typically result in lower costs for extended mission operations, but there may be counteractive effects that can create upward pressure on operational costs. After the first two Senior Reviews, most missions have implemented all (or almost all) practical steps to reduce costs. Further budget cuts often then result in disproportionate cuts to project-funded science activities, increasing risks that science will be diminished or not performed at all.
This report consists of five chapters. Chapter 1 introduces the issues. Chapter 2 describes some of the valuable science discoveries that have been made during the extended phase of science missions. Chapter 3 discusses the Senior Review process and the requirement for conducting reviews every 2 years. Chapters 4 and 5 address the issues identified in the statement of task concerning balance and innovative approaches to reducing costs. The committee’s recommendations appear below and in their relevant chapters.
Recommendation: NASA’s Science Mission Directorate (SMD) policy documents should formally articulate the intent to maximize science return by operating spacecraft beyond their prime mission, provided that the spacecraft are capable of producing valuable science data and funding can be identified within the SMD budget. (Chapter 5)
Recommendation: NASA should strongly support a robust portfolio of extended-phase science missions. This support should include advance planning and sufficient funding to optimize the scientific return from continued operation of the missions. (Chapter 2)
Recommendation: If a Senior Review recommends termination of a mission due to funding limitations rather than limited science return, NASA should allow the team to re-propose with an innovative, possibly less scientifically ambitious, approach at reduced operational cost and increased risk. (Chapter 3)
Recommendation: NASA science divisions should be allowed to conduct reviews out of phase to allow for special circumstances and should have the added flexibility in organizing their reviews to take advantage of unique attributes of each division’s approach to science. (Chapter 3)
Recommendation: Each of the divisions should ensure that their timelines allocate sufficient time for each stage of the Senior Review process, including a minimum of 6 to 8 weeks from distribution of proposals to the panels until the panel meets with the mission teams. The panels should have at least 4 weeks to review the proposals and to formulate questions for the mission teams, and the mission teams should be allocated at least 2 weeks to generate their responses to the panel questions. (Chapter 3)
Recommendation: NASA should conduct full Senior Reviews of science missions in extended operations on a 3-year cadence. This will require a change in authorizing language, and NASA should request such a change from Congress. The Earth Science Division conducts annual technical reviews. The other divisions should assess their current technical evaluation processes, which may already be sufficient, in order to ensure that the divisions are fully aware of the projected health of their spacecraft, while keeping these technical reviews moderate in scope and focused on changes since the preceding review. (Chapter 3)
Recommendation: In order to obtain best value for money, NASA should encourage extended mission proposals to propose any combination of new, ground-breaking, and/or continuity science objectives. (Chapter 3)
Recommendation: NASA’s Science Mission Directorate should assemble Senior Review panels that
- Are comprised primarily of senior scientists knowledgeable about and experienced in mission operations so as to ensure that the operational context of the science being proposed and evaluated is considered in the review (individuals with operations and/or programmatic expertise may also be included as needed);
- Are assembled early to avoid or accommodate conflicts of interest, and ensure availability of appropriate expertise;
- Include some continuity of membership from the preceding Senior Review to reap advantage of corporate memory; and
- Include some early-career members to introduce new and important perspectives and enable them to gain experience for future Senior Reviews.
Recommendation: NASA’s Science Mission Directorate division directors should continue to communicate among themselves to identify and incorporate best practices across the divisions into the Senior Review proposal requirements and review processes and procedures. (Chapter 3)
Recommendation: In its guidelines to the proposal teams and the Senior Review panels, NASA should state its intention to solicit feedback from its proposal teams and review panels about the suitability of the proposal content and review process. After obtaining such feedback, NASA should respond and iterate as needed with stakeholders to improve the review process, where possible. (Chapter 3)
Recommendation: NASA should continue to provide resources required to promote a balanced portfolio, including a vibrant program of extended missions. (Chapter 4)
Recommendation: NASA should provide open communications and dissemination of information based on actual experience with extended missions so that all missions are aware of and able to draw on prior effective practices and procedures, applying them during development of ground systems and flight
procedures, as well as when formulating staffing and budgetary plans for the prime and extended-mission phases. (Chapter 5)
Recommendation: NASA should continue to encourage and support extended missions that target new approaches for science and/or for national needs, as well as extended missions that expand their original science objectives and build on discoveries from the prime phase mission. (Chapter 5)
Recommendation: NASA should continue to assess and accept increased risk for extended missions on a case-by-case basis. The headquarters division, center management, and the extended-mission project should discuss risk posture during technical reviews and as part of the extended mission and subsequent Senior Review proposal preparation process and should make all parties fully aware of all cost, risk, and science trade-offs.(Chapter 5)
Recommendation: NASA should continue anticipating that missions are likely to be extended and identify funding for extended missions in the longer-term budget projections.(Chapter 5)
Recommendation: Given the demonstrated science return from extended missions, NASA should continue to recognize their scientific importance and, subject to assessments and recommendations from the Senior Reviews, ensure that, after the first two Senior Reviews, both operations and science for high-performing missions are funded at roughly constant levels, including adjustments for inflation. (Chapter 5)
NASA’s extended science missions provide excellent science return and, in some instances, also meet national interests and needs. Missions that have already been paid for and successfully launched can continue to provide very high return at a modest incremental cost. Although the committee has recommended a number of refinements, including a 3-year cadence for Senior Reviews, there is a strong consensus that NASA’s approach to extended missions is fundamentally sound and merits continued support.