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Evaluating the Effectiveness of the Mission-Extension Paradigm

The mission-extension paradigm is based on planning and funding missions only up through the end of a nominal lifetime, with a mission-extension decision, to determine whether operations will be extended, made as the mission approaches the end of this nominal lifetime. The Committee on Extending the Effective Lifetimes of Earth Observing Research Missions first looked at whether this process is indeed an effective approach to funding and managing missions over their life cycles. Other mission-planning and -funding paradigms can certainly be envisioned. For example, a simpler approach could be to fund missions for the planning horizon of the federal budget, operating them as long as they were functioning, unless a specific decision was made to terminate a mission.

REASONS FOR MISSION EXTENSION

It is common today for a well-designed mission—including its spacecraft and instruments—to be operating properly at the end of its design life. When this happens, there are often many reasons for extending operations. For Earth science, these generally fall into one of two categories.

The first category of reasons for extending operations covers scientific considerations. Completely new scientific capabilities often are identified by analyzing the data received during the nominal mission lifetime. It is also common to find that a measurement series started during nominal mission lifetime would have considerable scientific value if it were extended over a longer period of time. In some cases, other missions or measurements may be achieving significant benefit from synergy with the mission that has reached the end of its nominal lifetime. Finally, it is not unusual that highly desirable scientific investigations were simply eliminated from an original mission plan owing to cost constraints. Because the cost of extending mission operations is only a fraction of that required for developing new systems,1 approving mission extensions provides a means for achieving high-quality science for relatively low cost in many cases. Box 2.1 provides historic examples of missions extended for scientific reasons.

The second category of reasons for extending operations is associated with the value of the measurements for applications, future operational use, and other-agency or international partners’ objectives. For a number of missions today, the data are already used by the National Oceanic and Atmospheric Administration (NOAA) and other agencies on a quasi-operational basis, and mission extension serves to continue the availability of this type of national capability. For other missions, it may be of benefit to continue evaluating use of the data in order to determine if a future operational system is warranted. Box 2.2 provides historic examples of missions extended for applications and operational reasons. The dependence on international partners to fund missions also means that their objectives must be considered in any mission-extension decision.

1  

Mission operations for small to medium Earth-orbiting missions are typically $2 million to $5 million per year.



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Extending the Effective Lifetimes of Earth Observing Research Missions 2 Evaluating the Effectiveness of the Mission-Extension Paradigm The mission-extension paradigm is based on planning and funding missions only up through the end of a nominal lifetime, with a mission-extension decision, to determine whether operations will be extended, made as the mission approaches the end of this nominal lifetime. The Committee on Extending the Effective Lifetimes of Earth Observing Research Missions first looked at whether this process is indeed an effective approach to funding and managing missions over their life cycles. Other mission-planning and -funding paradigms can certainly be envisioned. For example, a simpler approach could be to fund missions for the planning horizon of the federal budget, operating them as long as they were functioning, unless a specific decision was made to terminate a mission. REASONS FOR MISSION EXTENSION It is common today for a well-designed mission—including its spacecraft and instruments—to be operating properly at the end of its design life. When this happens, there are often many reasons for extending operations. For Earth science, these generally fall into one of two categories. The first category of reasons for extending operations covers scientific considerations. Completely new scientific capabilities often are identified by analyzing the data received during the nominal mission lifetime. It is also common to find that a measurement series started during nominal mission lifetime would have considerable scientific value if it were extended over a longer period of time. In some cases, other missions or measurements may be achieving significant benefit from synergy with the mission that has reached the end of its nominal lifetime. Finally, it is not unusual that highly desirable scientific investigations were simply eliminated from an original mission plan owing to cost constraints. Because the cost of extending mission operations is only a fraction of that required for developing new systems,1 approving mission extensions provides a means for achieving high-quality science for relatively low cost in many cases. Box 2.1 provides historic examples of missions extended for scientific reasons. The second category of reasons for extending operations is associated with the value of the measurements for applications, future operational use, and other-agency or international partners’ objectives. For a number of missions today, the data are already used by the National Oceanic and Atmospheric Administration (NOAA) and other agencies on a quasi-operational basis, and mission extension serves to continue the availability of this type of national capability. For other missions, it may be of benefit to continue evaluating use of the data in order to determine if a future operational system is warranted. Box 2.2 provides historic examples of missions extended for applications and operational reasons. The dependence on international partners to fund missions also means that their objectives must be considered in any mission-extension decision. 1   Mission operations for small to medium Earth-orbiting missions are typically $2 million to $5 million per year.

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Extending the Effective Lifetimes of Earth Observing Research Missions BOX 2.1 Historic Examples of the Scientific Basis for Extending Missions Data set extension and continuity through overlap. Measurements of solar irradiance tell us how solar variations contribute to climate change. The sensitivity of these measurements is such that any increased overlap between older instruments, such as ACRIM on the UARS mission and TIM on the recently launched SORCE mission, provides substantially improved science. TOPEX/Poseidon was extended in 1996 because its successor, Jason, was not ready for launch. Ensuring an overlap between the two missions allowed for calibration in order to establish that both satellites were measuring the same physical phenomena, significantly increasing the value of the Jason data. Improved sampling. The TOPEX/Poseidon spacecraft also was moved to interleave between the ground tracks of Jason, providing improved spatial coverage and resolution. Unique measurements. UARS was launched in 1991 with a 3-year design life, but it has already been extended for more than a decade because its six operating instruments offer the sole capability of profiling atmospheric chlorine and fluorine for ozone monitoring. Unanticipated science. QuikSCAT was launched in 1999 to monitor ocean winds, but scientists are now exploring whether the scatterometer can also measure the freeze-thaw transition at high latitudes, which is a sensitive measure of climate change. Synergy of multiple instruments. The MODIS instrument on the Terra mission provides a global land cover data set. The higher spatial detail provided by the ETM+ instrument on the Landsat mission, launched many years before the Terra mission, has proven essential to algorithm training for this data set. NOTE: Definitions of the acronyms are provided in Appendix C. BOX 2.2 Historical Examples of the Applications and Operational Basis for Extending Missions Established operational utility. The National Oceanic and Atmospheric Administration (NOAA) currently makes extensive use of the NASA QuikSCAT mission for providing ocean surface wind measurements. NOAA will provide these measurements itself using a radiometer instrument onboard NPOESS, but that capability is not expected to be available until at least 2010. Demonstration of operational potential. The TRMM mission, launched in 1997, monitors rainfall in the Tropics. The initial potential of TRMM for improving predictions of hurricane intensity, among other things, was demonstrated during the 3-year nominal lifetime of the mission. But its full potential and the strong need for a follow-on operational capability were only revealed as the extended mission life enabled the sampling of a greater number and variety of hurricanes and tropical cyclones. Unanticipated applications. Following the 1998 launch of Terra, scientists began to use MODIS data for discovering wildfires and monitoring their spread. The capability proved so useful that a rapid-response data communications system was established with a U.S. Forest Service center in Salt Lake City. This system has been expanded to include routine MODIS monitoring of the conditions that lead to wildfires. NOTE: Definitions of the acronyms are provided in Appendix C.

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Extending the Effective Lifetimes of Earth Observing Research Missions UNIQUE CONSIDERATIONS FOR EARTH SCIENCE MISSIONS As the examples in Box 2.2 illustrate, establishing a standardized process for extending missions involves additional factors for Earth science compared with the situation for space science. For space science, the community impacted by the mission-extension decision is largely limited to those scientists in research disciplines for which the mission was originally conceived and flown. For Earth science, however, NASA data often are used by numerous other government agencies, and many such missions are relied on by international or other partners as precursors to follow-on systems or activities. TRADING DESIRABILITY AGAINST FEASIBILITY A mission-extension decision is always a trade-off. From the mission perspective, one needs to balance the desirability of extending the mission’s nominal lifetime against the feasibility of doing so. Critical considerations include (1) the ability to complete an extended mission, taking into account the functional status of the spacecraft and the instruments; (2) the cost of extending the mission; and (3) the risk of extending the mission, particularly with respect to de-orbiting issues. These issues are rarely equal in importance, and the ability to de-orbit safely has become a key factor in recent years.2 From an overall NASA perspective, the benefits of extending a particular mission also need to be balanced against the use of the same funds for another purpose, in particular for the development of new observational systems.3 A mission-extension decision needs to address all of these complex issues. Mission-extension decisions thus warrant a formal, deliberate, and uniformly applied process that effectively balances benefits against costs and risks. Despite the complexity and importance of the mission-extension decision itself, much of the challenge for any mission-extension process arises from longer-term NASA budgeting issues. The federal budget cycle, under which NASA operates, forces resource requirements to be identified effectively 3 years in advance of when the funds are expended. Yet the desirability and feasibility of a mission extension are typically most clear when the nominal mission is near its end. The tension between these two valid objectives—advanced budget planning and just-in-time decision making—presents a fundamental problem that must be addressed for an effective mission-extension process to be achieved. USE OF THE MISSION-EXTENSION PARADIGM The committee found that, when all factors are considered, the mission-extension paradigm provides an effective means to plan and fund mission life cycles. In particular, it allows NASA to dynamically reallocate resources on the basis of evolving priorities. Yet use of the mission-extension paradigm does not preclude other approaches to funding a mission life cycle, and NASA would benefit from considering other approaches in particular cases. Such cases could include missions for which it is known prior to launch that the mission will likely continue to provide substantial benefits if it exceeds its nominal lifetime. This is often true for missions with known operational utility but no funded operational follow-on mission.4 It is also true for missions with science returns that are not expected to decline over time, such as those contributing to long time-series data sets. 2   NASA safety guidelines call for a controlled reentry when a satellite would pose a greater than 1 in 10,000 chance of harming people or damaging property on the ground if it were left to reenter in an uncontrolled manner. 3   Much of the controversy around the extension of the Tropical Rainfall Measuring Mission (TRMM) has been associated with the trade-off between extending TRMM operations and using the resources to begin a TRMM follow-on mission. 4   The NASA Quick Scatterometer (QuikSCAT) satellite is an excellent example: NOAA has routinely used QuikSCAT ocean surface wind data, but there are no plans for an operational active scatterometer.

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Extending the Effective Lifetimes of Earth Observing Research Missions Finding. NASA’s mission-extension paradigm for accomplishing research missions—which is based on planning and funding nominal operational lifetimes, with a separate decision process for extending operations when this nominal lifetime is exceeded—is fundamentally sound. Implementation of the mission-extension paradigm warrants a structured and uniformly applied process that balances the desirability of extending a mission against the feasibility of doing so. An effective mission-extension process must carefully reconcile the long lead times required for budget planning against the benefits of deciding as late as possible which missions will be extended. Earth science missions have unique considerations, such as future operational utility and interagency partnerships, that distinguish them from space science missions; these considerations should be explicitly included in a mission-extension decision-making process. Recommendation. NASA should continue to formally plan and fund research missions on the basis of the mission-extension paradigm, but it should (1) ensure that the unique requirements of Earth science missions are satisfied and (2) investigate alternative approaches to mission life-cycle funding in particular cases.