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Defending Planet Earth: Near-Earth-Object Surveys and Hazard Mitigation Strategies 8 Optimal Approaches This committee was asked to address “the optimal approach to completing the NEO census called for in the George E. Brown, Jr. Near-Earth Object Survey section of the 2005 NASA Authorization Act.” The committee was also asked to address “the optimal approach to developing a deflection [i.e., orbit change] capability.” The committee concluded that there is no way to define “optimal” in this context in a universally acceptable manner: There are too many variables involved that can be both chosen and weighted in too many plausible ways. A key question nevertheless is: Given the low risk over a period of, say, a decade, how much should the United States invest now? This chapter discusses the cost implications of typical solutions that it considered for survey completion and mitigation. A summary of the background on these cost implications is presented first. Government funding, primarily through NASA, now supports a modest, ongoing program of sky surveys to discover and track NEOs. NASA also supports analysis and archiving activities. According to NASA, total expenditures are approximately $4 million annually, which does not include any funding for the Arecibo Observatory in Puerto Rico. As the committee concluded in its interim report and confirmed in this final report, current expenditures are insufficient to achieve the goals established by Congress in the George E. Brown, Jr., Near-Earth Object Survey Act of 2005. The committee was asked and did perform independent cost estimates of the solutions that it considered. However, most of the survey and detection and mitigation options that were cost estimated are technically immature, and cost estimates at this early stage of development are notoriously unreliable. At best, these estimates provide only crude approximations of final costs of pursuing any of these options. The committee therefore did not use these cost estimates in reaching its conclusions. The committee outlined three possible levels of funding and a possible program for each level. These three, somewhat arbitrary, levels are separated by factors of five: $10 million, $50 million, and $250 million annually. $10-million level. The committee concluded that if only $10 million were appropriated annually, an approximately optimal allocation would be as follows: $4 million for continuing ground-based optical surveys and for making follow-up observations on long-known and newly discovered NEOs, including determining their orbits and archiving these along with the observations; the archive would continue to be publicly accessible; $2.5 million to support radar observations of NEOs at the Arecibo Observatory; $1.5 million to support radar observations at the Goldstone Observatory; and
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Defending Planet Earth: Near-Earth-Object Surveys and Hazard Mitigation Strategies $2 million to support research on a range of issues related to NEO hazards, including but not necessarily limited to (see Chapter 6) the study of sky distribution of NEOs and the development of warning-time statistics; concept studies of mitigation missions; studies of bursts in the atmosphere of incoming objects greater than a few meters in diameter; laboratory studies of impacts at speeds up to the highest feasible to obtain; and leadership and organizational planning, both nationally and internationally. The $10-million funding level would not allow on any time scale the completion of the mandated survey to discover 90 percent of near-Earth objects of 140 meters in diameter or greater. Also lost would be any possibility for mounting spacecraft missions—for example, to test active mitigation techniques in situ. (A caveat: The funds designated above to support radar observations are for these observations alone; were the maintenance and operations of the radar-telescope sites not supported as at present, there would be a very large shortfall for both sites: about $10 million annually for the Arecibo Observatory and likely a larger figure for the Goldstone Observatory.) $50-million level. At a $50-million annual appropriations level, in addition to the tasks listed above, the committee notes that the remaining $40 million could be used for the following: Support of a ground-based facility, as discussed in Chapter 3, to enable the completion of the congressionally mandated survey to detect 90 percent of near-Earth objects of 140 meters in diameter or greater by the delayed date of 2030. The $50-million funding level would likely not be sufficient for the United States alone to conduct space telescope missions that might be able to carry through a more complete survey faster. In addition, this funding level is insufficient for the development and testing of mitigation techniques in situ. However, such missions might be feasible to undertake if conducted internationally, either in cooperation with traditional space partners or as part of an international entity created to work on the NEO hazards issue. Accommodating both the advanced survey and a mitigation mission at this funding level is very unlikely to be feasible, except on a time scale extended by decades. $250-million level. At a $250-million annual budget level, a robust NEO program could be undertaken unilaterally by the United States. For this program, in addition to the research program a more robust survey program could be undertaken that would include redundancy by means of some combination of ground-and space-based approaches. This level of funding would also enable a space mission similar to the European Space Agency’s (ESA’s) proposed Don Quijote spacecraft, either alone, or preferably as part of an international collaboration. This space mission would test in situ instrumentation for detailed characterization, as well as impact technique(s) for changing the orbit of a threatening object, albeit on only one NEO. The target could be chosen from among those fairly well characterized by ground observations so as to check these results with those determined by means of the in situ instruments. The committee assumed constant annual funding at each of the three levels. For the highest level the annual funding would likely need to vary substantially as is common for spacecraft programs. Desirable variations of annual funding over time would likely be fractionally lower for the second level, and even lower for the first level. How long should funding continue? The committee deems it of the highest priority to monitor the skies continually for threatening NEOs; therefore, funding stability is important, particularly for the lowest level. The second level, if implemented, would likely be needed at its full level for about 4 years in order to contribute to the completion of the mandated survey. The operations and maintenance of such instruments beyond this survey has not been investigated by the committee. However, were the Large Synoptic Survey Telescope to continue operating at its projected costs, this second-level budget could be reduced. The additional funding provided in the third and highest level would probably be needed only through the completion of the major part of a Don Quijote-type mission, under a decade in total, and could be decreased gradually but substantially thereafter. Finding: A $10-million annual level of funding would be sufficient for continuing existing surveys, maintaining the radar capability at the Arecibo and Goldstone Observatories, and supporting a modest level of research on the hazards posed by near-Earth objects. This level would not allow the achievement of the
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Defending Planet Earth: Near-Earth-Object Surveys and Hazard Mitigation Strategies goals established in the George E. Brown, Jr. Near-Earth Object Survey Act of 2005 on any time scale. A $50-million annual level of funding for several years would likely be sufficient to achieve the goals of the George E. Brown, Jr. Near-Earth Object Survey Act of 2005. A $250-million annual level of funding, if continued for somewhat under a decade, would be sufficient to accomplish the survey and research objectives, plus provide survey redundancy and support for a space mission to test in situ characterization and mitigation.
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