Finding: The current near-Earth object surveys cannot meet the goals of the 2005 George E. Brown, Jr. Near-Earth Object Survey Act directing NASA to discover 90 percent of all near-Earth objects 140 meters in diameter or greater by 2020.
The charge from Congress to the NRC committee was stated as two tasks (see the Preface for the full statement of task). The first asks for the “optimal approach” to completing the George E. Brown, Jr. Near-Earth Object Survey. The second asks for the same approach to developing a capability to avert an NEO-Earth collision and for options that include “a significant international component.”
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. Recognizing this fact, the committee first took a broad look at all aspects of the hazards to Earth posed by NEOs and then decided on responses to the charge. The body of this report contains extensive discussions of these many issues. This summary concentrates on responses to the charge and at the end provides a few comments on some of the other main conclusions drawn from the report.
Regarding the first task of its charge, the committee concluded that it is infeasible to complete the NEO census mandated in 2005 on the required time scale (2020), in part because for the past 5 years the administration has requested no funds, and the Congress has appropriated none, for this purpose. The committee concludes that there are two primary options for completing the survey:
Finding: The selected approach to completing the George E. Brown, Jr. Near-Earth Object Survey will depend on nonscientific factors:
If the completion of the survey as close as possible to the original 2020 deadline is considered more important, a space mission conducted in concert with observations using a suitable ground-based telescope and selected by peer-reviewed competition is the better approach. This combination could complete the survey well before 2030, perhaps as early as 2022 if funding were appropriated quickly.
If cost conservation is deemed more important, the use of a large ground-based telescope is the better approach. Under this option, the survey could not be completed by the original 2020 deadline, but it could be completed before 2030. To achieve the intended cost-effectiveness, the funding to construct the telescope must come largely as funding from non-NEO programs.
Multiple factors will drive the decision on how to approach completion of this survey. These factors include, but are not limited to, the perceived urgency for completing the survey as close as possible to the original 2020 deadline, the availability of funds to complete the survey, and the acceptability of the risk associated with the construction and operation of various ground- and space-based options.
Of the ground-based options, the Large Synoptic Survey Telescope (LSST) and the Panoramic Survey Telescope and Rapid Response System, mentioned in the statement of task, and the additional options submitted to the committee in response to its public request for suggestions during the beginning of this study, the most capable appears to be the LSST. The LSST is to be constructed in Chile and has several science missions as well as the capability of observing NEOs. Although the primary mirror for the LSST has been cast and is being polished, the telescope has not been fully funded and is pending prioritization in the astronomy and astrophysics decadal survey of the NRC that is currently underway.
Unless unexpected technical problems interfere, a space-based option should provide the fastest means to complete the survey. However, unlike ground-based telescopes, space options carry a modest launch risk and a more limited lifetime: ground-based telescopes have far longer useful lifetimes and could be employed for continued NEO surveys and for new science projects. (Ground-based telescopes generally have an annual operating cost that is approximately 10 percent of their design and construction costs.)