For different size regimes, some overarching conclusions can be drawn:
Ninety percent completeness for the detection of potentially hazardous NEOs 140 meters in diameter or larger—In theory, this goal could be achieved by 2020. Experience suggests, however, that the congressional goal cannot be met by 2020. Most options could complete this survey within 20 years, including those involving only ground-based telescopes.
Ninety percent completeness for the detection of potentially hazardous NEOs 50 meters in diameter or larger—All space-based or combination space-based and ground-based options could complete this survey, although not all in 20 years. No currently planned ground-based-only option is able to complete this survey.
Ninety percent completeness for the detection of potentially hazardous NEOs 30 meters in diameter or larger—No combination of telescope systems discussed above can complete this survey within 20 years, although significant progress could be made.
Combined ground- and space-based surveys have a number of advantages. Such surveys discover more NEOs of all sizes, including a substantial number smaller than 140 meters in diameter. These combined surveys also provide more characterization data about the entire NEO population. With both infrared and visible data for most targets, it would be possible to obtain accurate diameter estimates for all objects, as well as measurements of their albedos and their surface and thermal properties. These high-value characterization data could help to guide mitigation campaign studies. Additionally, a dual survey provides much information on the population of objects smaller than 140 meters in diameter.
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