supporting further reconnaissance missions is that they can draw on the technological heritage of previous spacecraft and thus have lower costs.

Augmentation 1: Develop technological advances in spacecraft capabilities, including nonchemical propulsion and autonomous navigation systems, low-power and low-mass analytical instrumentation for remote and in situ studies, and multiple penetrators and other sampling and sample-handling systems to allow low-cost rendezvous and sample-return missions.

The definition and development of new analytical instruments to be flown on flyby, orbital, and landed spacecraft must be a high priority. In situ imaging and measurements of physical and chemical properties are the justification for NEO spacecraft missions that do not return samples, and the severe mass and power limitations imposed by smaller spacecraft will demand a new generation of instruments. With increased emphasis on low-cost, rapid-pace, and highly competitive missions, new instrument development is a difficult challenge, and programs such as NASA's Planetary Instrument Definition and Development Program (PIDDP) have to be supported. However, in the case of some NEOs, it may be easier to collect and return samples than to do adequate in situ analyses.

Flight instrument development focused on sampling devices and on autonomous navigation and control systems would enable NEO sample-return missions. Spacecraft and instrument miniaturization and multiple penetrators or landers are among other potential mission-enhancing developments. Nonchemical propulsion concepts hold particular promise for NEO missions. Sampling missions would be most effective if focused on collecting samples from well-characterized geologic units or the subsurface of NEOs and from an object exhibiting cometary behavior. Sample return involves many complex manipulations that pose engineering challenges.

Augmentation 2: Study technical requirements for human expeditions to NEOs.

Human exploration of NEOs would provide considerable improvement in understanding because of the ability to make intensive geologic observations and take carefully chosen samples. The technical requirements for human expeditions to NEOs, although undefined, are intermediate between those for lunar and martian missions. A particularly attractive aspect is that human spaceflight beyond the Moon will probably require incremental steps, and an expedition to a NEO would be of considerably shorter duration and risk and lower in cost than one to Mars.

References

1. Space Studies Board, National Research Council, An Integrated Strategy for the Planetary Sciences: 1995–2010, National Academy Press, Washington, D.C., 1994, p. 3.

2. Space Science Board, National Research Council, Strategy for the Exploration of Primitive Solar-System Bodies—Asteroids, Comets, and Meteoroids: 1980–1990, National Academy Press, Washington, D.C., 1980, p. 52.

3. Space Studies Board and Board on Physics and Astronomy, National Research Council, A Strategy for Ground-Based Optical and Infrared Astronomy, National Academy Press, Washington, D.C., 1995, p. 2.

4. H.Y. McSween, “The role of meteorites in spacecraft missions, and vice versa,” Meteoritics and Planetary Science, 31:272–738, 1997.



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