On Robotic Lunar Precursor Missions of the Office of Exploration

Scientific Assessment of Proposed Robotic Lunar Missions of NASA'S Office of Exploration

The Space Studies Board's Committee on Planetary and Lunar Exploration (COMPLEX) met in Washington, D.C., on April 27-28, 1992, to review the robotic lunar probes proposed by NASA's Office of Exploration (OEXP) as precursor missions for its program of human exploration. The committee's intention was to determine the extent to which OEXP's program was consistent with recommendations for lunar science outlined in previous COMPLEX reports. 1,2,3

During its deliberations, COMPLEX was briefed on the current status of OEXP's lunar exploration program by Dr. Michael D. Griffin, NASA's Associate Administrator for Exploration. The committee was particularly keen to discuss the Lunar and Planetary Institute (LPI) report, Workshop on Early Robotic Missions to the Moon. 4 This report, sponsored by OEXP, outlines the instrument complement for a flight program of two lunar orbiters and a single lander intended by OEXP to gather scientific and engineering data necessary to facilitate the safe return of humans to the Moon. While COMPLEX recognizes that these are not primarily scientific missions, they have the potential to gather data addressing scientific questions discussed in past COMPLEX reports.

The committee concludes that the LPI workshop's recommendations for the instrument payloads of Orbital Missions 1 and 2 are responsive to the priorities for lunar science stated in past COMPLEX reports. In particular, Orbiter Mission 1 would address COMPLEX's highest-priority goal for lunar exploration, to "determine the chemistry of the lunar surface on both a global and regional scale." 5

The committee has some concerns, however, about instrumentation proposed to perform these observations. The LPI report states that the instrument of choice is a "gamma-ray/neutron spectrometer with a germanium detector." COMPLEX concurs with this preference but disagrees with the report's subsequent advice that "if development concerns arise regarding this detector, we recommend use of a NaI detector with subsequent flight of a germanium system." 6 Because the spectral resolution of the germanium detector is far superior to that of the NaI detector, COMPLEX recommends that OEXP fly a germanium detector, even at the expense of a modest launch delay.

With regard to the other proposed instruments for Orbital Missions 1 and 2, COMPLEX finds that the proposed visible and infrared imaging spectrometers as well as the imaging, laser altimetry, and gravity mapping (using two spacecraft for far-side gravity determinations) experiments would satisfy high-priority measurement objectives that COMPLEX has presented previously. 7

The lander mission appears to have scientific value, but its present lack of definition precludes an adequate assessment of its potential contribution to the achievement of COMPLEX's objectives.

1 Strategy for Exploration of the Inner Planets: 1977-1987, Committee on Planetary and Lunar Exploration, Space Science Board, National Academy of Sciences, Washington, D.C., 1978.

2 1990 Update to Strategy for Exploration of the Inner Planets, Committee on Planetary and Lunar Exploration, Space Studies Board, National Academy Press, Washington, D.C., 1990

3 Assessment of Solar System Exploration Programs: 1991, Committee on Planetary and Lunar Exploration, Space Studies Board, National Academy Press, Washington, D.C., 1991, page 3.

4 Workshop on Early Robotic Missions to the Moon, Lunar and Planetary Institute, Houston, Texas, February 1992; proceedings of a workshop organized by NASA's Office of Exploration.

5 Reference 3, page 7.

6 Reference 4, page 2.

7 Reference 2, page 18.

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