LUNAR EXPLORATION CONCLUDED

Apollo 15's Science Dividend

It was clear even before Scott and his crew returned that Apollo 15 had surpassed all prior missions in both the quantity and variety of information it returned. More than 350 individual soil and rock samples aggregating 77 kilograms (170 pounds), ranging in size from 1 or 2 grams (0.03 to 0.06 ounce) to more than 9.5 kilograms (21 pounds) and taken from two distinct selenological regions (the mare plain and the foot of Hadley Delta), were the richest geological haul of the program.46 The seismometer and the heat flow probes emplaced with the surface experiments package were important in obtaining data on the moon's interior, while the instruments Al Worden had operated in lunar orbit gathered information on the chemical composition of large areas on the front and back sides of the moon.

If the scientists had been unhappy with MSC's cooperation in the early missions, they were overjoyed with the way Apollo 15 was conducted, and several graciously congratulated MSC on it. Gerald Wasserburg of Caltech wrote to Robert R. Gilruth to offer his congratulations "on one of the most brilliant missions in space science ever flown." He particularly praised the fairness and wisdom of the decisions made during the astronauts' explorations, even though he had not always got what he wanted.47 Larry A. Haskin, vice chairman of the lunar sample analysis planning team, told Gilruth that

Scott and Irwin had not been on the surface very long before . . . we felt comfortable and confident that the scientific aspects of the mission were in competent hands. . . . We always felt that the decisions made in real time . . . were fair with respect to priorities given to various activities and that the mission was wen balanced.

Preliminary examination of the samples began as soon as the containers were returned. Documentation of these samples was unusually complete, except for some taken on the last traverse when time ran short. Taking advantage of the fact that the astronauts were not quarantined after this mission, the preliminary examination team asked Scott and Irwin to be present while the containers were opened, to provide whatever information they could remember about some of the less well-documented specimens while the circumstances were still fresh in their minds.49

The preliminary examination team concluded that three distinct types of structures had been sampled at Hadley: the Apennine Front, which had been produced by collision of an asteroid-sized object with the moon; a series of horizontal lava flows that filled part of the impact basin; and a ray of ejecta from a large young crater produced after the basin was filled. Samples from the mountain front were very diverse, including both breccias and igneous rocks. Those from the mare plain, where Falcon landed, were of two basic types: basaltic rocks and glass-coated breccias. The "Genesis Rock," so designated by the press, did turn out to be an extremely pure anorthosite substantially altered by shock, which suggested that it was involved in a severe impact after it crystallized. Its age was determined to be 4.15 billion years, with a possible error of 0.2 billion either way, making it the oldest whole rock so far returned from the moon.50

The core tubes, one containing a 2.4-meter (almost 8-foot) section of the soil, were not opened during the preliminary examination, but x-ray examination indicated 58 individual layers, from 0.5 to 21 centimeters (0.2 to 8.25 inches) thick, showing that the soil contained a substantial stratigraphic record.51

Instruments in the service module provided information about the large-scale chemical variations across the lunar surface. The x-ray fluorescence experiment measured the x-rays emitted by light elements (magnesium, aluminum, and silicon particularly) when struck by x-rays from the sun. From these data scientists could determine the ratio of aluminum to silicon over large areas under the orbit of the command and service module. Initial examination of the results found distinct chemical differences between the maria and the highlands. The highlands showed an aluminum/silicon ratio characteristic of anorthosite, which, according to some theories, was formed in the first major event of the moon's geologic evolution. The maria, on the other hand, were chemically different; sample analysis showed them to be basalts formed by lava flows, and the x-ray fluorescence results were consistent with this interpretation.52

The preliminary examination team completed the first stage of its work with descriptions of more than 50 rocks larger than 50 grams (1.7 ounces) correlated with the astronauts' descriptions and photographs at the end of August. MSC recommended release of samples to 20 research teams as soon as possible, since their results would be useful in planning future lunar surface activity.•53 The rest of the samples were less time-critical and were released to principal investigators two months later.54

46. Apollo 15 Preliminary Examination Team; "The Apollo 15 Lunar Samples: A Preliminary Description," Science 175 (1972):363-75.

47. Gerald Wasserburg to Robert R. Gilruth, Aug. 9, 1971.

48. Larry A. Haskin to Gilruth, Aug. 5, 1971.

49. "Apollo 15 Science Briefing, Manned Spacecraft Center, August 11, 1971, 3:30 PM (CDT)."

50. "The Apollo 15 Lunar Samples"; Petrone to multiple addressees, "Report of Preliminary Scientific Results of Apollo 15," Sept. 28, 1971, with encl., "Preliminary Scientific Results of Apollo 15 (As of September 24, 1971)."

51. "The Apollo 15 Lunar Samples."

52. I. Adler, J. Trombka, J. Gerard, R. Schmadebeck, P. Lowman, H. Blodgett, L. Yin, E. Eller, R. Lamothe, P. Gorenstein, and P. Bjorkholm, "X-Ray Fluorescence Experiment, Preliminary Report," Goddard Space Flight Center X-641-71-421, October 1971.

53. Gilruth to Myers, TWX, Aug. 31, 1971.

54. "Distribution of Apollo 15 Lunar Samples," NASA Release 71-223, Nov. 9, 1971.

Email darren@apolloexplorer.co.uk