Laser Ranging Retroreflector

Description

The purpose of this experiment was to permit ground-based stations to conduct short-pulse laser ranging to a corner reflector array on the lunar surface at the Fra Mauro site. This instrument, those at Apollo 11 (Tranquility base), and at the Apollo 15 site in the Hadlye/Apennine region provided a network of stations (well-separated in longitude and latitude) to permit a complete geometrical separation of the lunar librations. The reflectors permitted a discrimination of the 3-yr physical librations. They also provided information about the earth and its continental drift motions, as well as very accurate determinations of the earth-moon-distance and the moon's orbital motions. The earth's north pole position could be determined to plus or minus 15 cm. The instrument was an array of 100 small fused-silica corner cubes, each 3.8 cm in diameter. It was deployed on the first EVA, 30 m west of the central station (200 m west of the LM), was leveled, and was faced toward the earth. Each corner cube reflected light parallel to the incident direction, insuring that the reflected laser pulse returned to its place of origin on the earth.