Miniature Laser Retro-Reflector Arrays (LRA) for Lunar Landers

Small laser retro-reflector arrays (LRA) on lunar landers can serve as permanent fiducial markers for the landing sites. The arrays can be tracked from an orbiting lidar to within a few centimeters to precisely geolocate the lander and the on-board science experiments. The LRA can also be spotted by a flash lidar on future landers as precision landmarks for guidance and navigation when landing at the same site or a nearby location. Although these LRAs are too small to be tracked from Earth, they can be used to establish a geodetic network on the Moon when tracked by future orbiting lidar that are designed to track both the large and small LRAs. Small LRAs can also be deployed on an asteroid as precision landmarks and be tracked by an orbiting or co-orbiting lidar to precisely measure the orbit, rotation speed and axis, and other geophysical properties of the asteroid.

A set of small and lightweight laser retro-reflector arrays (LRA) were fabricated and tested for use on lunar landers under NASA's Commercial Lunar Payload Service (CLPS). Each LRA contains eight 1.27-cm diameter corner cubes on a dome shaped aluminum structure. The LRA is 5.0 cm in diameter at the base, 1.6 cm in height and 21 g in mass. They underwent a series of environmental tests to verify they can withstand the vibration during launch and landing and remain functional on the lunar surface for several decades. To simulate thermal conditions on the lunar surface, the arrays were thermally-cycled in vacuum from 85 K to 385 K. They were also exposed to gamma radiation to a total accumulated dose of 17.8 Mrad(Si) and showed no degradation. The optical performance of the retro-reflectors were verified using an optical interferometer. The far field patterns of the arrays were tested using a long-focal-length collimator and a camera at both 532 nm and 1064 nm laser wavelengths. The optical cross section of the LRAs are sufficient for tracking by an orbiting laser altimeter, such as the Lunar Orbiter Laser Altimeter (LOLA), from a few hundred km distance. These LRAs on the lunar landers are expected to remain functional and serve the fiducial marks on the Moon for many decades to come.