Longevity validation of the LOLA laser design by extended vacuum testing of the LOLA engineering model laser

The Lunar Orbiter Laser Altimeter (LOLA) is one of seven instruments aboard the Lunar Reconnaissance Orbiter (LRO) spacecraft with the objectives to determine the global topography of the lunar surface at high resolution, measure landing site slopes and search for polar ices in shadowed regions. The LOLA laser transmitter is a passively Q-switched crossed-Porro resonator. All components used in the laser have space flight heritage. The flight laser bench houses two oscillators (a primary and a cold spare) that are designed to operate sequentially during the mission. If the primary laser can no longer provide adequate scientific data products, the secondary laser will be turned on. The baseline mission calls for LOLA (and LRO) to spend about one year studying the Moon. Since LOLA operates at 28 Hz, the laser system needs to produce approximately one billion pulses during the primary one year mission. To validate that the LOLA laser design is capable of meeting this requirement, the LOLA Engineering Model (EM) laser has been subjected to extended operation testing in vacuum. In this paper we will summarize the longevity validation test effort of the LOLA EM laser.