Development Effort of the Lunar Orbiter Laser Altimeter Laser Transmitter
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Development Effort of the Lunar Orbiter Laser Altimeter Laser Transmitter George B Shaw, Anthony W Yu, and Anne-Marie D Novo-Gradac Laser & Electro-Optics Branch, NASA Goddard Space Flight Center, Mail Code 554, Greenbelt, MD, 20771 ABSTRACT The Lunar Orbiter Laser Altimeter (LOLA) is one of six instruments on the Lunar Reconnaissance Orbiter (LRO) 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. The flight laser beryllium bench houses two oscillators (a primary oscillator and a cold spare). The two oscillators are designed to operate sequentially during the mission. The secondary laser will be turned on if the primary laser can no longer provide adequate scientific data products. All components used in the laser have space flight heritage. In this paper we will summarize the development effort of the LOLA laser including the material choice, design criteria and contamination control as applied to the flight laser build. INTRODUCTION Announced in 1961 and ended in 1975, NASA’s Apollo program successfully conducted six manned landings on the Moon between 1969 and 1972. In early 2004, NASA defined its new Vision for Space Exploration whose overarching strategy is to conduct investigations and prepare for future human exploration of the Moon, Mars and beyond. A manned mission to the Moon is slated to occur by 2020, but could happen as early as 2015. NASA’s return to the moon is initiated with the Lunar Reconnaissance Orbiter (LRO) [1,2]. The spacecraft is scheduled to be launched from the Kennedy Space Center in late 2008 and will spend at least a year mapping the surface of the Moon. Data from the six instruments aboard the orbiter will be evaluated to help select safe landing sites for future manned missions, identify prospective lunar resources and study the Moon’s radiation environment. The LRO (figure 1(a)) baseline mission is one Earth year at 50 ± 20 km circular, polar orbit.
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Figure 1. (a) Depiction of LRO showing the six scientific instruments as well as the Mini-RF technology demonstration; (b) Rendering of the LRO spacecraft in lunar orbit.
Lunar Orbiter Laser Altimeter The Lunar Orbiter Laser Altimeter (LOLA) is one of seven instruments on the LRO spacecraft. The LOLA mission objectives are to produce a high resolution three-dimensional map of the Moon’s surface, measure slopes and surface roughness of potential landing sites, and search for the presence of water ice in permanently shadowed regions. The LOLA instrument shown in figure 2 (a) pulses a single laser through a diffractive optical element (DOE) [3] to produce five beams that illuminate the lunar surface. For each beam, LOLA measures time of flight (range), pulse spreading (surface roughness), and transmit/return energy (surface reflectance). With its two-dimensional spot pattern (figure 2 (b)), LOLA unambiguously determines s
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