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A lunar laser system is being developed for Air Force Cambridge Research Laboratories. It has been designed to detect, photoelectrically and photographically, ruby laser pulses which are retro-reflected from optical cube corners loca-ted on the moon. From criteria established for range and photography experiments, designed laser instrumentation is combined with selected transmitting and receiving optics and retroreflectors to form the system. Return signals can be photographed at times of favorable combinations of light aberration and local seeing conditions. They can be detected by a receiving photomultiplier on a one return basis for range measurements under most aberration and seeing conditions. For photography the laser operates in its ordinary mode (40 Joules in 0.4 msec); for range the laser operates in a Q-switched mode (10 Joules in 10 nsec). Because the round trip travel time per pulse is about 2.5 sec, a mechanical switch is used so that one telescope transmits and receives the range signal. Except for the uncertainty in the speed of light, each range measurement will have a maximum error of about 1.5 meters. Such precise range measurements have numerous scientific uses. The number of observations acquired depends on the uncertain observational lifetime of retrore-flectors in the lunar environment. The lunar observatory is the only site in the U. S. now being developed primarily to satisfy ranging and photographic criteria. It is the result of a co-operative research effort between AFCRL and the NASA.
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