Design criteria for space based laser ranging systems

Criteria for the design of space-based laser ranging systems, including output signal-to-noise as a function of the received signal power for various types of photodetectors, search field of view, search duration, maximum range, ranging accuracy, transmitter beam divergence and transmitter power are discussed. Semiconductors and photomultiplier tubes (PMT's) are considered. Among the semiconductors, avalanche photodiodes (APD's) are preferred because pin-diodes have strong thermal noise in addition to the shot noise at the low power levels of interest. Multiplier tubes show almost ideal features with regard to thermal noise and therefore are preferable to APD'S. Based an APD, the performance of pulsed and continuous wave ranging systems is analyzed.