Earth laser beacon sensor for earth-oriented geosynchronous satellites.

Geosynchronous satellites are often required to maintain accurately their orientation with respect to a selected point at the earth surface. Precise attitude determination of these satellites may be achieved using a laser beacon from ground to the satellite as a directional reference. Four simple implementations of this principle are analyzed, and the influence of the cloudy atmosphere on the laser beacon and, therefore, on the accuracy of the method is discussed. All-weather operation is not possible; for normal cloudiness conditions, however, two analyzed systems (pulsed Nd:YAG laser with photomultiplier and CO(2) laser with cryogenic detector) appear to be feasible.