Optical Propagation Tests Study

Abstract : The Optical Propagation Tests Study has analyzed the effects of atmospheric turbulence on atmospheric laser links. Analyses have found that scintillation (beam breakup), beam spread and beam wander will preclude operation of a high data rate uplink at 1 Gbps with an average P sub E of 0. 000001 unless special techniques are utilized in the ground transmitter design. It is predicted that focusing the beam at or above the tropopause will reduce the scintillation effects sufficiently, and pointing the uplink beam along the instantaneous normal to a downlink wavefront of a beam which originates at the satellite transmitter (reciprocity tracking) will remove most of the wander effects. A number of possible experimental techniques, suitable for testing these predictions have been explored. The recommendation is to perform an experiment in May/June 1974 using a variable focus reciprocity tracking ground transceiver and a balloon-borne (altitude 100,000 feet) system that is a modification of that developed in the Balloon Atmospheric Propagation Experiment. This recommendation allows for full utilization of the techniques (and equipment) developed under the 405B Acquisition/Tracking Brassboard programs and will specify the design constraints for the ground station by June 30, 1974.