An Earth-to-Deep-Space Optical Communications System With Adaptive Tilt and Scintillation Correction Using Near-Earth Relay Mirrors

The performance of an Earth-to-space optical telecommunications system is degraded by distortion (scintillation and tilt) of the beam as it propagates through the turbulent atmosphere. Conventional approaches to correct distortions that are based on natural or artificial guide stars are useful in, for example, astronomical imaging, but have practical difficulties or are not adequate to correct the distortions important for Earth-to-deep-space optical links. A beam-relay approach that overcomes these difficulties is presented. A downward-directed laser near an orbiting relay mirror provides a reference source for measuring and correcting atmospheric distortion. The ground station preprocesses its uplink communications beam such that, after passage through the atmosphere, uplink propagation effects are removed, delivering a diffraction-limited beam to the mirror. The orbiting mirror then directs the corrected beam to the distant spacecraft. We discuss this system.