NASA's flight-technology development program: a 650-Mbit/s laser communications testbed

摘要

Abstract: NASA-Goddard Space Flight Center (GSFC) is designing and building a 650 Mbps laser communications testbed for the development of flight qualifiable hardware suitable for near-term operation on geosynchronous-to-geosynchronous (GEO-GEO) crosslink missions. The primary purpose for the program is to develop and optimize laser communications unique subsystems. The design incorporates technologies that have previously been developed at GSFC, such as the quaternary pulse position modulation (QPPM) receiver, the GaAlAs diode laser beam combiner, and the integrated low-power digital gimbal controller. Requirements for the testbed experiments are to optimize the acquisition processes; to fully simulate the long range (up to 21,000 km) and the fine tracking characteristics of two narrow-beam laser communications terminals; and to fully test communications performance which will include average and burst bit error rates (BERs), effects of laser diode co-alignment, degradation due to internal and external stray light, and the impact of drifts in the optical components. Transmit-to-receive alignment techniques will also be tested and optimized. Trade studies and analyses have been performed to optimize the aperture, laser power, pointing requirements, modulation, number of channels, servo design, and receiver design. The gimballed telescope assembly (GTA) and the imaging optics assembly (IOA) are in the final critical design phase while the rest of the subsystems are still in the analysis, breadboard and preliminary design phases. The testbed will be fully operational in 1993.!