SPACE COMMUNICATIONS PROTOCOLS FOR FUTURE OPTICAL SATELLITE-DOWNLINKS

Abstract

As telemetry downlink data rates from EO-satellites increase and available radio frequency transmission spectrum narrows, optical data downlinks based on directed modulated laser sources become a beneficial alternative. While solving the bottleneck of data rate by providing licensing-free transmission at up to multi-Gigabit per second data rates, the required onboard terminal hardware is at the same time small and uses low transmit power. However, the transmission channel is very different to RF downlinks as new atmospheric effects have to be regarded, mainly cloud blockage, increased attenuation at low elevations, and index of refraction turbulence. To enable also with optical downlinks the level of global cooperation prevailing in RF downlink operations, it is necessary to elaborate and standardize optimized optical transmission formats. We present here the characteristics of optical LEO downlinks and the requirements they impose on the transmission data formats and protocols. We consider how existing RF satellite transmission-securing formats can be adopted and extended to enable reliable and efficient optical downlinks.