Telescope Arrays for Deep Space Optical Communications

The Deep Space Optical Communications (DSOC) project has demonstrated free-space optical communications from beyond lunar orbit for the first time. Three ground telescopes in Southern California – the Ground Laser Receiver (GLR) at Palomar Observatory, the Optical Communications Telescope Laboratory (OCTL) at JPL’s Table Mountain Facility (TMF), and the RF-Optical Hybrid (RFO) at the Goldstone Deep Space Communications Complex – have successfully received the DSOC signal in a variety of channel conditions over the course of nearly one year. Through a separate NASA program, we have developed a scalable architecture and algorithms for arraying together multiple independent ground stations, allowing for cooperative reception of standards-compliant High Photon Efficiency signals. By coordinating operational plans across the three ground stations, we have taken concurrent recordings of the digitized single-photon-detected signal using high temporal resolution time to digital converters (TDCs). We subsequently combined these recordings using a post-processing software-based realization of our array algorithms to show that we can achieve essentially perfect combining over the 100-200+ km baselines in our array. This experiment has demonstrated the utility of arrays by showcasing near-lossless signal combining, fading diversity gain, and operational robustness to individual-telescope outages. We provide analysis on the quality of temporal synchronization across a wide range of signal format and power conditions, as well as analysis on the statistical correlation of the fading processes between the three stations.