Ground Terminal Evaluation for Deployable Optical Receiver Aperture (DORA)

Deployable Optical Receiver Aperture (DORA) is developed jointly by Jet Propulsion Laboratory (JPL) and Arizona State University (ASU). The project aims to reach Gigabits per second (Gbps) connectivity at a distance of hundreds to thousands of kilo- meters. Such connectivity will contribute to the LunaNet communication network consisting of multiple cislunar orbital and surface assets including astronauts, landers, rovers, instruments and the Lunar Gateway as well as other lunar orbiters. In this paper, we evaluated the Optical Ground Terminal (OGT) for the DORA project. A two-axis gimbal is used to control the outgoing laser pointing and tracking when the OGT receives the incoming laser. A similar multi-panel optical receiver as the DORA payload [1] is implemented as a part of the OGT. The developed DORA software module for the gimbal and Angle of Arrival (AoA) algorithm will enable autonomous tracking of the satellite by receiving and analyzing the AoA data. The ground experiment emulated a ground-satellite scenario between the OGT and the DORA payload. The pointing accuracy of the gimbal system has been evaluated by performing time and frequency domain analyses of the jitters data collected from indoor and open-air experiments. Due to atmospheric effects, the average beam divergence was found to increase in the open-air test with a distance of 34.69 m. Greater fluctuations were observed in the open-air beam divergence measurements comparing to indoor tests. We observed and analyzed fluctuations in beam size, beam position, and intensity distribution within the beam due to atmospheric inhomogeneities with digital image processing techniques. Keywords: Deployable Optical Receiver Aperture (DORA), Optical Ground Station (OGT), Angle of Arrival (AoA), Position Sensitive Detector (PSD), Degree of Freedom (DoF), Free Space Optical Communication (FSOC).