Ground Terminal Evaluation for Deployable Optical Receiver Aperture (DORA)

DORA (Deployable Optical Receiver Aperture) is a collaborative project between JPL and ASU aiming to achieve high-speed connectivity in the cis-lunar communication network using small satellite technology. This paper evaluates the Optical Ground Terminal (OGT) that could potentially be used in the initial low-earth-orbit to ground demonstration. A two-axis gimbal controls laser pointing and tracking, while a similar optical receiver as the DORA payload is implemented in the OGT to enable autonomous satellite tracking by analyzing the satellite-ground Angle of Arrival (AoA) data. Experimental results show the pointing accuracy of the gimbal system and fluctuation in beam divergence due to atmospheric effects. The ground experiment partly simulated a ground-satellite scenario between the OGT and the DORA payload. The pointing accuracy of the gimbal system was assessed using time and frequency domain analyses of jitter data from indoor and open-air experiments. Atmospheric effects caused an increase in average beam divergence during the 35 m open-air test, with expected greater fluctuations observed compared to indoor tests. Variations in beam size and position are analyzed using digital image processing techniques. The study highlights a few important aspects affecting OGT's pointing accuracy and could therefore help in increasing the effective aperture for Free Space Optical Communication (FSOC) architectures.