GUIDANCE, NAVIGATION, AND CONTROL FOR THE DEEP SPACE OPTICAL COMMUNICATION MISSION

NASA’s Deep Space Optical Communication (DSOC) mission is currently operating on-board the PSYCHE spacecraft and has demonstrated the first optical communication link from beyond the Earth-Moon system. The opti- cal link requires micro-radian level pointing stability which DSOC achieves through a combination of passive isolation, to reject high frequency distur- bances from the spacecraft, and active pointing control, to track the uplink and downlink stations. The passive isolation is enabled by a floating platform that is tethered to the main spacecraft with soft cables. The floating platform holds a telescope assembly for both receiving the uplink and transmitting the dowlink signals. The floating platform is actively controlled to both reject disturbances from the main spacecraft and to track an uplink signal, which is in turn used as a reference for downlink pointing. In this architecture, down- link pointing control is only used to track the slowly varying drift between the uplink and downlink directions; all pointing isolation is provided by the floating platform control. This allows the dowlink pointing to operate at a nearly fixed point which improves the calibration of the dowlink pointing bias between operational activities. Current experience confirms that the softness and strain in the tethering cables are key design parameters. Furthermore, idiosyncrasies in the sensors used for platform control have, in some instances, hampered pointing performance, which could be resolved in future missions.