Thermal Control Design for Deep Space Optical Communication (DSOC) Docking Mechanism High-Output Paraffin Actuator

Deep Space Optical Communication (DSOC) is a technology demonstration laser communication payload riding on the Psyche spacecraft that will demonstrate data transmission via laser up to 2.76 AU (probe to sun). The payload achieves fine acquisition and tracking control by utilizing Lorentz force actuators to perform dual functions: mechanical isolation from the bus to provide a stable floating platform for the optical assembly, and to perform fine-grain pointing and tracking of the optical uplink receiver. To satisfy a Psyche requirement, during DSOC off periods, the floating platform is mechanically docked to the stationary side through the use of a pair of Docking Mechanisms (DMs). During an optical pass the optical platform has to be undocked by the DMs which each utilize a High-Output Paraffin (HOP) actuator to perform the undocking function. The DMs need to be in the undocked phase for up to 8 hours without any interruption or dithering of the HOP pin. Dithering has to be prevented because this could cause disruptions to the pointing of the optical assembly. Spacecraft bus voltage is also static so there inability of changing the power output to the HOP heater, which is critical due to strict paraffin temperature limits, thus, a pulse-width modulation (PWM) heating scheme was developed to achieve the desired power output. This PWM was then adapted and implemented in Psyche Flight Software (FSW). The flight unit DMs were tested successfully meeting all Verification & Validation requirements using this method for all temperature and voltage ranges. The DMs have been proven to work for 8+ hours in thermal vacuum, which is required for compliance of DSOC Project Level 1 requirements. This paper describes the development of the algorithm from inception to the final Psyche flight software implementation.