Solar Radiation Disturbance Torque Reduction for the Parker Solar Probe Observatory

摘要

This paper examines the methodology used for reducing solar pressure disturbance torques for the Parker Solar Probe (PSP) Observatory by minimizing the offset between spacecraft's Center of Gravity (CG) and Center of Pressure (CP). The force due to solar radiation pressures encountered by the PSP spacecraft, particularly at the 9.86 solar-radii (Rs) closest approach point in the orbit, are of a sufficient magnitude to produce significant disturbance torques. Inside of 0.25 AU, the Observatory is required to keep its Thermal Protection System (TPS) pointed precisely towards the Sun in order to ensure the survivability of the observatory. It was crucial to reduce disturbance torques encountered during this phase of flight to a low enough level such that the guidance and control system of the spacecraft would be able to control attitude without requiring excessive or untimely propellant usage. We present the process used for proactively packaging a balanced spacecraft and analytically determining the spacecraft's mass properties throughout the entirety of the mission, including associated CG and inertia tensor changes due to propellant usage and movement of deployable hardware and mechanisms. We also present the process used for deriving the spacecraft's CP based on the geometry and optical properties of the hardware exposed to the full solar environment, as well as its shift due to degradation of those properties throughout the life of the mission. Using both of those data sets, we present the approach used to install ballast masses on the observatory in order to minimize the offset, as well as data collected during spacecraft mass properties testing concluded towards the end of PSP's assembly, test, and launch operations campaign. Finally, we present test correlated center of gravity and center of pressure data, and examine expected effects for the duration of the Parker Solar Probe mission.