MINIMIZING STAR TRACKER OCCULTATIONS FOR NASA’S LUNAR RECONNAISSANCE ORBITER IN SUN-SAFE MODE

Due to degradation of the NASA’s Lunar Reconnaissance Orbiter’s (LRO) Inertial Measurement Unit, the LRO relies solely on its star trackers to maintain gyroless attitude control. In the event of an anomaly, the LRO is placed in sun-safe mode in order to reestablish normal operation, which constrains its attitude. While in sun-safe mode, the LRO’s star trackers experience occultations from local orbiting bodies and cannot maintain an attitude solution during these periods. This poses the risk of total loss of the spacecraft due to tumbling or depleted power supply. This thesis provides mission operators with a software-based tool for determining alternate sun-safe attitudes that reduce the occultation time, minimizing operational risk. Ephemeris data from orbiting bodies and the LRO are utilized to investigate occultation occurrences. Periods of star tracker occultations for any given time frame are determined based on the LRO’s fixed attitude. The goal of this thesis is to iterate alternate attitudes to define the ideal attitude that minimizes occultation occurrences. Additionally, data analysis is conducted to determine the ideal attitude update frequency for sun-safe mode based on operational constraints. The design of this software-based tool yields appropriate results for acquiring an ideal attitude solution for minimizing star tracker occultations, giving mission operators the freedom to choose attitude constraints, simulation fidelity, and attitude update frequency. ; Approved for public release. Distribution is unlimited. ; Lieutenant, United States Navy