GP-B Post-Flight Analysis—Final Report - Gravity Probe B - Stanford ...

8.2.3 TCS Accomplishments• No major thermal limits violated throughout mission duration• Thermal model matched extremely well with on orbit temperatures• Robust designs allowed for harsh thermal environment to have little effect on spacecraft operations ormission lifetime• Well set limits can be attributed to extensive preflight testing and modeling• Outstanding mission operations team training for monitoring the system health and data trending• All thermal transients identified have been explained, as were any small limit violations8.2.4 TCS SummaryThe GP-B spacecraft is complex in many regards, the thermal control system is no exception. With seasonalvariations experienced by all subsystems combined with the high number of eclipses each day, made designing athermal system is no minor feat. With that in mind one can look back over the data from the mission and easilyconclude that the thermal design was indeed robust and a success. Very few thermal transients wereexperienced during the mission and even fewer limits were violated. Most importantly the thermal systemperformed almost exactly as expected with no effect to science data or data collection.8.3 Electrical Power Systems (EPS)The Electrical Power System (EPS) is one of the most critical subsystems on the Gravity Probe B space vehicleand performs vital functions essential to achieve the vehicle science objectives during vehicle on orbit lifetime.The EPS primary objective is to maintain positive power supplied to the vehicle bus elements throughout theorbital eclipse and sun periods and ensure the flight batteries are fully charged when exiting the orbit eclipses. Inaddition, the electrical power system provides functions for sustained communication and tracking with thevehicle during all mission orbits.8.3.1 System Features and CapabilitiesDue to the nature of the science mission, the GPB EPS design introduced unique technologies and methodsdeveloped to meet the vehicle requirement of pointing in a fixed direction at a distant guide star which requiresfor the satellite to be free from disturbances as possible. GP-B’s unique design includes four fixed double-sidedsolar array panels, canted at such angles to average solar power as a function of the orbital seasons. Mostsatellites that are designed to face the sun year around have moveable solar panels in order to maintain positivepower during orbit conditions (sun; eclipse; and gamma angle). The unique GP-B design also featured doublesidedpanels to minimize the thermal effects of entering and exiting eclipses with no noticeable effects ofthermal snapping.The EPS bus design demonstrated outstanding efficiency and stability showing little bus ripple levels beyond thevehicle requirements vital to mission science payloads and instruments and has proven reliability androbustness throughout the entire mission.The GPB EPS has met all requirements with flawless performance since launch supporting all missionoperations and objectives providing ample power margin necessary to plan and support any contingencyoperations, if required.Gravity Probe B — Post Flight Analysis • Final Report March 2007 223