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

8.3.2 Critical Mission RequirementThe GPB EPS primary function is to supply the required power to vehicle loads and science instrumentsnecessary to support mission Science Mode and precious data collection during mission lifetime with nointerruptions or dropouts. Additionally, the GPB science telescope must stay locked on the guide star IM Pegesito within 100 milliarcseconds with no disturbances to the science instruments. The GPB EPS designdemonstrated exceptional on-orbit performance with bus the ripple levels well below vehicle requirements of 2volts peak-peak. Figure 8-17 below, displays the daily peak bus ripple measurements for the duration of themission.8.3.3 System PerformanceFigure 8-17. Bus Ripple Metric (Ripple Value in Volts since Launch)The Gravity Probe B Electrical Power System has performed exceptionally well from launch through missioncompletion with all EPS elements demonstrating flawless performance and stability. Immediately afterspacecraft liftoff, the GPB EPS system delivered on-time exceptional performance with superb solar arraydeployment and continuous support to vehicle loads and mission operations during Initial and Orbit Checkout(IOC) phase. Successful on-orbit performance can be attributed to maintaining positive power to vehicle loadsduring vehicle mission operations and continuous system health and performance monitoring. It is alsoattributed to well-trained mission teams who effectively provided accurate data trending and comparison of realtime data to predicted analyses and models. At the completion of the mission, the EPS system was performingwell and continuing to support all science data collection and calibration activities. In fact over the missionlifetime, the system showed little degradation and could support extended missions if needed.8.3.4 EPS Accomplishments1. At vehicle launch, flawless solar array deployment in support of vehicle on-orbit initial operations2. Positive power to the space vehicle bus and its payloads during orbit seasonal periods3. Nominal and consistent performance during and post space vehicle Initial Operations and OrbitCheckout (IOC)4. Stable bus telemetry during all vehicle operations5. Very low bus ripple values better than specifications6. Successfully supported vehicle Science and Calibration Mode, and any required contingency operations7. Superb battery performance throughout all mission phases maintaining margin above minimum voltageand SOC thresholds for Safe mode.8. Consistent performance agreed and matched predicted analyses and models9. Outstanding mission operations team well trained to monitor system health and data trending224 March 2007 Chapter 8 — Other Spacecraft Subsystems Analyses