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

est solution. After a relatively short time however, the start and end time for the data dumps was changed toreduce the low elevation start and stop times (increased the masking); this reduced the dump time, but resultedin better quality data. GP-B is now using all sites without major concerns in the quality of the data.8.4.3.4 Mutual Interference Anomaly PotentialMutual Interference (MI) has not been a problem on GP-B. There are some incidences when another vehiclehas affected the TDRSS supporting GP-B, but the MI’s duration has not been very long and so are of noconsequence. However, GP-B does have MI potential to other projects (S-Band Frequencies) supported byNASA’s Deep Space Network (DSN). GP-B’s mission planning, with predictions provided by the DSN hassuccessfully managed the control of the GP-B downlink over DSN sites.8.4.4 Communications—Prime Mission and BeyondThe GP-B Communications subsystem provides the command and control reliability as per the pre-launchsystem requirements. With the exemption of the Transponder-A anomaly, the system has functioned asexpected, within or better than the expected link margins. The project has successfully sent approximately106,000 commands over the 17.3-month mission and has retrieved 99% of the SSR data.The management of the on-orbit problems, such as that of the transponder has given the project the ability tosuccessfully complete the mission and go beyond. The project would like to acknowledge the assistance inresolving many of the COM issues on GP-B; members from Stanford, NASA Goddard and Marshall, LockheedMartin and General Dynamics (with the issue of the transponder).8.5 Flight Software (FSW)The Gravity Probe B Flight Software (FSW) consists of all Mission Support Software (MSS) running on theCommand and Control Computer Assembly (CCCA). This software performs a wide range of duties, includingbut not limited to maintaining the spacecraft attitude and drag-free orbit, monitoring critical health and safetystatistics, and supporting the transfer of telemetry to the ground. This software is distinct from the codesrunning in the payload computers, namely the Gyroscope Suspension Software (GSW) and the SQUID ReadoutElectronics Software (SSW); these payload packages are described in their respective payload sections.This section will give an overview of the on-orbit performance of the flight software, as well as the steps taken bythe FSW team to both prepare for mission operations and make adjustments to the software and procedures asa result of on-orbit events. The discussion will show that the FSW proved to be an efficient and robust piece ofthe complicated GPB system, and that the FSW team successfully guided the software through pre-launchpreparations, on-orbit modifications, and several anomalous events.8.5.1 Requirements Satisfaction.The GPB Flight Software (FSW) played an important role in achieving mission success. The mission level roleof the FSW included the capability to provide functions to support all on-orbit activities of both the spacecraftand payload, perform autonomous health and safety monitoring of critical subsystems, and ensure properprocessing of telemetry data and ground commands. The Flight Software successfully performed these goals,configuring the vehicle and science payload to a state appropriate for data taking, safing the vehicle fromunexpected events on a number of occasions, and supporting the accurate transfer of > 95% of collected data tothe ground. The on-orbit performance of GPB, from system initialization through science data collection, is atestament to the satisfaction of high-level FSW requirements.Gravity Probe B — Post Flight Analysis • Final Report March 2007 239