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

5.2 Overview of GP-B Anomalies in OrbitThe Spacecraft’s Tale above typifies the anomaly discovery, review, and resolution process that our MissionOperations Team and Anomaly Review Board worked through time and again during all phases of the GP-Bmission. The details were different in each case, but the discovery, analysis, and resolution process was alwaysthe same.Over the course of the flight mission, the GP-B Anomaly Review Board (ARB) successfully worked through 193anomalies/observations. Of these, 23 were classified at true “anomalies,” five of which were sub-classified as“major anomalies,” including the B-Side computer switch-over and the stuck-open valve problems with twomicro thrusters early in the mission, as well as subsequent computer and subsystem reboot problems due toradiation strikes. Of the remaining 18 anomalies, 12 were sub-classified as “medium anomalies” and 6 were subclassifiedas “minor anomalies.”The 170 other issues (88%) were classified—at least initially—as “observations.” These observations typicallydocumented various unanticipated events, sub-optimal parameter settings, and other odd results that weremonitored until their root cause was understood. In several cases, observations were escalated to anomalystatus, and then necessary actions were taken not only to understand, but also to correct the problem. In allcases, the established anomaly resolution process enabled the team to identify the root causes and providerecovery procedures.Section 5.3 Anomaly Review Process below provides a complete description of the GP-B anomaly reviewprocess that was used to work through all observations and anomalies. Appendix D, Summary Table of FlightAnomalies, shows the complete list and status of all 193 observations and anomalies that were workedthroughout the mission.Section 5.4 Risk Analysis below provides an overview of GP-B’s risk management strategy, including a summaryof current risk items and their planned mitigations.5.3 Anomaly Review ProcessGravity Probe B uses a formal anomaly review process to assess, manage, and resolve vehicle or ground systemanomalies when they occur. Processes and training of team members are in place to ensure that all identifiedissues are addressed in a uniform manner and the entire team (Stanford/Lockheed-Martin/NASA) are keptapprised of the status of all anomalies and associated mitigation efforts.5.3.1 Anomaly DefinitionsAn anomaly is any unanticipated or undesired event, condition or configuration of the spacecraft or groundequipment. Anomalies are generally indicated by:• Timeline execution via pre-programmed failure paths• Safemode activations• Real-time monitoring of subsystem behavior• Off-line data analysis (engineering or science trending)126 March 2007 Chapter 5 — Managing Anomalies and Risk