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

Figure 8-43. A-side CCCA Single Bit Errors during January 20, 2005 solar flare8.5.7 CCCA Multi-Bit ErrorsOther less common manifestations of charged particle collisions with spacecraft circuitry are Multi-Bit Errors(MBEs), defined as the simultaneous corruption of more than one bit within a 32-bit memory word. If thememory scrub routine detects a MBE, the flight software cannot autonomously correct the error, as it does witha SBE. As a result, other methods are needed to protect the spacecraft from corrupted memory caused by MBEs.Most spacecraft experience MBEs infrequently (on the order of ~1 per year). The MBE rate observed by GPBwas significantly higher than expected. This rate is apparent when plotting the locations corresponding todetected MBEs during the first year of GPB on-orbit operations, as shown in Figure 8-44. This plot also showsthat the majority of MBEs occurred near the North / South poles and the SAA. The higher-than-expected MBErate resulted in a concentrated post-launch effort to further understand the increased susceptibility to multi-biterrors, further protect the vehicle from problems as a result of MBEs, and accelerate the process of identifyingcorrupted memory locations and patching the errors.252 March 2007 Chapter 8 — Other Spacecraft Subsystems Analyses