Friday 8 July 2011 12.00pm EDT
During the last week Chandra's observing schedule was interrupted by a spacecraft safemode event that occurred at 8:28am EDT on Jul 6. The safemode transition was identified at the first contact after the event, which started at 5:55pm EDT on Jul 6. The safemode transition was nominal and all systems functioned as expected. Playbacks of the Solid-state Recorder (SSR) to obtain the data containing the safemode transition contained an 80-minute data-gap ending ~12 minutes before safemode entry. Real-time procedures were executed on Jul 6 to perform a diagnostic dump of the Central Processing Electronics (CPE) and to swap to the SSR-B to preserve the data on SSR-A. A real-time procedure was executed on Jul 7 to patch the value of SSR-A playback pointer in the OBC to allow the recovery of the missing data from SSR-A.
The cause for the safemode transition is under investigation. The On-board Computer (OBC) reported cause was that the predicted versus measured change in spacecraft angular momentum was greater than allowed. However, telemetry from the gyroscopes and reaction wheels did not show any anomalous behavior in the time leading up to the safemode event. Analysis of telemetry leading to the safemode event and the contents of the OBC memory (halted at the time of the safemode) are on-going. At this time the leading candidate for the cause of the safemode is an upset or corruption of data within the OBC affecting its processing.
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