1、Lessons Learned Entry: 0560Lesson Info:a71 Lesson Number: 0560a71 Lesson Date: 1997-06-05a71 Submitting Organization: JPLa71 Submitted by: R. Gounley/D. OberhettingerSubject: Galileo Scan Platform Anomaly at Ida Encounter (1993) Abstract: A scan platform anomaly occurred shortly before Galileos enco
2、unter with the asteroid Ida. Because the Galileo architecture did not provide for revolving, short-term storage of downlink data, ground control lacked insight into the cause of the incident.Missions should continuously buffer at least a small amount of high-rate telemetry as it is being downlinked
3、at a lower rate. Storage of high-rate data for the period immediately preceding and following a fault would assist mission analysts in diagnosis of the problem. Description of Driving Event: A scan platform anomaly occurred 5 hours before Galileos August 1993 encounter with the asteroid Ida. During
4、a quiescent period in scan platform activity, it unexpectedly jerked. The fault response sequence interpreted the high rate of scan platform motion as a spacecraft gyro error and turned off the gyros. The flyby continued in cruise mode, using star-based platform pointing. Although the low data rates
5、 available from the low gain antenna provided poor insight into spacecraft condition, ground control received indications of at least 5 more incidences of unexpected platform motion during quiescent periods over the next few hours. Ida encounter continued successfully with the gyros off and with no
6、further signs of the anomaly.No conclusive explanation was found despite extensive ground testing and analysis and attempts to recreate the anomaly on the spacecraft. Consistent x-axis data from both gyros suggested that gyro hardware failure was improbable. Analysis did reveal that the anomaly woul
7、d have aborted the imaging sequence had the additional power drawn during the slew been enough to cause an undervoltage condition. Instead, the first level fault protection (gyros off) allowed the sequence to continue imaging Ida. After the science data had been safely recorded and before the gyros
8、were Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-required, ground control was able to command them back on. This conservative, “first, do no harm“ approach proved successful.The Galileo architecture did not provide for revolving, short-term stora
9、ge of downlink data, which would have been useful in compensating for low telemetry data rates. Galileo telemetry provided data needed to troubleshoot the anomaly only once every two hours. Running intermittently, the tape recorder failed to capture any of the scan platform jerks. Subsequent to the
10、Galileo era, some low data rate missions are being designed to provide for some storage of transient data to improve fault visibility to ground control.Additional Keyword(s): System Design, Transient Event RecordingReference(s): ISA 04013GLesson(s) Learned: 1. Establish “First, do no harm“ as the ov
11、erriding principle guiding both fault protection design and the ground response to in-flight anomalies.2. Where it is not practical to record and downlink all telemetry, future missions should continuously buffer a small amount of high-rate telemetry as it is being downlinked at a lower rate. Should
12、 a fault occur, high-rate data for the period immediately preceeding and following the fault could be stored for later retrieval. This would assist mission analysts in real-time diagnosis of the problem.Recommendation(s): See Lesson(s) LearnedEvidence of Recurrence Control Effectiveness: N/ADocument
13、s Related to Lesson: N/AMission Directorate(s): N/AAdditional Key Phrase(s): Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-N/AAdditional Info: Approval Info: a71 Approval Date: 1997-08-13a71 Approval Name: Carol Dumaina71 Approval Organization: 125-204a71 Approval Phone Number: 818-354-8242Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
