1、Lessons Learned Entry: 0288Lesson Info:a71 Lesson Number: 0288a71 Lesson Date: 1993-07-13a71 Submitting Organization: JPLa71 Submitted by: J. O. BlosiuSubject: Galileo Spacecraft Safing During Star Scanner Calibration Abstract: An unintended in-flight mode change impacted a planned Galileo sequence
2、only because of a hardware failure during the sequence. The spacecraft entered safing, necessitating a difficult recovery process that could have impacted science return had it happened during encounter. When simulating and testing command sequences, assure that the software and hardware states exac
3、tly match the expected in-flight states. Any anomaly that changes a fundamental spacecraft state must be scrutinized for potential impacts.Description of Driving Event: An Attitude and Articulation Control Subsystem (AACS) sequence designed to collect data for calibration of the spacecraft star scan
4、ners in the AACS inertial mode (gyros on), was tested on the Galileo test bed simulator.Prior to the transmission and execution of this calibration sequence on the spacecraft, a star misidentification event caused the AACS to switch from the “inertial“ to the “cruise“ mode (gyros off).Because of the
5、 importance of getting the calibration data and limited open time in the few weeks before venus encounter, it was decided to proceed with the star scanner calibration. The mode change was evaluated and not believed to have an effect on the planned sequence.However, during the execution of the calibr
6、ation sequence, a spin bearing controller instability occurred due to an unexpected incompatibility between the mode and AACS software. This caused a series of hardware swaps within the AACS, ultimately causing the spacecraft to go into safing. A subsequent test on the Galileo test bed simulator dup
7、licated the spacecraft response.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-This event occurred twenty-five days before Venus encounter and the difficult recovery process from safing took three weeks. Had this anomaly occurred closer to the encou
8、nter, significant impact on science data return could have resulted.Reference(s): PFR #52608Lesson(s) Learned: 1. Test bed simulators provide a valuable tool for analyzing/verifying spacecraft operations and anomalies.2. Spacecraft mode changes caused by in-flight anomalies can affect subsequent pla
9、nned activity sequences.Recommendation(s): 1. When simulating and testing command sequences, care must be taken to guarantee that the software and hardware states used during the test exactly match the software and hardware states that are expected in flight.2. Whenever a spacecraft anomaly changes
10、any of the fundamental spacecraft states, all subsequent activities must be scrutinized for potential impacts.Evidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): a71 ScienceAdditional Key Phrase(s): a71 Flight Operationsa71 Spacecrafta71 Test & Ve
11、rificationAdditional Info: Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Approval Info: a71 Approval Date: 1991-04-18a71 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-,-,-
