1、Lessons Learned Entry: 0574Lesson Info:a71 Lesson Number: 0574a71 Lesson Date: 1997-07-31a71 Submitting Organization: JPLa71 Submitted by: Kevin ClarkSubject: Eliminate Potentiometers from Flight Critical Position Indicators (1995) Abstract: Potentiometers (pots) are low reliability items. Yet Mars
2、Global Surveyor used 8 pots for confirming solar panel deployment that were non-essential, yet a single failure could have jeopardized the mission. Eliminate potentiometers from deployment designs unless intermediate position readings are essential and the spacecraft lacks a redundant sensor.Descrip
3、tion of Driving Event: Mars Global Surveyor incorporated eight potentiometers (pots) used to confirm the position of the solar panels following their deployment away from the main body of the spacecraft. This event was the only time the eight potentiometers were needed in the mission. For each solar
4、 panel, the design permitted one of the two inherently low reliability devices to fail without losing the ability to ascertain mechanism position.If a potentiometer failed before launch, and a decision was made not to repair it, this could result in a mission critical single point failure. The fligh
5、t computer would assume that the solar array had not been deployed and issue commands to reinitiate the deployment sequence. If this occurred at a late phase of the aerobraking maneuver, the mission could be jeopardized.The pots proved nonessential since body rate data generated in flight by the Att
6、itude and Articulation Control Subsystem (AACS) provided quite accurate measures of solar panel deployment position.Lesson(s) Learned: Eliminate potentiometers from deployment designs unless:Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-1. Intermed
7、iate position readings are essential, and2. The spacecraft lacks a redundant capability for measuring deployment mechanism position.Recommendation(s): See Lesson(s) LearnedEvidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): N/AAdditional Key Phrase(s): N/AAdditional Info: Approval Info: a71 Approval Date: 1997-10-29a71 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-,-,-
