1、Lessons Learned Entry: 0403Lesson Info:a71 Lesson Number: 0403a71 Lesson Date: 1996-04-26a71 Submitting Organization: JPLa71 Submitted by: J.A. RobertsSubject: Thrusters Fired on Launch Pad (1975) Abstract: Inadvertent commanding of the safing sequence while the Viking (VO-2) spacecraft was still on
2、 the launch pad enabled the RCS thrusters. The thrusters fired in an attempt to compensate for the Earths rotation, resulting in a significant loss of attitude control gas. When command sequences intended to be exercised only in the event of abnormal spacecraft activity are stored onboard, consider
3、the consequences of their activation during system test or the pre-launch phases.Description of Driving Event: (Relevant Historical Lesson(s) Learned)On Viking Orbiter (VO)75, a launch pad problem developed involving the flight software program and the Reaction Control System thrusters. The flight s
4、oftware, intended for use only after launch, contained within it a “safing sequence.“ The intent of the safing sequence was to automatically place the spacecraft in a safe state should some anomaly be detected. The safing sequence included commands to enable the Reaction Control System (RCS) and its
5、 thrusters.In spite of procedural safeguards, a problem developed which inadvertently resulted in the issuance of the safing sequence while VO-2 was still on the launch pad. This, in turn, enabled the RCS thrusters. The Attitude Control System then sensed the Earths rotation, causing the RCS thruste
6、rs to fire in an attempt to compensate. Thruster firing continued until disabled by the test team, resulting in a significant loss of N2 attitude control gas. The launch was conducted without replacing the lost gas, rather than take the spacecraft down off the launch vehicle for replenishment. The s
7、afing sequence was also inadvertently issued several times during system test, but no adverse consequences resulted.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Additional Keyword(s): Ground Operations, Pre-Launch ConstraintsReference(s): VO75 P/F
8、R # 34869Lesson(s) Learned: When command sequences are stored on the spacecraft and intended to be exercised only in the event of abnormal spacecraft activity, the consequences should be considered of their being issued during the system test or the pre-launch phases.Recommendation(s): Had the abili
9、ty of the safing sequence to enable the thrusters been constrained in some manner until after launch, for example, the VO75 problem would not have occurred.Evidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): N/AAdditional Key Phrase(s): a71 Ground
10、 Operationsa71 Softwarea71 SpacecraftAdditional Info: Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Approval Info: a71 Approval Date: 1995-10-16a71 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-,-,-
