1、Lessons Learned Entry: 0463Lesson Info:a71 Lesson Number: 0463a71 Lesson Date: 1994-07-25a71 Submitting Organization: LERCa71 Submitted by: Maria HavenhillSubject: Atlas Booster Engine Precision Regulator - Atlas/Centaur Program Description of Driving Event: On March 25, 1993 an Atlas/Centaur launch
2、 vehicle (AC-74, Atlas1) inserted a Hughes UHF follow-on spacecraft into orbit with an apogee altitude of 4,967 nmi instead of the targeted nominal of 9,098 nmi. Although functioning normally, the satellite was declared a loss by the Navy due to the unacceptable orbit.The investigation team conclude
3、d that the precision regulator in the booster engine system failed. The output pressure of this regulator controls the output power level of the booster engine, which caused the decline in thrust. This failure was caused by the stem screw rotating and decaying the output of the precision regulator.T
4、his precision regulator had been reworked twice during its build to repair excessive vent port leakage. The first authorized rework required loosening and retorquing the set screw. The set screw has been redesigned so that it is custom made for each mission. The length of each screw is predetermined
5、 and inserted so that rotation is impossible to achieve.Further information can be found in the AC-74 Anomaly Investigation Summary Report.Lesson(s) Learned: Reworked screws can be the cause of decayed precision regulator output if rework instructions lack requirements for set screw torquing and ver
6、ification by a quality inspector.Recommendation(s): Provide corrective action to prevent the stem screw from undesired rotating, improve system Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHSmargins, improve data evaluations, and improve quality processi
7、ng.Evidence of Recurrence Control Effectiveness: With the redesign of the set screw, there have been no further failures of this type.Documents Related to Lesson: N/AMission Directorate(s): N/AAdditional Key Phrase(s): a71 Hardwarea71 Parts Materials & ProcessesAdditional Info: Approval Info: a71 Approval Date: 1996-10-25a71 Approval Name: Sell Jamesa71 Approval Organization: 501-4a71 Approval Phone Number: 216-433-8618Provided by IHSNot for Resale-,-,-
