1、Lessons Learned Entry: 1000Lesson Info:a71 Lesson Number: 1000a71 Lesson Date: 1997-02-01a71 Submitting Organization: HQa71 Submitted by: David M. LengyelSubject: Space Shuttle Program/Orbiter/Quality Assurance Description of Driving Event: Leaking Reaction Control System (RCS) Thruster ValvesLesson
2、s) Learned: The orbiter Reaction Control System (RCS) thruster valves continue to leak in flight. NASA has aggressively attacked this problem with some success. Procedural changes have improved thruster reliability, and the incidence of leakage has been reduced but not eliminated.Recommendation(s):
3、 Continued attention must be focused on the elimination of the root causes of RCS valve leakage/failures.Evidence of Recurrence Control Effectiveness: Several remedial actions have been and are being implemented as a result of a 1995 tiger team investigation into the causes of RCS valve leakage/fail
4、ure. This has resulted in many procedural changes and several potential hardware improvement concepts. The procedural changes are reducing the number of in-flight thruster valve failures. Many of the hardware improvements are entering a development testing phase. Examples of procedure and hardware c
5、hanges include:a71 Preventative maintenance flushing. Water flushing of the RCS pilot operated valves (POV) was developed at the White Sands Test Facility (WSTF) and has been verified to remove iron nitrate contamination from the POV.a71 Manifold thruster preventative change-outs. It is now required
6、 to change all thrusters on a Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-manifold when that manifold is drained for any reason. The removed thrusters are sent to WSTF for water flushing and then returned to spares.a71 Hard-filled manifold proces
7、sing. The POV has demonstrated substantially better sealing capability in a fully wetted, hard-filled condition. KSC procedures have been implemented that provide the ability to maintain a hard-filled manifold configuration when performing work on the RCS pods.a71 Minimization of moisture intrusion.
8、 Several additional recommendations have been implemented that specifically address minimizing moisture intrusion into the propellant system.a71 Redesigned POV (RPOV). Another result of the critical examination of the RCS POV failure history was the recommendation that the oxidizer POV be redesigned
9、 to improve the ability to withstand nitrate contamination. The resulting RPOV is proceeding through buildup and development testing. The RPOV design addresses the areas in the current valve that are known to be sensitive to nitrate contamination.a71 Minimization of oxidizer moisture and iron conten
10、t. The presence of iron and water in nitrogen tetroxide greatly increases the potential for precipitation of iron nitrate internal to the POV pilot cavity. Therefore, a molecular sieve is being designed and fabricated to reduce the levels of iron and water in nitrogen tetroxide.Documents Related to
11、Lesson: N/AMission Directorate(s): a71 Space Operationsa71 Exploration SystemsAdditional Key Phrase(s): a71 Aerospace Safety Advisory Panela71 Ground Operationsa71 Hazardous/Toxic Waste/Materialsa71 Logisticsa71 Research & Developmenta71 Safety & Mission Assurancea71 Spacecrafta71 Test & Verificatio
12、nAdditional Info: Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Approval Info: a71 Approval Date: 2001-11-01a71 Approval Name: Bill Loewya71 Approval Organization: QSa71 Approval Phone Number: 202-358-0528Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
