1、Lessons Learned Entry: 0439Lesson Info:a71 Lesson Number: 0439a71 Lesson Date: 1996-07-19a71 Submitting Organization: JPLa71 Submitted by: D. OberhettingerSubject: Avoid Use of PFPE-based Lubricant on Moving Surfaces of Titanium (or Other Highly Reactive Metal) Bearings (1993) Abstract: A rotating p
2、rism motor aboard the TOPEX spacecraft experienced a sudden in-flight failure due to the use of perfluoropolyalkyether (PFPE) based lubricant on titanium bearings. Pure titanium debris produced by spalling of the motor shaft chemically reacted with the fluorocarbon-based lubricant, causing polymeriz
3、ation of the lubricant. Avoid the use of PFPE-based lubricants on titanium or other highly reactive bearing surfaces.Description of Driving Event: Following an April 1993 in-flight failure of an Upper Atmosphere Research Satellite (UARS) Earth Sensor Assembly (ESA), the vulnerability of identical ES
4、As aboard the TOPEX spacecraft was investigated. UARS experienced a sudden in-flight failure of the ESA rotating prism motor attributed to the use of perfluoropolyalkyether (PFPE) based lubricant on titanium bearings. Pure titanium debris produced by spalling of the motor shaft chemically reacted wi
5、th the fluorocarbon-based lubricant, causing polymerization of the lubricant. In the presence of debris, bearing race-to-ball friction produces enough heat for the titanium to react with the lubricant, given that titanium is very reactive when exposed. The degradation mechanism consists of two steps
6、: (1) the reaction of PFPE molecules with freshly exposed titanium particles to form an acid followed by (2) the reaction of the acid with unreacted PFPE molecules, resulting in cleavage of their molecular bonds. This failure mechanism was confirmed in a life test performed by GSFC on a spare UARS E
7、SA motor. The PFPE oil was suspected of causing problems in at least seven units identical to the TOPEX ESA.Reference(s):1. “UARS ESA-1 Failure Study,“ Martin Marietta Corp., August 3, 1993.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-2. “TOPEX Ea
8、rth Sensor Motor Review,“ June 23, 1994, ITHACO, Inc.3. “TOPEX/Poseidon Earth Sensor Assembly (ESA) Operation,“ Fairchild Space & Defense Memo No. 968:TOPEX:94-032 to Mark Fujishin (JPL), August 19, 1994.Lesson(s) Learned: 1. A state-of-the-art spacecraft lubricant, with high performance characteris
9、tics throughout the operating temperature range and low vapor pressure, may be vulnerable to polymerization. In such cases, and where thin film lubrication conditions prevail, a more stable lubricant than PFPE-based lubricant should be used on moving titanium bearing surfaces.2. Regardless of the be
10、aring lubricant used, metallic particle contamination of bearings is likely to affect bearing lifespan. Bearing designs which reduce the amount of bearing play may reduce debris generation.Recommendation(s): 1. Avoid the use of PFPE-based lubricants on titanium or other highly reactive bearing surfa
11、ces in spacecraft applications.2. Mitigate the risk of bearing failure by design measures which prevent the generation of metallic wear particles or which control the amount and migration of debris.Evidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s
12、): N/AAdditional Key Phrase(s): a71 Hardwarea71 Parts Materials & ProcessesAdditional Info: Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Approval Info: a71 Approval Date: 1996-06-20a71 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-,-,-
