1、Lessons Learned Entry: 0492Lesson Info:a71 Lesson Number: 0492a71 Lesson Date: 1997-01-16a71 Submitting Organization: JPLa71 Submitted by: D. OberhettingerSubject: Galileo High Gain Antenna (HGA) Failure (1991) Abstract: The Galileo spacecraft High Gain Antenna (HGA) was to open like an umbrella, bu
2、t it never reached the fully deployed position. The failure was attributed to the design of the rib retention mechanism. Recommendations involved the design of preloaded mechanisms, lubricant selection and use, hardware robustness, and fault tolerant design of one-shot, non-redundant, mechanisms.Des
3、cription of Driving Event: In April 1991, the Galileo spacecraft executed a deployment sequence which was to open the High Gain Antenna (HGA) like an umbrella, but it never reached the fully deployed position. A formal failure investigation attributed the failure to the design of the rib retention m
4、echanism. According to this scenario, the most likely failure mechanism is friction in the pin/socket interface on the antenna rib midpoint restraint. Preloading of the ribs when the antenna was stowed at the factory damaged the ceramic coating on the pin engaged by the V-groove socket; the coating
5、served to retain the molybdenum disulfide dry lubricant. Accumulated stresses from vibration testing, rib preloading, four cross-country trips, and the post-launch ignition of the upper stage further dispersed the lubricant film. The resulting friction caused asymmetrical deployment, resulting in re
6、straining forces which further reduced the torque available from the deployment drive system.The HGA was largely inherited from an antenna developed for the Tracking Data Relay Satellite (TDRS) system. JPL design changes included substitution of two conical Inconel pin sockets with one conical and o
7、ne V-groove Inconel socket. Selection of an Earth orbital antenna design, even though proven in that application, was not fully consistent with the Galileo mission. Inheritance and other design reviews failed to reveal the existence of high surface stresses. In addition, a lessons learned on Voyager
8、 II to use spring assisted mechanical deployments was not followed. The deep space mission subjected the redesigned antenna to environmental conditions not encountered by Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-TDRS in Earth orbit, and the VE
9、EGA mission profile instituted after Challenger extended both the duration of those conditions and the time to deployment.Galileo illustrates the difficulty of reproducing the spaceflight environment in the ground test of large and complex mechanisms, even when full design review and environmental t
10、esting are undertaken. Flight antenna deployment test failed to disclose the problem because (1) vacuum test was performed without the vibration-induced relative motion between the pins and sockets and (2) oxides and contaminants present during ground test on the bare titanium pins lubricated the me
11、chanism. Similarly, ambient ground tests did not reveal the failure mode due to the lower coefficient of friction of the titanium pin/socket interface in air. Additional testing of the deployment mechanism would only have worn out the deployment drive system.Work-arounds using the Low Gain Antenna,
12、new data compression techniques, and the spacecrafts recorder are expected to meet 70 percent of the mission objectives.Reference(s): “Galileo HGA Deployment Pin Walkout Analysis Final Report,“ JPL D-9932, July 1992Lesson(s) Learned: Design changes intended to improve the reliability of inherited ha
13、rdware may introduce new failure mechanisms. The mission impact of such design changes may best be understood through a “physics of failure“ approach to reliability analysis. Failure physics issues relevant to antenna support bearings, for example, may include oxidation, cold welding, galling, stati
14、c and sliding friction, lubrication transfer, Hertzian contact stresses, and plastic deformation, as well as operational issues such as long-term storage, ground handling, the mission environment, and mission duration.Recommendation(s): 1. In the design of preloaded mechanisms, consider the potentia
15、l for high contact stresses on pin/socket interfaces to destroy the integrity of the lubricant film. Take into account the potential for lubricant effectiveness to decrease over time.2. Due to its high wear rate in air, carefully evaluate the use of molybdenum disulfide drylube on a mechanism that w
16、ill be tested or operated under non-vacuum conditions.3. Hardware should be inheritently robust or redesigned to accommodate major changes in spacecraft system design, changes in spacecraft handling or the mission profile. Inheritance, design and peer reviews should fully consider the effect of such
17、 changes on known failure mechanisms.4. One-shot, non-redundant, mechanisms should be designed for simplicity and fault tolerance-particularly where the mechanisms are preloaded prior to long-term storage, or where they endure extended periods under atmospheric and vacuum conditions prior to actuati
18、on.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Evidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): N/AAdditional Key Phrase(s): a71 Environmenta71 Flight Equipmenta71 Hardwarea71 Parts Materials & Processesa71 SpacecraftAdditional Info: Approval Info: a71 Approval Date: 1997-03-7a71 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-,-,-
