1、Lessons Learned Entry: 0922Lesson Info:a71 Lesson Number: 0922a71 Lesson Date: 2000-11-02a71 Submitting Organization: JPLa71 Submitted by: D. Oberhettinger/W. MateerSubject: Bubble Formation in Dampers May Cause Transient Un-Damped Motion (1998) Abstract: Due to the formation of a “hydraulic deadban
2、d,” MPL solar panels “flopped” when deployed following thermal vacuum test. Sustained exposure to full or partial vacuum may create bubbles in viscous damping fluids. To varying degrees, all viscous dampers are believed to be subject to bubble formation. Early in-flight deployment may reduce the ris
3、k of deadband formation in viscous fluid dampers and of subsequent structural and electrical damage. During hardware design and deployment sequence planning, consider the impact of bubble formation upon damper deadband characteristics and the effect on deployment loads and dynamics.Description of Dr
4、iving Event: Viscous fluid dampers commonly used to control deployments may exhibit an initial transient of un-damped motion when actuated after prolonged exposure to vacuum. The Mars Polar Lander (MPL) solar panels “flopped“ when deployed following thermal vacuum test. It was determined that small
5、bubbles had risen to the top of the deployment dampers and coalesced, resulting in a region of reduced damping during the damper stroke- a hydraulic deadband. Although the array was not damaged, a study was undertaken to evaluate the risk to in-flight deployment of the Mars Global Surveyor (MGS) hig
6、h gain antenna (HGA), which uses a similar damper and is deployed following the cruise phase of the mission.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-refer to D descriptionDDeployment Hinge Assembly for the MGS HGAThe study determined that expo
7、sure of a damper to vacuum produces bubbles in the silicone fluid within the vane cavity. It was found that a 20-day exposure of this particular damper to vacuum/low pressure in a gravity field will allow the bubbles to coalesce; this results in a maximum deadband of 55 degrees, insufficient to caus
8、e structural damage in this application. To varying degrees, all viscous dampers are believed to be subject to bubble formation.Reference(s):1. “MGS High Gain Antenna Deployment Independent Review,“ Jet Propulsion Laboratory IOM No. 3501-WHM-98-001, William H. Mateer II, October 23, 1998.2. “Viscous
9、 Damper, (Sealed Damper Assembly, Non-Temp., Compensated),“ GIDEP Alert No. H6-P-98-01, January 30, 1998.Category: Subsystem and Instrument DevelopmentLesson(s) Learned: 1. Sustained exposure to full or partial vacuum may create bubbles in viscous damping fluids, affecting damping mechanism performa
10、nce.2. Early in-flight deployment may reduce the risk of deadband formation in viscous fluid dampers and of subsequent structural and electrical damage.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Recommendation(s): During hardware design and depl
11、oyment sequence planning, consider the impact of bubble formation upon damper deadband characteristics and the effect on deployment loads and dynamics.Evidence of Recurrence Control Effectiveness: The referenced GIDEP alert recommends a design approach to minimize bubble formation. This lesson will
12、be evaluated for possible corrective action and practices may be modified as appropriate.Documents Related to Lesson: N/AMission Directorate(s): a71 Exploration Systemsa71 Sciencea71 Aeronautics ResearchAdditional Key Phrase(s): N/AAdditional Info: Approval Info: a71 Approval Date: 2001-01-10a71 Approval Name: Eric Raynora71 Approval Organization: QSa71 Approval Phone Number: 202-358-4738Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
