1、Lessons Learned Entry: 0283Lesson Info:a71 Lesson Number: 0283a71 Lesson Date: 1993-07-12a71 Submitting Organization: JPLa71 Submitted by: J. F. ClawsonSubject: Magellan (MGN) High Electronic Temperatures Abstract: Magellan electronics bays ran 20 degrees C. hotter in flight than was anticipated. Co
2、ntaminants were believed to have off-gassed in flight and accumulated on the thermal tiles, thus increasing solar absorptance. Evaluate vacuum outgassing procedures, and demonstrate system operation at temperatures beyond those expected in flight. For missions to inner planets, the spacecraft system
3、 thermal control design should minimize or avoid solar exposure on critical thermal control surfaces.Description of Driving Event: Early in the MGN mission, sun viewing bus bays (and associated electronic subsystems) were at least 20 degrees C. hotter than anticipated. This effect increased as the m
4、ission continued. Temperatures were at or above flight acceptance levels, and for short periods of time, at or near qualification levels for some bays. Fortunately a special margin test phase during the MGN solar thermal vacuum ground test had demonstrated system operations at these temperatures. Ev
5、en higher equilibrium temperatures were anticipated as the mission progressed.The apparent solar absorptance increase (derived from the flight temperatures) for MGN is generally global and appears to be approximately twice that expected based on known data bases.Fairly recent theoretical and experim
6、ental work shows the possibility that contaminants (organic molecules in particular) outgassed by the spacecraft and/or solar panels may be the cause of increased absorptance (through interaction with solar ultraviolet radiation) and thus higher temperatures. The MGN effect may be due to the greater
7、 ultraviolet energy at Venusian solar distances compared to Earth (about 2 solar constants). The MGN solar panels received only minimal outgassing prior to flight (20 hours).Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-The impacts of these high su
8、bsystem temperatures were significant. Extensive unplanned analyses and mission planning activities were required, including spacecraft attitudes to prevent even higher temperatures, and some mapping science was lost. Were it not for the confidence gained during the solar thermal vacuum test at thes
9、e higher temperatures, significantly more science would have been lost. The long life of MGN is certainly threatened: concerns exist for both electronic part life and solder joint fatigue.Additional Keyword(s): High TemperatureReference(s): PFR # 52228, ISA # 5649Lesson(s) Learned: 1. Effects of con
10、tamination on critical thermal control surfaces can be more severe than previously assumed, resulting in higher than expected flight temperatures.2. The Mariner 10 thermal control concept (a sun pointing spacecraft with a large sun blocking thermal shade) would result in fewer thermal issues than th
11、e transient attitude thermal design employed on Magellan.Recommendation(s): 1. Vacuum outgassing procedures should be evaluated for consistency and effectiveness.2. System operation at temperatures beyond those expected in flight should be demonstrated during ground system thermal vacuum tests.3. Fo
12、r missions toward the sun from earth, the spacecraft system thermal control design should minimize or avoid solar exposure on critical thermal control surfaces.Evidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): N/AAdditional Key Phrase(s): Provid
13、ed by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-a71 Environmenta71 Spacecrafta71 Test & VerificationAdditional Info: Approval Info: a71 Approval Date: 1993-01-29a71 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-,-,-
