Mathematics – Probability
Scientific paper
Aug 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004esasp.558..291p&link_type=abstract
Proceedings of the 5th International Symposium on Environmental Testing for Space Programmes Noordwijk, The Netherlands (ESA SP-
Mathematics
Probability
1
Probabilistic Analysis, Stress Analysis, Fatigue Damage, Thermal Cycling
Scientific paper
A number of electronics units built for a spacecraft experienced performance degradation after acceptance thermal cycling due to cracked solder joints. Detailed finite-element stress and fatigue analyses showed that the combination of poorly formed solder joints and gold embrittlement was the main cause of the cracked joints. Since removal and repair of all similar units already integrated on a spacecraft would have resulted in a severe schedule slip, a risk assessment was first conducted. A statistical analysis was performed to assess the probability of failure during mission operations based on: (1) the test thermal cyclic history of all failed and operational units, (2) the test thermal cyclic exposure of the units awaiting launch, and (3) the expected thermal cyclic environment during the orbital mission. The statistical analysis was based on a Weibull failure distribution with an assumed shape parameter and a maximum likelihood estimate (MLE) for the scale parameter. Fatigue equivalency analysis was used to relate the fatigue damage for the large thermal excursions that the units were subjected to during ground testing and the smaller thermal shifts expected during the mission. The investigation showed that the risk of unit failure during the mission was low. Further mitigation of this risk was shown to be achievable by changing orbital operational procedures to limit the thermal swings that these units will be exposed to during the mission.
Ni Yang-Yang
Paden R. S.
Pierre-Louis E.
Womack J. W.
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