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Thermal testing of spacecraft electronic units prior to flight provides effective detection of design, process and workmanship defects. Thermal testing subjects units to cold and hot thermal environments beyond those expected in flight. The strength of screening effectiveness depends upon the number of cycles, the temperature range, and the temperature transition rate. MIL-HDBK-344 provides insight into the incurred stresses and quantitative value (precipitation efficiency) of the screening environment using these three test parameters. In this paper, MIL-HDBK-344 topics applicable to thermal testing of space hardware are summarized and comparisons are made between test environment strengths computed from MIL-HDBK-344 and MIL-STD-1540E. The weighting of these aforementioned test parameters in the precipitation efficiency equation are discussed and assessed.

In space vehicle applications, a thermal uncertainty margin, in the form of a temperature adjustment, is added to thermal model predictions to account for analysis uncertainties. As such, it is not so much a safety margin as it is a means of including nominal sensitivities of expected conditions and modifying analytic results for recognized model limitations. The intent of the thermal uncertainty margin for military space programs is to ensure that 95 percent of thermal model predictions are within ±11°C of flight temperatures. Recent flight thermal telemetry was compared to thermal model predictions to assess the continued use of the thermal uncertainty margin.

For spacecraft whose missions are considered low risk, it is typical for units to be subjected to unit-level thermal cycle and thermal vacuum testing. In recent years, however, the desire to reduce program costs and shorten development schedules has the aerospace testing community questioning the value of thermal vacuum testing all units. There may be instances where unit-level thermal vacuum testing is unnecessary if it can be shown that the unit’s design and performance is insensitive to the vacuum environment and that failures associated with the vacuum environment can be detected in other unit-level testing. The prescription of conditions under which unit thermal vacuum testing may be exempted should focus on establishing proven heritage, demonstrating design robustness through analysis and development testing, and reducing incurred risk. A general list of considerations by which vacuum-sensitivity may be assessed is provided herein.

Flight temperatures were compared to thermal balance test correlation data for two spacecraft. Results show that locations that were correlated with ground test data did not necessarily have similar correlation with flight data. Thermal models that were correlated extremely well showed the tendency toward better flight correlation. Thermal model correlation was successful in eliminating large temperature discrepancies in flight and providing a necessary understanding of the thermal design. Furthermore, flight correlation data verified the importance of the continued use of an ±11°C thermal uncertainty margin in spacecraft thermal design.

A method of calculating heat transfer coefficients across a bare bolted interface was developed using a finite element approach. Using an interface that represented an electronic box attached to a spacecraft mounting surface, contact pressures were analytically predicted and used to determine heat transfer coefficients. The resulting values were compared to similar predictions made using a finite difference approach and to experimental data. The predictions obtained from the finite element approach agreed well with the finite difference predictions and provided insight regarding the interface areas that conduct heat efficiently.