Investigation of Thermal Test Effectiveness for Spacecraft Electronic Units Using Precipitation Efficiencies of MIL-HDBK-344

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. It was found that the fatigue equivalency equations in MIL-STD-1540E specify a significantly larger number of required cycles for various test temperature ranges as compared to cycles computed from MIL-HDBK-344 equations.Cross Reference: