Fatigue Margins Established by Unit and Spacecraft Protoqualification Tests

Abstract

Protoqualification (PQ) testing, typically performed on the first assembled electronic units and spacecraft, establish random vibration and thermal cycling fatigue margins for subsequent builds that are only subjected to the acceptance test program (ATP). Considering the fatigue damage induced by both unit- and spacecraft-level testing, fatigue margins are calculated for equipment exposed to ATP-level testing. Probabilistic analyses are also performed to determine the relationship between the fatigue margin and the demonstrated reliability for the unit to survive the mission. Parameters such as the number of retests and the material dependent fatigue acceleration exponent are considered.Using MIL-STD-1540E,1 PQ random vibration test guidelines of three decibels (+3 dB) above the acceptance input level for 2-minute-per-axis duration, the assessment shows that the test establishes ample fatigue margin for units subjected to the less stringent ATP. The probabilistic analysis shows that the established reliab...