Considerations for Waiving Thermal Vacuum Testing for Mechanical Units



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47th International Conference on Environmental Systems


Environmental testing standards, such as MIL-STD-1540E, provide criteria to assess the vacuum sensitivity of electronic units in order to specify appropriate unit thermal testing conditions. When an acceptance unit complies with the criteria, its design and performance are deemed insensitive to vacuum conditions and in such cases, the unit thermal vacuum test can be waived with all unit thermal testing conducted in a thermal cycle test. As compared to electronic units, the development of similar criteria for mechanical units is more difficult given the wide variety of mechanical units and different failure mechanisms. Electronic units are generally comparable in construction, thermal design, thermal environment, operational use and performance, whereas mechanical units include structural members, moving mechanical assemblies, thermal heat transport devices and propulsion units. As a result, instead of specific criteria for determining vacuum sensitivity of mechanical units, a list of considerations is proposed that should be addressed by subject matter experts before a thermal vacuum test waiver is pursued. When the evaluation indicates that the mechanical unit is insensitive to vacuum conditions, tailoring proposals to waive the unit thermal vacuum test and conduct all thermal testing in thermal cycling may be submitted.

Thermal testing of mechanical units typically requires thermal vacuum testing only (no thermal cycle testing). For many mechanical units, the primary purpose of thermal testing is verification of performance in a flight-like thermal environment. This verification requires vacuum test conditions to properly simulate flight-like temperatures, vacuum and thermal gradients within the unit. To waive a mechanical unit’s thermal vacuum test, there needs to be high confidence that the unit’s operation and performance are not affected by vacuum or radiation heat transfer. The considerations discussed in this work provide the framework for gaining the necessary confidence in a mechanical unit’s insensitivity to the vacuum environment.


John Welch, The Aerospace Corporation, USA
ICES203: Thermal Testing
The 47th International Conference on Environmental Systems was held in South Carolina, USA on 16 July 2017 through 20 July 2017


Environmental Testing, Mechanical Units, MIL-STD-1540E, Thermal Vacuum Testing