OVERCOMING UNINTENDED CONSEQUENCES OF AMBIENT PRESSURE THERMAL CYCLING ENVIRONMENTAL TESTS

摘要

A low-earth-orbit (LEO) satellite is expected to undergo 58,400 temperature cycles in its 10-year life, and its owner has a substantial economic incentive to ensure that it does. That is why satellite material coupons are subjected to extensive test programs prior, not only to launch, but, in the case of new materials and manufacturing processes, to building the satellite. This is problematic because an average satellite production cycle lasts 3 years, and a comprehensive test program can require much of that. For example, 58,400 temperature cycles in a vacuum chamber require, at 4 hours/cycle, 27 years. Clearly this is inadequate. Similar testing in a regular chamber can be completed, at 9 minutes/cycle, in 342 days, or just under 1 year. This gives a developer time to verify his materials prior to committing to hardware and still launch his satellite within the 3-year schedule. Unfortunately tests on some newer aerospace laminates in a regular chamber have led to unexpected discoloration and even delamination. The cause was eventually determined to be the presence of greater than 10,000 ppm of oxygen and moisture in the chamber, even with a heavy nitrogen purge. Following numerous iterations, a chamber was designed that contains substantially less than 100 ppm oxygen, in fact, as low as 5 ppm.