Cryocooler reliability issues for space applications

Analyzing cryocooler reliability has been problematic from the beginning, Classic reliability analyses rely on statistical sampling and comparing modes to other similar systems where statistical results are available. These approaches do not apply to cryocoolers, particularly cryocoolers for aerospace applications. The industry has not built enough total cryocoolers, let alone a single type or cooler, to provide any meaningful statistical sample. This forces us to rely on comparing failure modes of similar systems to that of the cryocooler. which leads to the next problem: today's aerospace cryocooler is designed to have no failure modes. What can it be compared to? Any classic reliability study performed on a cryocooler makes several critical assumptions that completely dominate the results. Change the assumptions and you get a different answer: the results are dictated by the assumptions not the hardware. There are no easy answers to these problems. This paper attempts to show why classic reliability studies do not apple to cryocoolers and that as an industry we must work together to show that all cryocoolers have high levels of reliability. (C) 2002 Elsevier Science Ltd. All rights reserved.