Reliability growth of coolers for advanced optical systems and instruments

Cryogenic coolers have historically been the weaklink in the overalireliability ofoptical systems and instruments incorporating these devices. The reliability limitation of these coolers incorporating rotary reciprocating compressor mechanisms (commonly referred to as rotary drive coolers) has been predominantly associated with contamination that can freeze out and foul critical operating surfaces within the cooler. This paper reports on the results of significant breakthroughs that have been made in controlling this life limiting feature leading to fivefold increases in coolers reliability over the last two years. Extensive testing ofcoolers with manufacturing improvements has been conducted since mid-1988. Twenty-five coolers (four cooler models) have been subjected to rigorous reliability cycle testing per military usage requirements, accumulating 50,000 hours of operation with only 9 failures. Mean-time-to-failure (MTTF) has been demonstrated to have increased from 300 to 1000 hours to 1500 to 3000 hours for this family ofcoolers. This breakthrough in cooler reliability has resulted in a family of miniature cryogenic coolers that can satisfy system reliability requirements heretofore considered unattainable with rotary driven machines.