Introduction

Achieving high reliability is a key design driver for most cryogenic systems required to provide continuous cooling during multiyear space missions. Key activities critical to achieving high reliability are

• the use of extensively tested, robust subassemblies, such as cryocoolers and electronics that incorporate well-understood design principles with a proven history of high reliability

• the thorough characterization, qualification, and lifetesting of the individual cryosystem subassemblies for the intended space mission application, including environmental extremes and system interface issues

• the incorporation of redundancy, in the form of redundant coolers and/or redundant drive electronics, to protect against individual subassembly failures

• the thorough prediction of the cryogenic refrigeration load over the mission life cycle and incorporation of significant margin to cover load growth and cryocooler performance loss over time

• the thorough testing of the full-up cryosystem hardware to verify its design robustness with respect to the actual as-built cryogenic loads (including the effects of expected on-orbit contamination), the actual system-level interfaces, and the predicted environmental extremes

This chapter provides means of predicting the reliability of a one-of-a-kind cryocooler or cooler system subassembly, quantifying the reliability performance of a proposed cooler system design, including any incorporated redundancy, and trading off the reliability gain achieved from redundancy against the losses associated with increased system complexity and cryogenic load growth caused by adding redundancy.

Life Test and Flight Operational Data

An examination of some...