Failure analysis of the space Stirling cryocoolers

摘要

With extensive application of infrared detective techniques, Stirling cryocooler, used as an active cooling source, has gained a good chance to prosper because of its special advantages, such as the variability of cooling capacity, compact configuration and non-sensitivity for the satellite attitude. After the cooler's cooling performance can satisfy the mission's request, its reliability level is crucial for its application. Today's Oxford-type Stirling cryocooler is designed to be no failure, but due to the variability of material and workmanship, there are still some failures. Some of them are infant mortality, which occur by chance, and can be eliminated by ageing test. However, some of them are persistent problems, which are unavoidable, and can only be minimized. These failure modes restrict the cooler's lifetime. To the long-life Oxford-type Stirling cryocooler, after the ageing test to eliminate defective products, four crucial failure modes affecting the cooler's life were found out by failure analysis, which included wear, gaseous contamination, gas leakage and fatigue. These failure modes occur in different phase of cooler's lifetime. Wear takes place in cooler's early life, due to the design of linear motor driving, flexure bearing supporting and clearance sealing. Gaseous contamination will not arouse severe performance degradation until the contaminants accumulate to a certain amount, but it could be fatal when it works. So it is more serious to the coolers whose lifetime is more than 10,000 h, and it belongs to cooler's wearout life. Based on FEM analysis and screening test, the chance of fatigue failure is very small now. Helium leakage is a persistent problem and degrades cooler performance, and the degree of degradation relates to the amount of helium leakage.