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With extensive application of infrared detective techniques, Stirling cryocoolers, used as an active cooling source, have
been developed vigorously in China. After the cooler's cooling performance can satisfy the mission's request, its
reliability level is crucial for its application. Among all the possible failure mechanisms, gas contamination has been
found to be the most notorious cause of cooler's performance degradation by failure analyses. To analyze the
characteristic of gas contamination, some experiments were designed and carried out to quantitatively analyze the
relationship between failure and performance. Combined with the test results and the outgassing characteristic of
non-metal materials in the cryocooler, a degradation model of cooling performance was given by
T(t)=T0+A[1-exp(-t/B)] under some assumptions, where t is the running time, T is the Kelvin cooling temperature, and
T0, A, B are model parameters, which can be given by the least square method. Here T0 is the fitting initial cooling
temperature, A is the maximum range of performance degradation, and B is the time dependent constant of degradation.
But the model parameters vary when a cryocooler is running at different cooling temperature ranges, or it is treated by
different cleaning process. In order to verify the applicability of the degradation model, data fit analysis on eight groups
of cooler's lifetime test was carried out. The final work indicated this model fit well with the performance degradation of
space Stirling cryocoolers due to gas contamination and this model could be used to predict or evaluation the cooler's
lifetime. 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. The measures taken to control or minimize its damage were discussed as well. To the long-life cryocooler,
internal materials must be baked and organic/epoxy materials should be used as few as possible. Further more, pipeline
for filling working fluid must have purifying facilities.
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