Cryocooler Prognostic Health Management System

Abstract

The use of cooled sensors in ever more complex, integrated applications has made determination of the cryocooler and related component "health or remaining reliable useful life" a critical factor in successfully meeting mission requirements. Sest Inc. has been actively developing a Cryocooler Prognostic Health Management System (CPHMS) under U.S. Air Force sponsorship to address this issue. Using non-invasive means to measure performance of a cryocooler with limited data availability, a variety of failure mechanisms have been evaluated based on a combination of "physics of failure" assessments as well as the results of extensive cryocooler testing carried out on "healthy" and selectively "degraded" cryocoolers. Used in conjunction with simple models of the fundamental dynamic behavior of linear drive free-piston systems, it is possible to identify the presence and type of potential degradation mechanisms. For a diagnostic system, identifying that a problem exists is half the battle. In the CPHMS with the results from the earlier diagnostic evaluation available, it is possible to carry out prognostic estimation of the reliable remaining useful life (RRUL) by the use of Bayesian statistics. The latter are used to continuously improve the estimations of RRUL for the cryocooler under various failure modes. While the CPHMS is focused on "tactical" class cryocooler, the basic approach is easily adapted to other cryocooler types, as well as more complex integrated systems.