HALT process for Thales rotary cooler reliability release

Rotary Stirling cooler reliability was considered as a limitation compared to linear Stirling coolers. Nevertheless, cooler reliability is a major performance requested by customers, especially for 24/7 applications, which are a growing market. Indeed, most of the time, coolers are one of the components dimensioning the lifetime of the system. This is due to the fact that the cooler remains a mechanical system with moving parts.

On the other hand, rotary Stirling coolers are a very good solution to reduce SWaP (Size, Weight and Power) at system level as they are more compact and efficient. Thus, several improvements have been made on rotary coolers in order to fill-in the reliability gap between linear and rotary coolers. Reliability improvement is an important part of Thales rotary coolers' roadmap in order to propose on the market coolers able to answer to SWaP and reliable applications. For instance, Thales claims that the RM2 reliability is higher than 50,000h for a typical mission profile.

Increasing the cooler reliability becomes a challenge when the times come to validate evolutions. Indeed, lifetime tests are necessary before releasing an evolution but it is necessary to wait the end of the tests. For instance, with a reliability higher than 25,000h, several years are needed before the results. This is an important aspect that can explain the difficulty to increase the reliability.

The paper will focus on the latest works made at Thales on rotary coolers in the frame of that target. Works on Thales coolers will be used as an example. Firstly, we will illustrate the latest reliability improvements made on this cooler. In a second part, we will describe how to accelerate lifetime tests. Finally, the lifetime tests results will be presented.