The RMs1 is the new SWaP rotary cooler qualified by Thales in 2018. The architecture and the building blocks used to design that cooler have led to significant improved efficiency. The paper will describe the performances of the product, especially its thermal efficiency. An updated presentation of the reliability figures will also be done. The current available cryogenics power and the thermal efficiency allow RMs1 to be used for a wide range of applications. Either large detector arrays could be cooled by an RMs1 at High Operating Temperature, either smaller dies could be cooled down to lower temperature. The presentation will focus on the associated tuning of some parameters like the filling pressure to find the best trade-off adapted to the application. For instance, 24/7 applications will focus on reliability while HHTI may be more concerned by the power consumption. Also a first reflection will be presented on the potential definition and performance of a splitted RMs1 cooler where the cold fingers is detached from the compressor enabling a more flexible integration with a significantly reduced length in the axis of the cold finger. As a result, a mapping of cryogenics performances will be presented.
With miniature high operating temperature cryocoolers becoming commonplace, there is an increasing importance of accurate determination of the thermal properties of infrared dewars such as heat load and thermal mass, as well as an increasing challenge to obtaining these properties. Especially in the case where operating temperature in the application is far from liquid nitrogen temperature, such as with HOT detectors, the use of the various known methods should be carefully evaluated. Inconsistencies in results between the various available methods, such as nitrogen boil-off, multi-slope warm-up calorimetry, and theoretical thermal modelling will be discussed, and the work being done at Thales Cryogenics to resolve these inconsistencies is presented.
For five years, Thales Cryogenics has led a new development cycle in order to design and deliver a new generation of SWaP cryocoolers. Both linear and rotary Stirling coolers have been developed. SWaP coolers are especially designed to cool the emerging High Operating Temperature IR detector (HOT). Insofar as optimal detector performance for HOT technologies are still challenging, Thales forced himself to develop a rotary cooler that can cool detector at intermediate cold temperatures, ie. 90 to 140K, even if the optimal performances are reached for 150K. A first demonstrator was shown during the SPIE DS 2015 exhibition. That prototype was useful to investigate technologies to be introduced in order to drastically improve the compactness and the weight. Both aspects were reduced by 50% compared to a legacy RM2. The achieved compactness was identified as an optimal trade-off between mass and volume versus the associated production costs. Last year, Thales worked on new prototypes of the RMs1 SWaP rotary cooler. That product is the results of the previous RT and design phases, on one hand, and the adoption of generic standards on interfaces like the cold finger in order to simplify integration – and thus reduce overall cost – by our customers on the other hand. Associated performances were presented and commented. The current paper is focused on the qualification results obtained at the end of 2017. Especially, the available cooling power versus the cold temperature will be shared, next to other important key cryogenics performances such as the cool down time for dedicated detectors, characterized by a thermal masses and operational temperatures. Moreover, a particular effort has been made on other “soft” performances, in order to greatly improve the user experience, that is to say noise and induced vibrations. At last, first lifetime figures for the RMs1 are also presented and commented. As a conclusion, the compliance of the RMs1 performances with expectations for HOT IR detectors is discussed, in order to highlight the next steps of the development of the SWaP cryocoolers.
The cooler reliability is a major performance requested by the customers, especially for 24h/24h applications, which are a growing market. Thales has built a reliability policy based on accelerate ageing and tests to establish a robust knowledge on acceleration factors. The current trend seems to prove that the RM2 mean time to failure is now higher than 30,000hr. Even with accelerate ageing; the reliability growth becomes hardly manageable for such large figures. The paper focuses on these figures and comments the robustness of such a method when projections over 30,000hr of MTTF are needed.
The trend for miniaturized Integrated Dewar and Cooler Assemblies (IDCA) has been confirmed over the past few years with several mentions of a new generation of IR detector working at High Operating Temperature (HOT). This key technology enables the use of cryocooler with reduced needs of cryogenics power. As a consequence, miniaturized IDCA are the combination of a HOT IR detector coupled with a low-size, low-weight and low-power (SWaP) cryocooler. Thales Cryogenics has developed his own line of SWaP products. Qualification results on linear solution where shown last year. The current paper focuses on the latest results obtained on RMs1 prototypes, the new rotary SWaP cryocooler from Thales Cryogenics. Cryogenic performances and induced vibrations are presented. In a second part, progress is discussed on compactness and weight on one side, and on power consumption on the other side. It shows how the trade-off made between weight and power consumption could lead to an optimized solution at system level. At least, an update is made on the qualification status.