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Publications - Thales Cryogenics

ICEC 2002 – Development of high reliability cryogenic coolers at Thales cryogenics

The demand for more cooling power for infrared imagers, which may require up to 3W of cooling power at 77K, is nowadays surpassed as other industries are getting interested in commercial attractive cryogenic cooling as well.  These potential markets require robust, efficient and affordable coolers with cooling capacities up to 6000mW at 77K.  Thales Cryogenics has been working on the development of a complete range of long lifetime coolers in the past years able of generating cooling powers up to 6000mW at 77K.

Tonny Benschop (a), Jeroen Mullié  (a), Peter Bruins (a), Jean Yves Martin (b)

(a) Thales Cryogenics BV, PO box 6034, NL-5600HA Eindhoven, The Netherlands

(b) Thales Cryogenie SA, 4, Rue M. Doret, BP22, 31701 Blagnac, France

ICC 12 2002 – MTTF prediction in design phase on THALES CRYOGENICS integral coolers

A continuous improvement of Stirling integral coolers MTTF is necessary to answer the new market requirements. The time spent in the design phase is critical to get the product ready at the right time and to reduce the development costs. In order to reduce the development risks (be sure to get in the new design a higher MTTF), we have developed a calculation method for prediction of the expected MTTF of our coolers. Early in the design phase, we use the method of predictive calculations on MTTF. For that, we needed the MTTF data for each critical single part or function in the cooler. In order to fill the lack of data available on failure rates for mechanical parts (tightness, coating…) in our particular application, we built a list of the different functions inside the cooler from the failure point of view. The data collected from the extensive lifetime tests results already performed allowed us to determine the MTTF for each function. These elements are introduced into the predictive calculation of the new design. The expected MTTF of the new cooler is then available. The results obtained by calculation are still only indicative. These results have to be verified as quickly as possible. To reduce the duration of lifetime tests, we apply the accelerated tests procedure developed and verified since 2 years. This method allows obtaining in some weeks results on MTTF equivalent to several thousand hours. This method was validated on previous definitions. This MTTF calculation is today applied on all the design of our integral coolers and in particular on the new design of RM2 cooler being under development at Thales cryogenics. This method will be discussed and the results of the calculations performed on the new RM2 design will be presented. Introduction Among the performances of a cryogenic cooler, the MTTF is an important element. The market requirement for MTTF is strongly increasing for several years. A continuous improvement of our Stirling integral coolers is essential to remain competitive. Up to now, the MTTF is determined by lifetime tests realised on the coolers. The standard test profile applied during the lifetime test is representative of operation in typical application with alternative stops (periods of storage), starts and running at room and hot temperatures. The duration of such lifetime tests is very long. In addition, the customer is requiring to know the MTTF of the cooler very early in his system design process and is also interested in having information regarding the MTTF of the cooler in his specific application. Because of the duration of such standard lifetime test (several months), it is generally not possible to wait until the standard lifetime test is finished before providing the expected MTTF data to our customers. For costs reasons, it is not possible for us to run lifetime tests representative for each customer’s application. In the same time, it is essential for us to have a good estimation of the expected MTTF early in the design process in order to reduce the duration of the design phase and to reduce the development risks (design in accordance with the targeted MTTF, verify the design by calculation followed by actual tests).
In that context, we worked on a methodology allowing the calculation of the expected MTTF of our coolers. The lifetime test performed after design are then used as a confirmation of these calculations. Nevertheless, the actual test remains necessary in order to increase our knowledge on the coolers and validation of our calculations. In parallel and in order to reduce the duration of the lifetime tests, we developed an accelerated lifetime test protocol. This method for calculating the expected MTTF of the coolers will be presented. The results of these calculations will be presented for the RM2 cooler. We will present the MTTF results for the RM2 cooler in the configuration produced in serial production today and on the new design of RM2 cooler at this moment under development. The Thales cryogenics RM2 (Photo 1) cooler is a light weight, high efficiency integral Stirling cooler. It provides a total cooling power of 400 mW at 77K and 23°C ambient temperature at 9 Wac input power. Its maximum mass is 275g. This cooler has been produced in a total quantity over 4000 units in the past years. An upgraded version of this cooler is under development in our facilities. The serial production of this new version is planned to start in the second half of 2002.

J.M. Cauquil (a) and J.Y. Martin (a), P. Bruins (b) and T. Benschop (b)

(a) Thales cryogénie SA, Blagnac, France

(b) Thales cryogenics BV, Eindhoven, The Netherlands

ICC 12 2002 – Miniature 50 to 80 K Pulse Tube Cooler for Space Applications

A Miniature Pulse Tube Cooler is presently under development in partnership between AL/DTA, CEA/SBT and THALES Cryogenics. The Engineering Model foreseen is aiming to provide 800 mW at 80 K with 50°C ambient temperature and 40 watts maximal input power to the motors of the compressor. A development phase has been performed with an in-line architecture for the Pulse Tube cold finger connected to an existing flexure bearing compressor from Thales Cryogenics. Presently, more than 900 mW at 80 K has been achieved at 288 K ambient temperature provided by water cooling, in inertance mode and with less than 25 watts PV work.  The development phase is presented as well as the various trade-offs made, both on the cold finger and compressor side, to cope with the thermal, mechanical and electrical environmental specifications. The impact of the matching between compressor and Pulse Tube cold finger is also discussed. This work is performed in the framework of a Technological Research Program funded by the European Space Agency. An Engineering Model will be delivered to ESA/ESTEC in February 2003. This coming generation of Miniature Pulse Tube Cooler will be used for the cooling down of detectors in future earth observation missions.

T. Trollier and A. Ravex (1) I. Charles and L. Duband (2) J. Mullié, P. Bruins and T. Benschop (3) M. Linder (4)

(1) Air Liquide Advanced Technology Division, AL/DTA Sassenage, France

(2) Atomic Energy Committee, Low Temperature Div., CEA/SBT, Grenoble, France

(3) THALES Cryogenics B.V. Eindhoven, The Netherlands

(4) European Space Agency, ESA/ESTEC, Noordwijk, The Netherlands

ICC 12 2002 – Low Vibration 80 K Pulse Tube Cooler with flexure bearing compressor

In order to provide cryogenic cooling for applications that are extremely sensitive to vibrations, a Pulse Tube Cooler and associated cooler drive electronics are developed at Thales Cryogenics. Initially, the development focussed on the double inlet design because of its potential high efficiency. The DC flow arising in this design can decrease the performance significantly. Although this DC flow is successfully suppressed in prototype double inlet pulse-tubes, the solution proves to be too complex to be acceptable for large production quantities. It is therefore concluded that due to the DC flow, the double inlet design is not suitable for mass production, and the research further focussed on the development of an inertance type pulse tube. Optimisation of the U-shape inertance-type pulse tube results in a very reproducible cooling system that is easy to produce in large quantities. The cooling performance of 500 mW at 80 K, for 60 W of electrical input, is comparable to that of a double-inlet system without DC flow. Based on previous experience with the vibration reduction of Stirling coolers, a DSP-based cooler drive unit is designed that reduces the vibrations of the dual-opposed piston flexure bearing compressor. The paper describes the results of a reduction method for DC flow, gives the design trade-offs for the inertance pulse-tube, and describes the vibration control algorithm, -hardware and results.

P.C. Bruins, A. de Koning and T. Hofman  Thales Cryogenics BV. NL 5626 DC Eindhoven,  The Netherlands

ICC 12 2002 – High Capacity Flexure Bearing Stirling Cryocooler On-Board the ISS

A high capacity Stirling cryocooler has been demonstrated at Development Model level during the year 2001 under AL/DTA and THALES Cryogenics co-funding. This development is based on a commerciallyoff-the-shelf LSF9320 type cryocooler from THALES Cryogenics (flexure bearing compressor and a standard wearing Stirling cold finger). It is now featuring a dual opposed piston compressor modified in order to drive pneumatically a Stirling cold finger also implementing flexure bearing technology. The pneumatically driven cold finger does not use any motor to obtain the movement and correct phase shift between the Stirling displacer and the pressure wave. The absence of this motor enhances the reliability of the system and simplifies the electronic control required to drive the system. This reliable and powerful cooler concept has been selected as the cooling system for the ESA / CRYOSYSTEM vial freezers to be delivered by AL/DTA to ASTRIUM for use on board the International Space Station in 2006. The CRYOSYSTEM is a set of facilities for ultra-rapid cooling, preservation and storage of biological samples and protein crystals at -180°C. The actual performances are presented for various water heat sinking locations taking into account the benefit of the Medium Temperature Loop (MTL) available on-board. Future performance improvements are discussed.

T. Trollier, A. Ravex and P. Crespi(1) J. Mullié, P. Bruins and T. Benschop (2)

(1) Air Liquide Advanced Technology Division, AL/DTA Sassenage, France

(2) THALES Cryogenics B.V. Eindhoven, The Netherlands