This PDF file contains the front matter associated with SPIE Proceedings Volume 10626, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

Lockheed Martin’s Advanced Technology Center has developed a series of long life small cryocoolers for avionics and space sensor applications. We report the technology readiness level and performance of the Lockheed Martin Space Mini cryocooler thermal mechanical unit (TMU). The design is based on the standard unit originally developed for NASA/GSFC and a higher capacity developed for ESA. This Mini TMU provides a single stage cold head separated from the compressor and is an ideal choice for medium size cryogenically cooled instruments.

Three miniature Joule-Thomson cryogenic coolers and a testing set up were built to investigate the cooling performance in this work. Shell-and-tube heat exchanger and plate fin heat exchangers with rectangular micro channels were designed to achieve high specific surface area. The main processing technology of micro mixed refrigerant cooler (MMRC) was described. The design and fabrication processing of the plate fin heat exchangers were also described. The new developed micro plate-fin type heat exchanger shows high compactness with the specific heat surface larger than 1.0x104 m²/m³. The results of experimental investigations on miniature mixed refrigerant J-T cryogenic coolers driven by a Mini-Compressor were discussed. The performance evaluation and comparison of the three coolers was made to find out the features for each type of cooler. Expressions of refrigeration coefficient and exergy efficiency were pointed out. No-load temperature of about 112 K, and the cooling power of 4.0W at 118K with the input power of 120W is achieved. The exergy efficiency of the SJTC is 5.14%.

A Stirling cryocooler is under development for small satellites where weight and packaging volume must be minimized while achieving high thermodynamic efficiency. The challenge is exacerbated by the requirement to operate efficiently down to at least 80K. Small size and weight are achieved by operating at a frequency well in excess of the current state of the art, up to and beyond 200 Hz. The efficiency requirement motivates the implementation of a moving Stirling displacer instead of a pulse tube. The latter has the benefit of simplicity, but at the unacceptable expense of thermodynamic efficiency since the expansion power in a pulse tube is dissipated, not recovered as in a Stirling. While using a Stirling displacer avoids several critical loss mechanisms inherent in a pulse tube, it does introduce the “shuttle loss,” which arises from the motion of the displacer within a fixed cylinder/bore. While both the displacer and the bore have nearly linear axial temperature distributions, the relative motion results in instantaneous radial temperature gradients across the clearance gap, which causes heat transfer between the structures. The direction of this heat transfer changes during a cycle, but ultimately “shuttles” heat from the warm end to the cold tip. This paper reports on a computational fluid dynamics (CFD) study aimed at quantifying this loss in the size and frequency range of interest as a function of relevant geometries and piston materials, and assessing its sensitivity to various design parameters. Parametric calculations show that among the various design parameters the overall conductance of the displacer has the most significant effect on the shuttle loss.

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.

Minimum size, weight and power (SWaP) is a key requirement for state-of-the-art high performance IR Integrated Detector Cooler Assemblies (IDCA). In the past, the cryocooler was predominantly impact all of the three SWaP characteristics. High operating temperature (HOT) detectors allowed the development for dedicated HOT cryocoolers with significantly improved SWaP. Power consumption for instance, can now be in the same order of magnitude as the detector electronics. AIM developed a family of linear cryocoolers to meet the demands for HOT, SWaP applications. The coolers are also optimized to meet Harsh Environments. Methods to meet such requirements will be discussed for different designs like single and dual piston compressors. Performance data for new cooler models will be presented.

In the modern design approach, the cold portion of Integrated Dewar-Detector-Cooler-Assembly (substrate, infrared focal plane array, cold shield and cold filter) is directly mounted upon the distal end of a cold finger of a cryogenic cooler with no mechanical contact with the warm Dewar shroud. This concept allows for essential reduction of parasitic (conductive) heat load. The penalty, however, is that resulting tip-mass cantilever is lightly damped and, therefore, prone to vibrational extremes typical of the modern battlefield. Without sufficient ruggedizing, vibration induced structural resonances may affect image quality and even may cause mechanical failures due to material fatigue. Use of additional front supports or thickening the cold finger walls results in increased parasitic conductive heat load, power consumption and mechanical complexity. The authors explore the concept of wideband dynamic absorber in application to ruggedizing the Integrated Dewar-Detector-Cooler Assembly.

In this paper, a pulse tube cryocooler used in a wide-field survey telescope is described, this telescope is going to be launched in 2020 in China. And in the telescope, large focal plane array (FPA) detectors working at 188K generate 100W heat which need to be cooled. In order to cool the detectors, three 50W@170K pulse tube cryocoolers are used, with designed life-time of l0 years. To decrease the vibration and electromagnetic interference to the detectors to the minimal limit, two cryogenic loop heat pipes (LHPs) are used to transfer heat from the detectors to the cold tips of the pulse tube cryocoolers. And each cold tip is specified to match the condensers of the LHPs. The cryolooer is driven by a dual-opposed piston compressor with a pair of moving magnet linear motors, one of the motors is also used as the adaptive active vibration suppressor. The cryocooler reaches 16.6% Carnot efficiency at cooling power of 50W@170K with 230Wac input power.

The widespread use of rotary Stirling coolers in high performance thermal imagers used for critical 24/7 surveillance tasks justifies any effort to significantly enhance the reliability and predictable uptime of those coolers. Typically the lifetime of the whole imaging device is limited due to continuous wear and finally failure of the rotary compressor of the Stirling cooler, especially due to failure of the comprised bearings. MTTF based lifetime predictions, even based on refined MTTF models taking operational scenario dependent scaling factors into account, still lack in precision to forecast accurately the end of life (EOL) of individual coolers. Consequently preventive maintenance of individual coolers to avoid failures of the main sensor in critical operational scenarios are very costly or even useless. We have developed an integrated test method based on ‘Micro Electromechanical Systems’, so called MEMS sensors, which significantly improves the cooler EOL prediction. The recently commercially available MEMS acceleration sensors have mechanical resonance frequencies up to 50 kHz. They are able to detect solid borne shock pulses in the cooler structure, originating from e.g. metal on metal impacts driven by periodical forces acting on moving inner parts of the rotary compressor within wear dependent slack and play. The impact driven transient shock pulse analyses uses only the high frequency signal <10kHz and differs therefore from the commonly used broadband low frequencies vibrational analysis of reciprocating machines. It offers a direct indicator of the individual state of wear. The predictive cooler lifetime model based on the shock pulse analysis is presented and results are discussed.

Optical refrigeration of rare-earth-doped solids has reached the boiling point of argon, 87 K, and is expected to cool to that of nitrogen, 77 K, in the near future. This technology is poised to pave the way to compact, reliable, and vibrationfree all-solid-state optical cryocoolers. By attaching the Yb:YLF cooling crystal to a cold finger via a double 90° kink thermal link, we have cooled a silicon temperature sensor to below 151 K. An advanced design of the thermal link and the clamshell surrounding the cooled assembly successfully controlled the flow of heat and radiation to allow cooling of a payload to cryogenic temperatures. Key elements of the design were a low-absorption thermal link material, an optimized thermal link geometry, and a spectrally-selective coating of the clamshell.

With the achievements made in the last decade with respect to reliability and cryogenic performance, the use of Stirling and Pulse Tube cryocoolers for new application areas has become viable. Thales Cryogenics has been challenged by its customers to deliver robust and compact solutions for a variety of applications. The test approaches within the Thales Environmental Test Lab – a center of excellence within the Netherlands – have been refined significantly, departing from the classical robustness testing principles, which typically consist of submitting the product to an environment with a compressed energy allocation - shorter time duration and higher PSD levels. An overview is given of recent activities at Thales Cryogenics regarding the development and testing of linear Stirling cryocoolers for extreme environmental conditions. A novel cooler will be presented that has been developed specifically for operation in high ambient temperature conditions. In addition, an overview will be given of ongoing test and development activities regarding coolers for operation under severe mechanical loads. Design aspects, margin philosophy, test plans (including robustness testing) and test results will be presented.

This paper designs a vacuum packaged Dewar for meteorological satellites. It integrates an 80 × 1 long wavelength photodetector with a wavelength of 13.2 μm to 13.8 μm and a dual band focal plane detector with a wavelength of 10.3um-11.3um / 11.5um-12.5um. The detector uses a mechanical cooler to reach an operating temperature of 60K. The theoretical calculation and simulation analysis are carried out from two aspects: cold load and mechanical vibration of Dewar. The analysis shows that when the ambient temperature is room temperature and the detector operating temperature is 60K, the total heat loads of the cold plate is 1.25W. Where the wires loss accounts for about 36% of the total heat load and the detector Joule heat accounts for about 21%. The mechanical vibration analysis of Dewar shows that the cold plate pillar is the main factor affecting the mechanical properties of the structure. Increasing the pillar support increases the base frequency of the Dewar from 379 Hz to 539 Hz, thereby increasing the mechanical base frequency of the Dewar components.

The growing demand for EO applications that work around the clock 24hr/7days a week, such as in border surveillance systems, emphasizes the need for a highly reliable cryocooler having increased operational availability and optimized system's Integrated Logistic Support (ILS). In order to meet this need, RICOR developed linear and rotary cryocoolers which achieved successfully this goal. Cryocoolers MTTF was analyzed by theoretical reliability evaluation methods, demonstrated by normal and accelerated life tests at Cryocooler level and finally verified by field data analysis derived from Cryocoolers operating at system level. The following paper reviews theoretical reliability analysis methods together with analyzing reliability test results derived from standard and accelerated life demonstration tests performed at Ricor's advanced reliability laboratory. As a summary for the work process, reliability verification data will be presented as a feedback from fielded systems.

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.

To meet the increasing demand for compact cryocoolers for commercial applications, AIM developed the MCC cooler family. A key requirement for such applications is long MTTF life as mostly a 24/7 operation is needed. Further technical solutions have been investigated and implemented in the cooler design to comply with common industrial standards and regulations. Cooler types, technical solutions and performance data will be presented.

Recently developed high operational temperature (HOT) infrared detectors are designed to be integrated upon very short, small diameter cold fingers and to show their best performance when cooled to 150K and above. This implies severe limitations on the routinely used LN2 boil-off isothermal calorimetry of Integrated Dewar-Detector Assemblies (IDDA). The authors adapted technique of warm-up calorimetry and show that the accurate heat load evaluation may be performed by precooling the IDDA and comparing the warm-up slopes of the thermal transient processes under different trial added heat loads. Because of the simplicity, accuracy and ability to perform calorimetry literally at any temperature of interest, this technique shows good potential for replacing traditional boil-off calorimetry. The authors are reporting on developing computerized test station performing automatic warm-up calorimetry of HOT IDDA. They also reveal some statistical data in support of attainable repeatability and accuracy.

The Northrop Grumman Aerospace Systems (NGAS) has expanded the cryocooler product line to include a single stage High Efficiency Cryocooler (HEC) cooler with a coaxial pulse tube cold head that operates at temperatures down to 45K. The HEC coaxial pulse tube cooler has been adopted by several customers, and has completed acceptance testing to meet program flight requirements. The NGAS TRL 9 HEC is a pulse tube cryocooler with a flexure bearing compressor which has been delivered for a number of flight payloads that are currently operating in space. To date, NGAS has delivered space cryocoolers in several configurations including single stage with a linear cold head and two stage with both linear and coaxial cold heads. The new HEC coaxial cooler uses the same TRL9 HEC compressor with a passive pulse tube cold head, to maintain the flight heritage of the HEC linear cooler. In this paper, we present the flight acceptance test data of the HEC coaxial cryocooler, which includes thermal performance, launch vibration and thermal cycling. The HEC coaxial cooler has demonstrated excellent performance in family with the flight qualified HEC linear cooler. The HEC coaxial cooler provides users with additional flexibility in selecting the cold head configuration to meet their particular applications.