High-capacity 60 K single-stage coaxial pulse tube cryocoolers

A high-capacity single-stage coaxial pulse tube cryocooler operating at around 60 K has been developed to provide the appropriate cooling for the next-generation very-large-scale long wave infrared focal plane arrays under development. The application background and cooler design process are described, and the performance characteristics are presented. At present, the cooler typically provides 4.06 W at 60 K with the input power of 180 W at 300 K reject temperature. 4.72 W can also be achieved when the input power increases to 200 W, and over 9.4% of Carnot efficiency at 60 K has been realized. The larger pulse tube diameter of 14.2 mm is used and the evident orientation sensitivity is observed in the range of 55–65 Hz. The experiments also observe the obvious reject temperature dependence.     

空间用4 K温区预冷型JT制冷机研究进展及关键技术分析

综述了空间用4 K温区预冷型JT制冷机方案及其相关的空间项目,研究表明该类型制冷机一般由斯特林或斯特林型脉管制冷机和JT制冷机组成,前者为后者提供预冷,后者通过节流效应降温获得4 K温区的制冷量。总结了制冷机的性能参数和系统结构,对比分析了该类型制冷机与GM/JT制冷机间存在的性能差距和关键技术差别,阐明了预冷温度和压力等参数对制冷机效率的影响,指出了当前该类型制冷机的改进空间和方案。     

Raytheon long life cryocoolers for future space missions

Over the last several years, Raytheon has made significant advances on two long-life cryocoolers designed for efficient operation on space platforms. The first is the Low-Temperature Raytheon Stirling/Pulse Tube 2-stage (LT-RSP2) hybrid cryocooler, which is capable of providing simultaneous cooling at 55 K and 10 K nominal first and second stage temperatures. The LT-RSP2 design was finalized in mid-2009, with fabrication of the prototype unit taking place in late 2009 and early 2010 and execution of the production program in 2011–2015. During this period the LT-RSP2 has undergone extensive characterization testing and has successfully been integrated with an optical bench. The second cryocooler is the Raytheon Advanced Miniature (RAM) cryocooler, a flight packaged single stage pulse tube cooler with an integrated surge volume and inertance tube. It has been designed for high frequency operation and has been fully optimized to make use of the Raytheon Advanced Regenerator, resulting in improved efficiency relative to previous Raytheon pulse tube coolers. In this paper, aspects of both the LT-RSP2 and RAM mechanical and thermodynamic designs will be presented as well as information regarding their capabilities and performance.     

Development of mechanical cryocoolers for the Japanese IR space telescope SPICA

The next Japanese infrared space telescope SPICA features a large 3.5-m-diameter primary mirror and an optical bench cooled to 4.5 K with advanced mechanical cryocoolers and effective radiant cooling instead of using a massive and short-lived cryogen system. To obtain a sufficient thermal design margin for the cryogenic system, cryocoolers for 20 K, 4 K, and 1 K have been modified for higher reliability and higher cooling power. The latest results show that all mechanical cryocoolers achieve sufficient cooling capacity for the cooling requirement of the telescope and detectors on the optical bench at the beginning of life. Consequently, the feasibility of the SPICA cryogenic system concept was validated, while attempts to achieve higher reliability, higher cooling capacity and less vibration have continued for stable operations at the end of life.     

Development of high performance moving-coil linear compressors for space Stirling-type pulse tube cryocoolers

This paper presents a review of the recent development of moving-coil linear compressors for space Stirling-type pulse tube cryocoolers in National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences. The design, manufacture and assembly methods are described with special emphases laid on linear motor, clearance seal, flexure springs, dual-opposed configuration and flexible design. Several key components are focused on and studied in a detailed way in terms of material selection, geometry design, configuration optimization, manufacture approaches and optimal assembly to achieve high efficiency, easy producibility, high reliability and long life. Experiences from the forerunners and the state-of-the-art approaches are reviewed and used for useful references, while our own successful experiences are emphasized and discussed in more detail together with some lessons learned. A series of compressors for space applications have been worked out with high confidence of reliability and long life expectation, which achieve input capacities of 0–500 W with motor efficiencies of 74.2–83.6%. Single-stage pulse tube cryocoolers driven by these compressors have already covered the temperature range of 25–200 K with cooling capacities varying from milliwatt levels to over 30 W. The commonly-used compressor types and purposes, performance characteristics and their applications in typical space cryocooler projects are also presented.     

Joule-Thomson cryocooler for space applications

A J-T cryocooler is being developed for space applications. It is under laboratory testing and will be flight-tested aboard the Space Shuttle in middle to late 1997. A seal-ability study confirmed that the EDM design is robust and can accommodate a wide range of heat loads while maintaining the development heritage.     

Design guidelines for large Stirling cryocoolers

A simplified design guideline for the refrigerating capacity of Stirling cryocoolers is presented.     

Impedance match for Stirling type cryocoolers

Impedance match in Stirling type cryocoolers is important for the compressor efficiency and available acoustic power. This paper generalizes the basic principles concerning the efficiency and acoustic power output of the linear compressor. Starting from basic governing equations and mainly from the viewpoint of energy balance, the physical mechanisms behind the principles are clearly shown. Specially, this paper focuses on the impedance match for an existing compressor, where the current limit and displacement limit should also be taken into consideration when selecting a suitable impedance. Some case studies based on a commercial compressor are also provided for a deep understanding.     

Optical black coatings for space applications

The durability properties of PTX-205 optical black coatings deposited on metallic and non-metallic substrates are studied. The coatings are stable against adverse environmental requirements for space applications. Typically, coatings with 8–11 μ thickness are opaque and have an average reflectance loss (<5%) in the spectral range of 200–1500 nm. The absorption to emission ratio is 1·01.     

Cryocooler reliability issues for space applications

Analyzing cryocooler reliability has been problematic from the beginning. Classic reliability analyses rely on statistical sampling and comparing failure modes to other similar systems where statistical results are available. These approaches do not apply to cryocoolers, particularly cryocoolers for aerospace applications. The industry has not built enough total cryocoolers, let alone a single type of cooler, to provide any meaningful statistical sample. This forces us to rely on comparing failure modes of similar systems to that of the cryocooler, which leads to the next problem; today's aerospace cryocooler is designed to have no failure modes. What can it be compared to? Any classic reliability study performed on a cryocooler makes several critical assumptions that completely dominate the results. Change the assumptions and you get a different answer; the results are dictated by the assumptions not the hardware. There are no easy answers to these problems. This paper attempts to show why classic reliability studies do not apply to cryocoolers and that as an industry we must work together to show that all cryocoolers have high levels of reliability.     

Multisalt-carbon chemical cooler for space applications

Conclusions  The conclusions are summarized as follows:

Development of parallel wire regenerator for cryocoolers

This paper describes development of a novel regenerator geometry for cryocoolers. Parallel wire type is a wire bundle stacked in parallel with the flow in the housing, which is similar to a conventional parallel plate or tube. Simple and unique fabrication procedure is developed and fully depicted in this paper. Hydrodynamic and thermal experiments are performed to demonstrate the feasibility of the parallel wire regenerator. First, pressure drop characteristic of the parallel wire regenerator is compared to that of the screen mesh regenerator. Experimental result shows that the steady flow friction factor of the parallel wire type is three to five times smaller than that of the screen mesh type. Second, thermal ineffectiveness is determined by measuring the instantaneous pressure, the flow rate and the gas temperature at the warm and cold ends of the regenerator. The measured ineffectiveness of the parallel wire regenerator is larger than that of the screen regenerator due to the excessive axial conduction loss. To alleviate the intrinsic axial conduction loss of the parallel wire regenerator, segmentation is introduced and the experimental results reveal the favorable effect of the segmentation. Entropy generation calculation is adopted to compare the total losses between the screen regenerator and the parallel wire regenerator for various operating ranges. Simulation results show that the parallel wire regenerator can be an attractive candidate to improve cryocooler performance especially for the case of smaller NTU and lower cold-end temperature.     

Discussion on refrigeration cycle for regenerative cryocoolers

Based on review and analysis of thermodynamic efficiency ε of the Carnot cycle and the cycle with two isothermal and two polytropic processes, another thermodynamic cycle with two isentropic and two polytropic processes, which can achieve the Carnot value of thermodynamic efficiency, is testified theoretically. Thermodynamic efficiency expressions of a number of ideal regenerative refrigeration cycles are derived, including the ideal pulse tube refrigeration cycle. A classified branch chart and a plot of ideal thermodynamic efficiency of regenerative refrigeration cycles are given for the purpose of comparison.     

Vibration analysis of cryocoolers

The vibrations of Gifford-McMahon (GM) and pulse-tube (PT) cryocoolers were measured and analyzed. The vibrations of the cold-stage and cold-head were measured separately to investigate their vibration mechanisms. The measurements were performed while maintaining the thermal conditions of the cryocoolers at a steady state. We found that the vibration of the cold-head for the 4 K PT cryocooler was two orders of magnitude smaller than that of the 4 K GM cryocooler. On the other hand, the vibration of the cold-stages for both cryocoolers was of the same order of magnitude. From a spectral analysis of the vibrations and a simulation, we concluded that the vibration of the cold-stage is caused by an elastic deformation of the pulse tubes (or cylinders) due to the pressure oscillation of the working gas.     

High-reliability SAW bandpass filters for space applications

High-reliability surface-acoustic-wave (SAW) bandpass filters have been developed for use in transponders for more than 25 earth-orbital and deep-space satellite programs. SAW filters have been incorporated in several NASA standard TTandC transponders and NASA standard tracking and data relay satellite system (TDRSS) user transponders. The author gives examples of the electrical performance, summarizes the manufacturing processes, and discusses qualification testing for these SAW devices. He identifies reliability problems encountered and their solutions.     

Aerogel insulation systems for space launch applications

New developments in materials science in the areas of solution gelation processes and nanotechnology have led to the recent commercial production of aerogels. Concurrent with these advancements has been the development of new approaches to cryogenic thermal insulation systems. For example, thermal and physical characterizations of aerogel beads under cryogenic-vacuum conditions have been performed at the Cryogenics Test Laboratory of the NASA Kennedy Space Center. Aerogel-based insulation system demonstrations have also been conducted to improve performance for space launch applications. Subscale cryopumping experiments show the thermal insulating ability of these fully breathable nanoporous materials. For a properly executed thermal insulation system, these breathable aerogel systems are shown to not cryopump beyond the initial cooldown and thermal stabilization phase. New applications are being developed to augment the thermal protection systems of space launch vehicles, including the Space Shuttle External Tank. These applications include a cold-boundary temperature of 90 K with an ambient air environment in which both weather and flight aerodynamics are important considerations. Another application is a nitrogen-purged environment with a cold-boundary temperature of 20 K where both initial cooldown and launch ascent profiles must be considered. Experimental results and considerations for these flight system applications are discussed.     

Micro-multi-plasmajet array thruster for space propulsion applications

Thrust performance tests were conducted for an arrayed multi-plasmajet structure consisting of rectangular nozzle elements each with an exit height of 0.5 mm and length of 0.5 mm. To evaluate the thrust characteristics of the arrayed micro-multi-plasmajet, the thrust was measured using a calibrated cantilever-type thrust stand in vacuum. Using 3 × 3 nozzle elements, the micro-plasmajet array showed stable DC operation. Compared to conditions with cold-gas flow, the application of a DC discharge showed a significant improvement in thrust performance of at least 20% for thrust and specific impulse. Typical values achieved for thrust, specific impulse and thrust efficiency at an input power of 6.3 W were 8.5 mN, 77 s and 0.21, respectively.     

Development of mechanical cryocoolers for Astro-H/SXS

The Soft X-ray Spectrometer (SXS) is a high-resolution spectrometer with an X-ray micro-calorimeter array onboard the Japanese X-ray astronomy satellite Astro-H, planned for launch in 2013. The micro-calorimeter is operated at cryogenic temperature of 50 mK provided by the Adiabatic Demagnetization Refrigerator (ADR) with a heat sink of 1.3 K liquid helium stored in the SXS Dewar. To extend the liquid helium lifetime to over 3 years in orbit, two types of mechanical cryocoolers are installed: 20 K-class double-staged Stirling (2ST) coolers and a 1 K-class Joule-Thomson (JT) cooler. Improvement of mechanical cryocoolers has been investigated and verified for higher reliability and cooling performance. The engineering model (EM) of upgraded mechanical cryocoolers was fabricated for a long lifetime test. The required cooling power of 200 mW at 20 K for the 2ST cooler and 10 mW at 1.7 K for the JT cooler are achieved by EM test.     

Outgas analysis of mechanical cryocoolers for long lifetime

Mechanical cryocoolers for space applications are required to have high reliability to achieve long-term operation in orbit. ASTRO-H (Hitomi), the 6th Japanese X-ray astronomy mission, has a major scientific instrument onboard—the Soft X-ray Spectrometer (SXS) with several 20K-class two-stage Stirling (2ST) coolers and a 4K-class Joule Thomson (JT) cooler, which must operate for 3 years to ensure the lifetime of liquid helium as a cryogen for cooling of its detectors [1], [2]. Other astronomical missions such as SPICA [3], [4], LiteBIRD [5], and Athena [6] also have top requirements for these mechanical cryocoolers, including a 1K-class JT cooler to be operated for more than 3–5 years with no cryogen system.The reliability and lifetime of mechanical cryocoolers are generally understood to depend on (1) mechanical wear of the piston seal and valve seal, and (2) He working gas contaminated by impurity outgases, mainly H₂O and CO₂ released from the materials in the components of the cryocoolers. The second factor could be critical relative to causing blockage in the JT heat exchanger plumbing and the JT orifice or resulting in blockage in the Stirling regenerator and thereby degrading its performance. Thus, reducing the potential for outgassing in the cryocooler design and fabrication process, and predicting the total amount of outgases in the cryocooler are very important to ensure cryocooler lifetime and cooling performance in orbit.This paper investigates the outgas analysis of the 2ST and the 1K/4K-JT coolers for achieving a long lifetime. First, gas analysis was conducted for the materials and components of the mechanical cryocoolers, focusing on non-metallic materials as impurity gas sources. Then gas analysis of the mechanical wear effect of the piston seal materials and linear ball bearings was investigated. Finally, outgassing from a fully assembled cryocooler was measured to evaluate whether the outgas reduction process works properly to meet the requirement levels.     

A capacitance based axial position sensor for cryocoolers

The recent development of a Stirling cryocooler designed to operate with a body temperature of less than 220 K required an axial motor position sensor which could operate over this temperature range. Although linear variable differential transformers (LVDTs), have traditionally been used, these are temperature dependent and would have required development due to integrated electronics, which could not be used at these low temperatures. A sensor was therefore developed based on the principle of measuring the capacitance between static and moving concentric rings. The design is presented along with the signal conditioning circuit. Experimental results show that the sensor had suitable bandwidth with a temperature independent gain between room temperature and 220 K. Future developments are described including a similar sensor to measure the radial motion of a motor during operation.