Kenneth D. Price

Protoflight Spacecraft Cryocooler Performance Results

The Protoflight Spacecraft Cryocooler (PSC) is a flight-qualified Stirling cryocooler that delivers 1.2 W refrigeration at 35 K and 3 W refrigeration at 60 K. This Oxford-class unit employs three finger tangential flexures in the compressor module. These flexures have been shown to provide smoother, lower vibration piston motion than previously obtained with conventional three finger spiral flexures. Acceptance Tests validated the required performance capabilities and Qualification Tests validated the cooler for flight. Acceptance Tests included performance mapping at rejection temperatures from 275 K to 325 K, residual vibration measurements for each module, temperature stability under various conditions, cold tip motion, cold tip side load capacity. Qualification Tests included three-axis random vibration, thermal cycling, hermeticity and EMI/EMC tests. The 12.5 kg cooler was delivered with a brassboard command and control module that provides simultaneous temperature and Adaptive Feed-Forward vibration control. The PSC with brassboard electronics have been delivered to the Air Force Research Lab in Albuquerque, where additional testing has validated the results obtained at Raytheon.

95 K High Efficiency Cryocooler Program

The Air Force / Raytheon 95K High Efficiency Cryocooler (95K HEC) Program is developing a new two-stage hybrid Stirling-pulse tube space qualified refrigerator with high heat lift capacity, high efficiency, low weight and size, and low production costs relative to the current state-of-the-art. The basic program will deliver a protoflight Stirling-class Thermo Mechanical Unit (TMU) with protoflight radiation hard electronics. The cooler is designed to support 10W heat lift from a 95K source to a 300K sink. Motor power consumption is to be less than 100W and system power (including electronics) is to be less than 137W. The cooler is to weigh no more than 6Kg. The TMU cold head and compressor designs are highly versatile to enable low cost tailoring to meet the needs of a wide variety of applications. The first demonstration of this versatility is a program option to deliver a companion high-capacity 35K cryocooler. This cooler will also have an aggressive efficiency requirement. The 95K and 35K TMU will share over 95% of components, resulting in significant production efficiencies. Another result of this high degree of commonality is that each cooler can be powered and controlled by standardized Command and Control Electronics (CCE). The only adjustments needed to match the CCE to a TMU design are in selected logic parameters stored in ROM and in minor changes to winding ratios in two transformers. The CCE is designed with radiation hard components, but the initial protoflight units will be delivered with lower cost commercial substitutes, where available with the same form, fit, and function. The 25 month program will deliver a fully flight qualified 95K system including both TMU and CCE and, if the option is exercised, a similar flight qualified 35K system.

A Novel Multi-Stage Expander Concept

Raytheon has developed a novel two-stage expander for use in long life, high reliability cryocoolers for space and commercial applications. The expander is classified as a Stirling machine and requires a conventional reciprocating piston compressor to drive it. The key feature is a new method for obtaining and controlling expansion at the two stages. Thermodynamic efficiency is higher than existing one and two stage coolers and the mechanical implementation is as simple or simpler. The expander device is described in both thermodynamic and mechanical terms and performance predictions given.

Two Stage Hybrid Cryocooler Development

Raytheon has demonstrated a two-stage hybrid Stirling/pulse tube cryocooler for long life space infrared (IR) sensor applications. The first expander stage is a conventional Oxford-class Stirling expander. The second expander stage is a U-turn pulse tube mechanically and thermodynamically extended from the first stage Stirling cold end.

Second Generation Raytheon Stirling/Pulse Tube Hybrid Cold Head Design and Performance

Raytheon is in initial test of a second generation two-stage Stirling/pulse tube hybrid cold head for use in long life space cryocoolers. The Stirling/pulse tube configuration provides excellent thermodynamic performance by optimally combining the strengths of both technologies. The cold head is designed for optimal performance at a second stage temperature of 40 K and a first stage temperature of 110 K with nominal capacity of 1 W at the lower stage and simultaneous 7 W at the upper stage. The inherent load shifting capability of this configuration permits efficient operation of the cooler over a wide range of temperatures and heat loads. Load shifting is accomplished through varying the phase angle of the Stirling displacer piston relative to the pressure wave. Load shift data on the new cold head is provided. Lessons learned from the testing of the initial brass-board regarding component sizing have been incorporated into this second generation design. The quantitative improvement provided by those design changes is presented. The second generation cold head design is currently being incorporated into a flight design warm-end expander motor assembly with Oxford-class flexure and clearance technology typical of Raytheon flight-qualified production cryocoolers for space. The expander is driven by an Oxford-class compressor of similar design legacy to other Raytheon designs.

Raytheon Stirling/Pulse Tube Two‐Stage (RSP2) Cryocooler Advancements

Raytheon is developing a two‐stage hybrid Stirling/pulse tube cryocooler for long life space infrared (IR) sensor applications. The first expander stage is a conventional Oxford‐class Stirling expander. The second expander stage is a U‐turn pulse tube mechanically and thermodynamically extended from the first stage Stirling cold end.Recent development work has been devoted to improving the math model correlation in preparation for construction of an optimized expander design. We have obtained a large performance database using a variety of phase shifters and surge volume arrangements with the cryocooler operating over a wide range of operating conditions and temperatures. This database not only forms the foundation of the model correlation effort, but it also is being used to identify the optimum phase shifter and surge volume designs for various operating regimes of interest.Development testing of the first unit is now complete and a second, improved expander is being developed based on lessons learned. ...

Low Cost, Lightweight Space Cryocoolers

Raytheon has developed a concept for compact, lightweight space cryocoolers that merges the existing company expertise in tactical cryocoolers and space cryocoolers. The compressor is an upgrade to the existing Raytheon 705X tactical compressor product line in which the rubbing seals are eliminated through the incorporation of a non-contacting, flexure bearing piston support system characteristic of that used presently on thespace cryocooler productline. To minimize cost and weight, the expander is a single-stage pulse tube. A concentric pulse tube configuration is used to simplify system integration by providing a distinct cold tip and radially symmetric structural stiffness. The cryocooler electronics module is essentially a radiation-hardened version of the existing tactical high reliability electronics design.