E. Tward

High Efficiency Pulse Tube Cooler

The High Efficiency Cooler (HEC) is being developed in order to provide a long life, low mass, high efficiency space cryocooler suitable for use on lightweight gimbaled optics on surveillance missions such as SBIRS Low. This paper reports on the development and testing ofthis next generation family of space pulse tube cryocoolers which feature high cooling capacity, lower mass, lower EMI and lower self induced vibration than the current state of the art. The HEC achieves low input power and large cooling power because of the efficiency of its pulse tube cold head and highly efficient compressor. The low mass (<3 kg) results chiefly from its next generation Oxford flexure compressor technology reported in a companion paper. The projected long lifetime and high reliability results from use of the proven low complexity flexure compressor and pulse tube cold head. Its low EMI is due to its self-shielding motor. The low self induced vibration results from its internal dynamic balancing. It features the ease of integration into an instrument of a small pulse tube cooler. The cooler achieves its 10 W at 95K cooling requirement with substantial margin while rejecting heat to 300K.

High Performance Flight Cryocooler Compressor

In this paper we report on the development of a next generation flexure bearing compressor which features high efficiency, high capacity per unit mass, enhanced producibility and ease of integration into payloads. The compressor was developed for the 95K High Efficiency Cryocooler programme.

High efficiency cryocooler

The High Efficiency Cryocooler (HEC) is a highly reliable, >10 year life, space cryocooler. Design goals included very high capacity with low mass. The HEC achieved its 10 W at 95 K load while rejecting to 300 K with considerable margin and a flight configured mass of 4 Kg. This flight cooler design is being fabricated for a number of payloads. This paper describes the cooler, its measured performance, and its flight qualification.

High Capacity Staged Pulse Tube

The High Capacity Cryocooler (HCC) is being designed to provide large capacity cooling at 35 K and 85 K for space applications in which both cold focal planes and optics require cooling. The compressor is scaled from the High Efficiency Cryocooler compressor and is capable of using input powers up to 700 W. The two linear pulse tube cold heads are integrated with the compressor into an integral cryocooler. Provision is made to provide a thermal strap between the cold heads in order to improve efficiency. The cooler is undergoing acceptance testing that includes thermal performance mapping over a range of reject temperatures and power levels, launch vibration testing and self induced vibration testing.

Miniature Long-Life Space-Qualified Pulse Tube and Stirling Cryocoolers

Cryogenic coolers for small satellites require low power and minimum weight. In this paper we report on the status of both our miniature flight-qualified pulse tube cooler as well as our miniature flight-qualified Stirling cooler. Both integral linear coolers are small, efficient, low-power, and vibrationally balanced, and incorporate Oxford-type single flexure-bearing compressors. Vibrational balance is achieved with a motor-driven balancer. The Stirling cooler cold head incorporates a colinear flexure-bearing suspended displacer/regenerator with a motor drive used for phase control. The larger capacity pulse tube cooler uses a completely passive cold head which contains no cold moving parts. Nonwearing clearance seals in both coolers advance the long 10-year life projections.

High Capacity Staged Pulse Tube Cooler

The High Capacity Cryocooler (HCC) is being designed to provide large capacity cooling at 35 K and 85 K for space applications in which both cold focal planes and optics require cooling. The compressor is scaled from the High Energy Cryocooler compressor and is capable of using input powers up to 700 W. The two linear pulse tube cold heads are integrated with the compressor into an integral cryocooler. Provision is made to provide a thermal strap between the cold heads in order to improve efficiency. Flight qualification of this novel cryocooler include thermal performance mapping over a range of reject temperatures and power levels, launch vibration testing and self induced vibration testing.

Can the throttling of a perfect gas through a free molecular orifice produce a cooling effect

A novel refrigeration cycle using throttling through free molecular orifice(s) was explored experimentally and theoretically, attempting to exploit the heat transfer that occurs by the entropy shift across a discontinuous system formed by a wall containing tens of thousands of micron or submicron free molecular throttling (FMT) orifices. Single stage free molecular throttle cooling is compared in terms of figure of merit and coefficient of performance (COP) against the analogous isothermal entropy shift cooling effect in thermoelectric junctions. Unlike thermoelectric materials, free molecular throttling is predicted to perform increasingly better as the temperature drops below 200K. Experimentally, the authors have shown in three rounds of progressively smaller dimensions and hence larger heat flux vector magnitude that the simple, isothermal movement of heat, taken in analogy with thermoelectric (Peltier junction) refrigerators, is not valid. By using this information, the authors then show that solid s...

A small‐scale, thermoacoustic‐Stirling electric generator for deep‐space applications

Although thermoacoustic‐Stirling hybrid engines (TASHE) have not been previously coupled to transducers to produce useful electric power, they have demonstrated high thermal‐to‐acoustic power conversion efficiencies. Electric generation is investigated by coupling a small TASHE to an electrodynamic linear alternator with an emphasis on satisfying NASA’s need for a small, lightweight, efficient electric generator for deep‐space missions. The combined goals of low mass and high efficiency require the TASHE to have the largest acoustic power output possible from a minimum enclosed volume, which imposes a relation between various impedances of the TASHE’s lumped‐element loop. The design of the TASHE and alternator used in this generator will be reviewed, performance data presented, and possible improvements discussed. [Work supported by NASA.]