GODDARD SPACE FLIGHT CENTER

Cryocoolers

PROGRESS REPORT

October - December, 1994

Two-Stage Stirling Cooler

Program Goals and Objectives

This program will result in an advanced engineering model of a two-stage linear Stirling cycle cooler for use by instruments on the Earth Observing System (EOS). However, the cooler will be of use to many other NASA programs in earth science, astronomy, microgravity sciences, interplanetary sciences and the Human Exploration Initiative.

The cooler must have long life, high reliability and low vibration, as well as being small, light weight, and efficient. The key cooler specifications are as follows:

• Long life: 5 years minimum; 10 year goal
• High reliability: 0.95 for 5 years
• 1000 start/stop cycles over mission life
• Low vibration: <0.05 lb force maximum; 0.02 lbf goal
• High efficiency: < 75 watts input power
• 0.3 watts of cooling power at 30 K
• Low weight: less than 15 kg
• Minimal size
• Simple interfaces
• Integration flexibility
• Designed to withstand Titan 4 or Shuttle loads
• Maximum cold finger displacement during operation of 0.001 inches
• 0.1 K temperature stability over a 24 hour period 28 volt dc input power
• Electromagnetic compatibility with EOS (GISS)
• Minimum magnetic signature
• Soft mounting cannot be used to meet vibration
• Cryocooler must operate in any orientation in a zero and 1-G environment.

GSFC - Cryocoolers

1st Quarter FY 95 - Report

Executive Summary

Highlights of the Past Quarter:

The engineering model two-stage Stirling cooler continued to progress at Ball Aerospace during the first quarter of FY95. Unfortunately, a reduction in the funding available in FY95 has reduced the rate of progress and delayed completion of the cooler development program.

The most important highlight for this quarter was the start of the concurrent build of a second cooler for the Air Force. This cooler will be identical to the NASA cooler except for the cold finger which is designed to meet the unique sensor cooling requirements of the Air Force. By producing two coolers concurrently, the cost of each cooler will be reduced. The cost savings is allowing the NASA cooler build to be continued at reduced cost.

With the concurrent build of the Air Force cooler, the progress on the manufacturing of the cooler has increased. In particular, the fabrication of the compressor should be completed in February.

As mentioned last quarter, tests performed at Goddard on the Technology Demonstration model and calculations performed by Ball both indicate that the Ball cooler can be used to cover a wide range of applications. The Technology Demonstration model has now been returned to Ball and is being prepared for a test at Berkeley with the detector system proposed for HESI. It is anticipated that this test will occur next quarter. This work is being performed on Ball IR& D funds.

The final details of the Air Force cooler fabrication are presently being finalized. This process will be completed by the end of February. At that time, an updated cost and schedule for the NASA cooler will be provided to NASA Headquarters. It is anticipated that substantial savings to NASA will result from the simultaneous build of the NASA and Air Force cooler and, therefore, a reduction in the funding required to complete the two-stage Stirling cooler in FY96.

Goddard continues to participate with industry in the attempt to produce a long life commercial cryocooler. An AITP has been issued to a consortium of Lockheed, Superconducting Technologies Inc. (STI), NIST, and NASA/Goddard to develop and test an inexpensive commercial cooler and to mate it to a high temperature superconducting microwave filter for cellular telephone applications.

Level 1 Two-Stage Cooler Milestone Status Report

Goal:

• Develop a long life, highly reliable two-stage Stirling cooler for use by Mission to Planet Earth and other space-based applications.

Approach:

• Contract with industry to develop the cooler, supported by Goddard-developed vibration control system and Goddard functional, environmental and life testing of the cooler.

Background:

• Two-stage Stirling coolers obtain lower temperatures than single-stage coolers and provide higher thermodynamic performance.

Status of Ball engineering model two-stage cooler:

• The design of the compressor and electronics for the engineering model cooler is compete and the design of the expander is nearing completion. The expander will incorporate a fixed regenerator to eliminate the delicate cold finger that is a major concern with the present generation of Stirling coolers. The electronics for the engineering model have benefited from the parallel development of cooler electronics under the X-Ray Spectrometer (XRS) flight program at Ball. As a result, the engineering model cooler will include surface mount electronics which will result in a compact, light weight, relatively low cost set of electronics to operate the cooler.
• Ball has fabricated the piece parts for the compressor. The assembly of the compressor is nearing completion.
• Ball has completed the breadboard expander and demonstrated non-contact at the clearance seals. The Ball two-stage Stirling cooler is the only Oxford style cooler that has reliably demonstrated non-contacting bearings under all operating conditions.

Goddard Commercial Cooler Program

Goal:

• Develop an inexpensive, long life, highly reliable cryocooler for use in commercial applications.

Approach:

• Work with industry and other government agencies to develop a viable cooler. Goddard will provide expertise to industry on long life compressors and on the Goddard-developed vibration control system. Goddard will also provide functional, environmental and life testing of coolers in the existing Cryocooler Test Bed.

Background:

• No low cost cooler has demonstrated the necessary reliability and lifetime. The primary problem is the compressor. The only low cost, long life compressors are oil filled compressors similar to those used in refrigerators. After many years of effort, no organization has yet demonstrated a low cost method of using such a compressor without contaminating the heat exchangers, throttle valves and/or regenerators in the cold portion of the cooler. The alternative now being pursued is reciprocating compressors using flexure and gas bearings. Such compressors are being developed for the space program. Concepts to reduce cost while maintaining lifetime and reliability are being explored by Goddard and commercial cooler manufacturers. These compressors can be used in either passive displacer Stirling coolers or pulse tube coolers.

Status of Goddard commercial cooler development programs:

• An AITP has been issued to Lockheed, STI, NIST and Goddard to develop and demonstrate a long life commercial cooler and integrate it with a high temperature superconducting microwave filter. Lockheed will provide a flexure bearing-based compressor. STI will provide a gas bearing-based compressor and the microwave filter (which is now an off-the-shelf item). NIST will provide the pulse tube and Goddard will provide testing services. For some time now, Goddard has been providing advice relative to cryocoolers to STI and to another company with which STI is collaborating.
• Goddard is working with several commercial and tactical cooler companies to produce a long life, low cost cooler. Goddard is providing a low cost vibration control system and is testing and evaluating low cost compressor designs to determine the feasibility for long life and high reliability. In addition, Goddard is providing expertise obtained from working for many years on the development of long life, space-based coolers.
• Goddard is participating in two TRP programs with ARPA and NRL. The first TRP program is to develop low cost, long life coolers. The second TRP program, which is presently being initiated, is to further develop such coolers and to integrate them into commercial applications. This program is similar to the existing NASA AITP project discussed above.
• A few of the hundreds of commercial applications that will be enabled by a low cost, highly reliable cooler with a 5 to 10 year lifetime are listed below:
  • Miniature microwave filters for cellular telephone systems
  • Cooled CMOS to improve workstation and mid-sized computer performance
  • High Q resonators for radar systems. Applications include improved airport safety and military applications
  • High speed switches for digital communications
  • Low vibration cryopumps for fine line silicon wafer fabrication
  • Infrared detectors for law enforcement night vision systems
  • Dermatologist instrument for skin care
  • Improved communications satellites, earth resources satellites and weather satellites (low cost may not be required: NASA two-stage Stirling cycle cooler may meet requirements).

Steve Castles
Head, Code 713
Goddard Space Flight Center

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