Stephen H. Castles

Design Of The Superfluid Helium Dewar For The Cosmic Background Explorer (CUBE)

The COBE satellite includes two cryogenically cooled instruments, which are housed inside a 664 liter superfluid helium dewar to achieve an operating temperature of 1.5K. The dewar will provide a 14 month operating lifetime, during which the far infrared absolute spectrophotometer (FIRAS) and diffuse infrared background experiment (DIHBE) will conduct full sky surveys from a 900 km, sun-synchronous polar orbit. The spectrum of diffuse radiation will be characterized by these instruments over the wavelength region from 1 micron to 1 cm. Launch is planned for autumn 1987. The dewar is very similar in design and function to that used successfully as part of the Infrared Astronomy Satellite (IRAS). Some design changes, as compared to the IRAS dewar, have been made to meet STS safety and operations requirements, to accommodate the CUBE instrument package, to increase lifetime, and to improve functional reliability in several areas. Most noteable design changes are a 23 percent enlargening of the cryogen tank, de-letion of the aperture cover helium tank, and improved thermal radiation baffling to mini-mize the heat input through the area at the interface between the main dewar and the aperture cover. Dewar system testing is scheduled to start in summer 1985. The dewar design and design drivers, especially as related to changes from the IRAS design, are discussed along with thermal performance predictions resulting from computer modelling and observed performance of the IRAS dewar.

Final cryogenic performance report for the NASA Cosmic Background Explorer (COBE)

The cryogenic operation of NASA’s Cosmic Background Explorer (COBE) ended on September 21, 1990, with the depletion of the liquid helium cryogen. The COBE had successfully completed more than 10 months of dewar and instrument operation. We report on the cryogenic performance of the COBE dewar and of the two cryogenic instruments throughout the mission lifetime. We discuss the steady state dewar performance, and the dewar and instrument response to a variety of transient thermal phenomena, including external radiation (from the earth and the sun) and instrument power variation. We present the effectiveness of using approximate mass gauging techniques in determining the liquid helium content. Finally we discuss the dewar behavior during the depletion of the helium, and the expected thermal performance of the dewar cryogen tank and the cryogenic instruments as they approach final thermal equilibrium.

Development of a space qualified Surface Tension Confined Liquid Cryogen Cooler (STCLCC)

The NASA-GSFC is developing a new type of cryogenic cooler for use with spaceflight payloads. This cooler will be capable maintaining instrumentation within the temperature range of 10–120 K Known as the Surface Tension Confined Liquid Cryogen Cooler (STCLCC), it will allow liquid cryogens to be flown in space without the risk of liquid being entrained in the vent gas. The cooler contains a low density (85–95% free volume) open cell material. This acts as a “sponge” with surface tension trapping the liquid cryogen within its pores. The surface tension effect keeps liquid away from the cooler’s vent during launch, zero-g operations, and landing. It also prevents any liquid slosh which can produce vibrations and microphonic noise in sensitive instrumentation. Other benefits of the STCLCC include the potential to be serviced on-orbit and an inherent simplicity of operation which enhances system safety. It also promises a reduction in cost, complexity, and prelaunch servicing requirements over the present state of the art, the solid cryogen cooler. The STCLCC program is in the preliminary design and verification stage, with early test results confirming acceptable thermodynamic, mechanical, and cryogen retention properties of several first generation sponge materials.

Functional and life test data for a two-stage stirling cycle mechanical cryocooler for space applications

We have been developing a long-life mechanical cryocooler for space applications since 1991. We started with a “clean sheet of paper” with this cooler to customize the best current technology for space applications. The space requirements include reliability, power efficiency, mass, system compatibility, and the ability to withstand adverse environmental conditions. We have delivered an engineering model and a flight prototype under the current contract. Each unit was typically preceded by several breadboard versions used to explore alternate configurations. We are reporting in this paper on test data for the flight prototype cooler, delivered from Ball to the Goddard Space Flight Center (GSFC) at the end of 1996. Verification tests on this cooler were performed at Ball. The performance tests were confirmed and expanded upon at GSFC, and the cooler is now in for a period of extended running to evaluate its long-term performance. We are building a version of this cooler for the High Resolution Dynamics Lim...

NASA/GSFC Cryocooler Test Program Results for FY93/94

This paper summarizes major results from testing efforts performed at NASA/Goddard Space Flight Center (NASA/GSFC) on the latest generation of long life cryocoolers produced by Ball Aerospace, Lockheed, TRW and Fairchild/Creare. All of these cryocoolers were installed on vibration dynamometers in a thermal vacuum chamber. Characterization tests include the measurement of cooling load as a function of temperature; power input; axial and lateral vibration measurements, both with and without vibration control implemented; stiction testing; thermal vacuum performance testing; and where possible, methods of alignment verification. Once initial characterization is completed, life testing will commence. Characterization testing will be repeated every 2000 hours to monitor performance degradation over time. Conclusions and lessons learned are presented.

Magnetic Shielding for a Spaceborne Adiabatic Demagnetization Refrigerator (ADR)

The Goddard Space Flight Center has studied magnetic shielding for an adiabatic demagnetization refrigerator. Four types of shielding were studied: active coils, passive ferromagnetic shells, passive superconducting coils, and passive superconducting shells. The passive superconducting shells failed by allowing flux penetration. The other three methods were successful, singly or together.

Current Developments in NASA Cryogenic Cooler Technology

NASA’s two main areas of observational scientific endeavor, astrophysics and earth science, have scientific requirements that dictate the use of sensors with more energy resolution than the sensors used in earlier space flight instruments. With present sensor technology these scientific goals can often only be met with the use of sensors and instruments operating at cryogenic temperatures. In response to this need, NASA is developing a broad range of cryogenic coolers and supporting technology. These coolers will be capable of providing sensors and instruments with stable operating temperatures from room temperature down to 0.1 K or less. In addition to providing the desired operating temperature and cooling power, these coolers must have working lifetimes commensurate with the 10 to 15 year lifetime expected for major future NASA facilities. To meet this lifetime requirement NASA is developing long lifetime mechanical coolers and the capability to service stored cryogen coolers on-orbit. The types of coolers currently being developed by NASA include radiative coolers, solid cryogen coolers, surface tension confined liquid cryogen coolers, mechanical coolers, liquid helium dewars, He3 adsorption coolers, adiabatic demagnetization refrigerators and dilution refrigerators.

Investigation into Vibration Issues of Sunpower M77 Cryocoolers

NASA/Goddard Space Flight Center (GSFC) has been evaluating Stirling cycle coolers produced by Sunpower, Inc. The particular coolers being evaluated are two versions of the Model M77 with active counterbalancers. This paper reports on an investigation into the residual vibration characteristics of these machines using several different techniques for activating the counterbalancer.

Spaceflight cryocooler integration issues and techniques

NASA/GSFC personnel in cooperation with other researchers are currently investigating a number of issues regarding the integration of cryocoolers into space flight missions. These issues include (I) integration of space flight cryocoolers with detector assemblies, (II) cryocooler-to-spacecraft interactions and vibration suppression with space flight and tactical cryocoolers, and (III) developments in cryogenic capillary pump loop technology to interface multiple cryocoolers to a common load.

Structural and thermal interface characteristics of Stirling cycle cryocoolers for space applications

Integration of a Stirling cycle cryocooler into a flight system will require careful attention to the thermal, structural, and electrical interfaces between the cryocooler, the instrument and the spacecraft. These issues are currently under investigation by National Aeronautics and Space Administration/Goddard Space Flight Center (NASA/GSFC) personnel in laboratory tests of representative longlife cryocoolers.