Space Shuttle

The first American-built, long-lived and low-vibration cryogenic cooler to operate in space was successfully tested aboard a recent space shuttle flight.

The Cryo System Experiment was flown on space shuttle Discovery on mission STS-63 in February to demonstrate that long duration, high-performance, smaller volume and lower power consumption mechanical cooling systems can be designed and fabricated for extremely sensitive, space-based scientific instruments using infrared and gamma-ray sensors.

Cryogenic, or very low temperature, coolers have the ability to reduce the temperature of infrared and gamma-ray sensors to cryogenic levels to enable precise measurements of celestial objects.

"Infrared sensors, which function much like those in a home video camera, must be operated at cryogenic temperatures, on the order of 65 degrees Kelvin to reduce the background noise that is inherent in sensors operating at room temperature," said Russ Sugimura, the experiment's project manager at NASA's Jet Propulsion Laboratory. "This improves the signal-to-noise ratio, resulting in a much clearer image."

Kelvin is a unit of temperature measurement; 65 Kelvin is equivalent to minus 208 degrees Celsius or minus 343 degrees Fahrenheit.

The cryocooler experiment, managed by JPL, was developed and built by Hughes Aircraft Co. The experiment validated the operation at zero gravity in space of two cryogenic technologies. One was a state-of-the-art Hughes 65 Kelvin Improved Standard Spacecraft Cryocooler designed to cool space-based optics for long-duration missions requiring a low-vibration, continuous cooling source.

The second technology was a Hughes experimental diode oxygen heat pipe. The heat pipe enables large physical separation of the cooling source from the element to be cooled, and provides on-off switching capability between the cooling source and heat load, thus limiting the amount of reverse heat flow when the cooler is turned off.

"The shuttle experiment resolved a key technical concern by demonstrating that cryogenic oxygen heat pipes do, in fact, work in the near-zero gravity of low-Earth orbit," Sugimura said.

The experimental data from these two cryogenic technologies showed that the experiment achieved 100 percent success and illustrated an important type of NASA space flight experiment in which an emerging technology is validated to provide the option for improving the performance of optical systems for scientific and defense applications in near-future space systems.

The cryocooler experiment demonstrated the ruggedness to withstand space shuttle launch vibrations, characterized the thermal performance of both technologies and established a flight-heritage database by demonstrating compliance with launch vehicle safety and cryosystem integration constraints, Sugimura said.

The successful cryocooler experiment represents a key milestone in allowing the incorporation of space cryocooler technology into a variety of multi-year NASA, Department of Defense and commercial missions. Until now the only long-life cryocooler in the world to have been flight qualified and successfully flown in space was the Oxford Stirling cycle cryocooler built by Oxford University in England.

The low-vibration, lightweight cooler, which provided 1.2 watts of cooling at 60 Kelvin (equivalent to 2 watts at 65 degrees Kelvin), is an improved version of the 65 Kelvin Standard Spacecraft Cryocooler developed by Hughes and the U.S. Air Force. Its continuous performance over the course of the eight-day mission equaled its performance during ground testing, a Hughes spokesman added.

In addition to the technical success, the experiment demonstrated a true teaming effort between Hughes and JPL. "This was an outstanding example of industry and government teamwork," said Sam Russo, Hughes program manager for the experiment.

Working closely together, the team was able to identify and overcome the technical challenges required to integrate a cryocooler into a space payload and actively transfer the lessons learned to a number of important ongoing NASA cryogenic missions, such as JPL's atmospheric infrared sounder instrument. The experiment development was begun in July 1991 and was completed ahead of schedule.

The cryocooler system was the first JPL In-Space Technology Experiments Program (IN-STEP) experiment to be flown onboard a shuttle mission. The IN-STEP program provides investigators with a rapid, low-cost opportunity to validate the performance of new technologies in the space environment.

Work on the IN-STEP Cryogenic Experiment was performed by the Jet Propulsion Laboratory and Hughes Aircraft Company under contract to NASA's Office of Space Access and Technology, Washington, D.C.

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