Volume 4, Number 2 May/June 1996
An instrument that can quickly cool infrared and other sensors to near absolute zero will fly aboard the Space Shuttle Endeavor's STS-77 mission in mid-May for microgravity tests.
The Brilliant Eyes Ten Kelvin Sorption Cryocooler Experiment, or BETSCE, developed at NASA's Jet Propulsion Laboratory, will be used to cool infrared sensors aboard spacecraft to ten Kelvin, or -441.6 Fahrenheit (Absolute zero is -459.6 F).
BETSCE is a space shuttle technology demonstration experiment to show that cryocoolers of this type, called "sorption coolers", can operate in the absence of gravity. Sorption coolers have essentially no vibration, are very efficient and can operate reliably for over ten years.
Sorption coolers work by using specialized metal alloy powders that absorb the hydrogen refrigerant. In the sorption compressor, the metal powder is first heated to pressurize the hydrogen, and then cooled to room temperature to reduce the pressure. By sequentially heating and cooling the powder, the hydrogen is circulated through the refrigeration cycle. Ten Kelvin is achieved by expanding the pressurized hydrogen at the cold tip of the refrigerator. This expansion actually freezes the hydrogen to produce a solid ice cube at ten Kelvin. The heat load generated by the device being cooled then sublimates the ice. This closed cycle operation is repeated over and over.
"Before this new technology, the only way to achieve temperatures in space as low as ten Kelvin have been to launch extremely large, heavy, and expensive dewars containing liquid helium or solid hydrogen. Unfortunately, these dewars have very limited lifetime because the cryogens eventually get boiled off and become depleted. The ability to achieve a lifetime of ten or more years, with no vibration, opens the door to a wide variety of future missions that could benefit from this novel technology," said Dr. Steven Bard, the principal investigator.
The cryocooler technology has significant commercial potential and is being transferred to industry in a number of ways. JPL and Aerojet Electronics Systems Division are pursuing a number of spin-offs, including using sorption techniques for commercial non-ozone depleting refrigeration, air conditioning and heat pump systems. For example, Jack Jones of JPL, is working with Aerojet under funding from the Los Angeles County Metrorail to develop a sorption air conditioner for a commuter train.
BETSCE was funded by the Air Force Space and Missiles System Center and the Department of Defense's Ballistic Missile Defense Organization. NASA's Office of Space Access and Technology is sponsoring the Shuttle flight for BETSCE.
For more information, contact Dr. Steven Bard at Jet Propulsion Laboratory. Phone: 818/354-4487, E-mail: steven.bard@jpl.nasa.gov Please mention that you read about it in Innovation.
