— Northrop Grumman engineers have made improvements in cryocooler technology that company officials say will improve the efficiency and sensitivity of future space telescopes and sensors.

In tests conducted in December, a Northrop Grumman cryocooler similar to the equipment designed to support the Mid-Infrared Instrument on the James Webb Space Telescope achieved cooling levels of 4.4 degrees Kelvin, or nearly -268.6 degrees Celsius. In comparison, the Mid-Infrared Instrument cryocooler is designed to reach 6 degrees Kelvin, or -267 degrees Celsius.

While ground-based cryocoolers used in materials research can achieve even lower temperatures, Northrop Grumman engineers are heralding their new achievement as a breakthrough because they were able to achieve temperatures of 4.4 degrees Kelvin using a modified version of the pulse tube Joule-Thomson cryocoolers that have proven their ability to operate in space. Similar cryocoolers are supporting the Atmospheric Infrared Sounder Instrument flying aboard NASA’s Earth-observing Aqua satellite, the Tropospheric Emission Spectrometer on the Aura satellite and the Japanese Advanced Meteorological Imager on the Multifunctional Transport Satellite.

“The trick to building cryocoolers for spaceflight is that they have to work perfectly and in some cases they have to last for more than 10 years,” said Mark Folkman, director of Sensors and Phenomenology for Northrop Grumman’s Aerospace Systems sector in
Redondo Beach

extract heat from sensors in order to eliminate the electronic noise that can undermine the clarity and performance of the sensitive instruments. Sophisticated cryocoolers are particularly important for improving the performance of X-ray, very-far-infrared and microwave instruments, Folkman said. When a cryocooler fails, instrument performance suffers and data return is jeopardized.

Programs like the James Webb Space Telescope that Northrop Grumman is building for NASA require large investments. “It would be a shame if its life was limited to a year or two” by using an expendable cryogen, such as liquid nitrogen, Folkman said.

Northrop Grumman will continue development of the cryocooler technology using company funds, striving to achieve cooling levels of 2 degrees Kelvin, or -271 degrees Celsius, said Jeff Raab, cryocooler systems manager for Northrop Grumman Aerospace. At the same time, company engineers will attempt to improve the efficiency of their cryocoolers and reduce the amount of power consumed, Raab added.

Future efforts also will focus on integrating the Northrop Grumman cryocooler with another type of cooler used in space applications, an Adiabatic Demagnetization Refrigerator (ADR). ADRs are heat pumps designed to cool detectors to between 4 degrees Kelvin and 50 degrees millikelvin. On the Kelvin scale, the absence of any thermal energy is zero. A millikelvin is one-thousandth of a degree Kelvin above zero.

said cooling devices that can reach 50 to 100 degrees millikelvin will be critical to the success of the next generation of astrophysics missions, including the International X-Ray Observatory, an X-ray telescope project being studied jointly by NASA, the European Space Agency and the Japan Aerospace Exploration Agency; the Terrestrial Planet Finder, a NASA program to study planets outside Earth’s solar system; and the Single Aperture Far-Infrared Astronomy Observatory, a space telescope designed to study the earliest formation of galaxies, stars and planetary systems.

Northrop Grumman Aerospace also is supplying the cryocoolers for the Geostationary Operational Environmental Satellite-R series, a collaborative project involving NASA and the National Oceanic and Atmospheric Administration to launch the next generation of weather forecasting satellites.