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Cryogenics and Fluids Branch

Space Cryocooler Overview

Quick Reference: Temperature Ranges

  • Passive Cooler -- down to 30 kelvin
  • Mechanical Cooler -- down to 6 kelvin
  • Adiabatic Demagnetization Refrigerator -- below 1 kelvin
  • Stored Cryogen Cooler -- down to 1.3 kelvin

In More Detail

Current Cryocooler Types

1. Passive Cooler

What it consists of:
Techniques that don't use any active machines. For example, sunshades (on the sunny side of the spacecraft) and radiators (on the shadow side of the craft.) These space radiators radiate waste heat to deep space.
As a stand-alone system, it's only useful when the heat loads are small.
Possible temperature ranges - 2 examples
  • The Cosmic Background Explorer (COBE): 60 kelvin in earth orbit. This was the temperature reached after the liquid helium coolant supply was exhausted and when the heat load was low (because most the electronics had been turned off.) The COBE sunshield was designed to block sunlight and also to block both earthlight and moonlight.
  • James Webb Space Telescope (JWST): predicted 35 kelvin or lower. NGST will be about as far from the Sun as the Earth is. However, NGST will be far enough from the Earth and the Moon that it won't have to worry about heating from moonlight or earthlight. For more info on this project, visit the JWST Website.
Use with other cooling systems
Spacecraft that use active cooling systems (such as mechanical coolers) also need passive cooling (sunshields and radiators) to get the most from their active coolers.

2. Mechanical Cryocooler

What it consists of:
a machine that cools, the hi-tech equivalent of a home refrigerator or freezer.
requires electric power.
Possible temperature ranges:
down to 30 kelvin now for flight use, predicted down to 6 kelvin by 2005. (Coolers for use in the laboratory can go colder, but they're too big and heavy to fly in a spacecraft.)
Use with other cooling systems:
Spacecraft with mechanical coolers should also use passive cooling (sunshades and space radiators.)
Mechanical coolers can be teamed with lower temperature coolers (such as the Advanced Adiabatic Demagnetization Refrigerator, discussed next) to reach even lower temperatures.
For more information:
See our mechanical coolers section.

3. Adiabatic Demagnetization Refrigerator (ADR) and Advanced ADR

What it consists of:
a magnetic cooling device. A block of a paramagnetic (weakly magnetic) substance warms up or cools down as the applied magnetic field strengthens or weakens. The Advanced ADR, now being developed here at Goddard, is a multi-stage ADR. It consists of a number of single stage ADRs end-to-end. Advantages of the Advanced ADR include greater temperature range and higher cooling power, as well as continuous operation.
limited temperature range. Currently available ADRs must be teamed with another cooler, one able to cool down to the range of 1-4 kelvin.
Possible temperature range:
Existing ADRs can cool down to 70 millikelvin, when teamed with a cooler that provides a 4 kelvin stage. By 2004, we expect to have an ADR that can reach 20 millikelvin, when teamed with a 10 kelvin cooler. Eventually, we may have an ADR that can be teamed with a 30 kelvin passive cooler.
Use with other cooling systems:
To reach temperatures below 1 kelvin, an ADR must be teamed with another cooler that cools the ADR's "warm" end down to a few degrees kelvin. For example, the ADR developed for the X-Ray Spectrometer (XRS) was connected to a bath of superfluid helium at 1.3 kelvin. The Advanced ADR will be teamed with the 6-kelvin mechanical cyrocoolers now being developed.
For more information:
See our Adiabatic Demagnetization Refrigerator (ADR) and Advanced ADR pages.

Cryocooler Types Being De-emphasized

Stored Cryogen Cooler

What it consists of:
a container of a cold substance, such as liquid helium. (Everyday counterparts of stored cryogen coolers are ice cubes and blocks of dry ice.)
stops working as soon as the stored cryogen is gone (that is, as soon as the helium has boiled away, or the ice cubes have melted, or the dry ice has sublimed away.) Because of this limited lifetime, future spacecraft will probably use long lifetime mechanical cryocoolers instead of stored cryogen coolers. Stored cryogens will continue to be used in systems where long lifetime is not important (for example, in laboratories and on airplanes such as SOFIA.)
Possible temperature ranges:
The lowest practical temperature is around 1.3 kelvin, possible with superfluid helium (as used in the XRS instrument.) Other temperature ranges are possible with other cryogens. For example, the Near-Infrared Camera and Multi-Object Spectrometer (NICMOS) instrument in the Hubble Space Telescope used solid frozen nitrogen to cool to 58 kelvin. (Unfortunately, NICMOS exhausted its supply of solid nitrogen ahead of schedule. Therefore, the solid nitrogen cooler will be replaced with a Turbo Brayton mechanical cooler.)
Use with other cooling systems:
Stored cryogen systems should be used with passive cooling (such as sunshades) to extend the life of the cryogen.
Stored cryogen coolers can also be used with ADRs to reach temperatures below 1 kelvin. On XRS, for instance, a liquid helium bath was used with an ADR to reach 60 millikelvin.
For more information:
See our Liquid Helium and Hybrid Systems section.
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