Miniature Long-Life Space-Qualified Pulse Tube and Stirling Cryocoolers

Abstract

Cryogenic coolers for small satellites require low power and minimum weight. In this paper we report on the status of both our miniature flight-qualified pulse tube cooler as well as our miniature flight-qualified Stirling cooler. Both integral linear coolers are small, efficient, low-power, and vibrationally balanced, and incorporate Oxford-type single flexure-bearing compressors. Vibrational balance is achieved with a motor-driven balancer. The Stirling cooler cold head incorporates a colinear flexure-bearing suspended displacer/regenerator with a motor drive used for phase control. The larger capacity pulse tube cooler uses a completely passive cold head which contains no cold moving parts. Nonwearing clearance seals in both coolers advance the long 10-year life projections.

The vibrationally balanced, miniature pulse tube cooler weighs 2.0 kg and delivers a maximum cooling power at 80 K of 800 mW for an input power to the compressor of 30 watts. The unit is suitable for cooling sensors and optics between 60 and 200 K, with cooling powers up to 3.5 watts at 200 K. Self-induced measurements indicate that the cooler can be balanced to reduce vibration forces below 0.1 newtons (N) from 0 to 1000 Hz in all three axes. Using adaptive vibration cancellation, vibration has been reduced below 0.02 N along the cooler axis. The cooler has passed launch vibration tests and is now in life test.

The miniature integral Stirling cooler weighs 1.4 kg. It was developed for cooling infrared sensors to temperatures as low as 50 K on lightsats. A number of the vibrationally balanced nonwearing Stirling coolers have been built and tested. Typical cooling performance is 0.25 watt at 65 K for an input power to the compressor of <12 watts. Cooler vibration forces have been balanced below 0.1 N in all three axes from 0 to 1000 Hz. The cooler recently passed launch vibration tests prior to its entry into an extended life-test and its first scheduled flight in 1995.