Adaptation of Tactical Cryocoolers for Short Duration Space-Flight Missions
NASA, the U.S. Air Force and industry have made a considerable investment during the last decade to develop low vibration mechanical cryocoolers for space applications with a typical-mean-time-to-failure (MTTF) goal of five years or more. The cost is expected to be about $1.0 million per cryocooler. Unbalanced tactical cryocoolers are readily available at comparatively low cost (< $20,000.00) with typical MTTF’s of about 2500–8000 hours. NASA/GSFC personnel have tested tactical cryocoolers from Magnavox, Texas Instruments & Hughes Aircraft, to determine if typical vibration and thermal requirements of shuttle or other short duration space-flight missions could be met. All of these cryocoolers were of the linear motor type with opposed compressors and a free piston, unbalanced expander. Typical vibration levels are 2 Newtons of force at the expander and 1 Newton of force at the compressor at the fundamental and harmonic frequencies through 1000 Hz. NASA/GSFC personnel designed and implemented a low cost active counterbalance to mount on each expander to reduce vibrations. NASA/GSFC’s vibration control algorithm was then used to further null vibrations to below 0.1 Newtons.
Characterization tests for each of these cryocoolers include load curves, power measurements, thermal vacuum testing and axial and radial vibrations measurements with and without an active vibration control system. Baseline characterization testing has been completed on all three cryocoolers. Life testing is currently underway. To monitor degradation processes characterization testing will be repeated every 1000 hours until cryocooler failure. Conclusions and a summary of results are presented.
KeywordsVibration Control Radial Force Texas Instrument Heater Load Piston Compressor
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