Active versus standby redundancy for improved cryocooler reliability in space
Long-life space cryocooler applications, such as NASA’s Atmospheric Infrared Sounder (AIRS) instrument, require that the cryocooler system possess a very high level of reliability. This need for high reliability not only demands that high reliability coolers be used, but often requires that some form of redundancy be incorporated. One common implementation is standby redundancy; however, active redundancy is another equally viable choice. Recently, experience with both types of redundancy has been gained with the AIRS instrument. The AIRS cryocoolers were initially designed and launched as standby redundant units; they were then switched over to active redundancy after six months of in-space operation.
Adaptation of the low-cost and low-power tactical split Stirling cryogenic cooler for aerospace applications
Cryogenic coolers are often used in modern spacecraft in conjunction with sensitive electronics and sensors of military, commercial and scientific instrumentation. The typical space requirements are: power efficiency, low vibration export, proven reliability, ability to survive launch vibration/shock and long-term exposure to space radiation. A long-standing paradigm of exclusively using "space heritage" equipment has become the standard practice for delivering high reliability components. Unfortunately, this conservative "space heritage" practice can result in using outdated, oversized, overweight and overpriced cryogenic coolers and is becoming increasingly unacceptable for space agencies now operating within tough monetary and time constraints. The recent trend in developing mini and micro satellites for relatively inexpensive missions has prompted attempts to adapt leading-edge tactical cryogenic coolers for suitability in the space environment. The primary emphasis has been on reducing cost, weight and size. The authors are disclosing theoretical and practical aspects of a collaborative effort to develop a space qualified cryogenic refrigerator system based on the tactical cooler model Ricor K527 and the Iris Technology radiation hardened Low Cost Cryocooler Electronics (LCCE). The K27/LCCE solution is ideal for applications where cost, size, weight, power consumption, vibration export, reliability and time to spacecraft integration are of concern.
Performance Characterization of the TRW 3503 and 6020 Pulse Tube Coolers
The Jet Propulsion Laboratory, under joint Ballistic Missile Defense Organization (BMDO)/Air Force Phillips Laboratory and NASA/EOS Atmospheric Infrared Sounder (AIRS) sponsorship, has conducted extensive characterization testing of the TRW Model 3503 and Model 6020 pulse tube cryocoolers. These coolers, built under BMDO/AFPL sponsorship, share a common design that utilizes a single-stage pulse tube integrally mounted onto 10-cc common compression space compressors, and are distinguishable by slight differences in the pulse tube designs which optimized cooler performance for operation at either 35 K or 60 K. The coolers were characterized over a range of heak rejection temperatures and cooler operating parameters (compressor stroke, piston offset, and drive frequency) to understand their effects on cooler thermal performance, cooler-generated vibration and cold block motion, and cooler-generated EMI. Pulse tube parasitic conduction as a function of cold block temperature has been studied for a non-operating cooler; the results show a strong angular dependence relative to gravity. The results of the parametric studies are presented.