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.
Performance of the AIRS Pulse Tube Coolers and Instrument—A First Year in Space
Launched on NASA’s Aqua platform on May 4, 2002, JPL’s Atmospheric Infrared Sounder (AIRS) instrument has completed a successful first year in space and captured a number of important lessons. AIRS is designed to make precision measurements of air temperature over the surface of the Earth and uses a redundant pair of TRW 55 K pulse tube cryocoolers to cool its sensitive IR focal plane. Soon after the instrument went cold, contamination of cryogenic surfaces led to increased cooler loads and the need for decontamination cycles. In addition, single event transients occurred while passing through the South Atlantic Anomaly (SAA) necessitating corrective actions. In November 2002 the fundamental operating strategy of the AIRS instrument was changed from the original strategy of running a single cooler and having the second cooler as a non‐operating backup. Instead, based on a new system‐level reliability analysis, both coolers began operation simultaneously. This change resolved the contamination and SAA driven interruptions and has enabled unprecedented levels of continuous science measurements. A review of the AIRS instrument cryogenic performance over the past year is presented including its contamination buildup and interrupt history. The reliability analysis conducted to justify two‐cooler operation is also reviewed.
Development of Advanced Cryogenic Integration Solutions
This paper describes the development of three advanced cryogenic integration devices for future space-based cryogenic systems. The first device is the cryogenic capillary pumped loop (CCPL), a miniaturized two-phase fluid circulator for thermally linking cryogenic cooling sources to remote cryogenic components. Two other devices, a nitrogen triple-point cryogenic thermal storage unit (CTSU) and a hydrogen gas-gap cryogenic thermal switch (CTSW), are also described. Each of the three components will fly on STS-95 in October 1998 as part of the CRYOTSU Flight Experiment. This paper describes the design, operation, flight configuration, and ground test results of each device and provides discussions of several new concepts for cryogenic integration.