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Two sorption coolers using Hydrogen as the working fluid are currently being fabricated and assembled for flight delivery by the Jet Propulsion Laboratory (JPL). These systems have been designed to provide a total cooling capacity (per cooler) of 1 W at a cold end temperature less than 19 K with a temperature stability of 100–450 mK over a cooler cycle. Being vibration free, scalable and with the capability for the cold end to be remotely located from the warm spacecraft are the major advantages of this class of cryocoolers. This sorption cooler design has been validated by tests on components, subsystems and a fully integrated breadboard cooler (including electronics) at JPL where the two flight units are now being assembled for delivery to Europe in 2005. They will be used for the Planck Surveyor mission, which will perform high-resolution measurements of the cosmic microwave background anisotropy. In this paper we present the level of maturity of the hydrogen sorption cooler technology at JPL by describing the design and how it has been validated at the subsystem and system levels. In addition, we will describe how such systems could be advantageously used for other space missions with similar needs and cooler attributes. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

A continuous-duty hydrogen sorption cryocooler is being developed for the Planck spacecraft, a mission to map the cosmic microwave background beginning in 2007. This cryocooler uses six individual compressor elements (CEs) filled with the hydriding alloy LaNi[SUB4.78]Sn[SUB0.22] to provide high-pressure (50 bar) hydrogen to a Joule-Thomson (J-T) expander and to absorb low-pressure (∼0.3 bar) gas from liquid hydrogen reservoirs cooled to ∼18K. Quadrupole Mass Spectrometry (QMS) showed methane in these hydride beds after cycling during initial operation of laboratory tests of the Planck engineering breadboard (EBB) cooler. These contaminants have caused problems involving plugged J-T expanders. The contaminants probably come from reactions with residual hydrocarbon species on surfaces inside the hydride bed. The hydride bed in each CE is contained in an annular volume called a "gas-gap heat switch," which serves as a reversible, intermittent thermal path to the spacecraft radiator. The gas-gap is either "off" (i.e., its pressure < 1.3 Pa), or "on" (i.e., hydrogen gas at ∼4 kPa). The hydrogen pressure is varied with an independent hydride actuator containing ZrNiH[SUBx]. Early EBB cooler tests showed increasing parasitic heat losses from the inner beds, suggesting residual pressures in the gas gap during its "off" state. The pressure was shown to be due to hydrogen from outgassing from metallic surfaces in the gas gap and hydrogen permeation through the inner sorbent bed wall. This gas accumulation has serious end-of-life implications, as the ZrNi actuator has limited storage capacity and any excess hydrogen would necessarily affect its operation. This paper summarizes experiments on the behavior of hydrogen in the gas gap switch and formation of methane in the CE sorbent beds. [ABSTRACT FROM AUTHOR]

Two continuous operation 18 K/20 K sorption coolers are being developed by JPL for the ESA Planck mission to provide about 200 mW of cooling at 18 K and 1.4 W at 20 K. A detailed performance prediction model has been developed to support the design process and to evaluate the results of prototype testing. The performance of these coolers depends on many related operating parameters (such as the temperatures of precooling thermal shield and the warm radiator) and they can only be assessed through a detailed modeling of each component coupling. This model predicts the time varying temperature, pressure and H[sub 2] concentration gradients within the metal hydride beds, the H[sub 2] flow rate, cooling power produced in the coldhead, and the oscillations of the coldhead temperature. Each component model has been parametrically described to allow trade off evaluation and the possibility to use it for different environmental and cooling requirements and for other sorption coolers. The full validation of the model will be obtained by comparison of the performance predictions to the experimental data for the engineering prototype cooler being built at JPL. [ABSTRACT FROM AUTHOR]

Continuous 20 K sorption-based coolers are being developed for the European Space Agency (ESA) Planck mission. Sorbent beds containing the hydrogen absorbing Lanthanum-Nickel-Tin alloy LaNi[sub 4.78]Sn[sub 0.22] are being tested to evaluate their performance as compressor elements for unprecedented two years of flight operation thus demonstrating the basic performances of the cooler: namely cold end temperature, input power and cooling power. To provide basic characterization and life cycling data, a test facility was developed to test three prototype compressor elements under all conditions expected for the flight cooler operation. Each compressor element is continuously cycled in concentration and temperature to follow the absorption and desorption process assumed for the flight cooler. We present data on the hydrogen mass flow rates and thermal characteristics for all phases of the compressor cycle, with an emphasis on the controlled absorption of hydrogen. This function of the compressor element is the major driver of the cold end temperature and its stability. We also present data obtained over thousands of temperature cycles from these beds to determine the extent of degradation of the compressor element performance from changes in the hydride properties or other sources. [ABSTRACT FROM AUTHOR]

We present the design of a Hydrogen Sorption Cooler, part of the cryogenic chain in the Planck Mission (ESA). This cryocooler will provide continuous cooling at a nominal temperature about 18K for a period of about 2 years. Two independent astrophysical instruments will be supplied with a minimum cooling power of 0.135W for the High Frequency Instrument (HFI) and 0.967W for the Low Frequency Instrument (LFI) given a 60 K precooling temperature. Both instruments need highly stable temperatures (stability goal on the ground of 4 mK peak-to-peak). We show several designs for reaching this stability and also present laboratory test results. Gravitational effects on the thermal performance of the liquid reservoirs were determined by measuring behavior in all three orientations. No significant changes in reservoir temperatures were found. A local heater simulated the heat load on each reservoir. [ABSTRACT FROM AUTHOR]

Continuous-duty hydrogen sorption cryocoolers are being developed for the European Space Agency (ESA) Planck mission. To achieve an acceptable level of performance and robust operation with these hydride refrigerators during flight, detailed investigations have been performed on the sorbent materials and on critical hardware components. The sorbent longevity has been verified for both the compressor alloy and the gas gap actuator alloy. Check valves that isolate the high- and low-pressure sides within the sorption compressor are potential single-point failures as internal leaks would short circuit hydrogen flow to the Joule-Thomson (J-T) expander. Check valves were operated using hydrogen gas for over 43,000 pressure cycles at various orientations and temperatures without leaks or other changes. The filters that will be used to protect check valves and J-T expander from particles were tested. The temperature gradients along the tubular heater elements for the compressor beds were evaluated to assess their impact on the dynamics of compressor element heating and hydrogen desorption. The durability and reliability of low-power heaters used for the gas gap actuators were determined by accelerated temperature cycling. [ABSTRACT FROM AUTHOR]

Two continuous operation 18 K/20 K sorption cryocoolers are being developed by the Jet Propulsion Laboratory (JPL) as a NASA contribution to the European Space Agency (ESA) Planck mission, currently planned for a 2007 launch. Each individual sorption cooler will be capable of providing a total of about 200 mW of cooling power at 18 K and 1.2 W at 20 K, given a passive radiative precooling at 50 K. These coolers work by thermally cycling a metal-hydride to absorb and desorb hydrogen gas, used as the working fluid in a Joule-Thomson (J-T) refrigerator. The major advantage of the sorption coolers is their truly vibration-free operation capability together with the fact that they can be readily scaled to perform over a wide range of cooling powers. The hydrogen sorption coolers will directly cool the Planck Low Frequency Instrument (LFI) HEMT amplifiers to approximately 20 K and will provide precooling at 18 K to the RAL 4 K closed-cycle Helium J-T cooler for the High Frequency Instrument (HFI). The concept design, the cooler operations and the predicted performances of the flight models are here presented. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]