D. L. Johnson

AIRS PFM Pulse Tube Cooler System-Level Performance

JPL’s Atmospheric Infrared Sounder (AIRS) instrument is being built to make precision measurements of air temperature over the surface of the Earth as a function of elevation; the flight instrument is in the final stages of assembly and checkout at this time, and uses a pair of TRW pulse tube cryocoolers operating at 55 K to cool its sensitive IR focal plane.

Cryocooler Resonance Characterization

Abstract An important issue in the design and scaling-up of Stirling cryocoolers is achieving good drive motor efficiency and launch survivability. The important common thread linking these two topics is the dynamic resonant response of the compressor and displacer moving masses. The fundamental equations governing cryocooler mechanical efficiency and launch vibration response are presented and explored in terms of their implications for cooler design. The resonant frequency, damping and drive motor force parameters associated with the cooler are shown to be key to efficient operation. Means of measuring these parameters are presented and shown to have broad applicability to additional parameters such as drive stiction and vibration transmitted to the instrument. The resonant parameters of the BAe 55 K AIRS proof-of-concept cooler are used as an example to demonstrate the good correlation between the analytical fundamentals and the measured characteristics of a state-of-the-art cryocooler design.

EMI Performance of the AIRS Cooler and Electronics

The TRW pulse tube cryocooler for JPL’s Atmospheric Infrared Sounder (AIRS) instrument is required to meet stringent requirements for radiated electric and magnetic fields, conducted emissions on the input power bus, and electromagnetic susceptibility. To meet the radiated magnetic field requirements, special mu-metal shields were designed, fabricated, and fined to the cooler following an extensive period of magnetic testing with mock-up cooler hardware. Excessive magnetic fields is a generic issue with linear-motor cryocoolers, as is excessive levels of input ripple current. Solving the ripple current issue required the addition of a dedicated ripple filter as part of the spacecraft power system.

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.

Electromagnetic Compatibility Characterization of a BAe Stirling-Cycle Cryocooler for Space Application

The intended use of Stirling-cycle cryocoolers to cool infrared and submilli-meter imaging instruments on 5- to 10-year missions brings with it major challenges to cryocooler development. In particular, the voice-coil driven cryocoolers need to be electromagnetically compatible with the host instrument’s detectors as well as with neighboring instruments; specifically the cryocoolers must not generate levels of interference that degrade performance or cause malfunction of the cooled imaging detectors, payload instruments, or host spacecraft.

Vibration Characteristics of Stirling Cycle Cryocoolers for Space Application

Vibration generated by small Stirling-cycle cryocoolers is an important concern for spacecraft designers planning to incorporate these cryocoolers into near-term space-science instruments. Under joint Air Force/Ballistic Missile Defense Organization (BMDO) and NASA Eos/AIRS Instrument sponsorship, JPL has an extensive ongoing cryocooler characterization program addressed to measuring the important cryocooler performance characteristics such as self-generated vibration; these measurements provide the interface and trend data needed by instrument designers as well as valuable feedback for improving cryocooler performance.

On‐Orbit Performance of the TES Pulse Tube Coolers and Instrument — A First Year in Space

Launched on NASA’s Aura spacecraft on July 15, 2004, JPL’s Tropospheric Emission Spectrometer (TES) instrument has completed a successful first year in space and captured a number of important lessons. The instrument contains four focal plane arrays in two separate housings cooled to 65 K by a pair of NGST pulse tube cryocoolers. The instrument includes a two‐stage passive cooler to cool the optical bench to 180 K. The cryocooler system design is tightly coupled with the overall thermal control design to maximize performance. Soon after cooling the optical bench and focal planes to their operating temperatures on August 20, 2004, ice contamination of the focal planes led to the need of a decontamination cycle. Ice buildup of cryogenic surfaces led to increased cryocooler heat loads. After six months of successful science operations, plans were developed to increase the optics temperature to 187 K to improve the interferometer optical alignment and obtain higher quality science data. The plan is in place a...

EFFECT OF HEAT REJECTION CONDITIONS ON CRYOCOOLER OPERATIONAL STABILITY

It is well known that cryocooler thermal efficiency is a strong function of heat rejection temperature, roughly following the dependency described by Carnot. An equally important and generally overlooked implication of cryocooler heat-rejection thermodynamics is the effect of the heat rejection temperature control mode on cryocooler performance and operational stability. Example heat rejection temperature control modes include constant reject temperature (generally maintained via closed-loop temperature control), heat rejection temperature rising linearly with power dissipation (typical of conduction/convection to a constant temperature heat sink), and heat rejection dependent on the fourth power of reject temperature (typical of radiation to deep space). This paper presents a useful algorithm for computing the effect of changing heatsink temperature on cryocooler performance and uses the algorithm to examine the implications of various heat rejection temperature control modes on cryocooler operation. A useful system-level thermal performance map is developed to display the stability boundaries and available stable operating space for coolers of interest for various typical heat rejection control modes.

Cryocooler Electromagnetic Compatibility

The Jet Propulsion Laboratory, under joint Ballistic Missile and Defense Organization (BMDO)/Air Force and NASA/Eos Atmospheric Infrared Sounder (AIRS) sponsorship, is conducting extensive space cryocooler characterization to provide a reliable and accurate data base on cryocooler performance for use by the space community. As the number of cryocoolers taken through the characterization program increases, it is possible to synthesize the test results to allow performance trends and similarities and differences among the coolers to be observed.

Performance Characterization of the TRW 35K Pulse Tube Cooler

The TRW 35K pulse tube cooler is configured as an integral cooler, with the pulse tube attached perpendicular to a pair of compressors operating into a common compression chamber. The cooler was optimized for 35K operation and has a nominal cooling capacity of 850 mW at 35 K with a cooler input power of 200 W. It also provides 2 W of cooling at 60 K for 90 W of input power. The cooler was extensively characterized by JPL, measuring the thermal performance and the cooler-generated vibration and EMI as a function of piston stroke and offset position. The thermal performance was found to be quite sensitive to the piston offset position. The pulse tube parasitic conduction levels were also measured and shown to have a strong angular dependence relative to gravity. Magnetic shielding studies were performed to examine radiated magnetic emission levels from compressors with and without shielding.