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ItemSpace Micro Pulse Tube Cooler(Georgia Institute of Technology, 2008-05) Nguyen, T. ; Petach, M. ; Michaelian, M. ; Raab, J. ; Tward, E.The Northrop Grumman space micro pulse tube cooler (micro) is a split configuration cooler incorporating a coaxial cold head connected via a transfer line to a vibrationally balanced back to back linear compressor. The micro compressor is scaled from the flight proven high efficiency cooler (HEC) compressor and contains non-wearing pistons suspended on flexure bearings. Designed for > 10 year operation with no performance change, the 800 gram mechanical cooler can cool sensors and optics to temperatures <50K while rejecting heat to radiators over a wide range of reject temperatures. The very small, low vibration, high frequency cooler is designed to be readily integrated into space payloads. The coaxial cold head can also be integrated with custom focal planes into an integrated detector cooler assembly (IDCA) similar to those used with the shorter lived tactical coolers. This paper reports on the performance of this cooler.
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ItemSelf-Induced Vibration of NGAS Space Pulse Tube Coolers(Georgia Institute of Technology, 2008-05) Colbert, R. ; Nguyen, T. ; Raab, J. ; Tward, E.Space cryocoolers are often used to cool the focal planes and optics of telescopes. Since telescope and focal plane jitter can affect the clarity of the image, space cryocoolers are designed for inherent low vibration. For very sensitive applications, many cryocooler systems incorporate active vibration control in addition to passive isolation from their mounting structures. The sole moving parts in all the NGAS pulse tube coolers, whether one, two or three stage, are the moving compressor pistons and their flexure supports that are inherently balanced in a back to back configuration. To further reduce the vibration below this already very low level, all the cooler systems are provided with single axis active control on the drive axis of the compressor that contains the moving piston masses. The cryocooler control electronics takes a signal from an accelerometer mounted parallel to the drive axis and feeds it back to the compressor motor drive signals to further reduce the vibration by >40dB. In this paper we present the self-induced vibration measurements made on a number of NGAS flight coolers including the single stage HEC cooler with both linear or coaxial cold heads and a micro cooler. We also present self-induced vibration measurements for the simultaneous operation of two HEC coolers mounted to the same platform.
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ItemMIRI Cooler System Design Update(Georgia Institute of Technology, 2008-05) Petach, M. ; Durand, D. ; Michaelian, M. ; Raab, J. ; Tward, E.NASA, under the Cryogenic Fluid Management (CFM) Project, in partnership with Ball Aerospace Technologies Corporation (BATC), conducted a reduced boil-off demonstration employing an actively cooled thermal radiation shield. The shield, designed and fabricated by NASA, consisted of overlapping panels of 1100 aluminum foil, and three parallel 1/8 inch cooling lines attached to the foil with adhesive and communicating with 1/4 inch inlet and outlet manifolds. The shield and gas distribution network were instrumented and integrated with BATC's 500 L liquid nitrogen (LN2) cryogenic propellant tank simulator, high-performance multi-layer insulation (MLI), and a cryocooler and pressurized helium circulator. Two test conditions were run to evaluate the thermal performance of the system. An initial test was performed to measure the baseline or passive steady state heat leak into the LN2 tank. In the second test, the cryocooler/circulator was driven at maximum power until the system again reached steady state. By removing heat from both the shield and the tank support structure via the circulating helium stream, the average shield temperature dropped from ~228 K to ~132 K and the total heat leak into the tank was reduced by 82 %. This was despite the fact that the flow rate in the distribution network was unexpectedly low due to a partial blockage in one of the recuperators.
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ItemPulse Tube Cooler with Remote Cooling(Georgia Institute of Technology, 2008-05) Raab, J. ; Maddocks, J. R. ; Nguyen, T. ; Toma, G. ; Colbert, R. ; Tward, E.Space pulse tube coolers are very efficient, but like all regenerative high frequency Stirling and pulse tube coolers, the cold head needs to be located near the compressor in order to minimize the input power to the cooler. For applications that require cooling some distance from the cooler or that require vibration isolation from the cooled object, the cooling can be effectively transferred with a fluid loop rather than with a higher mass conduction bar. This can greatly ease integration into a payload as well as readily transmit the cooling to multiple cooling points. In this paper we report on a proof of concept test in which we added cold reed valves to the pulse tube cold block of our flight proven high efficiency cooler (HEC) so that cold gas could be circulated without the need for an additional circulation pump and additional heat exchangers to cool the gas. In this test, the measured remote cooling and the parasitic heat loads were compared to our previously reported tests using warm reed valves. The two previous tests circulated gas from either a second circulator compressor or from the pulse tube compressor that also acted as a circulator and cooled the gas with a heat exchanger connected to the pulse tube cold head.
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ItemHEC Pulse Tube Coaxial Cold Head Coolers(Georgia Institute of Technology, 2008-05) Nguyen, T. ; Toma, G. ; Jaco, C. ; Michaelian, M. ; Raab, J.A large number of NGAS high efficiency coolers (HEC) have been manufactured for six different space payload designs using a linear configuration cold head that is integrally mounted to the compressor. One of the payloads has been in orbital operation since 2005 and a second since 2009. For some applications it may be desirable to have a different cold head mechanical and thermal interface in order to ease integration into the system. For that purpose we have developed both one and two stage HEC coolers that incorporate coaxial cold heads that are integrally mounted to the compressor. The single thermal and mechanical mounting interface of this integral configuration eases integration with a payload and reduces its complexity compared to a split cold head version that requires two warm interfaces rather than one. In this paper we present the measured performance of the single stage HEC coaxial cold head cooler in its integral configuration and compare its performance with the linear cold head version. We also present the measured performance of the parallel cold head two-stage version of the cooler designed for the simultaneous cooling of both focal planes at temperatures above 35 K and optics and filters at temperatures greater than 75K.