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Proceedings Paper

Advanced cryogenic thermal switches for JWST
Author(s): David C. Bugby; Matthew Beres; Charles G. Stouffer; Jose I. Rodriguez
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Paper Abstract

This paper describes two cryogenic thermal switches (CTSWs) under development for instruments on the James Webb Space Telescope (JWST). The first thermal switch was designed to extend the life of the solid H2 dewar for the 6 K Mid Infrared Instrument (MIRI) while the second thermal switch is needed for contamination and over-temperature control of three 35 K instruments on the Integrated Science Instrument Module (ISIM). In both cases, differential thermal expansion (DTE) between two materials having differing CTE values is the process that underpins the thermal switching. The patented DTE-CTSW design utilizes two metallic end-pieces, one cup-shaped and the other disc-shaped (both MIRI end-pieces are Al while ISIM uses an Al/Invar cup and an Al disc), joined by an axially centered Ultem rod, which creates a narrow, flat gap between the cup (rim) and disc. A heater is bonded to the rod center. Upon cooling one or both end-pieces, the rod contracts relative to the end-pieces and the gap closes, turning the CTSW ON. When the rod heater is turned on, the rod expands relative to the end-pieces and the gap opens, turning the CTSW OFF. During testing from 6-35 K, ON conductances of 0.3-12 W/K and OFF resistances greater than 2500 K/W were measured. Of particular importance at 6 K was the Al oxide layer, which was found to significantly decrease DTE-CTSW ON conductance when the mating surfaces were bare Al. When the mating surfaces were gold-plated, the adverse impact of the oxide layer was mitigated. This paper will describe both efforts from design through model correlation.

Paper Details

Date Published: 18 August 2005
PDF: 7 pages
Proc. SPIE 5904, Cryogenic Optical Systems and Instruments XI, 59040F (18 August 2005); doi: 10.1117/12.617676
Show Author Affiliations
David C. Bugby, Swales Aerospace (United States)
Matthew Beres, Swales Aerospace (United States)
Charles G. Stouffer, Swales Aerospace (United States)
Jose I. Rodriguez, Jet Propulsion Lab. (United States)

Published in SPIE Proceedings Vol. 5904:
Cryogenic Optical Systems and Instruments XI
James B. Heaney; Lawrence G. Burriesci, Editor(s)

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