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P.J. Shirron, E.R. Canavan, M.J. DiPirro, M. Jackson, J. Panek, J.G. Tuttle,
Code 552
NASA/ Goddard Space Flight Center
Greenbelt, MD 20771
We have designed, built, and tested a gas-gap heat switch that turns on and off passively, without the need for a separate, thermally activated getter. This switch uses 3He condensed as a thin film on alternating plates of copper. The switch is thermally conductive at temperatures above about 0.2 K, and is insulating if either end of the switch cools below about 0.15 K. The "on" conductance (7 mW/K at 0.25 K) is limited by the surface area and gap between the copper leaves, the saturated vapor pressure of the 3He, and the Kapitza boundary resistance between the 3He and the copper. The "off" conductance is determined by the helium containment shell which physically supports the two conductive ends. We have also designed and are building passive gas-gap heat switches that will passively turn off near 1 K and near 4 K. For these switches we rely on the strong temperature dependence of the vapor pressure of 4He adsorbed onto neon or copper substrates, respectively, when the coverage is less than one monolayer. The different binding energies of the 4He to the neon or copper give rise to the different temperatures where the switches transition between the on and off states.
Advances in Cryogenic Engineering: Transactions of the Cryogenic Engineering Conference, Vol. 47 Part B, ed. Susan Breon et al. pp. 1175 - 1182 (2002, American Institute of Physics).