The figure shows a tension/compression structure that provides rigid suspension and a high degree of thermal isolation for a small instrument assembly used in low-temperature experiments. The structure is designed primarily for use in a microgravitational environment; specifically, to support a sensor package in the Critical Dynamics in Microgravity Experiment (DYNAMX), which is scheduled to fly on the space shuttle as part of the Microgravity Science Payload in early 2002. The structure also is adaptable to scientific experimentation in normal Earth gravity in cases in which there are requirements for lightweight, rigid, thermally isolating structures in confining geometries.

High structural rigidity is necessary for low-temperature scientific experimentation in the microgravitational environment of a spacecraft in a low orbit around the Earth. The rigidity is needed not only to withstand loads encountered during launch but also to prevent amplification of low-frequency vibrations from the spacecraft (typically, the space shuttle), which vibrations can generate heat in an instrument and thereby bias the results of an experiment. High levels of thermal isolation are needed, not only between the instrument and the spacecraft, but also between components within the instrument, to prevent thermal "crosstalk"and the biases that such crosstalk could engender. In the case of a highly sensitive low-temperature instrument, the need for thermal isolation dictates minimization of instrument-component masses to minimize the bias attributable to heat deposited by cosmic rays.

In this Tension/Compression Structure polymeric cords under tensile preload provide rigid suspension and thermal isolation of the suspended mass.

Heretofore, tension/compression structures have seldom been used in cryogenic applications, even though they offer enormous advantages in thermal isolation and rigidity. The present tension/compression structure includes a cylindrical exoskeleton, within which instrument components are held in position by tensioned Kevlar (or equivalent) aromatic polyamid cords. The combination of strength of the exoskeleton and preload in the cords provides rigid mounting for the instrument components. Because the cross-sectional area of the cords is small and the thermal conductivity of the cord material is low, the cords provide a high level of thermal isolation. The narrowness and low density of the cords also limits the deposition of heat from cosmic rays.

A computational simulation was performed to compare the performance of this structure with the performances of mounting structures of conventional designs. The results of the simulation showed that this structure could provide a higher level of thermal isolation from surrounding structures and a lower level of thermal crosstalk between instrument components.

This work was done by Alfred Nash and Linda Robeck of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at under the category, or circle no. 21 on the TSP Order Card in this issue to receive a copy by mail ($5 charge).

This Brief includes a Technical Support Package (TSP).
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Thermal-Isolation Structure for LowTemperature Experiments

(reference NPO20338) is currently available for download from the TSP library.

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