Insulation systems usually do not operate on their own; they must work together with a structural system that is designed to support the article being insulated. Typically this structure penetrates the insulation, degrading it in some manner, and gives a pathway for the conduction of unwanted heat. High-performance insulation systems that use reflective foils are highly anisotropic (the heat flows more easily in one direction than the others), so disturbing the temperature gradients through the material can cause much greater effects than are due to the disturbances alone.

The guarded two-dimensional flat plate insulation test cryostat (Cryostat-600) is a boil-off calorimeter comprised of a flat-bottom test apparatus for measuring the absolute thermal performance of an insulated test article. Typical dimensions allow accepting test specimens 300 mm in diameter by up to 30 mm thick. Various solid or hollow tubes can be placed through the insulation to create two-dimensional heating effects, especially on anisotropic materials using four threaded ports machined into the bottom of the calorimeter. Temperature sensors are located on the side of the apparatus in addition to the boundary temperatures throughout the test specimen to allow for better thermal control of the test. The test chamber is guarded by a second cryogenic chamber to prevent parasitic heat loads. The system is designed to provide thermal stability for testing over a wide range of environmental conditions. The system is capable of any vacuum between 10–7 and 760 torr. Heaters internal and external to the vacuum chamber control the environmental temperature of the test device.

Using the threaded ports, hardware can be attached to the bottom of the cold mass assembly for heat load experiments, cold soak acceptance testing, or use as an environmental heat intercept.

The Cryostat-600 provides for measuring a wide range of heat flux performance over the full range of environmental conditions. Thermal insulation systems may be composed of one or more specimens that may be homogeneous or non-homogeneous at boundary conditions from 4 to 400 K, and in environments from high vacuum to ambient pressure of residual gas. The instrument has been proven through extensive testing of multilayer insulation (MLI) systems with both metallic and composite structural supports or penetrations. Cryostat-600 provides the steady-state thermal performance data of thermal insulation systems, with or without structural elements, allowing the levels of performance degradation to be determined.

The Cryostat-600 technology includes handling tools, instrumentation, methodology, data acquisition (hardware/software), and other ancillary equipment needed to provide consistent test results in a cost-effective, safe, reliable, and practical manner.

This work was done by Wesley Johnson, James Fesmire, Thomas Bonner, and Andrew Kelly of Kennedy Space Center. For more information, contact the Kennedy Space Center Technology Transfer Office at 321-861-7158. KSC-13726

Test & Measurement Tech Briefs Magazine

This article first appeared in the February, 2015 issue of Test & Measurement Tech Briefs Magazine.

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