Measurements of Low Hemispheric Emissivity at Low Temperatures - Designing a Cryogenic Test Bench 2000-01-2526

This paper describes the theoretical principle for measuring total hemispheric emissivity by a conventional calorimetric method. A sample, whose emissivity is to be measured, is suspended within a vacuum chamber (pressure < 10⁻⁷ mbar). The heater-equipped sample radiates to a “cold” thermal environment. In equilibrium state, knowledge of the heater-dissipated electric power, of sample temperatures, and of the environment will yield the total hemispheric emissivity of the area. Optimizing the measurement's delicate transition from theoretical principle to practical implementation was made possible by fine analysis of the error budget related to this experiment, leading on to designing a total hemispheric emissivity bench capable of measurements over the 300 K-to-80 K ranges to within 0.04 and 0.03 accuracies at these respective temperatures.

A measurement campaign was conducted on two types of space-application area coatings, respectively the MAPS2 PCBZ white paint and the AEROGLAZE Z306 black paint, at different temperatures: from 85 K to 300 K. The results obtained on Z306 were compared and contrasted with those obtained by two other research laboratories.