In the space industry, it is necessary to control heat exchange to maintain the thermal housekeeping within acceptable ranges. Heat exchanges between the spacecraft and the surrounding environment are only radiative exchanges. For this, knowledge of the emissivity with good precision is essential. Typical applications are radiators, Multi-Layer Insulation materials, and other thermal-control surfaces, which frequently operate at cryogenic
There are few devices capable of measuring emissivity at low temperature (T<77K) with sufficient precision. THEMACS Engineering on behalf of the European Space Agency (ESA) has developed a measuring bench to measure the emissivity on any substrate. At these temperatures, reflectometric methods for high emissivity are difficult to use because the useful spectral range is between 10 and 200µm and the reflected flux is low. Consequently, a calorimetric approach is usually more feasible and provide lower uncertainties. The measurement bench is inspired by existing devices [1-3] with the novelty of not needing to produce a specific sample geometry. For this we made a fluxmeter made with an emissive surface at a temperature slightly higher than the sample to be tested. To maintain it at a constant temperature, it is supplied with an electrical power that is continuously
measured. The advantage of this approach is that it does not have to regulate the temperature of the sample. Another advantage is to be able to cool down quickly. The fluxmeter is painted with an emissive paint which must be characterized at all temperatures. The first results allowed us to adapt the design in order to significantly lower the level of uncertainty for measurements on different types of materials.
1 The total hemispherical emissivity of painted aluminum honeycomb at cryogenic temperatures, J.Tuttle and all, Advenced in Cryogenic Engineering, AIP Conf. 1573,590-596 (2014)
2 Measurement of the total hemispherical emittance of different surfaces at temperature from 4K to 200K, Jamotton and all, Proceeding oft he sixth European Symposium on space environemental control systems, ESA SP-400, 1997
3 A high-resolution measurement of the low temperature emissivity of ball infrared black, J. Tuttle, Edgar R. Canavan, Michael DiPirro, et al., AIP Conference Proceedings 1434, 1505 (2012)