Characterization of MLI Thermal Performance Using Optical Fibers as Temperature Sensor

CaraTERM is a research project conducted by Aviotec with the support of Turin Polytechnic, aimed to the Characterization of Multi-Layer Insulation (MLI) for Space application. The project foresees the validation, in the frame of Space application, of an innovative instrumentation for MLI temperature measurement during on-ground Thermal Vacuum tests, in function of the thermal expansion of optic fiber sensors, with the aim of improving the performance characterization with respect to the traditional thermocouples, thanks to the sensors accuracy and the reduced disturbance from thermal conductivity and electromagnetic interferences. The MLI thermal behavior is typically described by a parameter called “Effective Emissivity” used to compute the overall heat flux going through all components of a MLI blanket. The analytic characterization of this parameter is difficult to achieve due to the large number of factors involved. These complications lead to the need to perform a series of thermal performance tests in order to estimate the effective emissivity of MLI. The operative phase of the CaraTERM project consists in a series of MLI Thermal Performance Tests, inside Thermal Vacuum chambers equipped with the innovative Fiber Optic instrumentation, for the acquisition of a catalog of thermal performance of MLI in different configurations. The expected result is an improvement of the measured/calculated thermal performance with respect to traditional thermocouples, considering the lower disturbance introduced in the temperature measurement. A large number of thermocouples leads to more reliable, but less accurate measures. This phenomenon will be reduced with the use of optic fiber sensors. The results of the test campaign will be used to perform a comparison between the different MLI configurations tested. Considering the relevance of the mass factor in a Space mission, a significant part will be the comparison of different MLI layups, in terms of number of layers and in typology of materials.