Thermal Performance testing of the BepiColombo high-temperature MLI

The performance of multi-layer insulation (MLI) is commonly tested with a flat circular double sided hot plate calorimeter with a temperature limitation of +100°C maximum. The BepiColombo mission demands insulation performance at considerably higher temperatures (up to +450°C), which requires different test set-ups and facilities to obtain thermal performance data on ideal flat blankets as an extrapolation of test data obtained from the standard calorimeter would not be suitable for this extended temperature range. Real MLI has disturbances causing a loss of MLI performance due to edge effects, overlapping areas, slits and cut-outs, attachments or simply due to bending to follow the 3-dimensional (3D) shape of a spacecraft. To account for the elevated temperatures and losses due to real MLI shapes different calorimetric test setups were developed to produce performance data, which support the system thermal analysis for the spacecraft. Both ideal flat circular and 3D cubic-box MLI samples of varying sizes with the two BepiColombo HT-MLI compositions have been tested at elevated temperatures for this purpose. Thermocouples have been placed at various locations within the MLI packages to determine temperature gradients over and through the blankets. This paper describes the tested MLI compositions, the test setups used and correlates the performance and test results of 2Dand 3DMLI samples for both compositions. The increase in the heat transfer coefficient (HTC) between ideal 2D blankets and box-shaped 3D blankets of different sizes is discussed. It is shown that the measured performance data for both MLI types are well within the design requirements set for the system analyses. The calorimetric tests prove that MLI insulation was developed which can cope with the severe thermal environment of the BepiColombo mission.