Characterisation of the insulation provided by a carbon dioxide gap for the ExoMars 2018

The European Space Agency is sending its first rover to Mars as part of the ExoMars 2018 programme. The driving requirements for the Thermal Control Subsystem (TCS) of the Rover Vehicle (RV) are to protect the systems from the large diurnal temperature range on the surface of Mars, while minimising the use of electrical power for heating during the cold nights. The sensitive rover systems are isolated from the external environment and structure with low conductance supports, low thermal conductance harness connectors and by a carbon dioxide ‘gas-gap’ cavity. A test has been carried out to characterise carbon dioxide gas-gaps for the ExoMars 2018 rover. Three configurations were tested; a configuration with a 30mm sized gap, a configuration with gaps representative of the rover (specifically those greater than 30mm) and a configuration with gaps representative of the rover with convection supressing baffles. The test was designed to simulate the conditions of the Martian atmosphere, with the pressure and temperature adjusted to simulate a similar Rayleigh Number to that on Mars. Testing was carried out in vacuum, carbon dioxide, nitrogen and in air. The performances of the configurations were compared and evaluated.