Thermal Characterization of Structure-Integrated Thermal Subsystems based on the MASCOT Landing Module

Abstract

Accurate thermal characterisation of composite structures can help structural designers in predicting thermal paths in a spacecraft structure and assessing the effect of modifying materials on the structure’s overall thermal performance. Existing spacecraft thermal analysis software lack the ability to model anisotropic thermal properties of composite materials. This in turn leads to inaccurate prediction of their thermal behaviour. The thesis describes the applied modelling methods and assumptions that are used to simulate the thermal characteristics of the MASCOT Landing Module’s (LM) composite structure. MASCOT is a 10 kg shoebox-sized lander platform developed by DLR in cooperation with CNES and JAXA for the Hayabusa 2 sample return mission from the asteroid 1999JU3. The MASCOT LM structure’s framework walls are made from a Carbon Fibre Reinforced Polymer/Foam sandwich. The M55J fibres used for the unidirectional sandwich face sheets are of Polyacrylonitrile (PAN) type and have high stiffness and strength properties, but poor thermal conductivity. Also, the glued connections between the framework walls are realised with PAN fibre patches. This is one reason, which necessitated a thermal sub-system consisting of heat pipes and a radiator. Both contribute with a total mass of 450 g, almost the same as the structural mass (550 g). Also, the structural design is itself influenced by the needs of the thermal subsystem. The modelling is carried out using Patran whereby methods to develop a thermal finite element model from the existing structural model are assessed and steady state analyses are carried out. To decrease the computational effort for radiation simulation, a novel method of developing radiation shell elements which are overlaid on the solid elements in the structure is described. Subsequently, the results from the finite element simulations are compared to actual temperature measurements, which were performed in a thermal vacuum chamber. The model is correlated with the test results and the method adopted is validated. The next phase of the thesis work involves the use of the developed thermal model to assess solutions for integrating the thermal functions within the LM structure. As a first step, the heat pipes are removed. The impact of the removal of the heat pipes on the LM is assessed and various design solutions are proposed for the MASCOT LM. From the simulations, it is concluded that it is indeed possible to remove the heat pipes from the LM and that a structure-integrated thermal subsystem can be achieved by introducing conductive interfaces in the structure.