Modeling of surface chemistry

Heat shields are essential for the atmospheric entry of spacecraft. The surface of the spacecraft must withstand both strong forces and significant thermal loads from the highly enthalpy gas streams and thermal and chemical non-equilibrium during the entry process. Therefore, the choice of material for the heat shield is critical to withstand these extreme conditions and to protect the lower layers of the spacecraft. At the same time, the shield should be as light as possible in order to reduce the overall mass of the spacecraft and thus the costs.

The heat flow during atmospheric entry is directly influenced by heterogeneous processes that can occur between the atmospheric gas and the surface of the heat shield. Even with only slightly catalytic materials such as reaction-hardened glass, a commonly used borosilicate compound, a non-negligible proportion can be attributed to these processes. In addition, catalytic reactions can lead to the formation of radiating products or ablation of the surface

Experimental measurement of the catalytic heat flow is complex and expensive and often does not allow an individual assessment of the influence of individual processes. In simulations, gas-surface reactions are generally not taken into account or are only described using simplified models, such as when modeling using recombination coefficients in CFD simulations, which cannot directly represent physical processes.