During ascent and reentry of a hypersonic airplane into the atmosphere of the Earth extreme thermal loads appear. Therefore an efficient lightweight thermal protection system is mandatory for the feasibility of the entire mission. We consider a trajectory optimization problem coupled with a modelling of the heat load at the stagnation point. From a mathematical view point, we a have a coupled PDE-ODE optimal control problem with state constraints. The presentation focuses on the mathematical modelling of the thermal protection system. By applying a finite volume discretization onto the layers in the thermal protection system a ODE constrained optimal control problem results, which still mimics the solution properties of the PDE. Finally numerical results are presented.