Material Thermal Degradation Under Reentry Aerodynamic Heating

For the spent upper-stage rocket and defunct spacecraft bodies reentering the Earth’s atmosphere, the extent of aerothermal degradation depends on the rate of energy dissipated during flight and on the thermal characteristics of the material. It is well known that the reentry trajectory and the aerodynamic heating are significantly influenced by the aerodynamic drag. In this paper, a study involving the measurement of rarefied drag and of material degradation under simulated reentry heating is reported. The rarefied drag coefficient was experimentally determined by direct pressure measurements in a rarefied wind tunnel. From the ensuing reentry trajectory, the aerodynamic heating was estimated. The material thermal response and the physical nature of degradation were studied experimentally through transient heat flux simulations. Results of the experiments are compared with numerical results of transient heat flux simulations. Various space faring materials were considered for study and the sensitivity of the thickness on degradation was brought out. It was found that aluminum alloys and carbon fiber reinforced plastics have the potential for early degradation, whereas columbium and similar high-temperature alloys would possibly survive the reentry heating environments.