Defining the critical depth of impact damage for thermal protection systems

Thermal protection systems for hypersonic vehicles are low- to zero-fault-tolerant. A self-healing capability for thermal protection systems is proposed to mitigate impact damage from micrometeoroids and orbital debris. An integrated self-healing system should be positioned within the thermal protection system at the critical depth, the minimum depth at which impact damage will cause mission failure. A method of calculating the critical depth is presented over mission and vehicle parameters of interest. The maximum allowable size and speed of impacting particles is determined as a function of critical depth. Results indicate that the critical depth is a strong function of the entry environment as well as the damage shape; changes in crater depth and width significantly affect bondline temperature.