Approximate Trajectories for Thermal Protection System Flight Tests Mission Design

A mission profile for advanced thermal protection system suborbital flight testing is identified. Its main goal is to achieve a constant heat flux at a specific area of the vehicle for a limited amount of time. A tool capable of exploring broad regions of the design space for these missions is developed, aiming at reducing possible design options to an extent manageable by conventional, more accurate, numeric-simulation-based methods. Based on a simplified model of the point mass dynamics, trajectories optimal for thermal protection system testing and compliant with prefixed path constraints are identified. The approximate method is validated comparing the obtained optimal trajectories with numeric-optimized standard solutions on three test cases. Then, to demonstrate the method effectiveness and flexibility, the mission design space is investigated for reasonable ranges of relevant parameters. Results show that increasing the vehicle's ballistic coefficient allows reducing the specific mechanical energy at reentry, and that the maximum admissible dynamic pressure plays a principal role in affecting the attainable testing performances. An illustrative mission design for novel ceramic thermal protection system testing is presented that minimizes in the analyzed design space the specific mechanical energy at the trajectory apogee