Entry Trajectory Model with Thermomechanical Breakup

A procedure for modeling the entry trajectory with aerothermal breakup is presented, Incorporating an accurate flow model and complete vehicle dynamics. The method accounts, for thermomechanical breakup into multiple fragments due to evolving surface thermal gradients and centrifugal stresses using an empirical model that produces a most probable cutplane. The detailed geometric and inertial modules have been coded to generate fragments of a general shape and size. The iteration over debris fragments includes complete thermal ablation and mechanical disintegration by centrifugal stresses. As soon as new debris is generated, its state vector and geometry is fed back to the dynamics and aerothermal loads modules. and simulation is performed over the next time interval. Only the largest surviving fragment is tracked for long-term simulation, whereas the other fragments are trucked for a prespecified duration. When a fragment is either completely ablated/disintegrated or reaches ground level, its simulation is ended. Hence, the scheme results in a complete simulation of-the entry trajectory with en route debris shedding events until either ground impact or complete ablation and mechanical disintegration. Sample trajectory simulations for an entry capsule representative of deboost from a circular (or, elliptical) orbit are considered. A dispersion analysis based on variations in the entry conditions bus been conducted and its effect on the probable debris field is calculated. The speed and flight-path angle have the largest effect on downrange dispersion, whereas the heading angle affects cross-range dispersion the most. Increase in the-object's entry mass (assumed nominally distributed) has a negligible effect on the debris Held, whereas a 10% decrease in the mass causes an appreciable variation in debris dispersion.