Modeling dispersions in initial conditions for air-launched rockets and their effect on vehicle performance

Abstract

Growing interest in air-launched rockets as a method for lofting satellites into orbit motivates the need to investigate the unique challenges that air launch presents. This thesis explores how uncertainties in an air-launched rocket's state at ignition can affect system performance and investigates a reference trajectory strategy to mitigate performance loss. First, representative vehicle configurations for a generic air-launch system are presented. Mass properties, propulsion characteristics, and vehicle aerodynamics are estimated for the generic rocket configuration. A six-degree-of-freedom (6-DOF) simulation models the vehicle's behavior during the uncontrolled drop phase prior to rocket ignition. The results of 1000 Monte Carlo runs with various initial conditions produce a statistical representation of the expected dispersions in vehicle state at ignition. A 6-DOF Simulink simulation of the rocket's first stage bum is used to quantify the vehicle's performance. The simulation is run for a variety of ignition states, reference trajectories, and constraints on the rocket's control system. The results indicate that for a highly responsive thrust vector control (TVC) system, the rocket experiences negligible performance losses due to dispersions in ignition conditions. However, for a rocket with a less responsive TVC system, dispersions will result in significant performance loss by the end of first stage burn. Finally, the thesis illustrates how selection of a reference trajectory that is optimized for a given dispersed ignition state can significantly reduce the system's performance loss due to dispersions..