Trajectory-based launch vehicle performance analysis for design-space exploration in conceptual design

Abstract

Trajectory optimization is an important part of launch vehicle conceptual design. Current methods for trajectory optimization involve numerical analysis, are computationally expensive and require trajectory experts in the loop, thus limiting efforts for design space exploration. A simplified performance analysis, like the rocket equation, is much better suited to the types of studies desired in conceptual design, where thousands of vehicles can be considered and compared. Unfortunately, the rocket equation does not take into account trajectory losses and therefore does not provide an accurate measure of performance. The lack of a fast and accurate method to evaluate launch vehicle performance represents a gap in the current capability that will be addressed in this thesis. The goal of this research is to formulate and implement a performance analysis method in the form of the rocket equation (i.e. closed-form) that takes into account the trajectory losses considered in a numerical trajectory analysis method. This goal is achieved by generating a surrogate model of launch vehicle trajectory data. Several challenges arise when generating this data in an automated fashion. For this reason, extreme value theory is used in conjunction with an industry standard optimization method. The trajectory problem is statistically posed finding the extreme value of a distribution representing the performance of all possible trajectories. The process of generating a surrogate model is formulated into a method named RAPTOR (Rapid Trajectory Optimization Routine). The method is successfully implemented on the Delta IV Heavy launch vehicle. Implementation of the RAPTOR method results in a capability that enables rapid and accurate performance evaluation of launch vehicles.