Onboard pseudospectral guidance for re-entry vehicle

Abstract

In this paper, a guidance scheme is developed for tracking constrained entry trajectory which is updated onboard. From an initial offline trajectory, the guidance system updates trajectories at every step of control command generation. This scheme models state error dynamics as a linear time varying system and updates the trajectory using a pseudospectral method. The solution provides an updated and optimal trajectory from the present position to the terminal state satisfying the path constraints. The guidance system continues updating the online trajectories and generates the control commands. This method is different from tracking methods purely based on linear quadratic regulator theory because it utilizes the pseudospectral method in generating control command; but it is also different from pseudospectral guidance because generation of new reference trajectories is done onboard. The method is validated through a number of test cases for initial state perturbations, aerodynamics and atmosphere modeling errors. In order to demonstrate improved accuracy relative to other methods, the method is also tested against linear quadratic regulator and pseudospectral guidance schemes.