In-Flight Entry Trajectory Optimization for Reusable Launch Vehicles

A novel in-flight trajectory command generation approach for Reusable Launch Vehicles was developed. This new approach has the ability to reshape the vehicle’s commanded trajectory onboard, in real-time for significantly changed energy conditions due to, for example, control effector failures. The approach also has the ability of retargeting the trajectory to abort to more appropriate alternative landing sites. The key feature of the new approach is an innovative optimization method: by describing decision variables in terms of appropriate basis functions, the trajectory optimization problem can be reformulated to find the relatively few basis function coefficients that characterize the desired trajectory. This significantly reduces the search domain, enabling rapid convergence to feasible solutions. An entry trajectory optimization problem was formulated, incorporating real-world vehicle constrains such as heating and dynamic pressure boundaries. It was demonstrated that the trajectory could be reshaped in-fight for both low and high energy cases. Furthermore, the approach was demonstrated to retarget to two defined alternate landing sites. The nominal landing site was defined to be Kennedy Space Center in Florida, while the two alternate landing sites were Atlanta and Houston. For a standard desktop computer, the time to realize a solution was reduced from one to two minutes using a traditional optimization method to only approximately 10 seconds for the new formulation. The ability to rapidly and accurately reshape trajectory commands to perturbations in energy, and the ability to retarget the trajectory to alternate landing sites was successfully demonstrated.