Guidance and Control for Re-entry Vehicles in the Terminal Area: Application of Pseudospectral Methods

One part of spaceflight technology that has always been in demand is to go to space using a vehicle that can be re-used without much additional costs. It is roughly five years ago that the last Space Shuttle mis- sion took place, and replacements are currently in development. Yet, much of the available literature is still based on architectures created during the development of the Space Shuttle. The goal of this thesis is to expand the current knowledge with modern computational methods. This thesis demonstrates if pseudospectral methods can be used as the basis of a guidance and control architecture in the terminal area. In the past, these architectures were based by decoupling the longitu- dinal and lateral dynamics, using the energy available to calculate the current state without knowing what is to come, and calculating many variables and possible scenarios before the flight has even commenced. The architecture presented here does not require this, and it demonstrates an integrated package that can do this on the fly, by deploying a type of non-linear optimization method called pseudospectral methods. The X-38 is chosen as the reference vehicle due to the compatibility of the aerodynamic data set with non- linear optimizers. A 3-DOF simulation is created to see what set of feasible trajectories can be created un- der nominal conditions. Subsequently, a single reference trajectory is used as a basis to determine if the guidance subsystem is able to cope with a wide variety of initial conditions. The guidance system proved to be quite robust. A set of winds and gusts have been simulated and it would return to the desired state as long as there is an approximate predictive ability. The research is later continued by extending to a 6-DOF simulation. A control subsystem based on LQR is implemented with good results. A PSM implementation is introduced after and the results are promising, but the computation time is too high to be feasible. The upside is that a result is found without calculating the deflection of the trimmed state and gains, which was required with LQR. The conclusion is that pseudospectral methods can be used as a robust real-time guidance method, but that using it as a control method is currently not feasible. It is thus proven that pseudospectral method is able to deal without calculating predictive trajectories and gains as was done with the Space Shuttle. This reduces the complexity of re-entry problems by a sub- stantial amount. The time it takes to solve problems with new conditions and spacecraft is reduced, which might encourage other people to continue in this direction. There is still much more possible than what is presented in this thesis.Aerospace EngineeringSpace EngineeringSpace Exploratio