Improved suboptimal control applied in re-entry tracking

A new suboptimal control method named Theta-D method is introduced in detail in this paper, which is wide-used in a large number of nonlinear control problems. An intermediate variable theta is introduced to expand the HJB (Hamiltion- Jacobi- Bellman) equation's result as a power series. And the HJB itself can be rewritten as a set of recursive algebraic equations, which can be solved on-line easily. When comes to design procedure, a large number of parameters need to be adjusted, and traditional method is based on experience. In order to solve this problem, this paper propose an innovative parameter-selecting method, and combine with theta-D method to improve the performance. The improved sub-optimal control method is applied in re-entry tracking problem, and continue with the numerical simulation result, which proves its performance.