Guidance and Control for Planetary Landing: Flatness-Based Approach

The guidance, navigation, and control problems for autonomous planetary entry descent and landing pose a number of interesting challenges. In this paper, the guidance and control problems for the descent phase are considered, and an approach based on the flatness property of the descent equations is proposed. A flat reformulation of the 2-D descent equations is presented and flatness-based analytical solutions and numerical schemes based on polynomial and pseudo-spectral approximations for the problem of guidance law design are compared. Subsequently, the problem of designing trajectory tracking control laws is considered and two design approaches are developed and compared in a simulation study. The first approach is based on feedforward linearization and leads to a nonlinear controller, while the second one is based on linear time-varying feedback computed by linearizing the descent equations along the computed trajectory. Finally, a simulation study is carried out, the results of which show that the nonlinear flatness-based controller provides a more satisfactory solution in terms of robustness.