Convex Guidance, Navigation, and Control for Pin-Point Lunar Landing

Convex Guidance, Navigation, and Control for Pin-Point Lunar Landing

de Ridder, K.M.

de Mooij, E. (mentor)

Aerospace Engineering

Astrodynamics and Space Missions

2016-07-12

Convex guidance is a developing guidance algorithm that seeks to unify the trajectory optimisation for pin-point landings. The unification would mean the elimination of the need of different optimisation techniques for different stages of the landing. Using convex optimisation, convex guidance is guaranteed to find the global-optimum of the design space. This study analysis the convex guidance algorithm in depth and establishes the magnitude of the errors introduced by simplifying assumptions. Subsequently, the performance and robustness of convex guidance is investigated in a full guidance, navigation and control loop. It is found that convex guidance can practically be used for a pin-point Lunar landing. However, the combination of a large discretisation step with a zero-order hold function for the optimal control proved to be an ineffcient solution for optimising the spacecraft’s attitude. A linear control function proved to greatly reduce the attitude control effort, and requires far less computational effort than reducing the discretisation step of convex guidance. Therefore, it is recommended to at least use a first-order function for the control vector. Furthermore, because no attitude dynamics are modelled by convex guidance, large attitude discontinuities can occur during the landing, and no initial- or final-boundary attitude conditions can be imposed. Carefully tuned controllers can deal with these discontinuities without upsetting the system, but deviations from the optimal trajectory cannot be avoided. Therefore, a future study is recommended into expanding convex guidance with angular rate limiters to improve the robustness of the algorithm.

Convex Guidance
GNC
Lunar landing
Moon
convex optimisation
convex programming
trajectory optimisation
fuel minimisation
Extended Kalman Filter
Quaternion Control

http://resolver.tudelft.nl/uuid:560656ea-4e16-4644-b68e-cae11ad30306

2017-07-01

Student theses

master thesis

(c) 2016 de Ridder, K.M.