Zheng Chen – Minimisation L^1 en mécanique spatiale
Soutenance prévue le mercredi 14 septembre 2016 à 10h00
Département de Mathématiques, Bâtiment 425 Faculté des Sciences d’Orsay, Université Paris-Sud, F-91405 Orsay Salle : petit amphi
Après avis des rapporteurs :
Heinz Schattler (U. Washington), rapporteur
Daniel Scheeres (U. Colorado), rapporteur
Composition du jury :
Jérôme Bolte (Univ. Toulouse Capitole), examinateur
Jean-Baptiste Caillau (Univ. Bourgogne Franche-Comté), co-directeur
Yacine Chitour (Univ. Paris-Sud), co-directeur
Frédéric Lagoutière (Univ. Paris-Sud), co-directeur
Francesco Topputo (Politecnico Milano), examinateur
Emmanuel Trélat (Univ. Paris 6), examinateur
Abstract. An important question in space mechanics is to control the motion of a satellite in the gravitational field of celestial bodies, in order that prescribed performance indices are minimized. In this work, we are interested in minimizing the $L^1$ norm of the control for the circular restricted three-body problem. (This cost models the consumption of the spacecraft.) Necessary conditions for optimality are obtained thanks to Pontryagin maximum principle, revealing the existence of both bang and singular controls. In finite dimension, minimizing $\ell^1$ norms is well known to generate parsimonious solutions; bang controls account for this property whereas the existence of singular ones is a peculiarity of the infinite dimensional setting. Building upon Marchal and Zelikin results, the occurence of the Fuller phenomenon is related to singular extremals of order two. The controllability of the two-body problem (a degenerate subcase of the three-body problem) with a control valued in a Euclidean ball is established, then easily extended to the restricted three-body case by using the recurrence of the drift on a appropriate submanifold. As a result, provided that the trajectories remain into a fix compact subset, existence of solution for the $L^1$ minimization problem is obtained by combining Filippov’s theorem with a suitable convexification procedure. Controllabilty under specific state constraints is also addressed. Although the maximum principle allows to select candidates to be $L^1$ minimizers, it cannot guarantee that these candidates are locally optimal unless sufficient optimality conditions hold. In this work, the idea to obtain such conditions for broken extremals is to embed these into a field of extremals, using moreover Ekeland and Kupka point of view (“competing Hamiltonians”). In the absence of
fold singularity, two types of conditions are devised. In the case of fixed endpoints, these conditions are sufficient for local optimality whenever switching points are regular ones. When the terminal point lies on a whole submanifold, an additional condition involving the geometry of this target manifold has to be taken into account. These results are eventually applied to the computation of neighbouring extremals for $L^1$ minimization.