Thesis (M.S. in Astronautical Engineering)--Naval Postgraduate School, March 2004. / Thesis advisor(s): I. Michael Ross, Don Danielson. Includes bibliographical references (p. 39-40). Also available online.

Thesis (Ph. D.)--Missouri University of Science and Technology, 2009. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed August 14, 2009) Includes bibliographical references (p. 68-71).

Approved for public release, distribution is unlimited / A Halo orbit about a libration point of a restricted three-body system provides additional opportunities for surveillance, communication, and exploratory missions in lieu of the classical spacecraft orbit. Historically libration point missions have focused on Halo orbits and trajectories about the Sun-Earth System. This thesis will focus on libration point orbit solutions in the Earth-Moon system using the restricted three body equations of motion with three low-thrust control functions. These classical dynamics are used to design and optimize orbital trajectories about stable and unstable libration points of the Earth-Moon system using DIDO, a dynamic optimization software. The solutions for the optimized performance are based on a quadratic cost function. Specific constraints and bounds were placed on the potential solution set in order to ensure correct target trajectories. This approach revealed locally optimal solutions for orbits about a stable and unstable libration point. / Lieutenant, United States Navy

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

This study focuses on the Sun's influence on the motion near the triangular libration points of the Earth-Moon system. It is known that there exists a very strong resonant perturbation near those points that produces large deviations from the libration points, with an amplitude of about 250,000 km and a period of 1,500 days. However, it has been shown that it is possible to find initial conditions that negate the effects of that perturbation, even resulting in stable, although very large, periodic orbits. Using two different models, the goal of this research is to determine the initial configurations of the Earth-Moon-Sun system that produce minimal deviations from the libration points, and to provide a better understanding of the dynamics of this highly nonlinear problem. First, the Bicircular Problem (BCP) is considered, which is an idealized model of the Earth-Moon-Sun System. The impact of the initial configuration of the Earth-Moon-Sun system is studied for various propagation times and it is found that there exist two initial configurations that produce minimal deviations from L₄ or L₅. The resulting trajectories are very sensitive to the initial configuration, as the mean deviation from the libration points can decrease by 30,000 km with less than a degree change in the initial configuration. Two critical initial configurations of the system were identified that could allow a particle to remain within 30,000 km of the libration points for as long as desired. A more realistic model, based on JPL ephemerides, is also used, and the influence of the initial epoch on the motion near the triangular points is studied. Through the year 2007, 51 epochs are found that produce apparently stable librational motion near L₄, and 60 near L₅. But the motion observed depends greatly on the initial epoch. Some epochs are even found to significantly reduce the deviation from L₄ and L₅, with the spacecraft remaining within at most 90,000 km from the triangular points for upwards of 3,000 days. Similarly to what was observed in the BCP, these trajectories are found to be extremely sensitive to the initial epoch. / text

Ce projet se place dans le contexte des futures missions habitées d’exploration du système solaire (avec un horizon de 2025), en respect de la feuille de route proposée par l’ISECG (International Space Exploration Coordination Group) [1]. Une nouvelle avancée serait de maintenir, à un des points de Lagrange du système Terre-Lune, en avant-poste, une station spatiale qui faciliterait l’accès vers les destinations telles que la Lune, Mars et les astéroïdes et permettrait de tester certaines technologies, notamment avant de les employer pour des missions plus lointaines. Un des principaux défis sera de maintenir en permanence et de garantir à bord la santé de l’équipage, à l’aide d’un centre médical (SMC) autonome arrimé à cette station. Se pose alors la problématique de la servitude d’une telle station, pendant la phase de déploiement (assemblage des différents modules constitutifs du centre médical) et la phase opérationnelle. Les enjeux résident, d’un point de vue global, dans la construction des scénarios opérationnels et, d’un point de vue local, la sélection de trajectoires, cherchant notamment à minimiser les incréments de vitesse (la dépense énergétique) et les temps de transport (sauvegarde des équipages). Quelles recommandations pourrait-on apporter en terme d’optimisation de trajectoire, satisfaisant des critères de dépense énergétique, durée de transport et sécurité ? Quels sont les verrous technologiques à lever pour permettre la réalisation d’une telle station spatiale? Quelles seraient les performances à viser pour les sous-systèmes critiques impliqués? Les résultats d’une telle étude permettraient d’ouvrir des perspectives de recherche et développement dans le domaine des vols habités, notamment dans le domaine du transport mais également dans l’optique d’une occupation de longue durée. / In the context of future human space exploration missions in the solar system (with an horizon of 2025) and according to the roadmap proposed by ISECG (International Space Exploration Coordination Group) [1], a new step could be to maintain as an outpost, at one of the libration points of the Earth-Moon system, a space station. This would ease access to far destinations as Moon, Mars and asteroids and would allow to test some innovative technologies, before employing them for far distant human missions. One of the main challenges will be to maintain permanently, and ensure on board crew health thanks to an autonomous space medical center docked to the proposed space station, as a Space haven. Then the main problem to solve is to manage the station servitude, during deployment (modules integration) and operational phase. Challenges lie, on a global point of view, in the design of the operational scenarios and, on a local point of view, in trajectories selection, so as to minimize velocity increments (energy consumption) and transportation duration (crew safety). Which recommendations could be found out as far as trajectories optimization is concerned, that would fulfill energy consumption, transportation duration and safety criterion? What would technological hurdles be to rise for the building of such Space haven? What would be performances to aim at for critical sub-systems? Expected results of this study could point out research and development perspectives for human spaceflight missions and above all, in transportation field for long lasting missions.Thus, the thesis project, presented here, aims at from global system life-cycle decomposition, to identify by phase operational scenario and optimize resupply vehicle mission. The main steps of this project consist in:- Bibliographical survey, that covers all involved disciplines like mission analysis (Astrodynamics, Orbital mechanics, Orthography, N-Body Problem, Rendezvous…), Applied Mathematics, Optimization, Systems Engineering….- Entire system life-cycle analysis, so as to establish the entire set of scenarios for deployment and operations (nominal cases, degraded cases, contingencies…) and for all trajectories legs (Low Earth Orbit, Transfer, Rendezvous, re-entry…)- Trade-off analysis for Space Station architecture- Modeling of the mission legs trajectories- Trajectories optimizationThree main scenarios have been selected from the results of the preliminary design of the Space Station, named THOR: the Space Station deployment, the resupply cargo missions and the crew transportation. The deep analysis of those three main steps sorted out the criticality of the rendezvous strategies in the vicinity of Lagrangian points. A special effort has been set on those approach maneuvers. The optimization of those rendezvous trajectories led to consolidate performances (in term of energy and duration) of the global transfer from the Earth to the Lagrangian point neighborhood and return. Finally, recommendations have been deduced that support the Lagrangian points importance for next steps of Human Spaceflight exploration of the Solar system.