5 research outputs found

    Transfers to a gravitational saddle point: An extended mission design option for LISA Pathfinder

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    Any possible LISA Pathfinder extended mission will immediately follow the primary mission after completion of scientific observations and technical demonstrations in a Sun-Earth L1 libration point orbit. One extended mission concept with scientific appeal is a spacecraft path that includes multiple encounters with a gravitational equilibrium point. This point, also termed a saddle point, exists where the total gravitational acceleration sums to zero and is distinct from the five Lagrange points in the three-body problem. This investigation seeks a strategy to design such a path subject to a variety of constraints. Periodic, quasi-periodic, and manifold structures are explored to supply useful transit behavior as well as arcs that repeatedly encounter the saddle point. A selection of these structures from the Earth-Moon and Sun-Earth circular restricted three-body problems are linked together via Poincaré mapping techniques and corrected in a higher-fidelity Sun-Earth-Moon bicircular restricted four-body problem (BC4BP) and in an ephemeris environment. Additionally, natural motion in the BC4BP is leveraged to achieve the required encounters, and is similarly corrected to meet mission constraints. Results from both methods are detailed and compared to the mission requirements

    Trajectory design in the spatial circular restricted three-body problem exploiting higher-dimensional Poincare maps

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    In this investigation, the role of higher-dimensional Poincaré maps in facilitating trajectory design is explored for a variety of applications. To begin, existing strategies to implement Poincaré maps for trajectory design applications in the spatial CR3BP are evaluated. New applications for these strategies are explored, including an analysis of the natural motion of Jupiter-family comets that experience temporary capture about Jupiter, and the search for periodic orbits in the vicinity of the primary bodies in the spatial problem. Because current strategies to represent higher-dimensional maps, generally, lead to a loss of information, new approaches to represent all information contained in higher-dimensional Poincaré maps are sought. ^ The field of data visualization offers many options to visually represent multivariate data sets, including the use of glyphs. A glyph is any graphical object whose physical attributes are determined by the variables of a data set. In this investigation, the role of glyphs in representing higher-dimensional Poincaré maps is explored, and the resulting map representations are demonstrated to search for maneuver-free and low-cost transfers between libration point orbits. A catalog of libration point orbit transfers is developed in the Earth-Moon system, and observations about the catalog solutions yields insight into the existence of these transfers. The application of Poincaré maps to compute transfers between libration point orbits in different three-body systems is additionally considered. Finally, interactive trajectory design environments that incorporate Poincaré maps into the design process are demonstrated. Such design environments offer a unique opportunity to explore the available trajectory options and to gain intuition about the solution space

    Low Thrust Trajectories in Multi Body Regimes

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    More and more stringent and unique mission requirements motivate to exploring solutions, already in the preliminary mission analysis phase, going far beyond the classical chemical-Keplerian approach. The present dissertation deals with the analysis and the design of highly non linear orbits arising both from the inclusion of different gravitational sources in the dynamical models, and from the use of electric system for primary propulsion purposes. The equilibrium of different gravitational fields, on one hand, permits unique transfer solutions and operational orbits, on the other hand, the high thrust efficiency, characteristic of an electric device, reduces the propellant mass required to accomplish the transfer. Each of these models, and even better their combination, enables trajectories able to satisfy mission requirements not otherwise met, first of all to reduce the propellant mass fraction of a given mission. The inclusion of trajectory arcs powered by an electric thruster, providing a low thrust for extended duration, makes essential the use of optimal control theory in order to govern the thrust law and thus design the required transfers so as to minimizing/maximizing specific indexes. The goal is, firstly, to review the possible advantages and the main limits of dynamical models and, afterward, to define methodologies to preliminary design non-Keplerian missions both in interplanetary contexts and in the Earth-Moon system. Special emphasis is given to the study of dynamical systems through which the main features of the Circular Restricted Three Body Model (the first one among the non-Keplerian models) can be identified, implemented and used. Purely ballistic solutions enabled by this model are first independently explored and after considered as target orbits for electric thrusting phases. Electric powered arcs are used to link ballistic phases arising from the balancing of different gravitational influences. This concept is applied both for the exploration of planetary regions and for interplanetary transfer purposes. Together with low thrust missions to selenocentric orbits designed taking into account both the Earth and the Moon gravity, also transfer solutions toward periodic orbits moving in the Earth-Moon region are presented. These are designed considering electric thrusting arcs and ballistic segments exploring for free specific space regions. In brief, theoretical models deriving from dynamical system theory and from optimal control theory are employed to design non conventional orbits in non linear astrodynamics models

    Natural and artificial orbits around the Martian moon Phobos

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    One of the paramount stepping stones towards the long-term goal of undertaking human missions to Mars is the exploration of the Martian moons. In particular, Phobos is becoming an appealing destination for future scientific missions of NASA and ESA. Phobos is a tiny celestial body that orbits around Mars at low altitude. The unique combination of these two characteristics yields the sphere of influence of the moon to be very close to its surface. Therefore, orbital dynamics around Phobos are particularly complex, because many strong perturbations are involved. The classical models of the Keplerian two-body problem, and the circular three-body problem are not accurate enough to describe the motion of a spacecraft in the vicinity of Phobos. In this thesis, the description of the relative orbital dynamics in proximity of this moon is extended to a more accurate nonlinear model. This is undertaken by the inclusion of the perturbations due to the orbital eccentricity and the inhomogeneous gravity field of Phobos. Subsequently, several classes of non-Keplerian orbits are identified, using the analytical and numerical methodologies of dynamical systems theory. These techniques exploit the improved description of the natural dynamics, enabled by the extended model, to provide low-cost guidance trajectories, that minimize the fuel consumption and extend the mission range. In addition, the potential of exploiting artificial orbits with lowthrust is investigated. The performance and requirements of these orbits are assessed, and a number of potential mission applications near Phobos are proposed. These low-cost operations include close-range observation, communication, passive radiation shielding, and orbital pitstops for human space flight. These results could be exploited in upcoming missions targeting the exploration of this Martian moon. Furthermore, the new model can provide evidence to support the accretion theory of Phobos' origin, and to explain the formation of the craters and grooves on Phobos
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