Inaug.-dis.-Ph. D.-Berlin. / Lebenslauf: p. [1].

Inaug.-dis.-Ph.D.-Berlin. / Lebenslauf: p. [1]

Satellite constellations provide the infrastructure to implement some of the most important global services of our times both in civilian and military applications, ranging from telecommunications to global positioning, and to observation systems. Flower Constellations constitute a set of satellite constellations characterized by periodic dynamics. They have been introduced while trying to augment the existing design methodologies for satellite constellations. The dynamics of a Flower Constellation identify a set of implicit rotating reference frames on which the satellites follow the same closed-loop relative trajectory. In particular, when one of these rotating reference frames is “Planet Centered, Planet Fixed”, then all the orbits become compatible (or resonant) with the planet; consequently, the projection of the relative path on the planet results in a repeating ground track. The satellite constellations design methodology currently most utilized is the Walker Delta Pattern or, more generally, Walker Constellations. The set of orbital planes and initial spacecraft positions are represented by a set of only three integers and two real parameters rather than by all the orbital elements; Flower Constellations provide a more general framework in which most of the former restrictions are removed, by allowing the use of resonant elliptical orbits. Flower Constellations can represent hundreds of spacecraft with a set of 6 integers and 5 real parameters only and existing constellations can be easily reproduced. How to design a Flower Constellation to satisfy specific mission requirements is an important problem for promoting the acceptance of this novel concept by the space community. Therefore one of the main goals of this work is that of proposing design techniques that can be applied to satisfy practical mission requirements. The results obtained by applying Global optimization techniques, such as Genetic Algorithms, to some relevant navigation and Earth observation space-based systems show that the Flower Constellations not only are as effective asWalker Constellations, but can also be applied to non-traditional constellation problem domains, such as regional coverage and reconnaissance.

In this research, constellations of satellites all having orbits compatible with rotating reference frames are considered. That is to say, no matter how many satellites are considered for the constellation, when viewed from an arbitrarily defined rotating reference frame of interest, they all follow a single, identical relative trajectory. In this regard, one could think of the relative trajectories as ?space trajectories on a rotating reference frame.? In particular, this research concerns itself with reference frames constrained to rotate with the planet under consideration (e.g. the Earth Centered Earth Fixed (ECEF) frame, a frame rotating with the Earth). When the axis of symmetry of these constellations is aligned with the spin axis of the planet, then the ground track as projected onto the planet surface will be repeating. Flower Constellations are identified by eight parameters. Five are integer parameters: the number of petals (Np), the number of sidereal days to repeat the ground track (Nd), the number of satellites (Ns), and two integers to govern the phasing (Fn and Fd). Three are orbit parameters that are generally equal for all satellites: the argument of perigee (w), the orbit inclination (i), and the perigee altitude (hp). Each of these parameters has a unique effect on the overall design of a Flower Constellation. Based upon specific choices of these parameters, some broad categories of constellation types are presented along with some unique cases. Often, a large number of satellites are used to completely visualize these constellations. While Flower Constellations lend themselves to micro- and nano-satellite constellations very easily, they are also readily scalable to any mission requirement. Also investigated are inverse design techniques where the governing equations are solved for the Flower Constellation parameters to achieve a desired final constellation or formation shape. Flower Constellations present beautiful and interesting dynamical features that allow us to explore a wide range of potential applications that include: telecommunications, Earth and deep space observation, global positioning systems, and new kinds of formation flying schemes among others. To demonstrate their potential, some specific Flower Constellations are described and discussed. Finally, the effect of perturbations such as the Earth?s oblateness are investigated and options for mitigating perturbations are discussed.

Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, June 1990. / Thesis Advisor(s): Moose, P. H. Second Reader: Terman, F. W. "June 1990." Description based on title screen as viewed on October 19, 2009. DTIC Descriptor(s): Signal processing, input, control, industries, real time, computers, signal to noise ratio, rates, coding, receivers, errors, data acquisition, vector analysis, throughput, microcomputers, data rate, modulation, data processing equipment, decoding, plug in units, frequency DTIC Indicator(s): Packet communications, frequency modulation, program listings, signal to noise ratio. Author(s) subject terms: MFM, Differential encoding, D16QAM Includes bibliographical references (p. 68). Also available in print.

The development of the Flower Constellation theory offers an expanded framework to utilize constellations of satellites for tangible interests. To realize the full potential of this theory, the beta version of Bouquet was developed as a practical computer application that visualizes and edits Flower Constellations in a user-friendly manner. Programmed using C++ and OpenGL within the Qt software development environment for use on Windows systems, this initial version of Bouquet is capable of visualizing numerous user defined satellites in both 3D and 2D, and plot trajectories corresponding to arbitrary coordinate frames. The ultimate goal of Bouquet is to provide a viable open source alternative to commercial satellite orbit analysis programs. As such, the coding of Bouquet puts heavy emphasis on flexibility, upgradability and methods to provide continued support through open source collaboration.

Dans les systèmes Store and Forward (S&F), le routage comme moyen d'optimisation a été largement étudie mais aucune règle générale n'a pu être établie. Des paramètres et des méthodes d'évaluation spécifiques à ces systèmes n'ont pas encore été définis. Jusqu'à présent seuls des critères appartenant aux réseaux traditionnels étaient utilises (temps, longueur de la route). Or la tolérance aux délais du réseau s&f minimise l'importance de ces critères. De ce fait, pour ces systèmes, il est nécessaire d'employer des mécanismes et des critères mieux adaptent à leurs caractéristiques. Cette étude a pour but de montrer que le routage dans les systèmes s&f peut être aborde a partir de perspectives nouvelles. Pour ce faire, nous utilisons une politique de routage pré calcule depuis la source. Nous présentons un état de l'art sur les systèmes s&f, leurs mécanismes et leurs scénarios d'application. Nous proposons un outil de calcul de routes pour un scenario de communications par satellite compose par deux constellations. Cet instrument est conçu à partir des techniques utilisées dans les systèmes de transport. Nous proposons ensuite un ensemble de nouvelles métriques pour le routage dans les systèmes s&f. Ces métriques permettent de caractériser le système s&f à partir de leur nature propre et d'établir des politiques de routage mieux adaptées à leurs conditions de fonctionnement. Enfin nous présentons les développements possibles dans cette thématique

The design of two-dimensional signal constellations for the transmission of binary non-uniform memoryless sources over additive white Gaussian noise channels is investigated. The main application of this problem is the implementation of improved constellations where transmitted data is highly non-uniform. A simple algorithm, which optimizes a constellation by re-arranging its points in a pairwise fashion (i.e., two points are modified at a time, with all other points remaining fixed), is presented. In general, the optimized constellations depend on both the source statistics and the signal-to-noise ratio (SNR) in the channel. We show that constellations designed with source statistics considered can yield symbol error rate performance that is substantially better than rectangular quadrature amplitude modulation signal sets used with either Gray mapping or more recently developed maps. / Thesis (Master, Mathematics & Statistics) -- Queen's University, 2009-10-06 22:22:40.096

No description available.

Akademisk avhandling--Teologi--Uppsala, 1982. / Bibliogr. p. 164-174. Résumé en allemand et en anglais.