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For close proximity flying on the order of 10-100 meters, Coulomb thrusting presents a promising alternative to other methods of propulsion. This clean and fuel-efficient propulsion method is being investigated for use in formation flying and virtual structures. In the latter application, the individual spacecraft assume fixed positions relative to each other through the use of Coulomb forces. In the work presented here, an analytical and numerical analysis is performed on such virtual structures. In the analytical portion, the constant, open-loop charges necessary to maintain a Hill-frame-static formation are determined for the cases of linear two- and three-spacecraft formations and for the case of equilateral triangular formations with spacecraft of equal mass. In addition, analysis is provided for the N-craft case so that the inter-craft charge products can be determined for any static formation. In the numerical portion, a genetic algorithm is employed to support the analytical results by determining formation geometries and charging schemes such that the formation craft remain static in the Hill frame in the absence of perturbation. The results of the numerical analysis include examples of static two-craft through nine-craft formations, including several formations that display a broader range of configurations than considered in previous works. Issues encountered during the numerical analysis are discussed, as well as the course of action taken to overcome these issues. Finally, a method is presented by which the genetic algorithm could be extended to take advantage of cluster computing. / Master of Science

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Multi-spacecraft interferometry imaging is an innovative concept intended to apply formations of satellites to obtain high resolution images allowing for the synthesis of a large size aperture through the combination of the signal from several sub-apertures. The design of such systems requires the design of trajectories that cover a specified region of the observation plane to obtain appropriate information to reconstruct an image of the source. A proposed configuration consists of symmetrical formations which use control thrust to actively follow spiral trajectories that would appropriately cover the specified regions. An optimization problem has to be solved to design the optimal trajectories with minimum fuel consumption. The present work introduces an algorithm to obtain near optimal maneuvers for multi-spacecraft interferometric imaging systems. Solutions to the optimization problem are obtained assuming the optimality of spiral coverage of the spatial frequency plane. The relationship between the error in the frequency content and the reliability of the image is studied to make a connection to the dynamics of the maneuver and define the parameters of the optimization problem. The solution to the problem under deep space dynamics is shown to be convex and is solved by discretization into a non-linear programing problem. Further, the problem is extended to include the effects of dynamical constraints and the effect of time varying relative position from the imaging system to the target. For the calculation of the optimal trajectories, a two-stage hierarchical controller is proposed that obtains acceleration requirements of near minimum fuel maneuvers for different target-system configurations. Several cases are simulated to apply the algorithm. From the obtained results some conclusions about the feasibility and dynamical requirements of these systems are described.

International Telemetering Conference Proceedings / October 20-23, 2003 / Riviera Hotel and Convention Center, Las Vegas, Nevada / The Consultative Committee for Space Data Systems (CCSDS), an international organization of national space agencies, is branching out to provide new standards to enhanced reuse of onboard spacecraft equipment and software. These Spacecraft Onboard Interface (SOIF) standards will be based on the well-known Internet protocols. This paper will provide a description of the SOIF work by describing three orthogonal views: the Services View that describes data communications services, the Interoperability view shows how to exchange data and messages between different spacecraft elements, and the Protocol view, that describes the SOIF protocols and services. This paper will give the reader an excellent introduction to the work of the international SOIF team.

This thesis pioneers the application of nonlinear dynamics to spacecraft power systems. Two areas of general interest are addressed. On the one hand, the fundamental dynamics of space power systems were investigated from a nonlineax dynamics perspective, and on the other, nonlinear dynamics concepts were used to realise a practical engineering application. The former examines four simple but relevant space power system models. The study revealed a variety of bifurcations, coexisting attractors and chaotic behaviour that could potentially shed light on some familiar but poorly understood effects in space power systems operations, including bus voltage collapse, spurious oscillations, and chaotic 'noise'. Because such behaviour manifests itself in nonlinear systems but could not be exposed by customary linear systems theory, potential anomalies may remain unpredicted which could lead to catastrophic consequences. As such, these results have important implications to reliability issues, critical in space. The exposition of the concepts and tools used in this thesis would serve the practising engineer by providing the basis and pave the way for studying larger and more complex systems, in the quest for improved system performance and reliability. In the course of this work, an algorithm to compute the maximum Lyapunov exponent from differential equations with discontinuities was required to confirm chaos. Although the concepts and tools for investigating smooth equations are well established, dynamics of non-smooth systems have not been extensively studied. Here, the algorithm proposed by Miiller to cope with the discontinuities in mechanics was reviewed and was found to be applicable to power electronics in general. As a confirmation, this algorithm was applied successfully to a well known Buck DC-DC converter. Although the exploitation of nonlinear dynamics to engineer direct practical applications is still in its infancy, one is presented in this thesis. A maximum power point tracker was synthesised via nonlinear dynamics principles, simulated and experimentally verified. Excellent static and dynamic performance were exhibited. In addition, a two-dimensional stroboscopic map was derived which adequately described the fundamental dynamics of the system. This is confirmed from the good agreement between the simulated and experimental return maps. Via this map and further bifurcation study, preliminary design guidelines were established.

Retrieval and analysis of space-exposed surfaces from Low Earth Orbit (LEO) can lead to an improved understanding of the space debris and micrometeoroid particulate environment. A large volume of data has been accumulated from analysis of space-exposed ductile materials, including the LDEF satellite. The Hubble Space Telescope (HST) and EURECA solar arrays provide a large, new source of information on the LEO particulate flux. Below a certain crater diameter, these solar arrays are equivalent to semi-infinite brittle material targets and thus the impact crater fluxes are analogous to impact fluxes on returned lunar rocks and Apollo/Gemini windows. An extensive shot programme has been executed onto glass, aluminium and spacecraft honeycomb (used as exterior spacecraft wall and solar array support structure). The data supplement the large database of brittle material hypervelocity impact tests used in this thesis. These data have been used to (i) develop new, target-dependent, empirically-determined brittle material damage equations, (ii) derive a conversion factor between the brittle material ,) conchoidal diameter( D, and the ballistic limit in aluminium for a particular exposure and shielding history (Fmax)a, nd (iii) investigatet he ballistic limit of spacecrafth oneycomb. In addition, the response of brittle materials to, hypervelocity impact has been explored via hydrocode modelling, including the implementation and validation of the Johnson-Holmquist brittle material model at velocities beyond the experimental calibration regime. The converted semi-infinite brittle material fluxes from the HST and EURECA solar arrays have been directly compared with both an experimentally-measured LDEF mean flux and a modelled flux prediction for meteoroids (excluding space debris). The solar array fluxes are in good agreement with the LDEF data and modelling results for F. greater than 20-30 μm. Below this value of F,,,, the data do not reproduce the space debris flux enhancement shown by LDEF. ll

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