Kinematic morphology of space systems

Hobbs, John D. (2007). Kinematic morphology of space systems. PhD thesis The Open University.



This thesis considers the robustness to faults of mechanical kinematic systems typical of the type applied to the locomotion sub-systems of planetary exploration vehicles. It is argued that, whereas the electronic, software and control methodologies for such kinematic systems have received extensive attention, the development of the theory supporting the corresponding mechanical architectures has not received the same level of attention. An introduction to the space systems context of the topic is provided, and used to illustrate the nature of the requirements that evolve for such missions, concentrating on aspects of'terrainability' - the suitability of a vehicle to manoeuvre on rough planetary surfaces. An approach is investigated which takes concepts from graph theory and linear algebra, and uses these to establish a means for representing kinematic topologies, and, in particular, the 'fault graph' structures, and 'fault classes' that result from the progressive application of faults to nominal kinematic system configurations. Ways whereby the eigenvalues and eigenvectors of the characteristic polynomials of the interchange graph adjacency matrices of various kinematic systems can be applied to represent such systems under nominal and fault conditions are investigated, including development of the 'constraints matrix'. Additionally, the relevance of entropy within a fault graph context is considered, and also techniques suggested for analysing systems in a way which allows a richer representation of the underlying kinematic structure. Various metrics are considered and a means is established whereby a selection of parameters representing some aspects of kinematic systems' behaviour is used in conjunction with these to provide a means of comparing system configurations with each other, in terms of several 'intersystem distance' measures. Some success was achieved - 'inter-system distances' were derived for a selection of systems exhibiting different topologies and showed that these can usefully be used to represent some aspects of kinematic system topologies. Some evidence was obtained that it is possible to discriminate between tree-based and looped systems using this method.

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