Numerical and experimental analyses of large composite skeletal satellite systems.

The World's ever increasing demand for communication capacity has been the catalyst for the development of a range of next generation satellite reflectors. This new generation are significantly larger than those currently in orbit. Their dimensions prohibit transportation into space in their operational configuration. This thesis investigates the use of deployable tetrahedral trusses for the reflecting surface support structures of a 50 m diameter Land Mobile Communication System. A deployable structural system was selected ahead of other possible forms, as it satisfied the majority of the criteria of low part count, quick assembly times and an economical packaging volume thereby minimizing transportation and on-orbit fabrication costs. The composite material examined is formed from a polyethersulphone thermoplastic matrix reinforced with high strength, low modulus carbon fibres, C-PES.The modal characteristics of a series of scaled sub-units of the proposed structure were examined. These units, manufactured from the two types of material considered, C-PES and Perspex, were subjected to a range of excitation functions. The C-PES units were thermally cycled under high vacuum to simulate the space environment. The accelerated thermal cycling of the composite structural units revealed that a shift in resonant frequency occurred, together with some surface cracking which could affect the long term stability of the material. The effects of surface pigmentation on the thermal response were also considered. An algorithm has been developed which allows low cost materials to be used to predict the behaviour of geometrically similar units manufactured from the composite material. The interaction between the predicted dynamic structural behaviour and the electrical performance of the satellite is also addressed and suggests that some form of active control system will be required if the maximum defocus parameter is not to be violated