A Continuum Vibrational Analysis for a Tetrahedral Space Platform

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Abstract
Antennas over 50 metres diameter are being considered for use in land mobile communication systems. As the satellite in geostationary orbit has an angular velocity equal to that of the earth, no tracking systems are necessary and low cost fixed ground antennas can be used. In addition, a typical early truss platform could possibly be a geostationary communication one of size up to 300m × 300m. In this paper structural stiffness, strength and dynamic characteristics of large skeletal frameworks for space applications are investigated by analysing the tetrahedral truss which is idealised as an equivalent continuum. Appropriate analytical relationships are presented in terms of the truss member properties which are taken as slender graphite/polyethersulphone composites. Fundamental and harmonic frequencies have been calculated and have been compared with those from a finite element skeletal analysis and a finite element plate analysis. It has been shown that the results of the simplified analysis technique are accurate to within 10 per cent of those of the analytical solutions provided the system is both large and flexible. In addition, the analysis provides a simple methodology for the preliminary assessment of vibration frequencies for large space structures.

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