

	Mekanik In English

Doktorsdisputation

Deployable Tensegrity Structures for Space Applications


Respondent	Huvudhandledare	Bihandledare	Datum
Gunnar Tibert	Anders Eriksson	Sergio Pellegrino	2002-04-15

Opponent
Robert Skelton, University of California, San Diego

Betygsnämd
Thorwald Larsson, Rymdstyrelsen Alf Samuelsson, CTH Zhong You, University of Oxford

Abstract

This thesis deals with the development of deployable structures, based on the tensegrity concept, for applications in space. A state-of-the-art review of deployable masts and reflector antennas for space applications is presented. A comparison is made between the various reflector antennas in terms of deployed and stowed sizes, mass and accuracy. The key step in the design of tensegrity structures is the form-finding analysis. Several methods proposed for this step are scrutinised and classified into two groups, kinematic and static methods, and the advantages and disadvantages of each method are investigated. Two of the statical methods seems to be identical. It is concluded that several form-finding methods are available, but no single method is suitable for general tensegrities. The force method, for the analysis of the kinematic and static properties of large bar frameworks, is presented. The analysis and design of deployable tensegrity masts, with three struts per stage, is described. A routine for the manufacturing of physical models is proposed and evaluated. Different schemes for deployment are investigated. A way to deploy the struts using self-deployable hinges is introduced and demonstrated by four- and eight-stage mast models. Finally, the tensegrity mast is compared with an existing deployable mast with respect to stiffness. The mast is relatively stiff in the axial direction but very weak in bending. The requirements for a deployable reflector antenna used on small satellites are formulated. A concept, which uses a triangulated cable network to approximate the reflecting surface, is adopted. The kinematically determinate triangulated cable network is thoroughly analysed. The achievable surface accuracy of the net, both to systematic errors arising from the triangular approximation of the surface and random manufacturing errors, is evaluated. The underlying principles and the statical and kinematical properties of the new concept are presented. A physical model is built to analyse the feasibility of the concept and to test various deployment schemes. The scheme using telescopic struts are identified as the most suitable and a preliminary design an antenna, with a diameter of three metres, for a future space mission is performed. Numerical computations show that the antenna is stiff and extremely light.
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