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 fourand 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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Deployable Tensegrity Structures for Space Applications

Future small satellite missions require low-cost, precision reflector structures with large aperture that can be packaged in a small envelope. Existing furlable reflectors form a compact package which — although narrow— is too tall for many applications. An alternative approach is proposed, consisting of a deployable ''tensegrity'' prism forming a ring structure that deploys two identical cable nets (front and rear nets) interconnected by tension ties; the reflecting mesh is attached to the front net. The geometric configuration of the structure has been optimized to reduce the compression in the struts of the tensegrity prism. A small-scale physical model has been constructed to demonstrate the proposed concept. A preliminary design o fa3m diameter, 10 GHz reflector with a focal length to diameter ratio of 0.4 that can be packaged within an envelope of 0.1 × 0.2 × 0.8 m 3 is presented. Nomenclature a = radius of tube cross section A = area b = number of bars D = aperture diameter E = Young's Modulus F = focal length H = depth j = number of joints L = triangle side length Le = effective length m = number of independent mechanisms N = mesh tension per unit length r = radius of gyration R = radius of approximating sphere s = number of independent states of self-stress T tension δrms = root-mean-square surface error θ = relative rotation between nets ρ = density

/pdf/deployable-tensegrity-reflectors-for-small-satellites-3sn80115ud.pdf

Deployable Tensegrity Reflectors for Small Satellites

https://hal.archives-ouvertes.fr/hal-00687936/document

Numerical form-finding of geotensoid tension truss for mesh reflector

The concept of the tension truss antenna is proposed. It is shown that a parabolic reflector surface can be formed by a three-dimensional integrated cable lattice system that can be called a tension truss. The tension truss antenna consists of a triangular-faceted cable truss, the rf reflector surface, and a supporting structure which provides support as well as pretension of the cable lattice. The primary feature of the antenna is that its shape is virtually determined by geometric quantities such as the lengths and arrangement of cable members. Because of this feature, the adjustment of antenna surface can be done directly by changing lengths of cable members which form the surface

Concept of the tension truss antenna

An approach for the design of stiff, prestressable tension truss antennas is presented. The approach combines a basic rule for the construction of stiff trusses with an efficient form-finding method for cable net structures. First, statically determinate tension truss configurations for a given supporting structure were created. Then, prestressable geometries of the tension trusses were generated using the form-finding method. Three tension truss antennas with different supporting structures were analysed to demonstrate the advantages of the approach.

Optimal design of tension truss antennas

A concept for approximating curved antenna surfaces using flat facets is discussed. A preliminary design technique for determining the size of the reflector surface facets necessary to meet antenna surface accuracy requirements is presented. A proposed large microwave radiometer satellite (MRS) is selected as an application, and the far-field electromagnetic response of a faceted reflector surface is compared with that from a spherical reflector surface.

/pdf/preliminary-design-of-large-reflectors-with-flat-facets-194pb4e4tq.pdf

P. K. Agrawal

Papers

Preliminary design of large reflectors with flat facets

Preliminary design of large reflectors with flat facets