A pantographic deployable mast

 Alan Shu Khen Kwan

Use of deployable structures is paramount in space to fulfil the current plans of the aerospace industry. A review of some existing and proposed satellites shows that many different deployable structures are already widely used in antennae, masts, and solar panels. Most of these structures, however, have been proposed by aerospace organisations for a specific project or need; there has been little central study of fundamental concepts. Due to their importance, research in deployable structures is a new and active field.

A new deployable mast is proposed and explained in detail in this dissertation. The backbone of the mast consists of a series of beams connected in a 'pantographic' manner, i.e. individual pantograph units made of two beams connected in their mid-points by a pin so that they behave like a pair of scissors. This pantographic backbone is prestressed, and hence stiffened, by a network of cable segments and 'active cables' which are not localised to one part of the structure but affect the structure globally. In fact, the length of such active cables determines the deployment and state of prestress of the fully deployed mast.

Statical analysis of the proposed mast is carried out with matrix methods. The pantograph and the active cables however, are rather special elements which cannot be modelled with standard matrices. Hence, a new technique of matrix assembly and condensation is specially developed and presented. The use if Singular Value Decomposition of matrices, and its superiority over other techniques is discussed. The deployment of the proposed mast, and framework structures in general, is analysed using techniques of Non-Linear Programming and computer simulation.

An experimental mast has been built to verify the feasibility of the proposed mast and validate the theoretical analysis. A 'Remote Measuring System' for measuring joint displacements using three-dimensional triangulation with electronic theodolites, and a tensometer for indirect measurement of cable tension were developed. Theoretical predictions of the mast under prestress and load given by the statical analysis compared favourably with experimental results. Tests on the length and shape accuracy of the mast have also been performed and recorded. Collectively, these tests showed some important characteristics of the proposed mast. In particular, the experimental mast could achieve its design length with high accuracy.

Keywords: Deployable structure. Mast. Pantograph. Cable. Prestress. Matrix methods.