Cable-Stiffened Pantographic Deployable Structures Part 2: Mesh Reflector

Abstract

The general concept of deployable structures based on pantographs that are deployed and stiffened by means of cables is applied to the design of the support structure for a large mesh reector. The two main components of this structure are a cable-stiffened pantographic ring that deploys and pretensions a cable network that, in turn, provides a series of stiff, geometrically accurate support points to which a reective wire mesh orexible membranewould beconnected.Thepantographicring isahighly redundantstructurewith an internalmechanism that permits synchronous deployment without any strain in the rods. The geometric conditions that have to be satis® ed in order for an n-sided ring to fold without any strain are investigated, including the effects of joint size. An experimental model has been designed and tested. In the folded con® guration, it has a diameter of 0.6 m and height of 1.2 m; in the deployed con® guration, it has a diameter of 3.5 m. Stiffness and deployment tests on this model have shown its behavior to be linear and the maximum shape error to be § 0.3 mm. HIS paper is the second in a series that deals with a new type of deployable structures where a foldable bar structure, which consists of pairs of straight bars connected by pivots and forming a pantograph, is deployed and stiffened by two sets of cables, known as active and passive cables. The passive cables are short cable elements connected to joints of the pantograph that get farther apart during deployment,and the length of each passive cable is such that it becomes taut when the pantograph is fully deployed. The active cables are longer elements that run over small pulleys and whose overall length is controlled by one or more electric motors. The layout of these cables is such that deployment of the pantograph can be activated by shortening the length of at least one of the active cables.Oncethepantographisdeployed,andhenceallofthepassive cables are taut, it is possible to set up an overall state of prestress in