A large number of proposals have been made to build large primary telescope mirrors or adaptive mirrors using circular membranes, usually controlled by electrostatic forces (see e.g. Labeyrie 1979). A related concept uses a rotating mirror made from ferrofluid mercury shaped by magnetic forces (Shuter & Whitehead 1994). In most proposals, the deformable membrane is attached at its edges to the supporting structure. This is difficult to implement in practice. Also, the control surface is rigid thus heavy.
In order to get rid of these difficulties, we propose a pre-shaped membranous mirror tied only at its center to the supporting structure and floating freely at its edges. It is secured and maintained in its requested shape by the repulsive/attractive actions of a number of electrostatic actuators located on an associated control surface. This surface is itself a membrane attached by its center to a support (Fig. 1 (click here)). In Sect. 2, we consider the behavior of such a system in a gravity field, with a control surface integrated with the support. A space version is considered in Sect. 3, with a floating control membrane tied only with its center. Section 4 contains a short discussion of the control system, and Sect. 5 is the conclusion.