Electrostatically-controlled large-aperture reflecting satellite antennas

A major practical limit to the size of antennas in space is the minimum feasible mass per unit reflecting area. To achieve low antenna mass the reflector could be constructed from a wire mesh or metalized plastic film. This structure has little inherent mechanical rigidity, but rigidity can be achieved by feedback control of surface deflections at many points. For geodesic reflectors with flat facets, for instance, D/93¿¿ control points are required to achieve an rms surface tolerance of E¿ for an antenna with aperture diameter D and focal length ¿D. Simple electrostatic actuators are considered which can reduce this required number of control points by a factor of 10 or more. As antenna geometry is adjusted to achieve increasingly precise electrostatic reflector figure control, the reflector will begin to exhibit Rayleigh-Taylor instabilities. It can be advantageous to operate within this unstable regime because achievable D/¿, and hence antenna beamwidth and gain, scale as M2, M-2, and M4 respectively, where M is the number of successfully stabilized reflector deflection modes. The origin and essential elements of this control problem are described and a control approach is proposed. A laboratory demonstration of three successfully stabilized modes on a meter-square wire mesh is also described which suggests that electrostatically-figured antennas with ¿ as small as 1 could perhaps achieve beamwidths of 1 to 10 arc-seconds.