The mesh reflector is the only type of large, in-space deployable antenna that has successfully flown in space. However, state-of-the-art large deployable mesh antenna systems are RF-frequency-limited by both global shape accuracy and local surface quality. The limitations of mesh reflectors stem from two factors. First, at higher frequencies, the porosity and surface roughness of the mesh results in loss and scattering of the signal. Second, the mesh material does not have any bending stiffness and thus cannot be formed into true parabolic (or other desired) shapes.

To advance the deployable reflector technology at high RF frequencies from the current state-of-the-art, significant improvements need to be made in three major aspects: a high-stability and highprecision deployable truss; a continuously curved RF reflecting surface (the function of the surface as well as its first derivative are both continuous); and the RF reflecting surface should be made of a continuous material. To meet these three requirements, the Membrane Shell Reflector Segment (MSRS) antenna was developed.

A MSRS antenna is composed of a deployable tetrahedral truss that supports a set of MSRSs to form a high-definition, smooth, and continuous surface. This high radio-frequency (RF) deployable reflector is implemented by leveraging and integrating several recently developed material technologies: shape memory polymer (SMP) composite material; high-precision MSRS casting process; near-zero coefficient of thermal expansion (CTE) membrane material; and polyvinylidene fluoride (PVDF) electro-active membrane. This reflector technology can potentially offer almost one order of magnitude higher precision than current state-of-the-art reflectors, and can provide very complex reflector shapes.

The structural part of this MSRS antenna is a tetrahedral truss that provides rigidity and integrity for the reflector. Tetrahedral trusses offer much higher precision than tensioning cable trusses that are employed by all current state-ofthe- art mesh reflectors. However, it is extremely difficult to package a tetrahedral truss by using traditional deployment mechanisms. The unique characteristic of the SMP composite makes it possible to package and deploy the whole reflector. The fundamental requirement on a high RF reflector, high precision, will naturally be met by the intrinsic accuracy characteristic of the tetrahedral configuration. The high-definition RF reflective surface is composed of a number of MSRSs made of either near-zero CTE Novastrat or PVDF membrane. The thickness and curvature of each MSRS provide sufficient shell stiffness for it to be supported by the tetrahedral truss at three points.

This work was done by Houfei Fang and Eastwood Im of Caltech, John Lin of ILC Dover LP, and Jim Moore of NeXolve Corporation for NASA’s Jet Propulsion Laboratory.

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Membrane Shell Reflector Segment Antenna

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This article first appeared in the December, 2012 issue of NASA Tech Briefs Magazine.

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