The replicated mirror panels being developed by MSFC and the membrane mirrors being studied by JPL offer the potential for the low areal mass densities (a few kg/m2 or less) that will be essential for very large space telescopes, but their value will by fully realized only if similarly low-mass means can be found to support them. The mass of "conventional" designs with a multitude of stiff members and strong moment-bearing joints tends to make them unsuitable for the advanced systems. Far more promising, instead, are tension-based truss structures, much like sailboat masts with their spreaders and stays, that can be very stiff without incurring the mass penalties. Active control would be needed to control deflections, but tension adjustments in the cables might be used to correct the trussÃs own structural deformations, and individual actuators could be used for final adjustment of the mirror surface. Sirius has long-standing interest in the design of such tensile-based structures, and proposes to produce a concept for at least one automatically-deployable optical bench structure that will enable packaging of a large aperture into a relatively small launch vehicle payload envelope, and to suggest means for providing an optical surface with the required figure.
Potential Commercial Applications:Tension-based structures offer significant mass and stored-volume advantages over more conventional compression-based designs for virtually any low load bearing application. Although the proposed Phase I effort will be directed specifically towards deployable optical benches for large space telescopes, commercial opportunities abound for similar concepts that result in easily transported, erected, and disassembled domed structures that can provide large contiguous floor areas without intrusive support columns for sports activities, trade shows, etc.
