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J. R. P. Angel, N. J. Woolf, J. H. Burge (U. Arizona)
Once terrestrial planets of other stars are detected, cryogenic space telescopes of large collecting area will be needed to obtain detailed atmospheric spectra in the thermal infrared. Our concept is for an ultralightweight telescope with area approaching 1000 m2, made from large flat panels of stretched plastic membrane. Thin reflective material held in tension from points around a plane perimeter is fundamentally stable; its flat shape is not critically dependent on tension, and will hold even against penetration by micrometeorites. The perimeter support points would be actively controlled to maintain their co-planarity. We envisage about ten panels each about 10 m square, arranged on a rigid carbon composite truss to approximate a 100 m x 10 m mirror with 1 km focal length. A separate free-flyer at the quasi-focus would complete the telescope. Where all the beams from the target star overlap, a 10 m concave secondary would be used to form an image of the primary array at about 1/10 scale, and slightly below the plane of incoming beams. At each panel image would be a 1 m tertiary, suitably shaped so as to recollimate each individual starlight beam, or to bring all the beams to a common focus. From this point on the instrument might use the focus directly, or multi-aperture interferometric nulling techniques as described by Angel and Woolf. The unaberrated field will be large enough for exoplanet studies. The new technology goes beyond that needed for an 8 m NGST in two main ways: 1) need for thin metallized plastic of large size and uniform thickness and 2) capability to assemble or deploy in space the structure to support the panels.