An infinitely expandable space radiotelescope

Abstract

Great rewards for radio astronomy lie in increasing antenna collecting areas and the distance between them. Both these possibilities, which determine sensitivity and angular resolution, can be developed essentially without limit if radiotelescopes can be built in space. Radio interferometers, with base lines up to 10 AU, assembled from large reflectors 1 to 10 km in diameter, could operate in the 1 mm to 1 m range with a sensitivity of 3 × 10 −37 W m −2 Hz −1 and an angular resolution of 1.5 × 10 −10 sec of arc. These parameters are a million times better than those of modern radio astronomical systems. Such instruments could solve many urgent problems: the search for artificial radio signals and other evidence of extraterrestrial civilizations; detection and study, within the RF range, of solar-like stars and planets; and holography of astronomical sources and direct measurements of their distance. The maximum distances of objects which could be studied would be comparable with the radius of curvature of the Universe. A possible space radiotelescope (SRT) configuration, with a modular spherical reflector and feeds providing multibeam operation, is analyzed here. An extendable reflector capable of operating at any intermediate stage is assembled from 200-m modules. These consist of a three-dimensional spar framework on which flat hexagonal subreflectors of about 4 m are mounted. The precise geometry required of such a reflector is provided by automatic adjustment of subreflector position relative to the framework and by adjustment of connections between modules. In this way, radiotelescopes for the 1 mm to 1 m range may be built with diameters up to 10 km. The problems of system delivery and assembly in orbit are assessed. Preliminary estimates for developing and constructing an SRT that is more than 1 km in diameter are lower than for a similar collecting area on Earth. State-of-the-art technology already allows the development and construction of a 200-m space module.