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Design of an orbiting stellar interferometer for planet detection

SONATA--Small OSI (Orbiting Stellar Interferometer) for Narrow angle Astrometry with Two Apertures--is a concept for a space based interferometer capable of detecting extra-solar planets. The instrument is an extension of the TOPS-0 interferometer testbed concept which is a ground-based dual feed interferometer, and the space-based OSI concept, which is being studied for the Astrophysics Division of NASA. The SONATA instrument uses a quadruple- feed interferometer which will be capable of measuring fringes on four stars simultaneously within a 10 arcminute field of view. The starlight is collected by two 0.4 meter telescopes separated by 7 meters. The use of common collecting optics results in cancellation of a large number of systematic errors found in multiple baseline designs. The targeted astrometric accuracy for SONATA is 0.5 uas. In the photon-noise limit, this performance can be achieved on 14th magnitude objects by integrating for 4 hours. This level of accuracy will enable detection of nearby Earth type planets. The SONATA design uses a non-deploying structure and will be launched on an Atlas II/Centaur for insertion into a 900 km Sun-synchronous orbit.