Design and analysis of the Astrometric Telescope Facility.

Abstract

The Astrometric Telescope Facility (ATF) is designed to be a space-based facility searching for planets and extra solar planetary systems. In order to be able to positively identify other planetary systems such as Uranus/Neptune-class planets, the ATF is required to be capable of surveying approximately 100 stars within about 10 parsecs of the earth, of measuring a change in the relative position of stars to an accuracy of 10 microarcseconds, and of being stable for about 10 to 20 years. The ATF approach to astrometry is to modulate the intensity on the focal plane of the telescope by a moving Ronchi ruling or grating and then to determine the relative star positions from the phases of the modulated signals. This approach reduces boise from background stray light and reduces random noise by averaging over many measurements. The optical performance of the ATF system has been modeled mathematically using the concept of the system transfer function. Each subsystem has been studied analytically. The relationship between the measured parameter and aberrations of the system has been established analytically. Error sources from the system have been identified and calibration for the system is provided. Design and optimization for the astrometric telescope and gratings have been investigated. The key issues to reach the 10 microarcseconds are addressed.