Performance Analysis of a Space-Based Multiple-Telescope Nulling Interferometer for DARWIN

The European Space Agency’s infrared space interferometer DARWIN is dedicated to the investigation of Earth-like extrasolar planets orbiting bright stars. A multi-aperture interferometer fed by free-flying telescopes allows spectroscopic analysis of the weak planet signal which could give hints on the possibility of the existence of Earth-like life. However, for a Sun/Earth-like constellation at an interstellar distance of some 50 light years, a star light suppression of about 60dB is required to make the weak planet signal visible. In this paper we investigate the nulling capability of a space-based Robin Laurance interferometer in the case of stochastic disturbances of the array geometry and of stochastic alignment errors of the optical components, which both will be actively controlled. Mismatch of amplitude transmission, optical path length, and polarization transmission among the interferometer arms is taken into account. We numerically analyze Sun/Earth-like constellations in the wavelength range of 6 to 18 microns and calculate the expected value of the star light rejection ratio for the Robin Laurance geometry. It is shown that maximum standard deviations of only σp = 2nm and σA = 5 ·10 −4 for the differences in optical path length and amplitude transmission can be allowed to obtain a rejection ratio of R = 60dB. These and other exemplary numerical results confirm the extreme requirements for interferometer uniformity and give a quantitative insight into the dependence of the attainable rejection ratio on individual and/or combined interferometer imperfections. Dipl.-Ing. Oswald Wallner, Institut für Nachrichtentechnik und Hochfrequenztechnik, Technische Universität Wien, Gusshausstrasse 25/389, A-1040 Wien, E-mail: [email protected] Dr. Klaus Kudielka, Contraves Space AG, Schaffhauserstrasse 580, CH-8052 Zürich, E-mail: [email protected]