Novel numerical model for dynamic simulation of optical stellar interferometers

Stellar interferometry at optical (visible and infrared) wavelengths is evolving into a mainstream branch of contemporary astronomy. Several Earth-based interferometer arrays are already observing or will become operational in the first few years of the next millennium. Both, the European Space Agency (ESA) and the National Aeronautics and Space Administration (NASA) are planning ambitious spaceborne interferometry missions to be launched within the next two decades. Ground- and space-based stellar interferometers involve a broad field of key technologies such as active / adaptive optics, actively damped lightweight structures or high-accuracy laser metrology. A comprehensive end-to-end simulation computing the time-dependent electrical and optical signal flows in the instrument is a useful tool to support the multidisciplinary system engineering in all project phases -- from the planning phase to the operational phase. The presented work deals with the development, validation and application of a numerical tool which generates models of the dynamic optical signal flows in a stellar interferometer. The created models are well suited for integration into an end-to-end simulation environment covering in addition structural mechanics, control system with its sensors and actuators, and various disturbances. Based on a hybrid propagation algorithm the developed simulation tool models light propagation in the optical system of a stellar interferometer in accordance with the laws of geometrical or physical (wave) optics. The simulation of the optical signal flow takes the polarization properties of the starlight into account. A radiometry model allows to compute the calibrated power flux from the observed source to the detector. Temporal and spatial coherence properties of the starlight are considered when superposing interferometric beams. The modeling concept is illustrated by its application to a set of existing or proposed instruments including the European Southern Observatory's Very Large Telescope Interferometer (VLTI).