The VLTI integrated model - A precursor model for integrated modeling of future telescopes

In a joint effort, the European Southern Observatory (ESO), the Institute for Lightweight Structures, Technical University of Munich, and EADS Astrium, Germany, have developed a set of software tools for integrated modeling of astronomical telescopes and interferometers. Integrated modeling aims at time-dependent system analysis combining different technical disciplines (optics, mechanical structure, control system with sensors and actuators, environmental disturbances). As example for the application of this modeling technique, we present an integrated model of the Very Large Telescope Interferometer (VLTI). It can be regarded as a "precursor" model for future telescope or interferometer projects. Besides its demonstrator role, it also serves for practical applications. An example is prediction of the dynamic VLTI output performance at interface-level to future scientific instruments, such as GENIE. The basic output of the integrated model is a complete description of the time-dependent electromagnetic field within a broad spectral range and for each interferometer arm. Alternatively, a more elaborated output can be created, such as a fringe pattern resulting from a superposition of several beams after modal filtering by single-mode fibers. The paper shows the architecture of the integrated model with its components such as telescope structures, optics, control loops and disturbance models for wind load, seismic ground acceleration and atmospheric turbulence. Results illustrating the capability of the model approach are presented.