Optical very large array (OVLA) prototype telescope: status report and perspective for large mosaic mirrors

The OVLA will be a kilometric-size interferometric array of N equals 27 or more 1.5 m telescopes. It is expected to provide visible to infra-red snap-shot images, containing in densified pupil mode N 2 10 -4 arc-second wide resolved elements in yellow light. The prototype telescope is under construction at Observatoire de Haute Provence and will be connected in 2000 to the GI2T, Grand Interferometre a 2 Telescopes, thus upgraded to a GI3T. The prototype telescope has a spherical mount, well suited for multi- aperture interferometric work, and a thin active 1.5 m f/1.7 mirror weighting only 180 kg with the active cell. This meniscus-shaped mirror, made of low-cost ordinary window glass, is only 24 mm thick and supported by 32 actuators. We describe the telescope optical concept with emphasis on opto-mechanical aspects and the test results of the active optics system. We also discuss the application of this mirror concept to large mosaic mirrors of moderate cost.