High-precision wavefront sensor for the SUNRISE telescope

摘要

SUNRISE is a 1m solar telescope for the visible and near UV wavelength range. It will be flown in long duration stratospheric balloon flights in Antarctica, with a first scientific flight in 2007. In this paper, we describe the development of a wave-front sensing system that will be used for the automatic in-flight alignment of the SUNRISE telescope and for high-precision tracking. The system is based on the principles of an adaptive optics system. A 19-element wavefront sensor is used to determine low order aberrations of the telescope, including defocus and spherical aberrations. The correction is achieved by controlling the position of the telescope secondary and a focusing mirror in closed-loop. In addition to these quasi-static aberrations, the system will also measure image motion with a dynamical range of at least 30 Hz and with a precision of about 0.005 arcs. To this end, the image displacement measured in all sub-apertures is averaged and used as tip-tilt correction signal. This signal will feed a second closed-loop system that drives the tip-tilt mirror assembly. The tip-tilt mirror unit is designed as a dual-stage system that consists of a slow component with a large range of 60 arcs and a fast component with high bandwidth.