Wide Field of View Wave-Front Sensor for Active Optics Correction Chain for Future Space Telescopes

The continuous strive for increased sensitiv ity and higher resolution of space based telescopes can only be sat isfied with larger primary mirrors. There are quite a few challenges in launching large mirrors in space such as surviving the stress created from the launch acceleration, deployment, thermoelastic deformations, the gravity release etc. Major constraint to space based application is weight which drives the development of thin, extremely lightweight mirrors. Such mirrors are prone for stress based deformations and need active optics correction chain (AOCC) in order to be operated at their full potential. An AOCC for large monolithic mirrors consists of three key active optics components: corrective element (e.g. deformable mirror or DM), wavefront sensor (WFS) and correction algorithm. In order to assess the feasibility of such a system we have developed an AOCC test stand in a collaboration with the European Space Agency (ESA) and Netherlands Organisation for Applied Scientific Research (TNO). With this development we aim to measure the performance and the long-term reliability of an AOCC in controlled laboratory conditions. Our design consists of two separate parts, one where the expected aberrations are generated and another where they are measured and corrected. Two deformable mirrors of 37.5 mm and 116 mm are used, the smallest mirror to generate aberrations and the largest to correct them. For wavefront sensing we are using two different wavefront sensors, an 11x11 Shack-Hartmann as well as phase diversity based at the science sensor. We are able to emulate the conditions for both, astronomy related, and Earth observations. Here, we present the design of the system, including the test stand and the correction algorithms, the performance expected from simulations, and the results from the latest lab tests.