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Pre-focal wave front correction and field stabilization for the E-ELT

Abstract 172

Submitted by Lieselotte JOCHUM


L. Jochum, E. Vernet, N. Hubin, P.-Y. Madec, M. Dimmler, M. Mueller


European Southern Observatory


The baseline optical design of the E-ELT is a five mirror telescope consisting of a three mirror anastigmat, plus two flat mirrors folding the light beam to feed the focal stations for science observation. Besides folding the light, the main function of these two flat mirrors is to correct wave front aberrations mainly caused by the turbulent atmosphere, but also wind shaking of the telescope itself and static aberrations. Image motion is compensated by the field stabilization unit which is a tip tilt mechanism for the telescope’s fifth mirror. Higher order aberrations are corrected by the quaternary mirror, an adaptive mirror with more than 6000 actuators and a maximum dimension of about 2.6m, sitting close to the telescope’s exit pupil. The requirements for both mirrors are driven by obtaining best science performance without overconstraining the requested actuator stroke, response time or magnitude of guide stars. In the scope of the ongoing E-ELT phase B study, ESO has signed contracts with three European industries to study overall feasibility, perform technology demonstration and deliver well advanced design concepts for the M4 adaptive unit and M5 electromechanical system. The requirements for both systems and technological issues are discussed in this article.

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