MOAO LQG control for CANARY: theory and first laboratory results
G. Sivo, C. Kulcsár, H.-F. Raynaud, J.-M. Conan, É. Gendron, F. Vidal
G. SIVO : L2TI Université Paris 13 & Onera DOTA/HRA C. Kulcsár : L2TI Université Paris 13 H.-F. Raynaud : L2TI Université Paris 13 J.-M. Conan : Onera DOTA/HRA É. Gendron : LESIA Observatoire de Paris F. Vidal : LESIA Observatoire de Paris
Single Conjugated Adaptive Optics (SCAO) is a proven technique used in order to correct the effect of atmospheric turbulence and vibrations of the WaveFront (WF). The corrected field of view (FoV) is however limited by the anisoplanetism effect. Many concepts of Wide Field AO (WFAO) systems are under development, especially for the design of Extremely Large Telescopes (ELTs) instruments. Multi-Object Adaptive Optics (MOAO) is one of these WFAO concepts that is particularly suited to high redshifts galaxies observations in very wide FoV. The E-ELT instrument EAGLE will use this approach. CANARY is the on-sky pathfinder for MOAO. It obtained the first compensated images on Natural Guide Stars (NGSs) at the William Herschel Telescope in September 2010.
The control and performance optimization of such complex system are a key issue. Linear Quadratic Gaussian (LQG) control is an appealing strategy that provides optimal control for an explicit minimum variance performance criterion. It also provides a unified formalism that allows accounting for specific multi WF Sensing (WFS) channels, both for Laser Guide Stars (LGSs) and NGSs, and for various disturbance sources (turbulence, vibrations). Furthermore, preliminary simulation results suggest that performance can be significantly improved with tomographic LQG control compared to MMSE static reconstruction. Our objective is to obtain a first on-sky demonstration of tomographic LQG control during CANARY Phase B, featuring LGS and NGS WFS.
We show how the specific MOAO CANARY configuration can be embedded in a state-space framework. The state-space model includes: stochastic auto regressive models of order 2 for the turbulent phase in each layer and for vibrations affecting the telescope; LGS and NGS measurement equations; DM model and delays in the loop. Model identification and off-line calculations necessary for a robust on-sky operation are discussed. First laboratory results and on-sky test plan for the coming observing run are presented.