A 25 m Live Optics Telescope

A 25 m four mirror live optics telescope is studied. M1 is spherical with 141 segments and f/0.96. M1 is reimaged onto M4 also with 141 segments. Image FWHM is <0.1 arc sec over > 20 arc min. A horseshoe solution with a simple azimuth platform is applied. M1 segments are supported by a fine meniscus form truss structure, tied to the horseshoe by a coarser mesh.

A FEM with 10^4 dof was developed and applied. Live optics control M1 and M4 segments (the latter with potential high bandwidth). Correction signals in tilt, coma and defocus are traced. A correlation tracker and a lase guide star system are included. Low and high wind speed regimes are studied. An end to end simulation model is developed, based on modal representation of our FEM.

Image quality dependence on wind load is studied from segment piston and tilt deflections. Eigenmodes are recorded. Using wind time series, we study dynamic effects and image quality resulting from the 141 segment spots. Automatic segment control at a bandwidth of only 1 Hz gives excellent image quality.

We foresee to reach a bandwidth > 50 Hz, securing a system partly adaptive, with effects of atmospheric wave front tilt removed through M4 segment tilting at high frequency. Further progress includes optimization of mechanical design and end-to-end simulation model, wind tunnel testing and studies of wavefrontsensor, correlation tracker and instruments.

A fully adaptive system is tentatively studied as is coherent operation at IR wavelengths.Key words: Very large telescopes - live optics - image quality - wind buffeting - end-to-end simulation model.