The ExoLife Finder Telescope (ELF): design and beam synthesis concepts

Currently planned massively segmented telescopes like the European Extremely Large Telescope (EELT)(1) or the Thirty Meter Telescope (TMT)(2), use Keck-era optics. Their mirror subapertures create a dynamically rigid primary optical surface from 100's of 1m-scale few-cm thick mirrors. We suggest that a dedicated telescope for distinguishing reflected exoplanet light from its host star may not follow these design principles. To reduce moving mass and telescope-scattered light, a post-Keck era large telescope could use new technologies that replace this opto-mechanical stiffness with massively parallel active electro-optics and interferometric concepts. This opens the intriguing possibility of building a dedicated ground-based exoplanet telescope with an aperture of 20m at a cost-scale of $100M. This is a compelling reason for exploring what we call synthetic aperture or hybrid optical telescopes. Even larger apertures that could be an order of magnitude less costly per square meter than comparable Keck-like optics are possible. Here we consider an optical system built from a relatively floppy optical structure and scalable interferometrically phased, moderate size (5m diameter), subapertures. This ExoLife Finder (ELF) telescope is sensitive to optical biomarker signals and has the power to map the surfaces of nearby M-dwarf exoplanets on subcontinental scales.