Scientists might be giving up on the notion of sending ridiculously large pieces of glass into space. Using a Fresnel-zone lens instead, astronomers at Observatoire Midi Pyrenees in France propose to take extremely high-contrast images at vast distances without a large lens or mirror. A 30-meter Fresnel telescope will provide visual confirmation of Earth-like planets up to 30 light years away. Since it can also observe a wide spectrum range including UV and IR, it can do follow-up detection of life signs, too. The main advantage of the Fresnel telescope is, of course, the fact that it's a perforated sheet of roll-up metal instead of heavy, breakable glass. But there are some major reasons it's not super easy to just whip up one of these telescopes in the machine shop:

Though a Fresnel sensor has the same sharpness as a glass lens, it only collects about 10% of the light. That's why the sheet has to be really really big, like the 30-meter one mentioned above. Even worse, the Fresnel lens brings light to focus far away from its own surface. A 30-meter panel may require a spaceship with secondary lens and camera located several kilometers away to line up within a few millimeters to capture the image precisely on camera. That's some tricky flying, and would require a lot of energy, especially when the panel itself is constantly tilting to look at new, wondrous things. [New Scientist via Kurzweil AI]

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