New kind of telescope lens

Neat. [Link]

Because it relies on a foil sheet rather than a massive mirror, it could be much more lightweight, and therefore less expensive to launch, than a traditional telescope.

A Fresnel imager with a sheet of a given size has vision just as sharp as a traditional telescope with a mirror of the same size, though it collects just 10% or so of the light. It can also observe in the ultraviolet and infrared, in addition to visible light.

The imager can take very detailed images with high contrast, which is great for "being able to see a very faint object in the close vicinity of a bright one," Koechlin told New Scientist. "We could obtain images of an exoplanet system," he says. Such images have so far been very difficult to make because planets are so faint they get lost in their host stars' glare.

Signs of life

A 30-metre Fresnel imager would be powerful enough to see Earth-sized planets within 30 light years of Earth, and measure the planets' light spectrum to look for signs of life, such as atmospheric oxygen. The Fresnel imager could also measure the properties of very young galaxies in the distant universe and take detailed images of objects in our own solar system.

Although it would be lighter than an ordinary telescope, a 30-metre Fresnel imager would still be daunting to launch and deploy. Such a large piece of foil would have to be folded up for launch and then unfurled in space – a potentially tricky manoeuvre.

Koechlin's team proposed a smaller mission to the European Space Agency, which would have used a 3.6-metre piece of foil. Their proposal was in competition with dozens of other proposed space missions seeking funding as part of ESA's Cosmic Vision 2015-2025 programme, and was not selected as one of the 10 finalists.

Despite its strengths, there are some serious challenges involved in mounting even a smaller Fresnel imager mission.

Precise alignment

For one thing, the light comes to a focus far away from the foil sheet – with distances measured in kilometres, which means the camera and other instruments have to be mounted on a separate spacecraft. The instrument spacecraft would have to stay precisely aligned with the foil sheet, to within a millimetre or so in the plane of the image.

That could be especially tricky considering how much the two spacecraft would have to move around. With every new target, the Fresnel plate would have to swivel around, and the instrument spacecraft would have to move to the new focal point. But Koechlin says the mission should contain enough fuel to observe up to 10,000 different objects.