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Proposed Telescope Focuses Light Without Mirror Or Lens
A team of scientists from Observatoire Midi Pyrénées in Toulouse, France have been working with an unusual technique for focusing light. It takes advantage of diffraction - the bending of waves when they encounter an obstacle in their path - to focus light as it passes through a foil sheet with precise holes in it. The scientists suggest that an orbital 30-meter imager could resolve planets the size of Earth within 30 light-years. In addition, the foil is much lighter than traditional materials, and thus easier to transport.
"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.'"
Hmm, a large flat surface with holes in it.
It looks like launching one of these babies would require solutions to the same technical problems as solar sails, ie stowing & unfolding once in orbit.
Would it be possible to have the sheet do double duty, acting as both a Fresnel "lens" and a means of propulsion for the spacecraft? That might be a neat way of getting the instruments to a good location.
Make a sphere with a central axis. Place the fresnel lens on the surface of the sphere. Rotate the sphere about the center (where the focal point is.) No more formation flying, etc. Since you don't need any part of the sphere but the place where the fresnel lens is, just create a radius - lens at one end, focal point at the other end. Use a track to adjust the focal point distance from the foil. Rotate the entire assembly to re-point. No formation flying. Precision alignment all the time. Slow adjustment means good fuel economy.
It seems to me that this is a great excuse for a foil-making plant in space. Imagine a veewwwwy large foil sheet. Then think of the available resolution. This is better than a dispersed array.
Well, one can hope. :-)
I've fallen off your lawn, and I can't get up.
I think it would be clear to anyone who examines it, the idea clearly has some holes in it.
I don't know about angles, but it's fear that gives men wings. -Max Payne
I was thinking hey neat till I read this in the article.
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.
Certainly not impossible, and still exciting, but this isn't going to be a mainstream or amateur tool any time soon.
Looks like there also may be a related patent to get past...
http://www.patentstorm.us/patents/6375326-claims.html
These posts express my own personal views, not those of my employer
This is actually a really clever solution to a number of thorny problems. The first being, how do you get a really big telescope into space without breaking the bank??? Another being how do you get great contrast to show up faint sources?
In short, this is a perfectly viable technology, and it poses a fascinating solution to a really challenging problem.
Bravo!