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.'"

Comments

Will they build it.

[FiestaFan]

Great, but will it get build before I'm dead?

Re:Will they build it.

[ArAgost]

Chromatic aberration is usually (in everyday optics) caused by refraction. Of course, since IIRC different wavelenghts diffract differently, there will be some problem of this kind, but still it's a neat idea.

ok...

[fyngyrz]

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. :-)

Much more fragile than a sail

[Mathinker]

I think you are missing a big point here. We're not talking about a solid sheet like a sail, but rather, a sheet which is X% holes, and for which the exact geometric arrangement of the holes is critical for the physics to work. Looks to me like one has even started to think about how it can survive the stresses of being launched at multiple G's.

Re:Not for amateurs...

[Overzeetop]

This is also somewhat complicated by the actual performance of objects in orbit. A project I worked on had two satellites in LEO - one main sat with a laser ranger, and one passive "following" sat with a corner cube. By ranging the distance between the two, the earths gravitational field could be mapped very accurately. In other words, two satellites in the exact same orbit will vary in distance with one another constantly throughout an orbit based on the gravitational field. As the orbit precesses, the variation will change from orbit to orbit.

I don't know how this would be dealt with, but it's a bit of a potential stumbling block. (well, that and getting a thin, light, high precision piece of anything into orbit without damaging it)

Re:Not for amateurs...

[Luyseyal]

These large earth-finder telescopes are all being proposed for Lagrange points, not LEO. However, I do wonder how big the fudge factor is for being sufficiently close to the Lagrange. E.g., if these satellites are both +/- 15km with the actual point in the middle, will the shearing effects of gravity be too much for attitude correction for such a sensitive scope?

Not an astronomer... yet.
-l