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Proposed Space Telescope Uses Huge Opaque Disk To Surpass Hubble
Required Snark writes NASA has funded a study of a geo-sychrounous orbit telescope that uses a half-mile diameter opaque disk to provide images with 1000 times the resolution of the Hubble. It uses diffraction at the edge of the disk to focus light, resulting in a very high quality image. It's named the Aragoscope, after the scientist Francois Arago, who first noticed how a disk affects light waves. "When deployed the Aragoscope will consist of an opaque disk a half mile in diameter parked in geostationary orbit behind which is an orbiting telescope keeping station some tens to hundreds of miles behind that collects the light at the focal point and rectifies it into a high-resolution image.
'The opaque disk of the Aragoscope works in a similar way to a basic lens,' says CU-Boulder doctoral student and team member Anthony Harness. 'The light diffracted around the edge of the circular disk travels the same path length to the center and comes into focus as an image.' He added that, since image resolution increases with telescope diameter, being able to launch such a large, yet lightweight disk would allow astronomers to achieve higher-resolution images than with smaller, traditional space telescopes."
As crazy as it might sound, the GP-B mission has validated means of following a zero acceleration orbit with sub-micron precision. The precision achieved was that the residual acceleration was on the order of 1E-11 g. So yeah, we can definitely follow a zero-acceleration orbit with crazy precision!
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It's basically an interferometer - the maximum separation of the telescope's mirror/lens is what gets you resolution. The surface area just makes dim objects brighter. Using a diffraction lens is irrelevant to the interferometry - it's just a way of bending the incoming light.
The catch is, the surface area of your lens needs to be aligned within a fraction of a wavelength of light for interferometry to work. It's been done on smaller optical telescopes and bigger radio telescopes (radio waves are much longer than light waves, so proper alignment is a lot easier). Getting the edges of a half mile diameter ring to remain within less than one wavelength of light from your sensor is going to be very difficult. There are methods to correct for differing distances. But I'd imagine rotating such a large annular scope would induce a lot of micro-vibrations (bigger than a wavelength) which may thwart such methods.
Why does it need to be geostationary? Hubble certainly isn't.
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You can. In the case of nested disks with the same focal spot, this is called a zone plate.