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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."
Looks like the opposite of a pinhole camera
Not "effects" you illiterate dumbshit!!!
So would a half mile opaque disk actually be visible from Earth in terms of blotting out stars behind it?
Maybe not naked eye visible, but it seems like anything that big might have an observable effect.
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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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Oops, I can't misspell properly. I meant "geo-sychrounous" orbutt.
This was my immediate reaction to skimming the front-page blurb.
Seriously, differentiation of "effect" and "affect" is neither a difficult nor novel concept. This just reflects editorial laziness, which does call into question in the mind of the audience the quality of information being conveyed.
Use the moon as your disk, it's much bigger, and it's already there.
I would presume that the bulk material in the inside has no need for accuracy, only the very rim. The question is more of whether you can have a coiled material that when uncoiled (deployment) can return to a shape with that level of accuracy. I would think it possible, but I really don't know.
I would forsee a super-precise rim with just a small bit of light shielding on its inside, deployed via uncoiling, and then attached to a much stronger, less precise uncoiled ring to which the bulk shielding material (and stationkeeping ion thrusters) are attached. The attachment between the two would need to provide for vibration and tension isolation (even the slowest adjustments in angle of such a huge, thin shield are going to set in motion relevant vibrations, you've got almost no damping - you want the structural ring to deal with those and not transfer them through to the precision ring). Not to mention that your shield will be acting as a solar sail whether you like it or not (unless you're at L2... but then your craft better be nuclear powered).
Your telescope behind it is going to need to do some real precision stationkeeping (either extreme precision on the whole spacecraft positioning, or merely "good" positioning of the whole spacecraft plus extreme precision adjustment of the optics within) . This means long development times and costs to demonstrate that you can pull it off before you actually build the shield. But I would think that also possible - just very difficult. If they take the latter route they could probably demonstrate that here on Earth, which would be a big cost-saver.
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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.
I'm wondering if you could improve this by having multiple edges?
I'm not a physicist, but does the disc have to be a disc? Would a very thin edge do the job of diffraction? If so, you could block out unwanted light that passes on the "wrong" inner side of the edges with a small disc in front of the telescope.
Then you could have multiple thin edges next to each other and thus get multiple Arago spots. Most of them would be a bit out of focus I guess, but that could probably be handled by software or using something like the lytro camera.
Just a thought - though if it has to be a disc before the diffraction occurs, then it doesn't work.
The unit for acceleration is m/s^2. In this case, 'g' is used as a unit to distinguish acceleration due to free-fall (gravitational) from general acceleration (and is usually measured with an accelerometer). The unit is defined as 1g == 9.80665m/s^2. This unit definition does not change with location - on the moon it is around 0.18g.
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Why does it need to be geostationary? Hubble certainly isn't.
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why not call it what it is -- a fresnel lens
Because it is not a Fresnel lens, and doesn't even use refraction to focus the light. This is closer to a really simplified zone plate, which uses diffraction. Sometimes zone plates get called Fresnel zone plates because of some contributions he made there, but they are still different in construction and principle than a Fresnel lens.