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ESO's Very Large Telescope has combined the light from all four of its Unit Telescopes into its ESPRESSO instrument for the first time, effectively creating a 16 meter aperture optical telescope:
The ESPRESSO instrument on ESO's Very Large Telescope in Chile has for the first time been used to combine light from all four of the 8.2-metre Unit Telescopes. Combining light from the Unit Telescopes in this way makes the VLT the largest optical telescope in existence in terms of collecting area.
One of the original design goals of ESO's Very Large Telescope (VLT) was for its four Unit Telescopes (UTs) to work together to create a single giant telescope. With the first light of the ESPRESSO spectrograph using the four-Unit-Telescope mode of the VLT, this milestone has now been reached.
After extensive preparations by the ESPRESSO consortium (led by the Astronomical Observatory of the University of Geneva, with the participation of research centres from Italy, Portugal, Spain and Switzerland) and ESO staff, ESO's Director General Xavier Barcons initiated this historic astronomical observation with the push of a button in the control room.
[...] Light from the four Unit Telescopes is routinely brought together in the VLT Interferometer for the study of extremely fine detail in comparatively bright objects. But interferometry, which combines the beams "coherently", cannot exploit the huge light-gathering potential of the combined telescopes to study faint objects.
Previously: First Light for VLT's ESPRESSO Exoplanet Hunter
(Score: 2) by bob_super on Wednesday February 14 2018, @08:14PM (1 child)
> Synchronizing the distance between the telescopes to in integral number of wavelengths (or figuring
> a correction factor) when they aren't attached to a stable platform is a bit questionable
It's absolutely amazing the precision that can be achieved:
https://arstechnica.com/science/2018/02/lisa-pathfinder-mission-a-glorious-success/ [arstechnica.com]
Now, that's with a much smaler mass than a telescope would be, but swarms of satellites keeping very precise tabs on each other to run observations are not a new topic.
(Score: 2) by HiThere on Thursday February 15 2018, @06:24AM
Well, my first thought was "I think that's only two independent pieces" and my second was "that sure wasn't any cubesat"...
But it *is* an sort of existence proof that the thing should be doable. I don't, however, think it would be doable with cubesats...at least not any way that they're normally launched. IIRC the LISA pieces needed to be in stable relation to each other to make that work (though I'm not sure quite what that means when things are in independent orbit...possibly it had to do with calculating a correction factor).
But the proposal was for lots of independent launches of the cubesats, which would make positioning them a real challenge, unless it's all done by calculating correction factors. But for that to work relative motion would need to be essentially nil (or at least calculable by a simple function) and accurate to a fraction of a wavelenght. Now the light collecting power of a telescope depends on the area of the mirror, but the resolution depends on the diameter. So for a decent telescope you'd need hundreds of cubesats whose position relative to each of the others was calculated to, I think, 1/8 of the shortest wavelength you want to observe, and for the advantage you'd want them spread in a plane over as wide an area as possible. (You'd need to talk to a telescope builder to get that figure accurate. but it's in the same range as the Lisa positioning.) This hasn't been done on the ground until recently, because accurate positioning was too difficult. I think I read when they started doing it with mirrors on tracks at one of the large telescopes a couple of decades ago...and ran into problems with getting position accurate enough. With radio telescopes they do it from one side of the earth to the other, but those wavelengths are between meters and kilometers, so positioning is a lot easier. (OTOH, since each cubesat would have it's own focal point, I think the plane over which they are spread can be flat rather than the surface of a parabola. Or if you're going to use fancy calculations to form your image, perhaps it could be spread in a 3-d cloud of known positions, and then you could look in any direction just by rotating the cubesats independently...which would mean they'd need to handle their gyroscopes with exceedingly fine precision.)
So, while it's got lots of possibilities as a design, I think it's well beyond the state of the art. (That said, I'm a programmer, not a satellite designer, and even then I'm essentially retired, so perhaps it isn't as far beyond the state of the art as I think.)
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