Timeline for Is there any role today that would justify building a large single dish radio telescope to replace Arecibo?
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| Feb 24, 2023 at 7:37 | history | edited | ProfRob | CC BY-SA 4.0 |
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| Dec 8, 2020 at 16:32 | comment | added | ProfRob | @MSalters I don't need to, the Chinese have done it. If they could build an array telescope with the same sensitivity, cheaper, then they would surely have done that. Especially since it comes with many other advantages in terms of resolving power and steerability. | |
| Dec 8, 2020 at 16:30 | comment | added | MSalters | @RobJeffries: It looks like the support towers at the edges of FAST are clearly taller than those in the middle. And the number of towers would already grow linearly with the area of the dish. Similar thing for the cables that hold the sensors up near the focal point - they need to be both longer and thicker, or made of stronger (more expensive) materials. You can move the focal point up so the curvature of the disc can be lower, but that's a trade-off.Guess you'd need to do the math to find out the tipping point. | |
| Dec 8, 2020 at 16:18 | comment | added | ProfRob | @MSalters I do not think we are at that limit (not for fixed dishes anyway). The Chinese FAST 500m dish is surely evidence of that? | |
| Dec 8, 2020 at 14:38 | comment | added | MSalters | My understanding of arrays was that they start making sense when the cost of scaling up a single sensor starts to grow superlinearly. To scale up Arecibo by 10% would require scaling up its support structure by far more than 10%. | |
| Dec 8, 2020 at 14:31 | comment | added | Darrel Hoffman | @SteveLinton Arecibo was steerable to a limited degree. Obviously the dish itself is fixed, but they could steer it by moving the azimuth arm and sub-reflector around on the receiver platform. | |
| Dec 8, 2020 at 11:30 | comment | added | ProfRob | @leftaroundabout That is what the first sentence says. To build an array with the same collecting area it would obviously have to cover much more (geographical) area. If you make them the same collecting area there is no difference in sensitivity beyond the additional noise you get from combining a lot of receivers. | |
| Dec 8, 2020 at 11:22 | comment | added | leftaroundabout | Is it not also simply a matter of area? Phased arrays give amazingly large linear extends in the form of long baselines, which is all that's needed for high resolution but the area only scales linearly with the number of units. In a single dish meanwhile, the area scales quadratically with radius, and the round-trip sensitivity scales quadratically with area, so basically a single dish's radar quality is $\propto \ell^4$ whereas with an array you only get $\propto \ell^2$. Does that make sense? | |
| Dec 8, 2020 at 11:04 | comment | added | ProfRob | @SteveLinton Yes, that is another plus for the array concept - you can point them where you like and set them up in different configurations to concentrate on different angular scales. | |
| Dec 8, 2020 at 10:47 | comment | added | Steve Linton | Presumably above a certain size steerable dishes become more expensive than multiple smaller dishes, and/or simply infeasible, for mechanical engineering reasons (I admit Arecibo wasn't steerable). | |
| Dec 7, 2020 at 16:44 | history | answered | ProfRob | CC BY-SA 4.0 |