I agree with that, but still it's sometimes worthwhile to have a few dull knives around as well as backup. I mean, Hubble isn't huge; it's a 2.4 meter aperture. Building and launching something equivalent shouldn't be that big a deal these days, especially if you can launch a couple different versions with slightly different capabilities rather than trying to build one space telescope that tries to do everything well.
The argument today is, additional Hubble(s) won't get "more science" per dollar put in. i.e. it's better to put those dollars elsewhere.
We've basically maxed out what Hubble can do. While a sharper visible light telescope would be nice, we need longer wavelengths to see "further back" in history. i.e. Webb
Another thing Hubble did was kick off Dark Energy, but then we needed different instruments to know more about the things that Hubble started. GAIA, Plank satellites are doing nutso things in that space.
All to say, Hubble is f'ing great, let's bring it home and put it in a museum to help inspire the next generation.
My understanding is that all major observatories, and certainly Hubble, are overbooked by a factor of 3 or more for months, and sometimes years, in advance.
Which implies that having 3 Hubbles would allow us to do more research than we can do today. It's not ready for the museum while astronomers still battle over who gets to use it.
An instrument doesn't have to be cutting edge in order to be useful and produce valuable results. Even today, amateur astronomers are still making discoveries (asteroids, sometimes comets) with telescopes that major observatories would have laughed at 100 years ago already.
"The telescope that ate astronomy" (Webb) will undoubtedly make important discoveries. Whether it will be worth its cost considering what we could have built for the same price (such as 10 ELTs!) remains to be seen.
This makes a lot of sense. Imagine being able to afford on a reasonable research budget to schedule within a few days notice the use of a visible light space telescope the equivalent of a Hubble but much cheaper due to optics advancements and miniaturization.
I do have to believe that any satellite designed specifically for one type of measurement would be more robust and cost less than something that did more than one, but I suppose that's not really true. Sometimes multiple measurements simply complement each other too much not to use.
We don't need to replicate Hubble exactly; I'm just suggesting we should put up some cheaper space telescopes with smaller mirrors than James Webb, if such a thing makes sense. Maybe give them a variety of different focal ratios too.
Usually with telescopes you need a huge aperture to see dim things, unless you're willing to wait a long time for an image to resolve. Not everything is super dim, though, so maybe having telescopes with an aperture much smaller than 6.5 meters would make sense for those tasks.
I don't know if there's some other reason James Webb needs a huge aperture than being able to resolve and image quickly. (Maybe the lower wavelengths don't behave on small mirrors?) If that's it, though, it seems like having backup would be good.
The point isn’t dimness. It’s resolution (well angular, the number of pixels also doesn’t matter that much). If you want to resolve things that are close together you physically can’t separate the signals. And what is too close depends inversely on the aperature, so yeah you really need the size, for some observations.
Fun fact for dimness: We are pretty much at “we can count every photon that comes” so if you want to pick up far away things, increasing the aperature is also one of the few things you can do. But at that point you’d probably prefer multiple telescopes if you can align them properly
Is it just that infrared light doesn't focus as easily as visible light unless you scale up the size of the telescope accordingly? (For instance, at some point light stops behaving like light and starts behaving like radio waves.)
The wave length of the photons also goes into it yes. I’d have to look up the precise formula. But it’s basically larger aperature -> smaller angle of separation. Longer wavelengths -> larger angle of separation.
From a physics point of view there really isn’t much difference between light and radio waves. Both is just em radiation. But the absorption by matter (well really gas, there is nothing else) changes with wavelength too. And you’d optimize the ccds for whatever you want to look at. So that would be the primary consideration and keep in mind these things tend to also be build as tech demos (which also means you typically don’t get to realize all design capabilities in action). So “because it’s the most we could get away with” is a reasonable reason
