Paul Sutter has a great astronomy and physics podcast called "Ask a Spaceman". His "Five Exciting Missions After James Webb" episode (20 min) got me really excited for the future: https://www.youtube.com/watch?v=DiYVsoxbxAI
I'd like to see a deep space version of the Gaia astrometry space telescope.
It measures the parallax shift of stars, and is basically the one reliable way of directly measuring how far away a star is from us. Unfortunately, it's at L2, and therefore has a baseline of 1 AU. Another Gaia way out at 20AU would have capacities no Earth-based telescope could ever have.
This seems like the kind of thing where two would actually be useful. Is there any benefit to making both observations at the same time? Or are the scales so great that it doesn't really matter?
You'd almost certainly want to launch several. You get one data point per half-orbit, when you're at opposite sides of the Sun. This is tolerable for the Earth, where an orbit is one year. But a full orbit out at 20AU takes eighty four years! Collecting a useful number of samples with one spacecraft would take centuries, while two spacecraft in opposition on the same orbit can measure parallax instantly.
There has been a lot of work on earth based telescopes (eg the 30 meter, giant Magellan, and some array based telescopes) that are going online in the next decade.
For the most part, yes, with adaptive optics and corrective measures being taken to deal with more satellites in orbit, ground telescopes are superior or at least comparable to space telescopes given their ability to be much larger.
Space telescopes these days are primarily being designed for observations that simply can't be done while in the atmosphere (eg the wavelengths JWST and NGR look at). The value of a space telescope in the same wavelength range as what ground based telescopes usually use would mainly benefit in terms of being able to have much longer exposures.
Yes they are very much possible, and cheaper than space too.
What starlink does is ruin part of the images, and if the thing you were interested in observing happens to be blocked by a starlink trail you're hosed: a thing literally blocked what you tried to see and you lost the nigh (because usually you get just a bit of the a night for your observation). Other things that ruins your night is clouds, so starlink effectively makes the weather at a site worse, only you find out after the night that it was all a waste.
To some extent you can plan around it, but as the mega constellations grow they'll have to avoid each other more frequently and there's no rules for how that shits coordinated, so you maybe you can know in advance that the night is wasted.
But the risk that a satellite is in an undocumented orbit by the time you try to observe will likely be very high in the future.
Have you taken a photo while someone else used a flash? The flash is also only on for a fraction of the camera exposure but you sure as hell notice when it happened and it went off close to what you wanted to depict you will just have to take a new photo.
The length of the occlusion isn't very relevant when the thing going in front is orders of magnitudes brighter than what you are trying to observe.
a leo telescope doesn't look anything like a star (mainly because it's moving too fast). the way you deal with this is by not taking hour long exposures, and instead take thousands of second long exposures. then you can composite them all together, cropping out the bits that look like satellites from each frame. it's a little annoying, but pretty easy to automate.
My understanding is ground based telescopes imaging in the same wavelengths also have to deal with distortion in the atmosphere, star link interference would be easier to filter out compared to the other stuff (which is why locations for these mega ground based telescopes are chosen with utmost care )
Disclaimer. Not a physicals or astronomer, just a enthusiastic backyard amateur astronomer who reads a lot about telescopes .
[1] https://roman.gsfc.nasa.gov/