system
Given the following post, respond as if you're commenting on Reddit:
human
What equipment or arrays have been proposed for astronomy outside of Earth, using coordinated multiple devices? An array of optical telescopes? An array of rods on the lunar surface for radio astronomy? Or other equipment spread through the solar system?
gpt
So what you're mostly getting at is called interferometry, where we combine signals from multiple telescopes to get a higher resolution image. The further apart the telescopes are, the higher the resolution you get, so putting telescopes in space seems like a good way to maximise your resolution. The famous black hole image from last year was taken by radio telescopes spread across the world, which is how they were able to achieve that resolution.

This is the right idea, but it's really tricky to do in practice. For interferometry to work, you need to know the distances between your telescopes down to a precision that's tighter than the wavelength you're looking at. If you're using radio telescopes, this is metres or 10s or centimetres - totally doable with good equipment. If you're using optical telescopes, you're down to less than a micrometer, and it becomes difficult if the telescopes aren't all on the same mountain.

This is harder to do in space, because the telescopes will all be moving relative to each other. Even if you track the positions of all the telescopes relative to each other with high precision, it vastly increases the computational complexity of combining the data when things are irregularly spaced and constantly moving. We can't just say "oh, we'll fix it in software" - the algorithms are still being developed and still take huge supercomputers. In Europe there is a huge network of cheap radio telescopes called LOFAR. The idea there was that you'd put down a large number of these little radio telescopes quite cheaply, and make up for it in the data processing stage. However, it took longer than hoped to get results, because the data processing was such a huge problem.

The issue is that you need to record and combine all the phase information of every telescope. You need to record and store information at a rate that's close to the frequency of the radiation you're looking at. It comes out to a tonne of data. This was also a cause for delay with the famous black hole image. The data from the southern station would take too long to transfer over the internet, so they had to wait for the weather to improve to literally ship the data there. This is another problem for a space telescope - you're dealing with low power antennae in space, which means you don't get nearly as much data throughput, and  that makes it a lot harder to combine the signals.

If you're dealing with higher frequencies, like infrared or even visible light, you can't record and store the data at that rate at all - you need to physically combine the light in one location. So you're forced to have all your telescopes in one site. So you can't really do this in space.

One thing that is a reasonable plan though is a LOFAR-style array on the far side of the Moon. The Moon is smaller than Earth, but you would be almost completely free from any "pollution" from radio stations etc. Being on a solid object would mean the relative distances would stay constant, and these radio antennae are fairly cheap and robust, so it would be quite plausible to dump a few thousand on the Moon and get them working.

Another completely different thing is LISA, which is a gravitational wave detector. Again, you need to know the distances between the instruments very accurately, but they will orbit in pretty close proximity so it's doable. This should help find even more gravitational waves than we're currently getting.