[astro123]

While yes, better launch capability == cheaper to put telescopes in orbit == good for astronomy, its not that simple.

Interferometry is HARD. The Keck telescopes which sit 100m apart on the surface of the earth were designed to be used as an interferometer and never lived up to the expectations. The interferometry abilities were shut down about a decade ago. Here's an article which includes a quote from one of the people who designed it who talks about spending 100s of nights trying to get this to work [1]. This only works because these telescopes are physically connected (see the discussion of the VLT in [2]). You are cavalierly talking about getting this working with 1000s of telescopes in space. If you are wondering how we got the event horizon interferometer if it is as hard as I am claiming, things become much easier at long wavelengths [2]. That's why we have lots of radio (ALMA, SKA) interferometers and almost no optical.

> At ~1.2Eur for the ELT, that would imply $45m per "hubble".

One of these is on a mountain, the other is in space. One you can plug into the mains, the other you need batteries and solar panels etc. One you know how it is oriented (its on the earth) the other you need gyroscopes and control systems and etc. One you can plug an ethernet cable into to get the data, the other you need some sort of transmitting receiving system. One I can go fix with a spanner if something goes wrong, the other costs another X if it does.

> Seems doable

If you ignore all the complexity of being in space, all the complexity of working with an array of telescopes, the fact that interferometry is way harder in optical, yeah it sounds great!

[1] https://skyandtelescope.org/astronomy-news/closure-looms-for... [2] https://www.eso.org/public/usa/teles-instr/technology/interf...

[Veedrac]

The LISA mission suggests we know how to formation fly to low-picometres accuracy already.

Physical connections aren't needed for optical signals when deep space is already perfectly transparent.

Communicating with satellites is a long-solved problem.

Hard? Sure. Impractical? That's not obvious.

[martythemaniak]

Well, you kinda have to weigh hard things against each other. A while back there was discussion here about the anti Thirty Meter Telescope protests in Hawaii and someone who lives on the big island gave a really good overview. It pretty much convinced me that that telescope will simply not be built there, period. I could not find the thread, sorry.

Apart from that SpaceX is building comms satellites that can handle gigabit speeds at costs around several hundred thousand dollars per satellite or at most the low-millions. Solar and batteries are far ahead from where they were when the Hubble was first built.

As I mentioned in another comment, the real reason is because Starship and Starlink are still not quite real. These telescope projects take a long time to design, fund, build, etc, so realistically they can only happen once those two have proven themselves, which will hopefully happen this decade.