<p>There are a mixture of factors here.</p>
<p>Firstly the telescopes used to photograph the black hole were radio telescopes.  Radio-waves are at a low enough frequency that we can process them directly as electromagnetic oscillations and use a technique called &quot;interferometry&quot; to combine the signals detected at different telescopes.</p>
<p>There's less benefit in putting radio telescopes into space.  The main reason for having a space telescope is to get above atmospheric distortion.  But radio waves aren't distorted much by the atmosphere. You might get a longer baseline (more resolution) but the size of each telescope would have to be smaller (weight restrictions on rockets).  There have been space based radio interferometers (<a href="https://arxiv.org/pdf/1303.5200.pdf" rel="noreferrer">https://arxiv.org/pdf/1303.5200.pdf</a>), but at the moment they don't really deliver more science than could be achieved with less money on Earth.</p>
<p>You can't do interferometry in the same way at optical or even infra-red frequencies (it's possible only if you have a direct <em>optical</em> connection). So each telescope would have to be a separate observatory.  And if you have separate observatories, one big one is probably better than 10 little ones.  Now, sure, it would be nice to have 10 big space telescopes, but the cost-benefit of such a plan needs to be considered. Is the extra science that could be done with 10 telescopes really worth the extra cost?  Probably not, especially if the capabilities of the telescopes overlap.</p>
<p>So we do have a swarm of telescopes, each doing something different: Chandra does X-ray astronomy.  The Fermi telescope observes in gamma rays. The Swift Observatory searches for gamma ray bursts. Gaia measures the position of stars with exquisite accuracy. Kepler and later TESS look for transiting exoplanets.  Planck mapped the cosmic microwave background, etc etc.</p>
<p>But a swarm of identical telescopes is not effective.  If they operate in the visible light wavelengths, they could not be linked up in the way you imagine, and if they are radio telescopes you can get most of the same results from Earth for far less cost.</p>

CC BY-SA 4.0
2022-05-21T22:54:22.707Z
There are some optical telescopes that can do interferometry, in theory, notably https://en.wikipedia.org/wiki/Large_Binocular_Telescope But in practice, they haven't been able to get it working properly yet. And in space, it'd be even harder to do. If the scopes weren't rigidly connected, there'd be a Doppler shift between the signals, which has to be cancelled before you can combine the signals.
PM 2Ring
CC BY-SA 4.0
2022-05-22T09:00:43.410Z
@PM2Ring related: [What are the raisons d'être for the Large Binocular Telescope "binocularity"?](https://astronomy.stackexchange.com/q/24163/7982)
uhoh
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2022-05-21T19:37:31.413Z
2022-05-21T19:37:31.413Z
James K
<p>James Webb Space Telescope (JWST) has not yet started doing science, yet its successor <a href="https://en.wikipedia.org/wiki/Large_Ultraviolet_Optical_Infrared_Surveyor" rel="nofollow noreferrer">LUVOIR</a> is being discussed already. However I am curious; some countries have invested billions of dollars in developing technologies for JWST. Building a second copy would be many times cheaper - it's just a matter of production now, not a new research.</p>
<p><strong>Why don't we build and launch a swarm of JWSTs and combine their results?</strong></p>
<p>Such a method was used for '<a href="https://en.wikipedia.org/wiki/Event_Horizon_Telescope" rel="nofollow noreferrer">photographing the black hole</a>' - telescopes, set apart by thousands of kilometers, all functioned as a single Earth-sized telescope, providing immense resolution. Imagine what the resolution would be, be those space-telescopes, placed in different Lagrange-points! Wouldn't that be a greater leap of possibilities, than 15-meter mirror of LUVOIR?</p>
<p>PS: I set aside different wavelengths LUVOIR would cover (nothing personal ;)) - same logic can be used to that project as well when it's launched into orbit.</p>

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2022-05-21T21:39:28.683Z
https://astronomy.stackexchange.com/questions/29082/is-optical-vlbi-theoretically-feasible-if-not-why-not
ProfRob
<telescope><space><angular-resolution><james-webb-space-telescope>
Why not build a swarm of space telescopes?
Sasha
# Why not build a swarm of space telescopes?

(Asked by: username_0 on 2022-05-21)

James Webb Space Telescope (JWST) has not yet started doing science, yet its successor [LUVOIR](https://en.wikipedia.org/wiki/Large_Ultraviolet_Optical_Infrared_Surveyor) is being discussed already. However I am curious; some countries have invested billions of dollars in developing technologies for JWST. Building a second copy would be many times cheaper - it's just a matter of production now, not a new research.

**Why don't we build and launch a swarm of JWSTs and combine their results?**

Such a method was used for '[photographing the black hole](https://en.wikipedia.org/wiki/Event_Horizon_Telescope)' - telescopes, set apart by thousands of kilometers, all functioned as a single Earth-sized telescope, providing immense resolution. Imagine what the resolution would be, be those space-telescopes, placed in different Lagrange-points! Wouldn't that be a greater leap of possibilities, than 15-meter mirror of LUVOIR?

PS: I set aside different wavelengths LUVOIR would cover (nothing personal ;)) - same logic can be used to that project as well when it's launched into orbit.

**Tags:** telescope, space, angular-resolution, james-webb-space-telescope
> **Comments:**
> **username_1**: https://astronomy.stackexchange.com/questions/29082/is-optical-vlbi-theoretically-feasible-if-not-why-not  

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## 1 answers

### Answer by username_2 on 2022-05-21. Score: 13 | Accepted answer

There are a mixture of factors here.

Firstly the telescopes used to photograph the black hole were radio telescopes. Radio-waves are at a low enough frequency that we can process them directly as electromagnetic oscillations and use a technique called "interferometry" to combine the signals detected at different telescopes.

There's less benefit in putting radio telescopes into space. The main reason for having a space telescope is to get above atmospheric distortion. But radio waves aren't distorted much by the atmosphere. You might get a longer baseline (more resolution) but the size of each telescope would have to be smaller (weight restrictions on rockets). There have been space based radio interferometers (<https://arxiv.org/pdf/1303.5200.pdf>), but at the moment they don't really deliver more science than could be achieved with less money on Earth.

You can't do interferometry in the same way at optical or even infra-red frequencies (it's possible only if you have a direct *optical* connection). So each telescope would have to be a separate observatory. And if you have separate observatories, one big one is probably better than 10 little ones. Now, sure, it would be nice to have 10 big space telescopes, but the cost-benefit of such a plan needs to be considered. Is the extra science that could be done with 10 telescopes really worth the extra cost? Probably not, especially if the capabilities of the telescopes overlap.

So we do have a swarm of telescopes, each doing something different: Chandra does X-ray astronomy. The Fermi telescope observes in gamma rays. The Swift Observatory searches for gamma ray bursts. Gaia measures the position of stars with exquisite accuracy. Kepler and later TESS look for transiting exoplanets. Planck mapped the cosmic microwave background, etc etc.

But a swarm of identical telescopes is not effective. If they operate in the visible light wavelengths, they could not be linked up in the way you imagine, and if they are radio telescopes you can get most of the same results from Earth for far less cost.

> **Comments:**
> **username_3**: There are some optical telescopes that can do interferometry, in theory, notably https://en.wikipedia.org/wiki/Large_Binocular_Telescope But in practice, they haven't been able to get it working properly yet. And in space, it'd be even harder to do. If the scopes weren't rigidly connected, there'd be a Doppler shift between the signals, which has to be cancelled before you can combine the signals.  
> **username_4**: @PM2Ring related: [What are the raisons d'être for the Large Binocular Telescope "binocularity"?](https://astronomy.stackexchange.com/q/24163/7982)  

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