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I want to know what difference does it make, in terms of observations made and the benefits for the astronomical society if we place a space telescope after the asteroid belt or near the Kuiper belt. I do understand it's either immensely expensive and technologically may not be feasible yet.

Bharath Simha Reddy
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    I guess you could make a bigger paralax measurement with the bigger orbit. Or alternativly if you want a realy big telescope the raw materials in the asteroid belt might be tempting. – lijat Apr 21 '20 at 22:11
  • In my opinion, it has will be better for the visibility for the other galactic things, as the galaxies are mostly flat. So, putting it after the asteroid belts will be like removing a lot of disturbances while studying other galactic things. – Amar Apr 22 '20 at 05:31
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    @Amar: The asteroid belt is not an obstacle to observations. – Christopher James Huff Apr 22 '20 at 20:27
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    The early projects of what now JWST (James Webb Space Telescope) considered placing the telescope at 3 a.u. from Sun, beyond asteroid belt. The reason was not asteroids but zodiacal dust (fine dust orbiting the Sun). It was speculated the telescope will have some better infrared capability because zodiacal dust emits infrared background radiation. (See Wikipedia-JWST#History). I can't say how much effect it would have, but I guess it would matter only for very faint objects. – Heopps Apr 23 '20 at 12:49
  • @ChristopherJamesHuff, why is that they don't obstruct? I meant in all ways including radiations. – Amar Apr 24 '20 at 16:31
  • I think every space enthusiast at some point has asked why telescopes haven't been put beyond Earth's orbit for parallax measurements. – Greg Apr 24 '20 at 17:01
  • @Amar: This is a bit like Marvin the Martian wanting to blow up Earth because it gets in the way of viewing Venus. First, to a very good approximation, there's nothing there. Uranus was discovered and its orbit determined before anyone spotted Ceres, the largest asteroid in the belt. Second, the "flatness" of galaxies is irrelevant, since the disk of the Milky Way is not aligned with the belt, and other galaxies are scattered across the entire sky. Note that the disk of the Milky Way does pose an obstacle, but it's hardly practical to wait millions of years for a probe to get past it. – Christopher James Huff Apr 24 '20 at 19:41
  • @Greg agreed. The discussion on a Gaia followup mission suggests that the answer is "because for the same money you can just increase the accuracy of your measurements from 1AU". An interesting counterexample though is Betelgeuse, where the problem is that the star is much wider than its parallax (and of uneven brightness) so there is independeny merit in actually observing from a place where the parallax is larger. – Steve Linton May 27 '20 at 13:53
  • @Steve Linton I have the wacky idea of letting ESA run their course with Gaia, then maybe someone can grab it with a Mission Extension Vehicle (Northrop Grumman is starting to do these) and push it wherever they want. Because a space taxi has to be cheaper than a space telescope, and the space telescope is already up there. – Greg May 27 '20 at 17:32
  • Alas, no one has answered my question on what are merits/ benefits for the astronomy society, I am sure that some new discoveries or further studies should be possible. If someone could tell me these benefits. I could use my lifetime to engineer a Kupier belt telescope. – Bharath Simha Reddy Nov 12 '23 at 17:35

3 Answers3

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Very little upside, lots of downside.

It's colder out there, which means that keeping your IR sensors cool is a bit easier.

The orbit is wider, so you get more parallax, but the orbit is slower, so you have to wait longer to get the results.

The sun is smaller and dimmer, so the area of the sky that you have to avoid (as it is too close to the sun) is smaller.

The downsides are much more significant:

You get less telescope per dollar. For a given budget your telescope must be lighter, smaller with lower resolution.

If something goes wrong, you can't fix it. You can send a rocket up to fit corrective lenses to Hubble; you can't do that if it is out beyond the asteroid belt.

If you put it in an ecliptic orbit in the plane of the planets, then your probe will go behind the sun every year. While it is behind the sun, you can't communicate with it.

If you put it in some other orbit it takes much more fuel (and so you get an even smaller telescope for your money)

Data transmission rates are much lower. Its acceptable for New Horizons to spend a year to download all its data from one day observing. But if you only had one observing day on your telescope per year that would be disappointing.

All in all this is a "why don't we build houses out of gold". There might be a few minor advantages (gold doesn't rust) but the disadvantages (gold is costly and weak) far outweigh the advantages.

James K
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  • I agree, it's hard to list all the downsides as there are so many, like needing much bigger solar panels, a bigger and more powerful antenna and many others. – GdD Apr 22 '20 at 09:05
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    @GdD I disagree! -1 I think this is overly dismissive and short-sighted, and the question as asked still deserves a good answer. – uhoh Apr 23 '20 at 03:01
  • Thanks for your efforts, but I would like to know the benefits in terms of Astronomy, not the technical feasibility, which I have already kept a note about in the question I have asked. – Bharath Simha Reddy Nov 12 '23 at 17:39
  • Goodness me, do you always take three and a half years to consider your response! The benefits, in terms of astronomy, are put in the opening paragraphs: It's colder (good for IR) It has a wider orbit (good for parallax, in some ways). The sun is less of a problem. – James K Nov 12 '23 at 17:46
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I don't see the down sides to be anywhere nearly as strong as @JamesK's answer suggests!

Some space telescopes use several kW of power but one of them is 500 W and these are all circa 1 AU where power is plentiful so there was no need to lower it. In deep space if you really need to just collect CCD images in cold space and process them with processors available in 2020 this could probably be done with much less power than these 20th century 1 AU telescopes used. Look at the processing power available in handheld devices these days!

Telescopes like GAIA spin constantly while collecting data and uses a phased array antenna to communicate while rotating, so spin-stabilization will be less power-hungry than some alternatives, there is a lot of room to optimize the design for low average power.

You don't need a bigger antenna or more powerful transmitter because you'd use an optical communications link and a 1 Watt laser diode. You'd deploy a separate, non-spinning smallsat to do that and connect by WiFi.

Here is a link budget calculation for an optical versus radio-based deep space link, and another mention of a next-generation deep-space telescope.

The cold will be a big power savings; you won't need refrigerators or an attitude control system to keep a sunshade pointed towards Earth.

Probably a 100 or 200 W RTG is all that's necessary to run a decent space telescope far from the Sun using technology from 2020.

So all of the merits pointed out in the other answer are really available and worth exploring in greater detail in yet another answer here rather than dismissing the question so out of hand!

Copied from Wikipedia articles:

Telescope    Launched      Power (W)
---------    -------
Spitzer        2003          427*
WISE           2009          550        
Herschel       2009         1000
Kepler         2009         1100
GAIA           2013         2010
Hubble         1990         2800

*http://www.spitzer.caltech.edu/mission/188-The-Solar-Panel-Assembly
uhoh
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    any science or engineering-based comments to go along with the silent anonymous down votes? – uhoh Apr 23 '20 at 10:41
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    I didn't downvoted but... The OP question is "what are the merits of placing telescope beyond asteroid belt or in Kuyper belt". I understand it - what such telescope can do better than if it's placed at Earth orbit or Lagrange point. – Heopps Apr 23 '20 at 11:21
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    @Heopps ya my answer is incomplete at the moment but it does address the feasibility of those merits which the other answer calls into question. In other words they can only be merits if the concept is practical, and that practicality was negated by the other answer. We need to re-establish the practicality, otherwise the big zero multiplier that the other answer attempts to add would be the answer. – uhoh Apr 23 '20 at 11:25
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While technically doable, there's substnatial risk involved and little perceived benefit.

  1. It would take YEARS to make it that far.
  2. Being that far from the Sun, means solar power is not an option for utilization as a power source. That leaves RTG's, but they produce far too little power to run a large telescope (The Hubble uses 2.1 kilowatts of power) A telescope Hubble sized would need 10 RTG's to run
  3. Being that far from Earth makes repair and servicing impossible.
  4. The Telescope would require a extensive and expensive monitoring network to retrieve data and imagery.
LazyReader
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