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.
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asked Apr 21, 2020 at 21:43
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1$\begingroup$ 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. $\endgroup$– lijatCommented Apr 21, 2020 at 22:11
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$\begingroup$ 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. $\endgroup$– AmarCommented Apr 22, 2020 at 5:31
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2$\begingroup$ @Amar: The asteroid belt is not an obstacle to observations. $\endgroup$– Christopher James HuffCommented Apr 22, 2020 at 20:27
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1$\begingroup$ 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. $\endgroup$– HeoppsCommented Apr 23, 2020 at 12:49
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$\begingroup$ @ChristopherJamesHuff, why is that they don't obstruct? I meant in all ways including radiations. $\endgroup$– AmarCommented Apr 24, 2020 at 16:31
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3 Answers
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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.
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$\begingroup$ 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. $\endgroup$– GdDCommented Apr 22, 2020 at 9:05
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1$\begingroup$ @GdD I disagree!
-1I think this is overly dismissive and short-sighted, and the question as asked still deserves a good answer. $\endgroup$– uhohCommented Apr 23, 2020 at 3:01 -
$\begingroup$ 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. $\endgroup$ Commented Nov 12, 2023 at 17:39
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$\begingroup$ 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. $\endgroup$– James KCommented Nov 12, 2023 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)
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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
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1$\begingroup$ any science or engineering-based comments to go along with the silent anonymous down votes? $\endgroup$– uhohCommented Apr 23, 2020 at 10:41
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1$\begingroup$ 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. $\endgroup$– HeoppsCommented Apr 23, 2020 at 11:21
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1$\begingroup$ @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. $\endgroup$– uhohCommented Apr 23, 2020 at 11:25
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While technically doable, there's substnatial risk involved and little perceived benefit.
- It would take YEARS to make it that far.
- 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
- Being that far from Earth makes repair and servicing impossible.
- The Telescope would require a extensive and expensive monitoring network to retrieve data and imagery.
