Why no telescopes on the moon?

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We are placing everyday more telescopes in satellites in orbit. Would't it be convenient to have some permanent telescopes placed on the moon's surface? I guess if we don't do that it's because that would be much more expensive than launching satellites? Are there no plans to place telescopes on the moon and why?
 

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  • #2
Drakkith
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I guess if we don't do that it's because that would be much more expensive than launching satellites?
Partly, yes. Satellites in orbit don't require heavy and expensive hardware that's required to land it on the Moon's surface. In addition, a telescope in orbit can be turned to point in nearly any direction at any time, whereas a telescope on the Moon is limited to whatever area of the sky is currently in view.
 
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  • #3
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If you Google this, you will find many objections. There are two immediate questions, though - 1) what question can be answered better by a lunar telescope than the alternatives, and 2) how will you get the images back to earth, given that the moon is between the telescope and the planet,
 
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Now this has raised the question of why such a telescope couldn't be positioned on the lunar poles to allow for observations, communications, and power? It wouldn't be ideal, but it would allow for a very large telescope.
 
  • #5
epenguin
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how will you get the images back to earth, given that the moon is between the telescope and the planet,
Er, no it doesn't have to be. And we could take astronomical selfies with it.
 
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You want to put it on the near side?
 
  • #7
epenguin
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I can see an advantage.
 
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The moon isn't ideal either, it has a very thin "atmosphere" of dust. The Apollo astronauts noticed a haze on the moon which turned out to be dust help in position by electro-static forces.
 
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But indeed a moon telescope could be much larger than one in orbit. Having rotation so it can be pointed to any direction (except the sky area blocked by the moon itself of course) doesn't seem a big problem either, and the moon / Earth rotation would allow for observing (I guess) any point in space. I don't know how much the dust could be a problem though.
 
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A single telescope you may be right, but not for a telescope array. An array of small telescopes is much more powerful than one large one, and the further you put them away from each other they better.
 
  • #11
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What could we observe from the surface of the Moon that we could not observe from other Earth orbiting scopes?
 
  • #12
Drakkith
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But indeed a moon telescope could be much larger than one in orbit.
How so?
 
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  • #13
davenn
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What could we observe from the surface of the Moon that we could not observe from other Earth orbiting scopes?
Exactly, nothing, and having scopes based on the moon adds an even bigger headache for maintenance issues
I cant see any point in moon based observatories unless there is already established significant manned moonbase

Dave
 
  • #14
Chronos
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A moon teledcope would be fabulous if we had a moon base, that is the bigger question in my mind - why do we not have a moon base on the drawing board? That is the logical first step for space exploration.
 
  • #16
russ_watters
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I have read that a moon telescope's mirror could be largely made out from lunar dust, so the payload to take from Earth would be rather limited. This article says that with this method a 50 meter telescope could be built on the moon, far larger than anything in orbit.

http://www.technologyreview.com/news/410253/a-moon-based-telescope/
That doesn't make any sense: You wouldn't have to carry the mirror to the moon...just an entire manufacturing plant for making mirrors, which, necessarily, would be larger than the mirrors it is making.
 
  • #17
Janus
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I can think of one type of telescope that could benefit by being placed on the far side of the Moon, a radio telescope. The distance and intervening bulk of the Moon would shield it from Earth based electromagnetic interference. Whether or not this benefit would be worth it is another question.
 
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That doesn't make any sense: You wouldn't have to carry the mirror to the moon...just an entire manufacturing plant for making mirrors, which, necessarily, would be larger than the mirrors it is making.
You would make the primary mirror segmented. A small plant that makes many mirrors. I think it would still need more material than the primary mirror, but the comparison is not as obvious as it might look like.
 
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I have read that a moon telescope's mirror could be largely made out from lunar dust, so the payload to take from Earth would be rather limited. This article says that with this method a 50 meter telescope could be built on the moon, far larger than anything in orbit.

http://www.technologyreview.com/news/410253/a-moon-based-telescope/
50m is nice, but an array of smaller telescopes put far apart in orbit can have an effective apature way beyond 50m.

What could we observe from the surface of the Moon that we could not observe from other Earth orbiting scopes?
Not all telescopes orbit earth, we have several at the L points and several orbiting the sun.

A moon teledcope would be fabulous if we had a moon base, that is the bigger question in my mind - why do we not have a moon base on the drawing board? That is the logical first step for space exploration.
Money. Both Russian and China have plans for a base in the later part of the 2020s, but they're still way too expensive.
 
  • #20
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My apologies for the brevity of my post. This is off the cuff without all the links to references that a more scholarly reply would have.

Drakkith is correct. And there are a couple of other factors as well.

Space telescopes in orbit around the Earth are closer than the Moon, so control signals don't take as long to get there. Remember the delays between asking a question of the astronauts on the Moon and receiving their reply?

It costs somewhat less to put a satellite telescope in orbit than it does to take it to the moon; much less land it as Drakkith mentions.

If you intend to perform periodic maintenance and upgrades on your telescope, it's much cheaper and faster to get to it in Earth orbit than on the Moon.
The Moon has a limited amount of surface area which limits the practical size of of a telescope, even if you build an array. You can theoretically build a much larger free floating array in orbit than you can on the surface of the Earth or the Moon.

In orbit, there's no gravity to distort the shape of your lens. While the Moon has only about 1/6th the gravity of the Earth, that would still limit the size of the reflective lens you can use; although that might be surmountable by placing actuators behind the lens to bend it into whatever curvature you needed. A lens 6 times larger than the Mount Palomar one would definitely flex, even if the backing was a glass honeycomb; although I don't know how brittle it would be in those temperatures (probably very.)

All of this applies to optical telescopes. Now there might be a good reason to place a radio telescope on the far side of the Moon as the bulk of the Moon should shield the telescope from most Earth radio transmissions.
 
  • #21
russ_watters
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You would make the primary mirror segmented.
The article is poorly written, but I'm pretty sure the intent was for a single-piece mirror.
 
  • #22
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We would have to establish a permanent base on the Moon first.
That is huge and expensive challenge and there would need to be a big economic reason for doing it.
Telescopes might get on the 'things-to-do ' list eventually.
 
  • #23
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The idea of putting a telescope of any sort whatever on the moon strikes me as nutty, for reasons largely already discussed in this conversation. As for building a large, high-quality telescope of moon dust on the moon... least said soonest mended. Let me know when we have achieved such a feat on Earth, never mind the moon. And let me know when we have achieved even a shaving mirror on the moon, let alone the equipment to direct it for astronomic purposes...! And if it is NOT high quality, it would be even nuttier, given what such a project would cost.
IMO if we had more scientists and fewer politicians in charge, we would decades ago have had many observatories in Earth orbit and many more around various other bodies in the solar system all the way out to Eris at least, but one of the first would have been a number of types in the lunar L2 point shielded from Earth noise, and a few in the L2 points of planets such as Venus and Mercury to shield them from solar noise.
Getting data back to Earth? Nothing special; where the orbit is small, park relay comms satellites at the L4 & L5 points. They always would have at least some channel open to Earth or to other relay satellites at various strategic locations in the solar system. Being largely specialised for comms, those satellites could do a good job of it, though they also could have secondary observation functions.
In special cases one could orbit three to six orbiting comms satellites around the bodies whose Lagrange points harboured observatories. There always would be at least one or more in view of the observatories and each would regularly be out of sight of the observatories and accordingly be able to signal Earth with minimal noise for the observatories.
 
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  • #24
Chronos
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I fail to see any great dfifficulty in placing a large telescope on a moon base. It need not be monolithic so manageable sized modules could be manufactured on earth and shipped to a moon base without inordinate difficulty or expense. A moon base would require supplies from earth indefinately before it could hope to become self sufficient, so, transport of telescope modules to the moon would not pose undue logistical complexity. A moon base would offer inumerable other advantages so it would make perfect sense to add an observatory to the host of other facilities required for a permanent moon base.
 
  • #25
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I fail to see any great dfifficulty in placing a large telescope on a moon base. It need not be monolithic so manageable sized modules could be manufactured on earth and shipped to a moon base without inordinate difficulty or expense. A moon base would require supplies from earth indefinately before it could hope to become self sufficient, so, transport of telescope modules to the moon would not pose undue logistical complexity. A moon base would offer inumerable other advantages so it would make perfect sense to add an observatory to the host of other facilities required for a permanent moon base.
Nice to find you so positive. Now all we need to know in the light of the current progress and cost in building the space station, when you think it would be realistic for us to expect a viable moon base (by which I mean something slightly more usable than our moon landers' exuvia.)
I'll refrain from asking what scale you might envisage for "inordinate difficulty or expense" or why a permanent moon base might be dependent on a competitive astronomic observatory, in particular one to rival far cheaper and less demanding units in lunar L2 orbit, let alone dirt cheap eyes in Earth orbit. We could manage such space units, even including comms relays for the L2 project, at a tiny fraction of the price and hazard, a century before we could get a single moon base off the ground, if you would excuse the expression. And that is without waiting till the moon base project even got round thinking of scientific instruments.
Nor does it take into account the superior quality and versatility of space-based observatories, whether manned or not. For the foreseeable future moon bases are for flag planting, not function.
 
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