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Knight of Honor

Registered: 11-2005
Posts: 1883
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Telescopes on the Moon?


I just got back from a fabulous seminar (huh -- not often those two words go together....) discussing whether or not we should put telescopes on the moon. Thought I'd share my new-found knowledge with others who might be interested.

The talk was by Dr. Dan Lester, one of the astronomers at the University of Texas at Austin (where I attend), who also does his research out at the McDonald Observatory in the mountains of western Texas. He's also one of the guys who reports to Congress about science. He was a pleasantly entertaining speaker who showed that adorable "Oooooh! Think about THIS new toy!" attitude that so many astronomers do. (If you've ever had dealings with an astronomer, you know what I mean. They're even worse than geologists!)

Anyhow, he started out by saying that when he was a grad student in astronomy, he was really gung-ho about putting telescopes on the Moon. Most astronomers were, in the 60s, 70s, and 80s. And for good reason: a telescope on the Moon would work vastly better than one on Earth. There would be no seeing problems, for example. Note that "seeing" in this case means not "viewing", but rather the distortion of light caused by diffraction through the atmosphere -- it's what causes stars to "twinkle" when viewed by eye and look fuzzy when viewed by an Earth-located telescoped. Also, since there is no appreciable atmosphere on the Moon, all wavelengths of the electromagnetic spectrum would reach the telescope, unlike on Earth. Also, light-pollution, reflection off heavy particulates , and cloudy skies would no longer be an issue. All of these seemed excellent reasons in the 70s and 80s to put a telescope on the Moon, so the scientists and engineers got together and figured out the technology to make it work.

Dan pointed out that these are STILL good reasons to put a telescope on the Moon rather than the Earth. But his opinion is that there is a third option for telescope location that would be even BETTER: open space.

Before the Hubble Space Telescope (HST) was launched in 1990-ish, the majority of astronomers were convinced that a space platform would be unable to meet the delicate pointing tasks needed for most astronomy. They also worried that without a reaction mass, the telescope would prove unwieldy to turn (they were partly right -- most "repair" missions to HST are to unspin the gyros, which provide effective reaction "mass"). However, HST met and exceeded these goals from the get-go and, once the mirror was repaired, proved beyond a doubt that astronomy can be done in open-space.

Dan pointed out that, while a lunar telescope is better than one on Earth, a space-based telescope is better than either. His reasons ranged from lesser cost and prior experience (with HST and other smaller space telescopes), to ease of maintanence and potential optical equipment upgrades, to the practical issues with dealing with lunar dust.

The latter I found particularly interesting. I knew, from astronauts' reports, that dust was an issue up there. But did you know that, even when no human is around kicking up dust, there are dust CLOUDS on the Moon? Honestly! The astronauts noted it as did un-manned lunar craft. Now, your first thought is hopefully, "Yeah, right! And how does the dust stay up there if there's no air?" The answer is static electricity, believe it or not. When the Sun shines on the regolith, ionized particles hit the dust and ionize it. Those electrically-charged particles fly off the surface (imagine two oppositely-charged magnets). They don't get far, of course, since the Moon has significant gravity, but the dust particles do rise up several meters or even kilometers before they lose their charge and drift downwards again. This is most obvious around dawn, when the backlit sky shows the reflection off clouds of dust on the horizon. Fascinating, hey? But while geologists might be thrilled, astronomers obviously are not. Backlit clouds are NOT dark -- and moreover, they'll rain dust down on the mirrors and lenses.

Other reasons he stated for putting a telescope in open-space rather than the Moon are:
-- Temperature consistancy, especially at Earth-Sun L2 or slow-moving orbits. This is less true in Low Earth Orbit (LEO), where HST is now.
-- Cooler average temperatures, which are critical for long-wavelength telescopes.
-- Full-sky viewing capabilities (rather than one hemisphere (or less, if you're in a lunar crater).)
-- Easier access for manned maintenance if you're in LEO Earth-Moon L1 or L2.
-- Less risk involved in getting the telescope to where you need it, since there's no risk of it crashing upon landing.

There was more, but it's already escaped my mind. Anyway, Dan's point was that there are a few good reasons to put telescopes on the Moon in specific locations -- putting a radio telescope on the far side would be great because the Moon's surface would block human-made radio waves from interfering, for example. But his conclusion was that technology has improved to the point where, for most telescopy, there is no reason that the lunar surface is better than an open-space platform, and several practical and financial reasons why it would be worse.

Any thoughts, anyone? I've heard a lot about putting a lunar telescopes in, but this was the first I've heard from a credible source on the opposing side.

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11/27/2007, 9:50 pm Link to this post Email Reythia   PM Reythia AIM MSN
 
QS2 Profile
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Shepherd

Registered: 03-2006
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Re: Telescopes on the Moon?


It sounds pretty close to what I've heard myself, which is that in practice open space is a superior location. I'm also wondering if one of the things you've forgotten about is Lunar quakes.

So anyway, all the space telescope missions are now set for open space now, so I guess the reasons are truly very compelling indeed for astronomers. emoticon

11/28/2007, 12:30 am Link to this post Email QS2   PM QS2
 
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Lady of the Land

Registered: 05-2003
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Re: Telescopes on the Moon?


It makes a lot of sense. And yes, I heard of lunar dust and knew about the static, but I didn't realize it was that bad.

There goes one reason for actually settling on the Moon. Ah, well.

*still wants to go on vacation there*

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11/28/2007, 6:55 am Link to this post Email Firlefanz   PM Firlefanz Blog
 
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Squire

Registered: 09-2003
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Re: Telescopes on the Moon?


NASA has been talking about retiring Hubble for years and replacing it with a bigger and better orbital telescope. But as with most NASA things they keep patching it up and keeping it in use...

According to a recent article (sorry, I can't remember where I read it but I'll try to find it again), they need to retire Hubble because the cost of keeping it running is draining the funds needed to pay for its replacement! I think they said that no more maintenance missions were scheduled for it, which basically puts the nail in the coffin.

One plan circulating a while ago was bringing Hubble back down in a shuttle and putting it in the Smithsonian museum. The problem is, although Hubble fitted in a shuttle cargo bay on the way up, they've been bolting new bits on in orbit and it won't fit any more emoticon


Are they still considering plans to put a pair of telescopes at the Earth-Moon L4 and L5 points and using them as an optical interferometer? (Or was the just science fiction? emoticon )

---
"Frankly, I think Word 2007 is half-baked. I’m sorry I upgraded. I’ve been an IT professional for over 20 years now - I’m no newbie and don’t mind learning new things - but this is silly."
11/28/2007, 9:12 am Link to this post Email David Meadows   PM David Meadows
 
Reythia Profile
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Knight of Honor

Registered: 11-2005
Posts: 1883
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Re: Telescopes on the Moon?


quote:

QS2 wrote:
I'm also wondering if one of the things you've forgotten about is Lunar quakes.


Well, he mentioned lunar quakes, but frankly, they're really not expected to be a major problem. First off, they're rather rare, and secondly, if we can build an observatory on a volcano and less than a hundred kilometers from an active fault on Earth, we can manage the same on the Moon. Lunar quakes are something to keep in mind, of course, but they're not really a technological deadblock.

quote:

Medows wrote:
NASA has been talking about retiring Hubble for years and replacing it with a bigger and better orbital telescope. But as with most NASA things they keep patching it up and keeping it in use...

According to a recent article (sorry, I can't remember where I read it but I'll try to find it again), they need to retire Hubble because the cost of keeping it running is draining the funds needed to pay for its replacement! I think they said that no more maintenance missions were scheduled for it, which basically puts the nail in the coffin.



Ugh. Yes, astronomers, engineers, and astronauts have all been trying to tell the government for years that it would be cheaper to put a shiny new telescope up in space every 5-10 years rather than continually updating and "fixing" the old one. NASA knows. It just can't get the government to provide the funding to get the project started (especially now, when NO sciences can find federal funding, thank you very much Mr. President.... Grr...) Oddly enough, it's proved easier to find MORE money to keep an old project going than to find LESS money to start a new, more modern one. One more reason I have to grumble about the government and how they portion out money. *grumble*

quote:

Are they still considering plans to put a pair of telescopes at the Earth-Moon L4 and L5 points and using them as an optical interferometer? (Or was the just science fiction? emoticon )


That idea has been bandied about for a while, yes. I haven't heard anything formally about it, though. My suspicion is that it's run into budget issues as well. emoticon I know TPF ("terrestrial planet finder") is still in the works for sometime around 2015-ish. It's not specifically set for a Lagrange point, but it may end up there.

Right now there's some interest in putting telescopes at Sun-Earth L2 (that's the one that's in Earth's "shadow", on the side of the Earth that's always away from the Sun). Basically, putting a telescope there means you could block out all emissions from the Earth, Moon, and Sun with one little shield, which would never have to move. That's a big plus in terms of energy and mass savings, as well as a huge decrease in complexity. Moreover, transfer from the Earth-Moon Lagrange points (such as L1, between the Earth and Moon) to Earth-Sun Lagrange points is quite cheap -- delta-v's of perhaps 20 m/s. (That's compared to typical velocity changes measured in tens or hundreds of km/s, FYI.) So there's a theory that maybe we could send the telescopes out to Sun-Earth L2, and if they need maintenance, just bring them back to Earth-Moon L1 to do it. Then send them back. And none of it would cost a whole lot of fuel for the telescope (though getting people to E-M L1 would). Anyhow, it's an interesting idea.

quote:

Firle wrote:
There goes one reason for actually settling on the Moon. Ah, well.
*still wants to go on vacation there*


Hahahahaha! Me too!

---
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11/28/2007, 5:15 pm Link to this post Email Reythia   PM Reythia AIM MSN
 
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Shepherd

Registered: 03-2006
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Re: Telescopes on the Moon?


Sadly the Terrestrial Planetary Finder has been placed on an indefinite hold, due to similar budget woes. A lot of good missions are similarly afflicted, never officially canceled, just perhaps never to be built.

The only good news in all of this is, is that the Europeans seem to be taking up some of the slack, albeit later, as their own programs get up to speed. emoticon
11/29/2007, 12:19 am Link to this post Email QS2   PM QS2
 
Reythia Profile
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Knight of Honor

Registered: 11-2005
Posts: 1883
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Re: Telescopes on the Moon?


quote:

QS2 wrote:
Sadly the Terrestrial Planetary Finder has been placed on an indefinite hold, due to similar budget woes. A lot of good missions are similarly afflicted, never officially canceled, just perhaps never to be built.



Such is the way things go. There's a well-known rule of thumb at NASA: If you project has been canceled for the third time, you know it's bound to fly eventually! (Historically, that's not so inaccurate...)

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11/29/2007, 5:09 pm Link to this post Email Reythia   PM Reythia AIM MSN
 
Blitzen Profile
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Squire

Registered: 12-2004
Location: falkirk
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Re: Telescopes on the Moon?


Reythia wrote
quote:

Right now there's some interest in putting telescopes at Sun-Earth L2 (that's the one that's in Earth's "shadow", on the side of the Earth that's always away from the Sun).



Is that a typo, or is there a part of the earth that is always away from the sun? Hows that work for like sunlight and stuff?

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12/5/2007, 8:49 pm Link to this post Email Blitzen   PM Blitzen
 
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Lady of the Land

Registered: 05-2003
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Re: Telescopes on the Moon?


L stands for Lagrangian Point - those are points in space where gravitational (and centrifugal) forces of different bodies in space are in balance. These points "move" through space in coordination with the bodies they relate to.

This means spacecraft "parked" on one of those points need only little fuel to hold their position, relative to Earth, for example. For Earth and Sun, there are five such points, numbered from 1 to 5. (There are different Lagrangian points for Earth and Moon, as well, but we weren't talking about those.)

One of those L points is "behind" Earth if you looked at it from the sun (L2, as it happens). Thus it's always in Earth's shadow, and won't have to deal with any sunlight. Perfect for telescopes that look for much dimmer stars than our own.

Here's a link to a wikipedia article on Lagrangian points that also has a nice diagram:

Wikipedia: Lagrangian points

I hope that makes the idea more clear. emoticon

Last edited by Firlefanz, 12/5/2007, 9:05 pm


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12/5/2007, 9:04 pm Link to this post Email Firlefanz   PM Firlefanz Blog
 
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Squire

Registered: 12-2004
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Re: Telescopes on the Moon?


Ah, ok, so its not actually on earth. Got you. Thanks.

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12/6/2007, 12:13 am Link to this post Email Blitzen   PM Blitzen
 
Reythia Profile
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Knight of Honor

Registered: 11-2005
Posts: 1883
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Re: Telescopes on the Moon?


Thanks for explaining, Firle. For some reason, Runboard stopped sending me emails when someone commented on this thread. Odd.

Anyhow, sorry to confuse you, Blitzen! Holler if there's anything else you need explained. I tried to avoid too much technical jargon, but sometimes it slips in when I'm not watching. (You DO know that NASA really stands for the "National Acronym Slinging Association", right?!)

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12/6/2007, 5:54 pm Link to this post Email Reythia   PM Reythia AIM MSN
 
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Lady of the Land

Registered: 05-2003
Location: Germany
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Re: Telescopes on the Moon?


Reythia, if you happen to use AOL, there was a disruption in mail service to them for the last few days. It has been fixed, though.

</support mod mode>

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12/6/2007, 9:30 pm Link to this post Email Firlefanz   PM Firlefanz Blog
 
Reythia Profile
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Knight of Honor

Registered: 11-2005
Posts: 1883
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Re: Telescopes on the Moon?


quote:

Firlefanz wrote:
Reythia, if you happen to use AOL, there was a disruption in mail service to them for the last few days. It has been fixed, though.



No, it's not that. It's something on Runboard itself. I've had it happen several times before, when Runboard just suddenly stops sending me emails on a particular thread. It's quite odd, since emails from other threads make it through. *shrug* Oh well. But thanks!

---
  -- YAR!
12/6/2007, 9:41 pm Link to this post Email Reythia   PM Reythia AIM MSN
 


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