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NASA Space Science

Lunar Lens Takes A Step Forward 95

Posted by CowboyNeal from the looking-to-the-future dept.
palewook writes "A recent breakthrough increased NASA's interest in a lunar-based space telescope. Researchers combined an ionic liquid surface and a layer of silver which produced a favorably reflective mirror."
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Lunar Lens Takes A Step Forward More

Lunar Lens Takes A Step Forward

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  • I guess these liquids are practically solid like ordinary glass.
    • I'm hoping they get their measurement systems in right on this telescope...you don't want to confuse metric and imperial again do you do you nasa!

    • Re: (Score:3, Informative)

      by AJWM ( 19027 )
      Not that old canard again. Glass is an amorphous solid, it is not a liquid (at ordinary temperatures). (And no, thickness differences in medieval stained glass windows don't prove anything - the pieces were installed thick side down for stability, and they didn't have the technology for uniform-thickness glass).

      They're talking about real liquids, spun to form a curved surface. Early liquid mirror experiments involved mercury.
  • if they're spinning the mirror, then they're gonna need some serious engineering to produce a support that is vibration free.

    • Re: (Score:3, Informative)

      by cy_a253 ( 713262 )
      Actually, I took a physics class a few years ago given by the lead researcher (Ermanno Borra) here at Laval U., and I remember him describing that for ionic liquids the damping can be extraordinarily high, so there are almost no image distortions coming from vibrations.
      • A modified "wobble mirror" could be used to cancel out distortion from mechanical vibrations but since it's a rotating liquid it might also be distorted by vorticies (like the earths atmosphere/oceans) - that would be very difficult to iron out.
    • This is actually a very old idea. American Scientist's May-June issue had a interesting piece on a liquid (mercury) telescope, and focused on some of the engineering challenges a team in Birtish Columbia tried to address. There is no rigid coupling - air cushions and a ring of permanent magnets serve to support and drive the mirror. (via a rotating magnetic field, produced by three stationary field windings). The other major issue was speed variations from the air currents and interfaces -- they ended up

      • Freezing metal mirrors (Score:4, Insightful)

        by Mal-2 ( 675116 ) on Saturday June 23, 2007 @07:01PM (#19623683) Homepage Journal
        Would the freezing of the mercury really be that much of a problem? How about a system where the mirror is formed of molten metal, then allowed to freeze (requiring no additional energy to hold its shape). If it gets scratched, chipped, warped, or otherwise marred, heat it up and shape it again.

        The down side of such a system would be that you would lose the ability to change mirror dimensions "on the fly", but I'm not sure they're doing that anyhow. Also the mirror makers would have to account for the contraction of the metal on freezing, but at least they have the ability to retry if they don't get it quite right, or if the secondary mirrors (which presumably will be the standard glass type) turn out to be imperfect.

        I also believe a telescope with a liquid mirror would have to be a "transit telescope", always pointed straight up relative to the local pull of gravity. Transit telescopes can track objects by moving their secondaries around, but not very far off-axis, and at the cost of focus and sensitivity. A solid-Hg mirror would remove this restriction, though it would possibly be too massive to reasonably move it around. Without this ability, observations would be at the mercy of whichever way the scope was pointed at any given time, give or take a few degrees.

        It also seems to me the dust problem is relatively easy to solve using a positive pressure system. Any amount of gas in the telescope enclosure will be positive pressure compared to what's outside. Either the enclosure will not leak (and dust will have no way in), or it will leak slightly, forcing dust away from the leaks anyhow. Then maintaining a clean mirror is as simple as pumping in replacement gas.

        Mal-2
        • I think crystallization is the problem with freezing a reflector. There's a lot of history in liquid mirror telescopes. Check this comment [slashdot.org], and NASA [nasa.gov], too.

          The transit telescope is useful for orbital debris studies, and even asteroid discovery. The mercury had to be cleaned (mostly by careful sweeping) every week or two. I'm told that one annoyance of the Cloudcroft, NM, site was "moth seaon", when moths would enter the dome and fall into the mercury.

          • Re: (Score:2)

            by Mal-2 ( 675116 )
            I can see why crystallization might be a problem with freezing the mirror, but I am also willing to bet there is some exotic way to freeze mercury (maybe by doing it extremely quickly) that will prevent or minimize this.

            As for transit telescopes, they are indeed useful, in large part because they can be made so much bigger than fully movable assemblies. For a radio example, take Arecibo. Of course, radio telescopes are a lot easier to construct because of the longer wavelengths involved, but that doesn't ch

    • Re: (Score:2, Informative)

      by ardiesr ( 861538 )
      They do have existing spinning liquid mirrors in service, one of which is in Whistler BC. At this time I don't remember the name of the observatory. The article I read outlined the stringent engineering requirements both to prevent vibrations as well as turbulence generated by the motion of the water.

      How that would be applied on a lunar observatory is another story.

    • Apparently, the serious engineering has been done and you can have ripple free liquid mirrors. [nature.com] There's a picture of both a huge mirror and an image obtained from it.

      It's too bad this article and all the references are published in non free magazines. The $18 to $30 cost per article is steep. When you consider that all of the actual research is government funded, the cost of the information itself should be zero.

  • Favorably reflective mirror? (Score:5, Funny)

    by Timesprout ( 579035 ) on Saturday June 23, 2007 @12:43PM (#19620613)
    The Lunar chicks are just gonna love this.

    • Re: (Score:2, Funny)

      by Tablizer ( 95088 )
      The Lunar chicks are just gonna love this.

      But if they find out they're ugly bimbos, they'll get really pissed and thrash out at Earth. The dinosours once gave them a polaroid camera...
             

    • Re: (Score:2)

      by Trogre ( 513942 )
      But what will the lunar-tics make of it?

      A hat, I suspect.

  • The interesting part (Score:5, Insightful)

    by meldroc ( 21783 ) <meldroc@fr3.1415926ii.com minus pi> on Saturday June 23, 2007 @12:50PM (#19620673) Homepage Journal

    Borra envisions a telescope with a liquid mirror measuring 66 feet to 328 feet wide.
    Anyone with any knowledge of telescopes will immediately see why astronomers are drooling right now.

    • Re: (Score:2)

      by 0racle ( 667029 )
      The universe in Widescreen format.

    • Re:The interesting part (Score:5, Informative)

      by Gerzel ( 240421 ) * <brollyferret&gmail,com> on Saturday June 23, 2007 @01:37PM (#19621057) Journal
      Hell the placement makes us drool as ANY functioning telescope data from the far side of the moon would probably give us new and tantalizing images.

      • Hell the placement makes us drool as ANY functioning telescope data from the far side of the moon would probably give us new and tantalizing images.

        Not really. There's nothing visible from the far side of the moon that can't be seen from the Earth's surface or LEO. What makes a lunar telescope tantalizing is the size theoretically possible, not the location itself.
    • From what I've heard at a recent lecture/conference though, placing a telescope on the dark side of the moon is exciting, but scientifically speaking, the astronomers would actually prefer orbiting telescopes at the Lagrange points. The dark side of the moon offers certain advantages, including cost if operated in conjunction with planned lunar activities, however will not necessarily provide the same scientific benefit as telescopes at the Lagrange points (#2 I believe) can. Of course though, I don't kno

      • Re: (Score:2, Funny)

        by Anonymous Coward
        The main inconvenient with a telescope on the darkside of the moon is that you have to build a 10921*cos(lat) km track around the moon at the chosen latitude that the telescope will travel every 29.5 days in order to track the darkness. Most proposals call for a farside telescope, accepting the fact that it will be usable only around full moon.

      • Re: (Score:1)

        by Kagura ( 843695 )
        There's a dark side of the moon? So where does the sun go when our side of the moon is dark?

        • Re: (Score:2)

          by stjobe ( 78285 )
          I know you were being facetious, but... The Moon actually has three sides; the near side, the far side and the dark side:

          The side of the Moon that faces Earth is called the near side, and the opposite side the far side. The far side should not be confused with the dark side, which is the hemisphere that is not being illuminated by the Sun at a given moment.

          -- http://en.wikipedia.org/wiki/Moon [wikipedia.org]

          • Re: (Score:1)

            by Kagura ( 843695 )
            Only three sides? I guess you forgot the light side. Don't forget any other arbitrary sides we decide to add.
      • If we can get such a huge benefit from putting telescopes out at Lagrange points, which I've heard are perfect for this sort of stuff, why are we thinking about investing in a complicated array on the moon (whose gravity well always adds to costs)? Is there some benefit to having this lunar based liquid telescope aside from sounding completely awesome? I can't remember correctly, but is James Webb going to L2 or something? If so, then at least we have one (upcoming) reasonably placed spaced telescope- wh
        • I think it's easier to convince the government to fund NASA projects that are completely awesome.
          And the more space telescopes, the merrier--this way we have a back-up on the moon if the one at L2 fails.
    • >>Borra envisions a telescope with a liquid mirror measuring 66 feet to 328 feet wide.

      > Anyone with any knowledge of telescopes will immediately see why astronomers are drooling right now.

      Okay, now they can start drooling:

      a telescope with a liquid mirror measuring 20.1168 m to 99.9744 m.

    • Re: (Score:2)

      by ozbird ( 127571 )
      Anyone with any knowledge of telescopes will immediately see why astronomers are drooling right now.

      Mercury poisoning?

    • Re: (Score:1)

      by Tablizer ( 95088 )
      Anyone with any knowledge of telescopes will immediately see why astronomers are drooling right now.

      Hmmm, spinning siliva also makes a parabolic shape...
         
    • My god, we could watch girls sunbathing topless from space!
    • 66 feet to 328 feet? Wow, that's some margin of error - even for astronomers.

      • Re: (Score:2)

        by stjobe ( 78285 )
        Pfft, 262 feet is nothing at the kind of distances we astronomers usually measure!
        We want to place a telescope 1,161,600,000 to 1,330,560,000 feet away, and you're grumbling about a piddling 262 feet?! Seriously!
        What was that you said? Diameter? No, no, no, you can't have a 1.2 billion feet mirror -- that's just silly! The tidal stresses alone would...

  • dust? (Score:5, Interesting)

    by Kristoph ( 242780 ) on Saturday June 23, 2007 @12:58PM (#19620739)
    The question I would ask is: would not this mirror have a very short lifespan as lunar dust covers/mixes with the liquid surface?

    ]{

    • Re:dust? (Score:5, Insightful)

      by Octorian ( 14086 ) on Saturday June 23, 2007 @01:02PM (#19620781) Homepage
      And what environmental factors could possible cause that on the moon, which has no atmosphere or tectonic activity?
      • Well... How about millions of tiny meteorites impacting the surface...
        • The meteorite craters you see on the moon are the result of billions of years of bombardment. Dust is not going to cover the telescope lens for a long time.
      • Comment removed based on user account deletion
      • Well, there is dust everywhere and it had to come from somewhere. So the exact same mechanism that caused the existing dust will cause new dust.

      • Answer (Score:5, Informative)

        by Ihlosi ( 895663 ) on Saturday June 23, 2007 @01:50PM (#19621165)
        And what environmental factors could possible cause that on the moon, which has no atmosphere or tectonic activity?



        Static electricity is one thing that keeps moving dust around on the moon. And then there's ejected material from meteor impacts (with gravity that low, stuff kicked up by meteors can travel quite far)

        • And what environmental factors could possible cause that on the moon, which has no atmosphere or tectonic activity?

          Static electricity is one thing that keeps moving dust around on the moon. And then there's ejected material from meteor impacts (with gravity that low, stuff kicked up by meteors can travel quite far)

          There is also space dust that is constantly falling onto the moon, earth, etc; I forget at what rate. I think it's 1" every 1000 years or something. That would definitely be something to worry about over a period of 50 years.

        • Re: (Score:1)

          by thechao ( 466986 )
          Thank God there's no way to get dust & stuff on the Earth-bound mirrors they already use. Otherwise, there might be problems.
      • I guess if you were to install a longterm telescope on the moon, you'd have to think of the impacting micrometeorites, etc that bombard the Moon daily. We don't get them on earth because our atmosphere protects us. Also, if that dust was bad enough that it has affected equipment that landed on the moon, I guess it would not be too silly to presuppose that it can get disturbed by a telescope built on the moon.

        I think that the dust problem can be avoided, but measures need to be taken and the dust needs to

      • Re: (Score:3, Informative)

        by GreggBz ( 777373 )

        And what environmental factors could possible cause that on the moon, which has no atmosphere or tectonic activity?

        The moon has tectonic activity. [nasa.gov]

        Also, as others have mentioned, it gets hit with stuff, since, as you mention, there is no atmosphere.

      • And what environmental factors could possible cause that on the moon, which has no atmosphere or tectonic activity?

        The haze and other problems caused by moon dust is well known. One of the principle causes is solar ionization [wikipedia.org]. Without an atmosphere to disperse charges, the dust ends up floating around like your hair while touching a van de graph generator. The irradiation is intense enough to be part of the weathering process that created the dust in the first place [wikipedia.org]. Micrometorites are another cause.

    • Re: (Score:2)

      by daeg ( 828071 )
      I'm guessing if it really is a liquid you could continuously filter it.

    • Re: (Score:2)

      by imroy ( 755 )

      would not this mirror have a very short lifespan as lunar dust covers/mixes with the liquid surface?

      There's no atmosphere on the moon, hence no wind to whip up dust. Except for the odd meteorite impact, any dust settled to the surface a long time ago. Just keep it covered when any sort of spacecraft (for service/maintenance/whatever) is near.

    • The footprints of the first astronauts will be visible for another... well...

      I forgot the number, but it is very, very large.

  • Lunar Lens Takes A Step Forward... (Score:4, Funny)

    by said213 ( 72685 ) on Saturday June 23, 2007 @01:00PM (#19620761)
    Lunar ant civilization takes two steps back.

    • Re: (Score:2)

      by mstahl ( 701501 )

      It's a good thing that the same side of the moon is always facing Earth. Otherwise, they'd fire this puppy up, and 180 degrees' rotation later, a loud, collective "Oh shit!" is heard 'round the world.

  • What I think they should do is build a huge telescope array on the moon... several miles in diameter.

    • Re: (Score:3, Interesting)

      by Cheerio Boy ( 82178 )

      What I think they should do is build a huge telescope array on the moon... several miles in diameter.

      It may sound kind of odd but couldn't you build a bunch of small "mars rover" style robots with dishes on their backs then set them up with swarm/clustering software so that you just keep launching them until you get the size array you want?

      Launch say 5 to start out so that four become the array and one transmits the data back.

      Of course this now has me wondering if Bluetooth will work on the moon... :-)

      • Re:A lunar telescope is cool and all but... (Score:4, Informative)

        by jbrader ( 697703 ) <stillnotpynchon@gmail.com> on Saturday June 23, 2007 @02:21PM (#19621455)
        Visible light interferometry is damned difficult because of the small wavelengths involved. Also, even though and interferometer gives you the same angular resolution as a similar sized single element telescope it doesn't give you the same sensitivity to faint objects because of the smaller overall surface area of the objective. Plus, really big telescopes are inherently cooler.

        • Re: (Score:2)

          by Plekto ( 1018050 )
          Visible light interferometry is damned difficult because of the small wavelengths involved. Also, even though and interferometer gives you the same angular resolution as a similar sized single element telescope it doesn't give you the same sensitivity to faint objects because of the smaller overall surface area of the objective.
          ****

          True, but the prospect of a major crater ringed with smaller 100 meter arrays to produce a several mile wide "lens" is intriguing to say the least. With the lack of any measurab
  • What about the orientation of this telescope? I guess that if it works with gravity, it can only look up and cannot be rotated. Luckily the moon rotates one full circle per 28 days, but still you miss one dimension to cover the sky. You could use another normal mirror to point it wherever you like (like shown here [hineslab.com]) but then you will need an enormous normal mirror, let alone that you might nor be able to manufacture it with the same smoothness a liquid mirror has.

    • Re: (Score:2)

      by hazee ( 728152 )
      Ah, no. The key is to move the (much smaller) secondary mirror around in front of the primary. Think off-axis satellite dishes, or the receiver above the Arecibo radio telescope that gets winched around above the dish, as the main dish itself is obviously fixed.
  • What are the advantages of putting this on the moon rather than in space? I suppose you don't need maneuvering jets, so can it can be sustained longer?

    • Re: (Score:2, Informative)

      by pyrrhos ( 227998 )
      The telescope works with gravity, there's no gravity in space. More precisely, there is, but you are continuously falling so you don't feel it. However, you could use a telescope that slowly falls towards the sun and use the solar wind to stop it from falling and also create a weak gravity force. Could be enough to build your telescope in space.
  • Atten: On July 5 of this year...America will blow up the moon.

    That is all.

    The American People, America, Earth
  • If it's spinning liquid, it will be a parabola, which is what you want, but it will only point in one direction. How can you get around that?
    • Freeze it before you tip it? Redirect light on the way in? Or maybe there's some optical trick that can be done on the receiving end? Or how about, put it on a railway track from the lunar north pole to the lunar south pole? I think I like the freezing idea best. Or the optical trick, if there is one.

    • Re: (Score:1)

      by Tablizer ( 95088 )
      but it will only point in one direction. How can you get around that?

      Simple: Send a postcard telling the aliens when and where to show up.
           

    • Re: (Score:2)

      by hazee ( 728152 )
      You move the (much smaller) secondary mirror around in front of the primary mirror. Think off-axis satellite dishes, or the giant Arecibo radio dish, where they winch the receiver array around above it.
      • The Arecibo dish is not parabolic though.

        • Re: (Score:2)

          by hazee ( 728152 )
          Good point. I don't know if corrective optics be used to eliminate the coma distortion incurred by viewing off-axis with a parabolic primary. But given that spherical aberration can be corrected (as with Hubble), I'd be a bit surprised if coma can't.

  • There's one in Canada already... (Score:3, Informative)

    by AliasMarlowe ( 1042386 ) on Sunday June 24, 2007 @03:18AM (#19626143) Journal
    UBC has a telescope whose primary reflector is a spinning liquid mercury mirror http://www.astro.ubc.ca/LMT [astro.ubc.ca]. It forms a paraboloidal reflective surface, which is one of the optimal reflector shapes, but can only be aimed at the zenith. A larger (6m diameter) version is being constructed for installation at the same facility near Vancouver.

    Smaller liquid-mirror telescopes were designed in the late 19th century, and a 51cm diameter example was built in the early 20th century (by Robert Wood) http://en.wikipedia.org/wiki/Robert_W._Wood [wikipedia.org]. Wood's design suffered from intermittent ripples on the surface, but performed well at other times.

    At least Canada is closer than the Moon, and easier to get to (not necessarily less inhospitable, of course).

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