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Space Science

100 Meter OWL Telescope Project 67

Posted by michael from the they-do-it-with-mirrors dept.
mindpixel writes: "The European South Observatory (my employer) is getting VERY serious about building the OWL (OverWhelmingly Large) 100 meter telescope. Check out this new site dedicated to the project. You can see some cool diagrams of what the OWL telescope will look like and some simulated images here." For more about telescopes of unusual size, you might read McKinstry's interview last year.
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100 Meter OWL Telescope Project More

100 Meter OWL Telescope Project

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  • Stars are so far away, they appear as point sources to us, eg. they have zero width (or, to be more precise, our viewing angle is zero). But when does a telescope that powerfull such that nearby stars aren't point sources anymore? If stars weren't as bright as they are, could this 100m telescope see planets orbiting Alpha Centauri, for example?
    • This doesn't apply to telescopes described in the article, but there's a method for removing the light of a star in order to see dimmer companions (such as planets) which is called nulling interferometry.

      An interferometer is an instrument with two telescopes, which uses the wave nature of light to combine them. When you separate 2 telescopes by say 100 meters and combine their light properly, you get the apparent resolution of a 100m telescope (minus the light gathering power and the cost).

      A nulling interferometer doesn't try to combine the wavelengths at the same place (think reinforcing the wave you're getting from the object). Instead it delays one of the the waves by 1/2 wavelength, so when the two are combined, they cancel each other out (at least in the center).

      So the light of the star is "nullified" while you can still measure the light coming from very close by.

      The technique has been demonstrated in the lab, but I don't believe it has been used in practice. It may be used in some astronomy satellites in the future.

      Doug
    • Alpha Centauri's distance is 1.3 parsecs. It means that a planet at one AU (Earth's distance from Sun) would be a bit less than one arc second from the star. That's well within the limits of VLT and most middle-sized (>2m) earth-based telescopes.

      The problem is that angular resolutions of telescopes are given for separating two objects of the same maginitude. A star is so damn bright compared to any orbiting planet (probably more than 1,000,000,000 times brighter) that, if the image is taken with an exposure time that would make the planet visible, the atmosphere will spread the star to many arc secs, even with the best adaptive and active optics. I think OWL would also have this problem.

      I don't know exactly why Hubble can't see such planets. Probably its angular resolution is still not good enough. Also, CCDs don't always behave nicely when they are grossly overexposed, as the CCD would be if there's a planet in one pixel and its star two pixels away.

      Btw, Alpha Centauri is a multiple star, and the close component stars probably can't have stable planets. Proxima Centauri (one of the components) is farther away from the others and might have planets (I guess).

    • when does a telescope that powerfull such that nearby stars aren't point sources anymore?

      I am not an astronomer, so take the following with a meteoroid the size of a grain of salt. Our own Sun has an apparent diameter of 30 arcmin at 1 AU. From Alpha Centauri, its apparent diameter would be about 0.006 arcsec. Neglecting the atmosphere, a 100m telescope could resolve a double star with apparent separation of 0.001 arcsec. Unfortunately the atmosphere rarely permits resolution better than 0.5 arcsec. Adaptive optics might improve it to 0.1 arcsec. Now if we use interferometry, e.g. with the twin 10m Keck telescopes, we can get synthetic resolution equivalent to a single mirror as wide as the separation between the two. I think the 100m telescope's biggest benefit is light-gathering power.

    • Some stars are already being images as non-point sources.

      The star Betelgeuse, which is the North-East bright red star in the familiar constellation Orion, is so large that it's atmosphere has been imaged.

      Betelgeuse - An outrageously big star imaged by Hubble [stsci.edu]

  • The article mentions that the current theoretical upper limit for one solid mirror would be about 140 meters in diameter.

    Do these maniacs have any appreciation for how much Windex and how many paper towels they're talking about?

    • That sounds like a crapload of eggs in one basket. Talk about a single point of damage, or earthquake related stresses, etc, causing millions and millions in damage.

      Precision mirrors are hugely expensive. For perspective, look at amatuer Dobsonian Scopes [starmastertelescopes.com] for instance. For $2895.00 you can get a nice 12" scope, about $2000+ of that pays for the mirror.

      Observatories with compound telescopes, with many "small" mirrors, probably make their owners sleep a lot better when they think about some telescope-tech shattering just one section by accident.

  • sweet... (Score:2, Informative)

    by crandall ( 472654 )
    More awesome pics from space... If anyone doesn't know about astronomy pic of the day over at nasa... I highly recommend you go looking through the archives. Some of the pics from hubble and others are so aweing. http://antwrp.gsfc.nasa.gov/apod/astropix.html

    • Re:sweet... (Score:3, Interesting)

      by Ubi_UK ( 451829 )
      For the same amount of money you can make awesome pictures of Africa without any national debts or children starving.
      Really, the costs going to these space projects is just insane. Where are our priorities?

  • Keanu says "Whoa!" (Score:2, Insightful)

    by jeko ( 179919 )
    When I read the title, I initially thought they would be talking about an array of smaller telescopes, taking data from a bunch of smaller mirrors and cobbling it together like the compound eye of an insect or something...

    Nope. Un uh, sorry, these bad boys are talking about one solid 100-meter MIRROR with a telescope assembly that would just fit under the Gateway Arch in St. Louis and stand almost 3/4 as tall.

    To put that in perspective, once the thing's built, you would have a good chance of seeing it on the horizon with your naked eye from 15-20 miles away (a rough guess, I know).

    You know that gargantuan telescope Marvin the Martian had in the Bugs Bunny cartoons? The OWL makes it look like a Cracker Jack prize.

    • Not quite solid, try made of hexagonal mirrors approx 2m across. It would be a huge pain in the ass to make a 100m diameter mirror, not to mention uneconomic. Thats why they plan to have it tiled. But all the tiles do make up the mirror for one large telescope. Cheers
  • Can't we just launch John Hill to the far side of the moon and see how big of a mirror he could cast up there? low grav, plenty of boron and silicone. He wouldn't even need the honey comb. With the honey comb he could probly lift and mount a hundred meter mirror by himself. Hell, that's what a block and tackle is for.

  • Nomenclature... crazy. (Score:3, Funny)

    by SouperMike ( 199023 ) on Saturday August 04, 2001 @05:39AM (#2141054)
    Everytime you read about the newest development in telecscope technology, it's given an outrageous name describing how large it is. I remember when the Very Large Telescope, or VLT, came about. Now we have OverWhelmingly Large? This is complete craziness. We've got Large, Very Large, OverWhelmingly Large, and the ultimate which will probably never be developed, My Penis!

  • My telescope is OverWhelmingly Large as well.
  • I think space based telescopes are better - put more money into space research! Why use alot of cash on ground based units when you know you can do it better in space where there's no atmosphear to block the sight?

    • Re:Why more ground based telescopes? (Score:5, Insightful)

      by Linguica ( 144978 ) on Saturday August 04, 2001 @05:05AM (#2155954)
      This very question was answered in the interview linked at the end of the article.

      What are the benefits of having an Earth-bound, optical telescope? Or rather, what can a larger optical telescope find better from Earth that we can't already find on other wavelengths and from other venues (i.e. The Hubble)?

      If there are no advantages here, is it more cost-effective, or what?

      Chris: What you should actually ask is what advantage does a space based telescope have over a ground based telescope? The only thing you gain from being in space for an optical telescope is better image quality due to lack of atmospheric turbulence. By for every other measure (maintenance, support, materials, etc.) being in space is much, much more expensive and limited. Which is why the Hubble and it's 2.4 meter primary cost a number of times more than the projected cost of of the 100 meter OWL. Recent advances in computer technology (adaptive and active optics) have greatly reduced the advantage that being in space provides at optical wavelengths. For some non-optical telescopes (x-ray, IR, gamma ray) there will always be an advantage to being in orbit.

  • This universe is millions upon billions of light years across, and all they can do with this piece of expensive equipment is watch owls?
  • .. either that they are looking for new planets, stars etc., or they are intent on making us look even smaller in the universe. ;)

  • Err... (Score:2, Interesting)

    by Scoria ( 264473 )
    You have to wonder what is on Michael's mind tonight with him posting stories about "overwhelmingly large" telescopes and "tech wars in meat space..."

    On a more serious note, why are we still building telescopes on Earth with the limitations we face on the ground? (Atmospheric distortion comes to mind... And I do understand they'll probably build this thing in a remote area to avoid the obvious: smog, city lights, etc. Still, though, there are some inherent limitations that they give a telescope like this by building it on and designing it for Earth.)

    It would seem much more logical to put this money toward a space based (a la Hubble, but much more advanced) telescope. (Yes, I know they're sometimes expensive and slow, but...) This way, it would seem, our returned photographs would be of optimal quality.

    Just a thought.

    • Re:Err... (Score:2, Informative)

      by at_18 ( 224304 )
      On a more serious note, why are we still building telescopes on Earth with the limitations we face on the ground? (Atmospheric distortion comes to mind... And I do understand they'll probably build this thing in a remote area to avoid the obvious: smog, city lights, etc. Still, though, there are some inherent limitations that they give a telescope like this by building it on and designing it for Earth.)

      Many ground-based telescopes are using "Adaptive Optics" systems, where an optic module tries to reverse the atmospheric distortion. They are already quite successful for very small fields-of-view, and a next generation of instruments are under development for bigger fields. The OWL would be practically useless without adaptive optics. I personally attended a talk by ESO's director, where he said that the success of the AO modules in the next years will be the deciding factor for the OWL.
      • I almost replied when I first posted that with, "I know how flawed my comment is, and I know that they're using different types of filtering and modules to reverse distortion."

        Too bad I didn't. D'oh!

    • Re:Err... (Score:2, Informative)

      by Marc Boucher ( 235490 )
      On a more serious note, why are we still building telescopes on Earth with the limitations we face on the ground? (Atmospheric distortion comes to mind... And I do understand they'll probably build this thing in a remote area to avoid the obvious: smog, city lights, etc. Still, though, there are some inherent limitations that they give a telescope like this by building it on and designing it for Earth.)

      I've recently seen a TV program about the building of the VLT. It showed the conception and the technical implications of the telescope. At one point they spoke of a device in charge of monitoring and correcting atmospheric optical aberrations, in real time.
      With this correction the telescope is providing hyper clear pictures of the sky.

      I've searched the ESO site and found a reference to this device on this page [eso.org] (scroll down to "Active Optics").

      Besides, given the limitation of the size of objects that can launched in space, a telescope based on earth, big enough and judiciously placed, and equiped with this device, will always achieve better results than a space's one.

    • Re:Err... (Score:5, Insightful)

      by bdeclerc ( 129522 ) on Saturday August 04, 2001 @05:50AM (#2141056) Homepage
      For the price of one small space telescope (HST mirror is only 2.4m in diameter) you can build the largest earth-based telescopes ten times over (the ESO VLT, 4 8m telescopes working as an array will, when fully operational in 2003-2004 have cost maybe 1/5 of what Hubble has cost until now). Furthermore, in visible light, earth-based telescopes are already producing images as sharp as, and even sharper than Hubble. At the time the HST was conceived, Adaptive Optics, which can eliminate most atmospheric turbulence, was still a US Military classified technology). The only short-term reasons for building space telescopes are: 1) observing in wavelengths absorbed by our atmosphere (like much of the IR and UV spectrum) 2) Getting spectra of earth-like planets surrounding other stars, this would require a space-based interferometer, because the earth probably isn't a sufficiently stable base to do this type of observations...
      • So how much would it cost to put it on the dark side of the moon?

        • Re:Err... (Score:2, Insightful)

          by deathcow ( 455995 )
          Super expensive, since the dark side of the moon is constantly rotating around the moon. You would need a railway system which was circum-lunar, and then you would drive the telescope around the moon every 28.xx days. During New Moons, the telescope would be facing Earth. There is no "dark" side of the moon that stays dark. There is a "far" side of the moon that never faces Earth, but it can no more be considered dark than any other part of the moon.

          • Re:Err... (Score:3, Insightful)

            by CheshireCatCO ( 185193 )
            I suspect "far" side was intended. The far side of the Moon would have many advantages as an observing site. No atmosphere to absorb light or to refract it and stability are the two biggest. Since there is no atmosphere, daytime observing isn't really a problem because there is not scatting of light and the sky is dark except when you look right at the Sun.

            On the other hand, it is far away relative to low Earth orbit. It is expensive to get there and, once there, manned missions to repair and upgrade it would be, at this time, out of the question. Hubble has benefitted massively from such upgrades, from the optics correction package to the replaced gyros and computer upgrade. You could do without them, but it's something to be considered.

    • I have thought that a really cool thing to do would be to put a mirror manufacturing facility in space. Launching a large mirror, or mirrors, is difficult. But launching raw materials would be much easier; and it could use unmanned rockets, for example. Then you could make truely huge mirrors, and make them (relatively) thin with none of the support structure needed for launch.

      Even more random speculation. The mirror facility could me near to but not neccesarily connected to the space station. It would be mostly automated, but someone from the space station could hop over on occasion for checkups and tweaks. Oh well, enough idle dreaming for now.

    • Re:Err... (Score:3, Informative)

      by mindpixel ( 154865 )

      Space based and ground based telescopes compliment each other. Right now, the Hubble's primary mission is that of a scout... it finds targets for the VLT (which I operate)... the Hubble's mirror is small and exposure times are limited by cosmic rays... the ground based VLT is much better at getting science data once the Hubble finds the target.

      The next space telescope will be the NGST (Next Generation Space Telescope) which will be about the size of a single VLT telescope (we have 4 here in Chile) and it again will act as a scout for the OWL.

      • Re:Err (Score:3, Informative)

        by magi ( 91730 )
        Space based and ground based telescopes compliment each other. Right now, the Hubble's primary mission is that of a scout...

        ;-) And for some reason, Hubble seems to get the 99% of the media time of all telescopes. Oh, and Arecibo. I don't read newspapers much (mostly just Excite and some local newspapers occasionally), but I've never seen an article about VLT in any news source. There probably are many, but compared to Hubble, they are quite rare. Well, I guess space is much sexier.

        One thing which I've been wondering about VLT is the usage of just digital imaging (FORS1, etc)...or at least I haven't noticed any VLT cameras using traditional film (correct me if I'm wrong). I know that CCDs are great for making photometric measurements because of their linearity, but their resolution is nothing compared to large photographic plates used in older cameras. For example, FORS1 is just 2048x2048.

        Well, ok, camera resolution might not be so important in most research, but I would imagine that doing the Palomar sky survey (hundreds of huge plates) with CCDs would be impossible (it would probably require trillions of pictures). ...And the best space poster pictures are still the ones taken with the Palomar 5m. ;-)

        So, how are surveys made now or in future, with CCDs or plates? Are surveys or other hi-res imaging still relevant?

        [I'm eagerly waiting for a job decision from ESO at Garching, should come next week. It would be great to get to mess up^H^H^H^H^H^H^Hdevelop the computer systems there. ;-)]

        • Future Surveys will be electronic (Score:4, Informative)

          by StupendousMan ( 69768 ) on Saturday August 04, 2001 @10:51AM (#2155929) Homepage
          Well, ok, camera resolution might not be so important in most research, but I would imagine that doing the Palomar sky survey (hundreds of huge plates) with CCDs would be impossible (it would probably require trillions of pictures).

          The Sloan Digital Sky Survey [sdss.org] is using CCDs to map one quarter of the entire sky, in five passbands. Its main camera uses a mosaic of 30 2048x2048 CCDs to cover an area about 2.5 degrees across (although there are gaps between the chips). Other mosaic cameras have even more pixels.

          Future ground-based surveys will use electronic detectors, not photographic plates. The increased sensitivity and linearity of electronic detectors, plus their inherent digital output, make them far superior to plates.

          • The Sloan Digital Sky Survey is using CCDs to map one quarter of the entire sky, in five passbands. Its main camera uses a mosaic of 30 2048x2048 CCDs to cover an area about 2.5 degrees across (although there are gaps between the chips).

            Ok, that sounds nice.

            There seems to be a Digitized Sky Survey [stsci.edu] project, which digitizes the Palomar and some other plates. They are scanned from 6.5x6.5 degree plates to 1.7 or 1.0 arc seconds per pixel. That makes about...23400x23400 pixels per plate, which is a lot less than I guessed (the plates are rather grainy after all), only 4.6 times more pixels than with the SDSS camera.

    • On a more serious note, why are we still building telescopes on Earth with the limitations we face on the ground? (Atmospheric distortion comes to mind... And I do understand they'll probably build this thing in a remote area to avoid the obvious: smog, city lights, etc. Still, though, there are some inherent limitations that they give a telescope like this by building it on and designing it for Earth.)


      It would seem much more logical to put this money toward a space based (a la Hubble, but much more advanced) telescope. (Yes, I know they're sometimes expensive and slow, but...) This way, it would seem, our returned photographs would be of optimal quality.
      All right. You have a flying 100 meter telescope. Ready for the problems? 1. 100 meters is the aperture. That means you've got a telescope that's going to be F^[/ing big. Let's say, oh, 500 meters long. (That's a guesstimate based on the scopes I saw at Yerkes, the observatory where Einstein is photographed in front of a huge telescope and was featured in the movie Chain Reaction.) That's a flying freight train bent on itself. And sizeable enough to cause eclipses and to be a threat to the planet (think meteor). 2. The weight of this thing is prohibitive to space travel. Yerkes' big telescope, a 36 incher (will confirm) is 6 tons. It's so large that it needs its own separate foundation. (And it has what's probably the world's largest elevator to let scientists view some different angles; it's the size of a basketball court.) 3. With a large enough aperture and a good location (think middle o' the desert in a ddesignated no-fly area), the atmospheric factors are reduced. What matters with telescopes is the size of the aperture. Larger aperture = more light collected = sharper images. (Example: Yerkes' big scope caught an image of Pluto below the plane of the solar system before the boys in Arizona found it. Why? It was the largest optical scope in the world.)
      • Larger aperture = more light collected = sharper images

        Minor quibble, perhaps only with the wording and not the intent: larger apeture means more light. It also means better resolution (sharper images). However, you can get the resolution effect without having a full-sized apeture. The VLA is the classic example: at full extention, it is something like a 20 mile-wide mirror as far as its resolution. But with 27 dishes doing the gathering rather than 1 big one, you don't get the same light gathering power. So increased resoltion does not always equate to increased light gathering power.

        For optical telescopes, resolution is not, typically, the reason for building them bigger as much as light gathering power (until adaptive optics started really kicking in, there was no point in getting better resolution in the telescope, since the atmosphere was setting the limit). If you wanted really good resolution in the optical, you would be best advised to use an interferometer, like the VLT. OWL, on the other hand, will have a staggering light gathering power.

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