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Space Science

Proposed Telescope Focuses Light Without Mirror Or Lens 165

Posted by Soulskill from the i-can-see-clearly-now dept.
A team of scientists from Observatoire Midi Pyrénées in Toulouse, France have been working with an unusual technique for focusing light. It takes advantage of diffraction - the bending of waves when they encounter an obstacle in their path - to focus light as it passes through a foil sheet with precise holes in it. The scientists suggest that an orbital 30-meter imager could resolve planets the size of Earth within 30 light-years. In addition, the foil is much lighter than traditional materials, and thus easier to transport. "A Fresnel imager with a sheet of a given size has vision just as sharp as a traditional telescope with a mirror of the same size, though it collects just 10% or so of the light. It can also observe in the ultraviolet and infrared, in addition to visible light. The imager can take very detailed images with high contrast, which is great for 'being able to see a very faint object in the close vicinity of a bright one.'"
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Proposed Telescope Focuses Light Without Mirror Or Lens More

Proposed Telescope Focuses Light Without Mirror Or Lens

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  • Great, but will it get build before I'm dead?
    • Yes, in the same sense that we will have practical fusion power in 10-20 years for the $BIGNUMBERth year in a row or that Duke Nukem is almost done.

      • Re: (Score:2)

        by Gerzel ( 240421 )
        No.

        Fusion power relies on theoretical advances and isn't really all that well known.

        Refraction of light has been around since before Newton and is very well known. The only major obstacle being the materials used in building one.

        • Re: (Score:3, Interesting)

          by TapeCutter ( 624760 )
          "The only major obstacle being the materials used in building one."

          I was under the impression that the main impediment to large refractors is the "halo" effect (coloured rings around the edge of the image), this was the problem Newton solved with the reflector and it is why Newtonian telescopes are the norm. The halo is unoticable with a small high-quality refractor (eg: binoculars) but the effect rapidly deteriorates the usefullness of refractors as the size increases.

          No mention of wether this design

          • Re: (Score:2, Insightful)

            by ArAgost ( 853804 )
            Chromatic aberration is usually (in everyday optics) caused by refraction. Of course, since IIRC different wavelenghts diffract differently, there will be some problem of this kind, but still it's a neat idea.

          • Re: (Score:2, Interesting)

            by Malekin ( 1079147 )
            Any aperture will cause diffraction. Reflector or refractor. The halos aren't visible in binoculars because they have magnification ratios too small.

            Reflectors are preferred over refractors because it's cheaper and easier to make a large mirror than it is to make a large set of refracting optics. A larger diameter aperture will result in less diffraction but the primary motivation for large diameter scopes (and thus the popularity of reflector designs) is that a large diameter is a large "light bucket".

          • Re: (Score:3, Informative)

            by hubie ( 108345 )

            The gravity probes, as far as I am aware, do not have precisely synchronized flight, but very good knowledge of where each of them are. The science is extracted by measuring the changes in the spacecraft separation (I think the relative distance is known at the tens or hundreds of microns). Flying a separated telescope requires measuring and controlling separations and rotations to a level much more demanding than the GRACE satellites. In principle it can be done now (such as in the lab), but in practice

            • Well, I have to say I've learnt a lot from that post. Kudos to you and the other replies for politely setting me straight. :)

    • It can also observe in the ultraviolet and infrared, in addition to visible light.
      ... and if you phone in the next 30 minutes, we'll throw in a free set of telescopic steak-knives, absolutely free. That's right folks, it slices, it dices, it focuses with razor sharp precision. Still not convinced, stay tuned and watch our chef Pierre demonstrate...
    • Give 'em a break.

      It'll take longer than a couple of weeks.

      Whoops. Sorry, you weren't supposed to know that.

  • Looks like a sail... (Score:5, Interesting)

    by sapphire wyvern ( 1153271 ) on Friday May 02, 2008 @01:18AM (#23271648)
    Hmm, a large flat surface with holes in it.

    It looks like launching one of these babies would require solutions to the same technical problems as solar sails, ie stowing & unfolding once in orbit.

    Would it be possible to have the sheet do double duty, acting as both a Fresnel "lens" and a means of propulsion for the spacecraft? That might be a neat way of getting the instruments to a good location.
    • Hmm, bad form to reply to my own post.

      I note that one objection raised in the article is that since the focal length of this thing is measured in kilometres, the instruments would have to be borne on a separate spacecraft to the focussing sheet, and that keeping the two aligned when changing the orientation of the instrument would require a lot of fuel.

      This seems like it would be a perfect use for the solar sail technique; hopefully it would allow you to keep the instrument craft on a pretty much ballistic
    • I think you are missing a big point here. We're not talking about a solid sheet like a sail, but rather, a sheet which is X% holes, and for which the exact geometric arrangement of the holes is critical for the physics to work. Looks to me like one has even started to think about how it can survive the stresses of being launched at multiple G's.
    • Wow, you might have just found a big problem with this idea. The telescope requires two space craft that have to be place very precisely. Light slowly pushes the spacecraft out of place, which means they have to burn fuel to get back in position, which makes things more expensive.
    • It sounds almost like a fresnel lens, but with parts being opaque. Wouldn't this cause diffraction patterns like in a double-slit experiment [wikipedia.org]? Wouldn't having this pattern everywhere screw up your image?

      • Re:Looks like a sail... (Score:4, Informative)

        by Agripa ( 139780 ) on Friday May 02, 2008 @09:29AM (#23274322)
        You can build ground based radio telescopes or satellite antennas using this technique. I have an old Radio Electronics with an article and plans for a greater than 4 foot refraction based satellite antenna using concentric strips of plywood with the focus behind the flat surface. The advantage lies in not having to form a curved three dimensional surface. The math is relatively straightforward.

        The difference with the space based proposal is using optical wavelengths instead of radio wavelengths so the edge spacing is much smaller.

  • ok... (Score:5, Insightful)

    by fyngyrz ( 762201 ) * on Friday May 02, 2008 @01:20AM (#23271656) Homepage Journal

    Make a sphere with a central axis. Place the fresnel lens on the surface of the sphere. Rotate the sphere about the center (where the focal point is.) No more formation flying, etc. Since you don't need any part of the sphere but the place where the fresnel lens is, just create a radius - lens at one end, focal point at the other end. Use a track to adjust the focal point distance from the foil. Rotate the entire assembly to re-point. No formation flying. Precision alignment all the time. Slow adjustment means good fuel economy.

    It seems to me that this is a great excuse for a foil-making plant in space. Imagine a veewwwwy large foil sheet. Then think of the available resolution. This is better than a dispersed array.

    Well, one can hope. :-)

    • Re: (Score:2)

      by Eivind ( 15695 )
      Except, offcourse that it's not all that trivial to create a "radius" with the fresnel-plate on one end and the camera-stuff on the other, and rotate the entire assembly quickly and accurately (to within less than a mm) when the radius is a dozen miles long. Indeed, unless the "radius" is a rod of unobtanium, flexing and bending is going to make it completely impractical.

      • Re: (Score:2)

        by fyngyrz ( 762201 ) *

        Quickly isn't really a problem from several points of view. First, make more than one. That increases the number of pointings. Second, just wait. :-)

        With regard to flexing, that's an engineering challenge, but not one that requires unobtanium. They've already said the idea is to put it where the gravity is lowest; to that, add something that *does* flex and it'll straighten itself out. This is ultra low-g space, remember -- there's no weather, air resistance, etc.

        With a system like this, "trivial" is

  • "anoptikon"

  • Problems (Score:4, Funny)

    by FearForWings ( 1189605 ) on Friday May 02, 2008 @01:26AM (#23271686)
    I think it would be clear to anyone who examines it, the idea clearly has some holes in it.

    • Re: (Score:2)

      by Whiteox ( 919863 )
      Not to mention all the additional ones caused by space debris, tiny meteors, even bigger meteors, alien spaceships and really, really big meteors.

    • Re: (Score:2)

      by skeeto ( 1138903 )
      Didn't they already put a satellite up without the optics? I believe it was called the Hubble something-or-other.

    • I'll say (Score:3, Funny)

      by thegnu ( 557446 )
      FTFS:

      The scientists suggest that an orbital 30-meter imager could resolve planets the size of Earth within 30 light-years.

      O RLY?! I suppose they haven't considered how unbearably LONG 30 light years is. I'm certainly not prepared to wait that long. Besides, we'll all be dead in 30 light years, what with the Hopi prophecy foretelling the end of time, and all.

      While I'm here, let me get this out of the way, save us some time:
      (joke) ------------->
      (you)----> O__O

  • I discovered that as a kid .. (Score:3, Informative)

    by Saffaya ( 702234 ) on Friday May 02, 2008 @01:28AM (#23271696)
    .. when I didn't have my glasses handy and still wanted to look at something in particular.

    I would form a small hole by curling my index then look through it for visual correction to my myopea.

    • Re: (Score:2)

      by evanbd ( 210358 )
      You discovered the pinhole camera, aka tiny aperture = increased depth of field. This is different -- they actually have a large imaging aperture and still keep good focus.

  • Not for amateurs... (Score:5, Interesting)

    by syousef ( 465911 ) on Friday May 02, 2008 @01:29AM (#23271702) Journal
    I was thinking hey neat till I read this in the article.

    For one thing, the light comes to a focus far away from the foil sheet - with distances measured in kilometres, which means the camera and other instruments have to be mounted on a separate spacecraft. The instrument spacecraft would have to stay precisely aligned with the foil sheet, to within a millimetre or so.

    Certainly not impossible, and still exciting, but this isn't going to be a mainstream or amateur tool any time soon.

    Looks like there also may be a related patent to get past...

    http://www.patentstorm.us/patents/6375326-claims.html [patentstorm.us]

    • Re: (Score:2)

      by jlowery ( 47102 )

      I was thinking hey neat till I read this in the article.
      Quit reading the articles!

    • Re: (Score:3, Insightful)

      by Overzeetop ( 214511 )
      This is also somewhat complicated by the actual performance of objects in orbit. A project I worked on had two satellites in LEO - one main sat with a laser ranger, and one passive "following" sat with a corner cube. By ranging the distance between the two, the earths gravitational field could be mapped very accurately. In other words, two satellites in the exact same orbit will vary in distance with one another constantly throughout an orbit based on the gravitational field. As the orbit precesses, the va

      • Re: (Score:3, Insightful)

        by Luyseyal ( 3154 )
        These large earth-finder telescopes are all being proposed for Lagrange points, not LEO. However, I do wonder how big the fudge factor is for being sufficiently close to the Lagrange. E.g., if these satellites are both +/- 15km with the actual point in the middle, will the shearing effects of gravity be too much for attitude correction for such a sensitive scope?

        Not an astronomer... yet.
        -l
        • long term it may also make a difference on which Lagrange point they use (stable or unstable), though they're using the unstable L1(?) for the solar observatory, aren't they?

          • Re: (Score:2)

            by Luyseyal ( 3154 )
            I thought all the earth-finders were being considered for the trailing-earth point (L5?)

            -l

    • Well, it would take a long time until amateurs could send things into space anyway.

      Also, aligning 2 satelites isn't easy even for professionals.

    • You can make diffraction gratings/screens that will focus at any distance you want. This is really old technology and not very complicated.

    • Re: (Score:2)

      by nasor ( 690345 )
      It's not really as bad as it sounds. A real implementation wouldn't use two separate spacecraft, it would simply have the lens connected to the camera with a really long, thin, light-weight scaffolding. The camera would be mounted with a system of precision motors and laser range finders that could adjust the exact position of the camera on its end of the scaffold. A scaffolding of three aluminum poles that were each 10 km long and 1 cm across would only mass something like 9 tons, which is easily within th
  • According to TFA the slotted lens would be much lighter but also MUCH MUCH larger than traditional setups. Also, the distance between the lens and the camera is so large that a second spacecraft is needed. Trying to maintain the alignment of two spacecraft would be difficult at best. Now consider that they would need to fire thrusters and move one of them every time they need to focus on a different object. How much fuel would be used up just looking at 10 different objects? I would expect a lot. Add to th
  • Has there been a severe rationing of mod-points recently?

    Perhaps the mod-point crisis is related to the credit-crisis?
    • Perhaps people are redeeming their mod-points for money.
    • Dunno, I've had two instance of "you have 10 mod points" in the last month or so but they vanished before I could use 'em. Kinda surprising since previously they were always in lots of 5 and not so close together.

  • This is crazy (Score:2, Interesting)

    by Plazmid ( 1132467 )
    So basically they're building A HUGE FRAKKIN' PINHOLE CAMERA. Frankly I find it strange that they would build a telescope that only collects 10% of the light, as this might present problems for planet finding. Not to mention that huge sheets of foil tend to crinkle and are susceptible to micro-meteoroids. But, if they could make it cheap enough, they could launch a bunch of them and do "brute force astronomy."

    • Re: (Score:3, Informative)

      by evanbd ( 210358 )

      10% of the light from a 30 meter telescope is the same amount of light as a regular 10 meter telescope. Hubble is a 2.4m telescope. I think it will have plenty of light.

      Foil doesn't have to crinkle. Look at the center of a mylar balloon -- not exactly crinkly. Obviously if you want telescope-grade not-crinkly you'll have to spend a bit more, but that's not really a problem. This is also a bit more sophisticated than a pinhole camera -- those have trouble collecting much light.

    • Heh. That's not even freaking close to "A HUGE FRAKKIN' PINHOLE CAMERA."

      It's actually closer to Fresnel lens [wikipedia.org], sorta. Well, not really, but just to get the idea started that you can use something very thin to the same effect as a bulky normal lens or telescope. This one actually a Fresnel zone plate [wikipedia.org] It uses light Interference [wikipedia.org] to act more like a lens, although it is really just a special pattern of lots and lots of pinholes.

      If you will, it's closer to the double-slit experiment [wikipedia.org] in light interference that sure

    • Re:This is crazy (Score:5, Informative)

      by Genda ( 560240 ) <mariet@nOspaM.got.net> on Friday May 02, 2008 @05:03AM (#23272462) Journal

      This is actually a really clever solution to a number of thorny problems. The first being, how do you get a really big telescope into space without breaking the bank??? Another being how do you get great contrast to show up faint sources?

      1. A) Not a Pinhole camera, It uses difraction caused by wave interaction through the holes of the lense.
      2. B) The lens has an aperture of 30 meters, with a surface area of over 700 Square meters. Even at 10% transmission, it would have more than 15 time the light gathering power of the Hubble, and more than 150 times the resolution.
      3. C) The best way to transport the lense would be to wrap the foil on a cylindrical spindle keeping it free of wrinkles, then having it unwound onto some kind of frame for mounting and stretching.
      4. D) It would have to be placed in some kind of protection housing to prevent damage from space debris.
      5. E) It would have to use some kind of laser/optical alignment system to get the lense and camera operating in conjunction. However this is not a big problem, long baseline interferometry in space would require much stricter positioning for constellations of satellites and such devices are already on the drawing boards.

      In short, this is a perfectly viable technology, and it poses a fascinating solution to a really challenging problem.

      Bravo!

  • more fun with diffraction (Score:3, Interesting)

    by heeeraldo ( 766428 ) on Friday May 02, 2008 @01:55AM (#23271846) Homepage Journal
    Canon has been using the same principle in a couple of lenses [canon.com] for some time now. The lenses themselves are pretty damn expensive but well regarded; I hope the telescope meets similar success.
    • In X-ray optics, we actually use bent crystals like silicon, germanium, diamond, graphite or multilayer to focus X-ray by diffraction for maybe 50 years. A short paper on the multilayer for X-ray optics I found at Argonne national lab is available at here (PDF) [anl.gov].
      • Yeah, this isn't new science. It's a new engineering of that science into equipment, though, and that's cool.

        Which beamline do you use at Argonne?
        • I was there for the national school on scattering and got some beam time at BRSC. I run a rotating anode in my lab. How is IPNS doing?
  • In the first 8 years of the 21st century I have witnessed an almost feverish acceleration of astronomer attention on the discovery of "exoplanets" [exoplanets.org] - planets around stars other than our own Sun. Already some solar systems very similar to our own have been discovered and some tentative measurements of the atmospheric content of these planets is underway. I believe it is only a matter of months or years before an oxygen-rich "earth-like" planet is discovered. Prognosticator of prognosticators that I am, I'll e

    • Re: (Score:2)

      by Ihlosi ( 895663 )
      Some serious questions would need to be directed towards the SETI program.. as it seems highly unlikely that a modern society could exist without emanating some signals that SETI should have picked up.



      Right now, SETI isn't really looking for "random" signals. It's looking for signals deliberately sent our way, with plenty of power. So it wouldn't really be surprising if they're not picking up TV signals from Alpha Centauri.

    • Re: (Score:2)

      by TheLink ( 130905 )
      What they should actually do is start building those spinning space stations that people can actually live on long term without "wasting away" due to weightlessness or getting radiation sickness.

      Once you can do that, then you can send people to Mars or the asteroid belt. People are no longer stuck on earth - they can feasibly live in space.

      Then people can build telescopes in space if they want - even if it takes a while - the sun and asteroids will be around for quite some time still.

      As it is, I think we're
    • The life question is easy. James Lovelock demonstrated that planets devoid of life will have a composition totally distinct from any planet bearing life. You do not need to know what the life is, the chemistry, the complexity, etc. You need only look at the stability of the system. Stable systems have no life. Unstable systems do. Indeed, he demonstrated by means of the Daisyworld hypothesis that in order for a system containing life to remain containing life, the life on it must alter the system so as to p
    • Yes, it's probably because of George W. Bush... ...probably just about the only way to get away from him.

    • Re: (Score:2)

      by Kelson ( 129150 ) *
      I recently read a science-fiction novel, Rollback by Robert J. Sawyer. Most of the book is about the social impact of rejuvenation technology, but the setup involves SETI, 4 decades after the first alien signal was received, decoded, responded to... and largely forgotten until the aliens' response arrives.
  • This isn't a pinhole camera - it's a giant diffraction grating that acts as a lens. What I can't figure out is how they're going to keep the "lens" accurate; very small bumps / wrinkles in the foil would disrupt the operation of the lens, so it'd have to be kept flat (or curved to a specific radius) constantly. That's going to be very difficult to do.

    This looks good on the drawing board but making a real-world example is going to require some very fancy engineering. Building larger scale structures in spac

    • >>so it'd have to be kept flat (or curved to a specific radius) constantly. That's going to be very difficult to do.

      Just off the top of my head, I'll bet that spinning it would keep it flat. I wonder if rotating the grating would affect the picture.

      -b
  • From the article: "It does not require a large primary mirror or lens, though it does use a smaller secondary mirror and lens."

    So it *DOES* use a LENS AND MIRROR to focus light. Honestly, when will journalists, and scientists, stop making claims that are obviously NOT true?!?

    • Re: (Score:2)

      by Dirtside ( 91468 )

      Honestly, when will journalists, and scientists, stop making claims that are obviously NOT true?!?
      Probably about the same time that humans in general stop doing so? Don't take this the wrong way, but are you new here, and by "here" I mean "among humans"? :)

  • Only advantage is the light weight (Score:3, Interesting)

    by helioquake ( 841463 ) on Friday May 02, 2008 @04:30AM (#23272404) Journal
    The article makes it sound like only a 30-meter "Fresnel" optics can allow to resolve an earth-size object within 30 light-years.

    The fact is that any conventional 30-meter telescope can resolve an earth-size object within 30 light-years (circa 6000Angstrom in wavelength). Spatial resolution can be determined by the ratio of wavelength to diameter of the optics:

        6000A / 30m ~ 2e-8 radian ~ 0.004 arcsec.

    So a 30m telescope can resolve an object in angular size of 0.004arcsec at 6000Angstrom.

    At the distance of 30 light-years, the earth-size object looks like

        6400km / 30lyr ~ 2e-8 radian ~ 0.004 arcsec.

    So that's that. This telescope doesn't give us any special resolving power per optics size. So the advantage is merely its light weight.

    Since the precise alignment of holes is required for this optics to work, I can see why this project got kicked out by ESA. It's probably too premature to attempt in deploying this kind of precision engineering in space today.
  • They're already widely used down here on Earth.
    • The article is about Fresnel zone plates [wikipedia.org], which are quite different from lenses. You can use any opaque material to make a FZP, whereas a lens must be made of transparent material.

      • Re: (Score:2)

        by solitas ( 916005 )
        A bunch of years ago I read an article (Popular Communications?) by a guy who was cutting zone plates out of foil-covered plywood at the proper specs to focus geosynchronous TV-satellites (C-band?) onto an LNA.

        He'd presented all the necessary math (pretty straightforward) and while I don't remember the performance specs I remember being pretty impressed how one of his plates fared (performance vs. cost) against a comparably-sized mesh-dish with all its mountings and hardware.

        I wasn't into sat-TV at the time

  • Why settle for a piddling 30 meters? Saturn's rings have a certain zone-plate like flavour to them. With a few artificial shepherd moons to tweak the periodic intervals, weought to get some sort of an interference pattern. The focal length will be huge so the rings don't have to be flat...

    Actually, this is pretty silly, but it might be possible to make a partially self-assembling zone plate out of a massive central body and a carefully seeded orbiting cloud of black dust, edge-on to the sun. You might be

  • make the foil into a parabolic shape to reflect light to a camera instead of cutting holes in it to defract light to a camera much further away?
  • IT occurs to me that is the focal length is THAT long we could put these very large systems in space and have a smaller GROUND based detector.

    Simply put the thing in GEO orbit and point it at a receiving station. This will dramatically increase the "lense" size.

    Of course you will get some interference from the atmosphere but this can be activly compensated.
  • the reason people build huge, $$ mirrors is to collect more photons - there just ain't a lot of photons from things a gazillion (or so) lightyears away.
    So, you really want to maximize the number of photons you collect; one way to do this is larger surface area (in a conventional mirror)
    I think (but don't know) that # photons scales with radius ^2
    If the fresnel thingy is 10% efficient that would appear to be a problem
  • Here we are with all this technology and we're studying the galaxy with nothing more than a glorified pinhole camera [wikipedia.org].
  • -You could spin the foil to keep it stretched. Might need some extra weight attached to the edges. This would make it difficult to steer.

    -The holes will probably cause some distortions in the surface from uneven distribution of stress. Maybe it would be better to replace holes with clear patches of film, just selectively deposit the silver film in some areas only. You would lose some portions of the spectrum based on what your film was not transparent to.

    -The focus problem is maybe the largest. I wonde

  • The chromatic aberration would be horrible (Score:3, Informative)

    by exp(pi*sqrt(163)) ( 613870 ) on Friday May 02, 2008 @01:41PM (#23277980) Journal
    The focusing of diffraction gratings is heavily wavelength dependent. The article makes it sound easy to shove in an extra Fresnel lens, but it's not that easy. Maybe it'd be better to use this only as a narrow band imager using suitable filters.

    Overall, I like this idea a lot.

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