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NASA Space

Proposed Space Telescope Uses Huge Opaque Disk To Surpass Hubble 126

Posted by timothy from the world-of-unlimited-resources dept.
Required Snark writes NASA has funded a study of a geo-sychrounous orbit telescope that uses a half-mile diameter opaque disk to provide images with 1000 times the resolution of the Hubble. It uses diffraction at the edge of the disk to focus light, resulting in a very high quality image. It's named the Aragoscope, after the scientist Francois Arago, who first noticed how a disk affects light waves. "When deployed the Aragoscope will consist of an opaque disk a half mile in diameter parked in geostationary orbit behind which is an orbiting telescope keeping station some tens to hundreds of miles behind that collects the light at the focal point and rectifies it into a high-resolution image. 'The opaque disk of the Aragoscope works in a similar way to a basic lens,' says CU-Boulder doctoral student and team member Anthony Harness. 'The light diffracted around the edge of the circular disk travels the same path length to the center and comes into focus as an image.' He added that, since image resolution increases with telescope diameter, being able to launch such a large, yet lightweight disk would allow astronomers to achieve higher-resolution images than with smaller, traditional space telescopes."
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Proposed Space Telescope Uses Huge Opaque Disk To Surpass Hubble More

Proposed Space Telescope Uses Huge Opaque Disk To Surpass Hubble

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  • Opposite of a pinhole camera (Score:3, Insightful)

    by Anonymous Coward on Tuesday January 27, 2015 @10:18AM (#48914097)

    Looks like the opposite of a pinhole camera

    • Looks like the opposite of a pinhole camera

      Dunno if you were joking or not, but that's exactly what it is. There are all sorts of principles of complementary apertures in optics; this one is perhaps the best known.

      Now, in general use you do have to play some games to eliminate background light (as opposed to a pinhole camera, where light from elsewhere is blocked out), but in (dare I say it) Spaaaaaaace!! it'll be easier to set up the phase blocking stuff at the camera itself.

  • AFFECTS (Score:5, Insightful)

    by Anonymous Coward on Tuesday January 27, 2015 @10:24AM (#48914145)

    Not "effects" you illiterate dumbshit!!!

    • It only effects it when it's in "geo-syncrounous" orbutt.

    • This was my immediate reaction to skimming the front-page blurb.

      Seriously, differentiation of "effect" and "affect" is neither a difficult nor novel concept. This just reflects editorial laziness, which does call into question in the mind of the audience the quality of information being conveyed.

      • Exactly!

      • Bless you. (Score:1)

        by Anonymous Coward

        The problem is that it wouldn't be steerable. It would sweep a slice of the sky rather than track a star

        • The problem is that it wouldn't be steerable. It would sweep a slice of the sky rather than track a star

          Why not? It's in space, not on Earth. It can be oriented in any direction and remain stationary for observations. The big issue with a disk that large is going to be solar wind.

          • Re: (Score:1)

            by Anonymous Coward

            The big issue with a disk that large is going to be solar wind.

            Solar wind is pretty weak, with a typical pressure around a couple nanopascals at Earth's orbit. For a half mile diameter disk, the total force on the disk would be on the order of 0.001 N. Thermal effects and light pressure will completely dwarf that.

          • That's what's so cool about this proposal. If it works, it will be hailed as a breakthrough in astronomy. If the solar wind blows it away, it will be hailed as a breakthrough in solar sail technology.

          • Re: (Score:2)

            by rtb61 ( 674572 )

            Space is not really empty we just sort of mostly empty. The bigger the satellite the bigger the target and probability becomes really problematic. Makes more sense to launch many smaller satellites that collectively can achieve the same output and although more expensive be far more durable, expandable and replaceable.

            • Re: (Score:2)

              by sjames ( 1099 )

              True, but the giant disk is just disk. A hit here or there won't degrade it much. The expensive precision part is much smaller.

              • Re: (Score:2)

                by rtb61 ( 674572 )

                True, but it sure will alter it's attitude and orbit. A distributed system can always do more and will always be more durable, it can point in more than one direction at once, when a major target is not the focus and of course find many more major targets of interest. Should the focus be in orbit or should the real global focus be a permanent moon base, a real achievement for humanity and the required step to really reach further out. We could do it easy if we just dropped the focus on murdering each other

          • Fortunately, the Lisa Pathfinder [esa.int] project has already developed ion engines that would be helpful against that. While they generate very minuscule thrust, unsuitable for space travel purposes, they have enormous specific impulse, meaning they can go on for years stabilizing given object against solar wind, gravitational influences and the likes. Several such engines attached to the disk would easily keep it stabilized against solar wind, and another couple on the telescope part would keep it aligned.

            Of cours

  • I can't see how that would work, there's only one geostationary track - and you only have to go a mile either side of it to be well out of sync (and no longer geostationary). The only way I can think of to keep relative station with a co-orbiting body is to lead or follow it in EXACTLY the same orbit. That would be a feat of orbital mechanics never before achieved. Even communication satellites have to carry propellant in order to correct their orbits periodically, and no two follow the exact same orbital t

    • They may be thinking of using one of the Lagrange points -- geostationary and stable. But, yeah, at least one component (I'd guess the small one) will need some sort of station-keeping propulsion. Ion drive with a big fuel tank?

      Actually, a half-mile disk would get some significant thrust from sunlight/solar wind. I don't know whether they could use that for station-keeping, or whether it would just be one more thing for them to fight.

    • Re:keeping station behind it? (Score:5, Interesting)

      by tibit ( 1762298 ) on Tuesday January 27, 2015 @10:34AM (#48914233)

      As crazy as it might sound, the GP-B mission has validated means of following a zero acceleration orbit with sub-micron precision [stanford.edu]. The precision achieved was that the residual acceleration was on the order of 1E-11 g. So yeah, we can definitely follow a zero-acceleration orbit with crazy precision!

      • Re: (Score:2)

        by ihtoit ( 3393327 )

        I remember that, it's what they used to plot the South Atlantic Anomaly and answer the question of what was causing HST to dip in its orbit every so often and why the ISS was being hit with unusually high plasma energies every time it passed over the same region. There were orbital anomalies, not least of which the SAO - which they were absolutely not expecting - and a glitch with the GPS system meant that the spacecraft apparently entered hyperspace (more than once) causing the onboard guidance and orienta

      • residual acceleration was on the order of 1E-11 g.

        The unit for acceleration is m/s. What does that mean? 1E-11 g on sea-level gravity?

        • Re:keeping station behind it? (Score:4, Informative)

          by PurpleAlien ( 797797 ) on Tuesday January 27, 2015 @12:25PM (#48915549) Homepage
          The unit for acceleration is m/s^2. In this case, 'g' is used as a unit to distinguish acceleration due to free-fall (gravitational) from general acceleration (and is usually measured with an accelerometer). The unit is defined as 1g == 9.80665m/s^2. This unit definition does not change with location - on the moon it is around 0.18g.

      • Re: (Score:2)

        by Rei ( 128717 )

        It makes sense. We can radiate individual photons for thrust if so desired. We can move individual electrons from one position in a spacecraft to another for tiny adjustments of angle and position if so desired. It seems you're going to be much more limited by your ability to precisely track your target than by your ability to make fine adjustments.

        I think a much bigger problem is going to be isolating standing waves from within the shielding material from distorting its perfect rim (with a shield that big

        • It makes sense. We can radiate individual photons for thrust if so desired.

          Well, you have to take the thrust from the black body radiation of your spaceship into count. This has the photon shot noise of sqrt(N) where N is the number of photons. So this will limit the accuracy of the trust, unless you can cool down the whole spaceship to absolute zero.

    • I too would like to know how to do this.

      I can think of a couple of ways that this could be done but none seems practical.

      Have both on the same orbital track, but then you are always pointing sideways.
      You could tether the two objects together, but I think that there have been issues with all of the experiments so far.
      A long time ago I read a theoretical paper that one could achieve a "geostationary orbit" with an active solar sail, but it has never been tried.

    • .... lead or follow it in EXACTLY the same orbit. That would be a feat of orbital mechanics never before achieved.

      The GRACE [nasa.gov] mission has been doing it for a few years now, tiny fluctuations in gravity can be inferred by the change in distance between the two probes. However it's not a geostationary orbit, just one probe following the other in low orbit. Personally I think it's a genius idea to turn the problem of keeping two probes in sync into a highly accurate gravity probe.

    • I would think the real engineers at NASA would have a clue how it would work. Why not ask them. Maybe you're just smarter than they are and they are just dumb as a sack of hammers?
    • It's a space-based telescope. They're not aiming it at the Earth, so it doesn't need to be geostationary. In fact, it doesn't even need to be in Earth orbit.

      • Re: (Score:2)

        by ihtoit ( 3393327 )

        taking into account orbital drift, it's easier to lock a geostationary position than it is to follow a satellite through potentially something like the South Atlantic Anomaly (which doesn't reach as far as GSO) and watch it drop 15 miles suddenly, only to pop up again 77 seconds later like a cork on the surf, then wait for its companion to do the same thing and HOPE it is still in precisely the same orbit.

  • Visible from Earth? (Score:3)

    by gstoddart ( 321705 ) on Tuesday January 27, 2015 @10:34AM (#48914231) Homepage

    So would a half mile opaque disk actually be visible from Earth in terms of blotting out stars behind it?

    Maybe not naked eye visible, but it seems like anything that big might have an observable effect.

    • That would be perfectly normal. Lots of small satellites are visible with the naked eye at just the right time of day. If they're still in the sunlight, and you're in the dark (dusk and dawn) you can see them.

      With this one being "geo-sychrounous" (probably geostationary) it would only be visible in certain locations.

    • Re:Visible from Earth? (Score:5, Informative)

      by RivenAleem ( 1590553 ) on Tuesday January 27, 2015 @11:02AM (#48914493)

      A disk 1/2 mile wide in geostationary would be the equivalent to a 1.4 inch disk a mile away (Geostationary orbit being 22,200 miles).

      So most definitely not naked eye visible.

      • Thanks ... sometimes these numbers cease to be anything you can relate to in any meaningful sense. :-P

      • The detector is not going to be on Earth. The detector is going to be "tens to hundreds of miles" from the disk.

      • There's a misconception going on here. Many satellites are "visible" in that they reflect a bunch of sunlight and we can see a bright point source.

        At the same time, these satellites are not resolvable with the naked eye, meaning you cannot observe and structure or shape.

      • why not put a 1.4 inch disk a mile up? so much cheaper!

    • We have satellites in orbit that are visible with the naked eye. The tend to be about the size of a school bus or smaller. School bus is 45 feet long. If you can see a 45 foot satellite as a point of light in the sky, this proposed telescope will be half mile diameter which is 58 times the length of a school bus.

      Yes, I do believe this thing would be visible with the naked eye.

      • Re: (Score:2)

        by ihtoit ( 3393327 )

        and several times further away.

        The ISS is shy of half a million kilogrammes and 108m on it's longest side. At an orbital height of ~430km it's visible to the naked eye, but only discernible to the naked eye for those with 20/20 visual acuity, since its angular diameter is at the limit (1 second of arc). For something at GSO to have the same angular diameter it would have to be 83 times larger (be 9km wide).

      • Those are in a close orbit about 100 - 400 miles this is a geostationary orbit at a distance of about 22,200 miles

    • Speaking of... how do they intend to control stray sunhlight reflecting off of this giant disk?

    • Re: (Score:2)

      by Rei ( 128717 )

      A sun-like star is about 1 1/2 million kilometers in diameter. To blot out all light from such a star that's 10 light years away, a 0,75 kilometer diameter disc could be no more than 1/200.000th of a light year, or around 50 million kilometers (1/3rd the distance between the earth and the sun).

      The brightest star in the sky is Sirius A. It has a diameter of 2,4 million km and a distance of 8.6 light years. This means your shade could be no more than 25 million kilometers away.

      The sun and the moon both take u

      • LOL ... you rock, that's cool ... a *very* localized, man made eclipse from an orbital body would be freakin' *awesome*.

        Hmmm ... Conversely, turn it around ... death ray! :-P

  • A half-mile diameter disk isn't going to be easy to rotate and point in different directions, and considerable motion by the light detector is also going to be required.

    Frankly, I think these disadvantages so severely reduce the utility of the telescope that I wouldn't want to deal with it.

    Not only that, but a half-mile diameter disk is one heck of a target for random space junk.

    --PM

    • Re: (Score:1)

      by Anonymous Coward

      Use a large radius ring.

      Block the light from the center with a smaller disk nearer the telescope. Or position your radio dish there.

    • Re: (Score:1)

      by Anonymous Coward

      Why do you need to point it?

      If it was really so incredibly powerful, wouldn't we - at our present stage of knowledge - learn an incredible amount just by pointing it in one direction? Its not as if we don't send a rover to Mars just because it can't be in more than one small area.

  • Use the moon as your disk, it's much bigger, and it's already there.

    • Re: (Score:2)

      by ihtoit ( 3393327 )

      interesting, the L1 Lagrange point is full of dust though, that might kill the optics very quickly.

    • But what would be the focal length?

    • You don't just want a circular object. You want a series of circular rings at the right intervals to interfere and give an intensity peak where the camera is. This s not as efficient as using a giant mirror, but it could be a lot lighter, and less sensitive to vibrations or distortions out of the plane of the disc. Saturn has a lot of rings. The shepherd satellites within the rings make some pretty complex patterns. It may be possible to use the natural structures. Or maybe we could add a few small moons o

  • This is fine in theory (Score:4, Interesting)

    by Solandri ( 704621 ) on Tuesday January 27, 2015 @11:12AM (#48914583)
    It's basically an interferometer [wikipedia.org] - the maximum separation of the telescope's mirror/lens is what gets you resolution. The surface area just makes dim objects brighter. Using a diffraction lens [canon-europe.com] is irrelevant to the interferometry - it's just a way of bending the incoming light.

    The catch is, the surface area of your lens needs to be aligned within a fraction of a wavelength of light for interferometry to work. It's been done on smaller optical telescopes and bigger radio telescopes (radio waves are much longer than light waves, so proper alignment is a lot easier). Getting the edges of a half mile diameter ring to remain within less than one wavelength of light from your sensor is going to be very difficult. There are methods to correct for differing distances. But I'd imagine rotating such a large annular scope would induce a lot of micro-vibrations (bigger than a wavelength) which may thwart such methods.
    • and we even have started to consider any small passing objects with trajectory intersecting the surface of the structure (PIx800^2 meters), and considering the probabilities of such impact, and the useful live of such a structure. Of course, the goal is to make 10,000 ( or x10) pictures or so, show it to the ignorant public and claim success, and let the structure it stay as garbage in space, this is different way of thinking.

    • Re: (Score:3)

      by ceoyoyo ( 59147 )

      I don't think it's an interferometer. It's a standard diffraction lens, just like the Canon one you linked, that produces a real image, not an interference pattern. You could stand at the focal point and see an image.

      It would be an interferometer if you put a ring of telescopes on the rim instead of at the focus.

    • It was my understanding that the Arago spot worked best with light of a single wavelength. Also, rather than the alignment of the surface area, it's the circularity that matters. And it's not the deviation from a circle WRT the wavelength, it's the deviation WRT to the circle itself. A larger circle can have a larger absolute roughness and still produce the Arago spot. I haven't studied optics in about 15 years, though, so maybe I'm wrong.

  • multiple edges? (Score:3)

    by DiniZuli ( 621956 ) on Tuesday January 27, 2015 @11:26AM (#48914753) Homepage
    I'm wondering if you could improve this by having multiple edges?
    I'm not a physicist, but does the disc have to be a disc? Would a very thin edge do the job of diffraction? If so, you could block out unwanted light that passes on the "wrong" inner side of the edges with a small disc in front of the telescope.
    Then you could have multiple thin edges next to each other and thus get multiple Arago spots [wikipedia.org]. Most of them would be a bit out of focus I guess, but that could probably be handled by software or using something like the lytro camera.
    Just a thought - though if it has to be a disc before the diffraction occurs, then it doesn't work.

  • Will "AOL" be painted on the disk in huge letters?

    • Re: (Score:2)

      by sl3xd ( 111641 )

      Sure, why not. At 22,000 miles away, the letters won't be visible (let alone legible) to most ground-based telescopes.

  • Especially with one party wanting to divert science to social programs and the other fearful of science or tightwad.
  • That disk had better be really black. I can imagine light coming up from the sun or earth or the moon giving a nasty background to the image one tries to obtain.Does anyone know how this works? Is the detector somehow focused on the edge of the disk?

  • Light gathering ability? (Score:1)

    by Anonymous Coward

    It seems like this would only collect light at the rim of the opaque disk -- perhaps this gives sharpness (like a pinhole camera), but wouldn't it have awful light gathering abilities, somewhat like having a really tiny aperture (also like a pinhole camera)? Are they planning to make up for this with extremely long exposure times?

  • http://www.edmundoptics.com/te... [edmundoptics.com] "Huge opaque disk" seems a lot more confusing then calling it a massive lightweight lens.

    • Re:why not call it what it is -- a fresnel lens (Score:4, Informative)

      by Anonymous Coward on Tuesday January 27, 2015 @02:12PM (#48916945)

      why not call it what it is -- a fresnel lens

      Because it is not a Fresnel lens, and doesn't even use refraction to focus the light. This is closer to a really simplified zone plate, which uses diffraction. Sometimes zone plates get called Fresnel zone plates because of some contributions he made there, but they are still different in construction and principle than a Fresnel lens.

  • A disk 1/5 mile with a sensor 10 to 100 miles away (precisely aligned on the axis of the disk) isn't going to be very steerable, especially if the distances from the EDGES of the disk to the sensor all have to match within a half-wavelength in order for the interferometry to work right.

    And wouldn't the changing relative positions of earth, moon, and sun cause disturbances in the disk? Is the solar wind sufficiently uniform over distances of 1/2 mile at earth orbit to not be a concern for causing non-unifor

    • Re: (Score:1)

      by Anonymous Coward

      If the sensor is slightly off the axis of the disk, it doesn't ruin the interferometer, it just images a point in the sky that is correspondingly slightly off the axis.

      • Thanks. That makes it more steerable (provided that the edges of the disk remain in a plane too.)

  • I cannot visualize this without the proper car analogy. Someone quick! Describe this using cars, Systemd, Hassleton, and women so I know which emotion to feel so I can respond accordingly.

    I am lost without the emotional trademarks of FUD andor cars!

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