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Space Science

Rotating Mercury Lunar Observatory 50

Posted by michael from the why-are-thermometers-suddenly-expensive dept.
Fraser Cain writes "Universe Today is reporting on a proposal under consideration by NASA from Dr. Robert Angel at the University of Arizona. He wants to build a 100-meter liquid mirror telescope into a crater on the Moon. It would only be able to look at a specific spot in the sky, but the view would bury Hubble's Deep Field Survey." The challenges of off-Earth construction are left as an exercise for the reader.
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Rotating Mercury Lunar Observatory More

Rotating Mercury Lunar Observatory

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  • Lake Erie? (Score:2, Funny)

    by Anonymous Coward
    Is it true that they are saving money by using Lake Erie as the mercury source?

  • Finally, this quote actually applies (Score:3, Funny)

    by Joe the Lesser ( 533425 ) on Friday January 28, 2005 @05:38PM (#11509105) Homepage Journal
    That's no moon...
  • Even if they could keep it clean during construction, how would they keep it from getting contaminated with lighter-than-mercury space dust over time?
    • It's easy, they just blow it off once in a while.

      OK.. just kidding. But really, there's no air to carry the dust either, so I can't imagine that anything short of a near-miss meteor is going to spread much around.
      • Yea, you are a joker.

        Moon is a very very dusty place and even worse, the dust is abrasive. Have you seen the pictures taken on moon landings? I have a very nice coffee-table book called "Full Moon" and it has some wonderful pictures of LM, inside. The astronauts look like coal miners, all black and dirty. The moon pictures look like it's all gray and white there but its albedo is actually very low and moon is quite a dark place, with lots of black, sticky and abrasive dust.

    • Even if they could keep it clean during construction, how would they keep it from getting contaminated with lighter-than-mercury space dust over time?

      The moon's atmosphere is basically hard vacuum. Sure, there are a few air molecules here and there, but certainly nothing that could lift and transport dust particles.

      So, short of nearby meteorite impacts kicking up dust and micrometeorites falling to the surface, there really isn't any way for dust to get on the mirror in the first place. And keep in min
    • The dust would tend to float on the mercury. They could just occasionally filter the mercury to clean it up. They'd probably have to stop observing while they did this though- it's bound to create ripples on the surface.
    • In addition to the large shield shown in the image, I would think that the dust particles would have some small amount of centripetal force acting on them, pulling them to the outside of the mirror.

      These mirrors work by spinning a pan of mercury. The force on the fluid is a function of its distance from the spin axis. The shape formed is a parabola, which is just what you would want for a telescope (collimated ray bundles formed into a point). If you put annular shield say 5 inches from the edge, then

      • I would think that the dust particles would have some small amount of centripetal force acting on them, pulling them to the outside of the mirror.

        However, the combined acceleration (of the gravity and rotation) on the mercury is the same as that of the dust, but the mercury forms a perpendicular surface to that force. So the mercury's curved surface supports the dust in place and the dust doesn't get thrown out to the rim as you might expect.

        Another way of looking at the same thing is that the surface o

  • Great idea (Score:5, Interesting)

    by mnmn ( 145599 ) on Friday January 28, 2005 @05:57PM (#11509292) Homepage
    I used to imagine a telescope of a pan filled with mercury, spinning, and attached to the lens assembly via rods on top, and the whole device turning to create gravity for the mercury so it stays in the pan, while the whole telescope like a lighthouse scans the skies.

    The moon will allow greater sized assemblies, and gravity doesnt have to be induced. The problem is the lack of control, which can be offset by building multiple telescopes at various lattitudes.

    So whats difficult? A large container which can carry mercury, even a large plastic bag in a satellite dish mesh can do. The structure will sit on a motor that spins. The motor will not induce any vibrations into the mercury pan, for the former telescope I had a magnetic levitation rotation device, or at least a string that dangles the pan while magnets rotate it. The magnets cannot be in two D structures like regular motors since thats vibration there, so a uniform magnetic field is applied while current is passed between the center of the pan and its sides to allow for a continuous DC motor. If the current can be passed with no contacts, we can achieve real smooth rotations and no frictions or vibrations... again magnetic levitation would be a great idea here since the moon can be cold enough for ceramic superconductors, and clear enough for solar panels to power the thing.

    The smaller we make the mercury pan, the more vibration prone it gets as we increase the resolution, so we can expect moon earthquakes to be a problem whenever something hits the surface. Shouldnt be frequent enough to cause a problem...

    Unlike Hubble, the structure should be radiation-hardened, low-maintenance, no mechanical parts, no chemical reserves object, except for the mercury container. If spun fast enough, the container can reflect light from greated angles removing the problem of lack of control.

    • Re:Great idea (Score:3, Informative)

      by CanSpice ( 300894 )

      I used to imagine a telescope of a pan filled with mercury, spinning, and attached to the lens assembly via rods on top, and the whole device turning to create gravity for the mercury so it stays in the pan, while the whole telescope like a lighthouse scans the skies.

      You mean something like this? [astro.ubc.ca]

      Sure, the LZT can only look straight up, but liquid mirror telescopes are being done, and done fairly well.

    • I used to imagine a telescope of a pan filled with mercury, spinning, and attached to the lens assembly via rods on top, and the whole device turning to create gravity for the mercury so it stays in the pan, while the whole telescope like a lighthouse scans the skies.

      Two problems with that: 1. You don't want it to scan the skies. You want it to look at one spot for a long time. 2. Your spinning arrangement wouldn't create a perfect paraboloid surface, so there would be aberration.

      • Two solutions to that: stacking of pictures and DSP.

        By using stacking even a crappy webcam can generate pretty astronomical pictures of many celestial objects with a rather small (4-8 inch) terrestrial telescopes. DSP can handle (upto a degree) the surface aberrations. It wouldn't be perfect but might work. On the other hand, I don't think spinning it longtitutally is a good idea. Actually I think it's a bloody stupid idea. The framerate necessary would be enormous, reducing the quality of the images.

        • I'm out of my feild here, but I'm pretty sure DSP can't make up for aberration. Aberration causes images to go out of focus, which is equivalent to a low-pass filter on the image, which means fine detail information is lost, and no amount of DSP can put it back in.

  • Difficult to send to space (Score:4, Insightful)

    by reverseengineer ( 580922 ) on Friday January 28, 2005 @06:21PM (#11509448)
    This is a neat idea, but liquid mercury has a density of 13593 kilograms/cubic meter. The article does not mention how deep the pool of mercury would be, but even if the mercury is only 1 cm deep, my back of the envelope calculations for a 100m mirror (which treat the mirror as a cylinder with radius 50m and height 1cm) would require 1068 metric tons of mercury.

    First off, this far outstrips our present launch capability. Second, we would require a much more reliable method of sending things into space before we decided to send up a significant amount of liquid mercury, given that a failed launch of a rocket carrying a large tank of mercury would be a major ecological disaster. It's a great idea in theory- pouring a bunch of liquid into a bowl would be certainly preferable to the tremendous amount of skill and effort required to properly build and polish large telescope mirrors- but I'm not sure how long it would be before this idea becomes even remotely practical.

    • Towards the bottom of the article they mention that Mercury would not be a viable option ont he moon anyway, due to its becoming close to solid at the super cold temperatures at which they are planning on working. They are trying to figure a way to use some of the lighter hydrocarbons which are found in liquid form a la Titan. I don't know if any of this exist ont he moon already or not, but they would certainly be lighter to ship up if required. That plus the initial telescope plan calls for a 2m since
    • The article mentions that, since the telescope would ideally be kept at temperatures near absolute zero, mercury would not be used at all. Instead, far lighter hydrocarbons (e.g. ethane or methane) that exist as liquids at those temperatures with light metals (e.g. aluminum) would most likely be used.
    • The depth of mercury used in LMTs is usually 0.5-1mm (reference [ulg.ac.be]), so it's more like 50-100 tonnes.

      As others have pointed out below, mercury doesn't work anyway, and the liquids they're looking at are much lighter. Of course, if you're not using mercury, you need to find a way of aluminizing the surface of the liquid, so you still need to get some metal up there. But aluminum is light, and you only need a thickness of about 0.1 microns.

      [TMB]

    • RFTA (Score:2)

      by p3d0 ( 42270 )
      They're not using mercury.

  • Frozen Mercury (Score:2, Insightful)

    by Anonymous Coward
    Has any one though of starting with a spinning liquid mecury mirror, letting it freeze, and then using it as a conventional telescope mirror. You could even remelt and respin it should it become contaminated. More complicated yes, but also more useful....

    • Re:Frozen Mercury (Score:3, Informative)

      by Quelain ( 256623 )
      If it changes density on 'freezing' that will cause distortions, probably bad enough that the surface is no longer very reflective. I tried it with wax once, and the main problem was that the edges froze first, which caused ripples in the rest of the surface.

      There's also a not-very-toxic alternative to mercury for anyone who wants to try building a small LMT; Gallium/Indium/Tin alloys which are liquid at room temp.

      http://www.scitoys.com/scitoys/scitoys/thermo/liq u id_metal/liquid_metal.html [scitoys.com]
      • The trick to doing it with wax is to hold the entire sample at the freezing point and let it cool slowly enough that the thermal energy has time to move through the system and be very nearly equal when those last few calories of heat are removed and the phase change occurs. You want the phase change to be a smooth continuous travelling wave. The barrier to that is that solids have different heat conductivities than liquids, when you try to remove too much heat at once, you remove from a continuous area, t

  • As long as we're suspending disbelief when it comes to building the damn thing, why not pick a bigger crater? C'mon, guys, think big...

    How about Tycho? Just think of the view with an 85,000 meter mirror. Or maybe a field of smaller craters in the neighborhood of Tycho...we could call it the Tycho Massive Array #1, or TMA-1 for short. Yeah, thats the ticket...

    • How about Tycho? Just think of the view with an 85,000 meter mirror.

      Part of the idea with a polar crater is to protect the instrument from temperature variations, something you would get a lot of on a monthly basis with a mirror anywhere else on the Moon. Tycho sits in sunlight for two weeks, then in darkness for two weeks. That's not a stable environment.

      Also, a telescope made with a liquid mirror can be aimed in one direction only, towards zenith. Even the slow, monthly rotation of the Moon wouldn't a

    • If NASA is considering far-out proposals like this mecury telescope. why don't we all send in our own ideas for technologies that are totally infeasible currently. I'd rather NASA spent money researching Star Trek style transporters than this telescope. The level of practicality and feasibility are about the same.
    • RTFA 100M is somthing imagined as a future goal. They want to start with 2 meters.
    • For that matter, why don't we just put it on Mars and use the entire Hellas Planitia crater? Imagine what kind of image we'd get with a 2,000,000 meter reflector. We could call it the Helluva Telescope!
  • With all the com sattelites and GPS sattelites we're sending up, why not just get them to attach small telescopes or somthing similar and build a sattelite array the size of earth's orbit?

    I'm sure there are parts of the rotation of some sattelites when these things are operating far under capacity. Is there some way to use that 'down time' to construct an array, or is it too problematic to turn the things to look in the opposite direction?
    • They don't do that for the same reason they don't operate telescopes hundreds of miles apart on Earth as arrays.
    • What you are referring to is known as interferometer-telescopes. They don't take pretty pictures but can do lots of other interesting science.

      The trouble is the timing mechanism sensitivity. Larger the wavelength is, better chance you have syncronyzing two separate data streams. With radio waves this is no problem with today's technology. With light waves we only managed to achive it in the last couple of years. The timing problem means you have to use a very sensitive and complicated optical system to merg

  • The limitation of a liquid mirror is that it only points straight up, so it's not like a standard telescope that can be pointed in any direction and track objects in the sky. It only looks at the area of sky that is directly overhead.

    Also, LMTs don't need expensive mounts, supports, tracking systems, or a dome.

    But if those mounts, supports, and tracking system were added either to the initial design or as an upgrade later then the telescope could be aimed. If you refer to this diagram [gtc.iac.es] you can understan

    • Nah, the way I'd do it is to give the telescope legs. Then you just make the telescope walk to the spot on the moon facing the region of space you want to look at.
    • 300 Standard scopes floating in a hexagonal pattern mounted by cables to the lake floor.Using super computers to syncronize and adjust for distortions.Plus 50 fulltime scientists and 70 illegal laborers woking fulltime cleaning and mixing cocktails(slaves)would be less expensive and more fun than even building a outhouse on the moon.We need to focus more attention on amanda projects also. I am a retard most of the time.
  • We should obviously build it on Mercury.

    -
  • How about changing the process of creating optics ?

    So far the only viable way has been reduction... IE shape glass add metal, polish metal etc... However with the new advances in ink jet manufacturing how about building optics piece meal by construction rather than reduction?

    • You need to catch up on mirror manufacturing technology. Large mirrors are cast in a rough parabolic shape in a spinning oven, then finish shaped/polished (which doesn't remove a lot of material), then coated with aluminum and usually some protective overcoating.

      The aluminum coating is very thin - it is not possible to polish the coating (nor is it necessary).

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