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Deformable Liquid Mirrors For Adaptive Optics

timothy posted more than 4 years ago | from the mirror-mirror-on-the-magnet dept.

Math 196

eldavojohn writes "Want to make a great concave mirror for your telescope? Put a drop of mercury in a bowl and spin the bowl. The mercury will spread out to a concave reflective surface smoother than anything we can make with plain old glass right now. The key problem in this situation is that the bowl will always have to point straight up. MIT's Technology Review is analyzing a team's success in combating problems with bringing liquid mirrors into the practical applications of astronomy. To fight the gravity requirement, the team used a ferromagnetic liquid coated with a metal-like film and very strong magnetic fields to distort the surface of that liquid as they needed. But this introduces new non-linear problems of control when trying to sync up several of these mirrors similar to how traditional glass telescopes use multiple hexagonal mirrors mounted on actuators. The team has fought past so many of these problems plaguing liquid mirrors that they produced a proof of concept liquid mirror just five centimeters across with 91 actuators cycling at one kilohertz and the ability to linearize the response of the liquid. And with that, liquid mirrors take a giant leap closer to practicality."

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dumb question... (3, Insightful)

girlintraining (1395911) | more than 4 years ago | (#32606864)

Why not just spin it, and while it's spinning, lower the ambient temperature so that it freezes? And if you remember your thermodynamics, you'll remember that raising or lowering *pressure* raises or lowers the temperature of a gas -- seal it up, spin it, then freeze it. Easy peasy.

Re:dumb question... (0)

Anonymous Coward | more than 4 years ago | (#32606896)

That was my first though too. I feel like it was probably a common first thought, but it would have been nice if they had addressed why that doesn't work - at least - I hope it isn't that easy and they completely overlooked the simple, obvious solution >

Re:dumb question... (3, Insightful)

DarkKnightRadick (268025) | more than 4 years ago | (#32606918)

Some liquids possibly lose the reflectivity as a solid that they had as a liquid.

Re:dumb question... (0)

Anonymous Coward | more than 4 years ago | (#32607022)

Probably, or it would have been done before. I'm not sure what frozen mercury is like. But after freezing, perhaps coat it with something that is reflective, or add some kind of impurity to the liquid metal that would inhibit the formation of surface roughness as it solidifies.

I expect that must be rather challenging for all sorts of reasons too, or it would already have been done.

Re:dumb question... (1)

Jenming (37265) | more than 4 years ago | (#32607522)

It doesn't have to be mercury (they are not currently using mercury). So if you pick something that is reflective as a solid, melt it, spin it, freeze it. Though it is possible that the freezing process would distort it.

Re:dumb question... (2, Insightful)

Quartinus (1678656) | more than 4 years ago | (#32607674)

That is how they make glass mirrors. I believe the purpose of making liquid mirrors is not only to get a good reflective surface, but to also use Adaptive Optics (nearly infinite possibilities for reflective surfaces, so it would be really easy to correct for atmospheric anomalies). So, a frozen mirror (e.g. a glass mirror) would not work nearly as well as a liquid mirror for this.

Re:dumb question... (1)

postbigbang (761081) | more than 4 years ago | (#32607780)

And maybe a fresnel lens would do the job.... seems to perhaps cure several of the ills cited.

Re:dumb question... (1)

gninnor (792931) | more than 4 years ago | (#32606974)

My guess, changes in temperature causes changes in density, the frozen stuff will sink and cause deformation.

Re:dumb question... (1, Insightful)

scorp1us (235526) | more than 4 years ago | (#32607448)

Usually frozen stuff floats, in comparison to its liquid state. (Apples, churches, very small rocks.)

Most things (water, metals) are polarized and will create a crystal lattice when cooled. The slower the cool, the bigger the crystals. This is what makes the "temper" of metals - the size of the crystals. When you crystallize anything, the atoms become locked and pulled into a lattice. This then roughs up the surface and destroys the reflection. By having mobile molecules or atoms, you allow a very fine, uniform surface needed for reflection.

The reason why it floats is because with the lattice mesh, it creates voids, which lowers the density.

Re:dumb question... (4, Informative)

clone53421 (1310749) | more than 4 years ago | (#32607506)

Usually frozen stuff floats, in comparison to its liquid state. (Apples, churches, very small rocks.)

False. Water is one of the rare exceptions. Usually frozen stuff sinks in comparison to its liquid state.

Mong (1)

Hognoxious (631665) | more than 4 years ago | (#32607544)

Usually frozen stuff floats, in comparison to its liquid state.

I'm sure several other people have replied already - and they're not laughing with you.

Re:dumb question... (3, Interesting)

fotbr (855184) | more than 4 years ago | (#32606976)

Freezing liquids changes their density. In a spinning environment, that causes movement, and there goes your perfectly uniform surface.

Re:dumb question... (4, Informative)

Bigjeff5 (1143585) | more than 4 years ago | (#32606990)

Mercury changes color as it solidifies, from silvery white (highly reflective) to tin white (not nearly as reflective).

In other words, if you freeze it it's not a good mirror any more, and then what's the point?

That's not even considering the serious difficulty in getting a spinning liquid to freeze uniformly.

Re:dumb question... (2, Insightful)

Moblaster (521614) | more than 4 years ago | (#32606994)

Probably because it would be almost impossible to assure a complete uniform freeze -- you have all kinds of complicated temperature and phase transitions between the underlying bowl material, the ferromagnetic fluid and the reflective film/fluid. The stuff would inevitably crystallize and distort in patches, creating a mess of a surface.

Re:dumb question... (1)

mea37 (1201159) | more than 4 years ago | (#32607004)

I guess I'm not seeing how the relationship between temperature and pressure in a gas is to be applied to liquid mirrors.

In any case, I think there are likely to be problems with freezing the mirror. Do most metals naturally freeze to a polished surface? Might the shape deform significantly during the freezing process, so that even if it remains "shiny" enough it still doesn't suit the application? Won't the act of spinning the liquid interfere with the process of freezing it?

Re:dumb question... (0)

Anonymous Coward | more than 4 years ago | (#32607266)

Don't you see? the top surface of the mercury pool is in contact with a gas at some temperature. Now as we evacuate that gas, the low-pressure gas remaining will get colder and colder. Eventually, the gas will be below the freezing point of mercury.

Of course, the rarefied gas will have neither the thermal conductivity nor the thermal mass to appreciably cool the mercury, but that was apparently the plan.

Re:dumb question... (2, Interesting)

PDX (412820) | more than 4 years ago | (#32607986)

What if we used natural gas deposition to produce a layer of diamond a few mm thick then use an atom thick silver layer. Apollo Corp did patent the gas to diamond layering technique. On a side note the Australians came up with a way to produce low grade diamonds by microwaving car exhaust. If we nuke liquid mercury it will boil and froth :-( How warm do polymers have to be to solidify?

Re:dumb question... (4, Funny)

Grishnakh (216268) | more than 4 years ago | (#32607110)

I've got a better idea. Just keep using spinning liquid mercury, but put it in an artificial gravity field so that you can point it in any direction with "down" still being at the base of the mirror. This only needs some small advances in the field of physics.

Re:dumb question... (4, Funny)

tlhIngan (30335) | more than 4 years ago | (#32607456)

I've got a better idea. Just keep using spinning liquid mercury, but put it in an artificial gravity field so that you can point it in any direction with "down" still being at the base of the mirror. This only needs some small advances in the field of physics.

What advance in physics is needed? Gravity works by the attraction of objects to each other, so all you need is a really, really, really massive object at the base of mirror. Such objects could easily range from a planet to a small black hole.

Problem solved.

Re:dumb question... (1)

sammyF70 (1154563) | more than 4 years ago | (#32607622)

why don't we just use a warp drive to fly where the telescope would be pointing at? Tss .. silly scientists always complicating things!

Re:dumb question... (1)

decoy256 (1335427) | more than 4 years ago | (#32607670)

So... we're going to solve with a black hole, what could be solved with some good magnets... do you work for NASA?

Re:dumb question... (1)

ultranova (717540) | more than 4 years ago | (#32607824)

What advance in physics is needed? Gravity works by the attraction of objects to each other, so all you need is a really, really, really massive object at the base of mirror. Such objects could easily range from a planet to a small black hole.

So just put it on the back of an airplane and fly the plane to a location where whatever direction you want to look at is straight up. Or would some kind of helicarrier be better?

You could use a ship or a barge, but then most of the atmosphere is goign to be between you and your target.

Re:dumb question... (1)

Grishnakh (216268) | more than 4 years ago | (#32608014)

The problem here is that the airplane has a lot of vibration, which would not only cause problems with a regular telescope, but will screw up the spinning-liquid lens badly. So you'll need some sort of antigravity or stasis field to remove all such forces. Inertial dampers might do the job.

Re:dumb question... (1)

EdZ (755139) | more than 4 years ago | (#32607908)

If you've got a black hole, just sit your telescope at it's gravitational focus and use IT as your lens. Of course you can do this with any massive body, the focal point is just much further away (the sun's is out in the Oort cloud), and you have to move evenfurther in or out to change the focal distance.

Re:dumb question... (0)

Anonymous Coward | more than 4 years ago | (#32607938)

No advances needed, only your mom.

Re:dumb question... (4, Interesting)

siddesu (698447) | more than 4 years ago | (#32607124)

Probably becaue you lose the biggest advantage of the "liquid mirror". With a liquid, you can make a very large, very thin spinning surface which will keep its perfect shape because of the motion. Now, freeze that, peel it off --- how do you keep the shape? If it is thick, it will pose the same problems as any large mirror - heavy, unwieldy, needs lots of time to come to equilibrium with the environment, etc. If it is thin - keeping the shape is probably hopeless.

Even if you could keep the shape somehow, freezing isn't a uniform process. As the temperature is lowered, crystals, lumps and whatnot starts forming in the melt. Some of these will inevitably go to the surface and spoil the figure of the resulting surface. And we're talking really, really small lumps here - on the order of less than quarter of the lightwave the surface is supposed to reflect. So, you'll need to work on the surface afterwards, just the same way you'd work on a surface of a "normal" mirror.

I am not sure enough effort will be saved by making the initial figure in this way vs. the traditional methods of preparing a surface for polishing to justify the spinning. Speaking from experience, "pregrinding" a piece of glass to a rough sphere with a piece of pipe (or, if you're hi-tech, a diamond saw) does a good enough job. And the professional mirror makers have more than that at their disposal.

Re:dumb question... (1)

Hurricane78 (562437) | more than 4 years ago | (#32607980)

The error is in your additional implications. Nobody said anything about peeling it off. You obviously make it in-place on the supporting bowl and frame, and then movie the whole thing to wherever you need it.
That’s already how it’s done. Because even huge glass mirrors deform under their weight, when not properly supported..

Re:dumb question... (0)

Anonymous Coward | more than 4 years ago | (#32607312)

You can't have the mirror surface at a substantially different temperature than the surroundings or you create air turbulence that can cause "blurred" images.

Adaptive Optics (4, Insightful)

c++0xFF (1758032) | more than 4 years ago | (#32607500)

I thought one of the points was that you don't want to fix the shape permanently. Adaptive optics [wikipedia.org] lets you adjust the mirror to account for atmospheric distortion. Think of it like being able to change the prescription of your glasses. A liquid mirror would allow for near-infinite possibilities to adjust how the light is reflected, with greater precision than current adaptive optics systems.

Re:dumb question... (-1, Flamebait)

Hognoxious (631665) | more than 4 years ago | (#32607566)

Yeah, clearly you know better than them. Simple matter of this, just needs that, all it takes is the other.

You stupid stupid stupid cow.

Re:dumb question... (1)

StikyPad (445176) | more than 4 years ago | (#32607620)

They already do this for many lenses and mirrors, except that the freezing process occurs well above room temperature. It's called spin casting [wikipedia.org] . If you wear soft contacts, there's a good chance they were produced through spin casting. The hexagonal mirrors [arizona.edu] of telescopes referenced in the article are also produced through spin casting, followed by polishing. I can only assume that keeping the mirrors in liquid form offers some benefit, otherwise there would be no point.

Re:dumb question... (1)

PigIronBob (885337) | more than 4 years ago | (#32607732)

That's the way large modern solid mirrors are cast. Known as spin casting.

Re:dumb question... (1)

PigIronBob (885337) | more than 4 years ago | (#32607744)

having said that, it still requires polishing once annealed.

Re:dumb question... (1)

Khashishi (775369) | more than 4 years ago | (#32607904)

try it in your freezer, and maybe you'll see the problem.

Oil lense (1)

jusdisgi (617863) | more than 4 years ago | (#32606886)

Sounds like the oil lenses from Dune.

Re:Oil lense (1)

Bigjeff5 (1143585) | more than 4 years ago | (#32606996)

Which sounded friggin cool.

There are (retarded looking) glasses that are similar, but they use water pumped into a bladder to alter the lense.

Re:Oil lense (3, Funny)

SnarfQuest (469614) | more than 4 years ago | (#32607174)

I know where you can get a lot of oil, but it might be a bit salty...

Re:Oil lense (1)

StikyPad (445176) | more than 4 years ago | (#32607728)

Sure, but do you really think everyone with latex sheets is just going to... Oh, right. That oil.

All mirrors liquid (0)

jamesyouwish (1738816) | more than 4 years ago | (#32606892)

Aren't all mirrors liquid sense glass is a liquid. Queue the debate:

Re:All mirrors liquid (1, Funny)

Anonymous Coward | more than 4 years ago | (#32606908)

Queue the debate:

First!

Okay, I'm in line for a debate. Now what?

Re:All mirrors liquid (3, Funny)

Jeng (926980) | more than 4 years ago | (#32607046)

Okay, I'm in line for a debate. Now what?

Now tell him he is wrong, and why he is wrong.

Re:All mirrors liquid (1)

blair1q (305137) | more than 4 years ago | (#32607320)

He has to pay him first.

Re:All mirrors liquid (1)

jamesyouwish (1738816) | more than 4 years ago | (#32607772)

If you think I hadn't seen this debate before and why I said "Queue". I love getting modded down.

Re:All mirrors liquid (4, Informative)

mea37 (1201159) | more than 4 years ago | (#32607100)

Ignoring the mischaracterization of glass that you're trying to start a debate about, the answer to your question is: No, becuase mirrors are not made of glass.

Bathroom mirrors have a protective layer of glass, but the reflective layer is silver. At best that would be "partially liquid" if we pretend that glass is a liquid. Many mirrors do not have such a protective layer, though; the mirror I use for backpacking is simply a thin metal sheet. Mirrors for lab optics typically don't include a glass layer because it would serve no purpose and would interfere with the mirror's intended use.

The defining element of a mirror is the reflective part, which is made of metal and is usually solid.

Re:All mirrors liquid (2, Interesting)

Antony T Curtis (89990) | more than 4 years ago | (#32607400)

Adding to parent comment..

I am pretty sure that most large "glass" mirrors used in astronomy actually use a very thin top layer of aluminium as the reflective layer, perhaps only 3 atoms thick... And I recall reading somewhere that this layer is cleaned off and applied every couple of years because of corrosion.

Re:All mirrors liquid (5, Informative)

siddesu (698447) | more than 4 years ago | (#32607796)

Actually, most telescope mirrors are made from glass (some are made of special glasses, that have low thermal expansion and so on, but nevertheless glass), glass being the important "ingredient" of the mirror. The reason is that glass has no crystal structure and can be polished to very high degree of accuracy and achieve the required figure (a paraboloid) with very high precision. Glass is also a very stable medium if prepared (annealed) properly.

Since the purpose of an astronomical mirror is to collect light in a precise way, the figure of the mirror is of most importance. The role of the metal layer on the surface is only to increase the reflectivity of the glass. There were (and, for some specialized uses probably are) some metal astronomical mirrors (made of speculum metal, mostly before glass got into wide use) but they allow a figure that is no better than the glass ones, and are difficult to polish and maintain.

In fact, metal coating isn't even necessary to use a glass mirror. When you make a telescope mirror, before you send it off for coating you'd perform what is known as "star tests". You'd set up your telescope, put in the uncoated mirror in it, and look at stars to see if the mirror shape is good. I could easily see a lot of planetary detail with my last (40") mirror while I was testing it without coating. Looking at the Moon was blinding.

Re:All mirrors liquid (2, Informative)

burris (122191) | more than 4 years ago | (#32607996)

In a front surface mirror such as in a telescope, the surface of the glass is in fact the mirror because the important part is the shape and smoothness of the surface. You do not need to coat it with a reflective material because the glass itself is somewhat reflective. A large noncoated mirror is good for viewing the moon, which has a lot of detail but is very bright.

After countless hours grinding and polishing or thousands of dollars spent on an optician with a good reputation or even tens of thousands spent on ion milling of the glass, you might want to have your mirror tested with an interferometer. That is done before the mirror is coated. That's because the glass is the mirror. The coating simply makes it more efficient.

It is true that some mirrors are made with non-glass materials such as quartz or zero expansion ceramic. ...or Mercury.

Re:All mirrors liquid (2, Informative)

kg8484 (1755554) | more than 4 years ago | (#32607118)

You are wrong in 4 ways:

  • You misspelled "since"
  • The proper term is "cue," as in, "Cue the lights," a direction for stage-hands.
  • The idea that glass is a liquid is an urban legend. See here [unl.edu] .
  • Not all mirrors are made from glass.

Re:All mirrors liquid (1)

StikyPad (445176) | more than 4 years ago | (#32607668)

Glass isn't a liquid [unl.edu] , despite what my (and possibly your) high school chemistry teacher taught.

Re:All mirrors liquid (1)

Kronon (1263422) | more than 4 years ago | (#32608038)

Glass lacks a crystal lattice, thus it is not a solid. When defining phases of matter, we consider in which ways the distribution of matter breaks symmetry. All fluids (gases and liquids) are both isotropic and homogeneous. At equilibrium, every point in the substance has the same conditions, on average, as every other point and everything looks the same when looking in any direction. Gas and liquid have the same symmetry with the only difference being in the incompressible nature of liquids. In fact, you can cause liquids and gases to smoothly transition from one to the other without crossing any phase transition.

Solids have fundamentally different symmetry properties. Starting from a lattice point, one must travel along a special direction by a distance called a lattice constant to reach the next nearest point at which conditions appear the same. Crystals can exist in a number of different symmetry groups.

Condensed matter physicists will tell you that there are actually a huge number of phases of matter including smectics, cholesterics, nematics (e.g. liquid crystals), etc., that all break the isotropy and homogeneity of liquids in different, intermediate ways, compared to the full breaking that occurs in solids.

I am not prepared to accept that glass is a solid without evidence of crystal structure. Crystalline silicon dioxide, however, has another name -- quartz. Quartz is unambiguously solid. It possesses crystal structure as evidenced by the diffraction of probe beams sent through it and has properties quite different from amorphous silicon dioxide.

bowl? (1, Funny)

RapmasterT (787426) | more than 4 years ago | (#32606932)

Put a drop of mercury in a bowl and spin the bowl. The mercury will spread out to a concave reflective surface smoother than anything we can make with plain old glass right now..

so our bowl making technology exceeds our bowl shaped mirror technology? seems like we could just hire the bowl makers and fire the current crop of mirror makers, problem solved.

Re:bowl? (0)

Anonymous Coward | more than 4 years ago | (#32606984)

Our bowl making technology can have minor imperfections that are smoothed out by the magic of surface tension and cohesion between molecules.

Re:bowl? (1)

Bigjeff5 (1143585) | more than 4 years ago | (#32607038)

It seems you missed the part where the mercury provides the smooth surface, not the bowl.

The bowl gives it shape, the mercury gives it the ultra smooth mirror.

Re:bowl? (2, Insightful)

NonSequor (230139) | more than 4 years ago | (#32607042)

Put a drop of mercury in a bowl and spin the bowl. The mercury will spread out to a concave reflective surface smoother than anything we can make with plain old glass right now..

so our bowl making technology exceeds our bowl shaped mirror technology? seems like we could just hire the bowl makers and fire the current crop of mirror makers, problem solved.

The liquid takes on a shape that minimizes its surface tension. Small imperfections in the bowl don't affect the surface tension and are smoothed over.

Re:bowl? (1)

selven (1556643) | more than 4 years ago | (#32607088)

The side of the mercury touching the bowl will be just as imperfect as the bowl. It's the inside. The centrifugal force will push most of the mercury to the sides, and the resulting shape will look like a bowl with a precise curve going from the center to the edges.

Re:bowl? (5, Funny)

goodmanj (234846) | more than 4 years ago | (#32607104)

The perfect shape comes from the spinning liquid: the bowl doesn't have to have any particular shape. You can even use a flat-bottomed bowl, you just need more mercury.

"Flat-bottomed bowls, you make the liquid scope go 'round..." -- Freddie Mercury

Re:bowl? (1)

geekoid (135745) | more than 4 years ago | (#32607534)

"Flat-bottomed bowls, you make the liquid scope go 'round..." -- Freddie Mercury

Bravo - *Applauds*

Re:bowl? (1)

Hurricane78 (562437) | more than 4 years ago | (#32608050)

“You spin me right round baby, right round, like a flat-bottomed bowl baby, right round right round...” — Mike Percy [wikipedia.org]

Global Vision 2020 (2, Interesting)

innocent_white_lamb (151825) | more than 4 years ago | (#32607010)

Global Vision 2020 [gv2020.org] is doing something similar to this, creating eyeglasses for people in third-world countries.
 
They have glasses with special lenses that can be filled with oil. The oil changes the shape of the lens.
 
The client puts the glasses on and fills the lens with oil until he can see clearly. Then the technician seals the glasses so the amount of oil (and shape of the lenses) won't change any further.
 
$10 per set of glasses, and no optometrist required to issue them.
 
If you're looking for a worthwhile charity to donate to, this may be one to consider.

Re:Global Vision 2020 (0)

Anonymous Coward | more than 4 years ago | (#32607412)

sound like the optical company in videodrome

Re:Global Vision 2020 (2, Informative)

questionsaddict (1277150) | more than 4 years ago | (#32607442)

um... it's nothing like the thing on the article.. what you're talking about is a lens with adjustable focus. what they're talking about is a mirror with ultra smooth adjustable shape. though they may seem similar, there's a big difference. also, you can afford a lot more focal dispersion (i just made that word up) in eyeglasses than telescopes**, hence the bitchiness about it being ultra smooth.

**just take think about it this way. if you have a small imperfection in the eyeglasses, you may get a really tiny solid angle of the image wrong. astronomers like to look at objects that cover very very very tiny solid angles from where they look :P

this might be a dumb question but... (1)

JustNiz (692889) | more than 4 years ago | (#32607020)

why can't we just spin it up then freeze it solid?

As long as its kept cold you can use it at any angle, and even make a precision mold from it then make a less temperature sensitive version.

Re:this might be a dumb question but... (1)

spleen_blender (949762) | more than 4 years ago | (#32607056)

Well, shit! Looks like you figured it out. Good job!

Re:this might be a dumb question but... (1)

JustNiz (692889) | more than 4 years ago | (#32607964)

Nice :-) I'm gonna have to remember that for my own sarcastic replies :-)

Re:this might be a dumb question but... (1)

questionsaddict (1277150) | more than 4 years ago | (#32607560)

i'm not sure about this, but i can think of a few reasons..

first, the bond it makes when crystallized is very weak (similar to a noble gas crystal) so maybe gravity is able to break it??? :S

second, the pressure at different points of the bowl is different, so the freezing point is not equal, and when the temperature drops more (you'd need to do this to get the whole bowl crystallized) different parts of the bowl would contract in different proportions ruining the shape.

and finally, ... well.. those are the two reasons i can think of :p someone more into this could give you a better answer, but i'm sure this guys already thought about it and found out it can't be done that way!

You've built a weapon, Kent. (2, Interesting)

goodmanj (234846) | more than 4 years ago | (#32607028)

Laslo: Well what would you use that for?
Ick: Making enormous Swiss cheese?
(Chris laughs.)
Mitch: The applications are unlimited.
Laslo: No. With the fuel you’ve come up with the beam would last for what15 seconds. Well what good is that?
Chris: Oh Laslo. That doesn’t matter. I respect you but I graduated.
Mitch: Yeah, let the engineers figure out a use for it. That’s not our concern.
Laslo: Maybe somebody already has a use for it. One for which it is specifically designed.

PS: I'm serious.

Re:You've built a weapon, Kent. (0)

Anonymous Coward | more than 4 years ago | (#32607956)

Props for the "Genius" reference.

the new mercury astronauts (3, Insightful)

RodRooter (1835462) | more than 4 years ago | (#32607044)

Sounds like something perfect for the next generation Hubble (or the next next one - the next one is getting ready for launch). Why fight gravity, when you can just spin it in space?

Course - making it spin for a long time between maintenance visits (on who knows WHAT vehicle) could be tricky.

Re:the new mercury astronauts (0)

Anonymous Coward | more than 4 years ago | (#32607142)

Wow -- did you forget that:
  (A) space is a vacuum
  (B) gravity is what keeps the mercury in the bowl
  (C) all of the above

Re:the new mercury astronauts (1)

the_other_chewey (1119125) | more than 4 years ago | (#32607160)

Why fight gravity, when you can just spin it in space?

How do you provide a vector for "down" in space? Without it, you're just coating
the inside of your telscope's tube with your reflecting liquid. Not too useful.

Re:the new mercury astronauts (0)

Anonymous Coward | more than 4 years ago | (#32607338)

If you're doing this in space, why use mercury?

There are resources in space, we do not need to boost them out of the gravity well.

Send rocket to asteroid. Deliver payload.
Use a ion thruster stabilized Mylar sheet to reflect sunlight onto a mostly nickle asteroid.
The photons will both push and heat the asteroid.
Controlling the beam by altering the geometry of the Mylar sheet, you can spin the asteroid as it heats.
Heat until molten. Volatiles will boil off. Increase the spin.
Spin will change the asteroid from lumpy weird shaped rock to oblate spheroid.
Spin more until disk shaped.
The force of spinning will make this disk thinner in the center, thicker at the edges, and extremely smooth.
By adjusting spin as it is still molten, you can change the level of concavity.
Allow to cool.

Instant, giant sized, space based mirror.

For bonus points, place multiple mirrors around the solar system for distributed array.

Re:the new mercury astronauts (1)

Red Flayer (890720) | more than 4 years ago | (#32607394)

How do you provide a vector for "down" in space?

You don't need to. The spinning will keep the mercury in place.

Of course, there's the issue of the scope's field of view moving as the structure spins, but surely we could figure out a way around that.

Re:the new mercury astronauts (1)

dominux (731134) | more than 4 years ago | (#32607426)

Rotate the telescope through another axis. So you have a spinning bowl and a telescope that is tumbling end over end. Sure it won't stay pointing at a particular point in the sky, it will sweep out a circular viewing path. With a slow spin (I think you just need to worry about the ratio of spin speed to tumble speed, the actual speed of both doesn't matter - but I haven't done the maths to prove this) and some fancy computer work I think the problem of it not pointing at one place might not be that big an issue. I expect you wouldn't need to enclose the scope either. So you could have a *big* bowl and a rod/axle coming out from the centre of the bowl and going to a distant collector CCD array/counterweight with the centre of mass (nearly said gravity there) of the whole thing that it will rotate about somewhere along the middle of the rod.

Re:the new mercury astronauts (1)

dominux (731134) | more than 4 years ago | (#32607492)

it is also frictionless spinning and there are no moving parts in the structure. Spin it up, let it go and it should keep going for years.

Re:the new mercury astronauts (1)

Jenming (37265) | more than 4 years ago | (#32607562)

You "tumble" it to point it at what you want to see, you "spin" it at a rate determined by the "tumble" rate and the mercury will stay inside the telescope and coat your surface.

Not a DIY project (1)

bfmorgan (839462) | more than 4 years ago | (#32607132)

My telescope will have to wait so that I can save up the $$$. This sounds cool in practice, but even at 7 cm the associated control circuitry and actuators would be prohibitive. Cool though!!

Some Typoes (2, Funny)

RevWaldo (1186281) | more than 4 years ago | (#32607214)

MIT's Technology Review is 'nalyzin a team's success in combating problems with a-bringin' liquid mirrors into the practical applications of astronomy.

FTFY

.

Re:Some Typoes (1)

blair1q (305137) | more than 4 years ago | (#32607372)

Information tunnelling from the future has quantum uncertainties associated with it.

Get over it.

Re:Some Typoes (1)

veg_all (22581) | more than 4 years ago | (#32607540)

That's "Typos [reference.com] "

What's that you say ... 91 parts to break ?? (1)

noshellswill (598066) | more than 4 years ago | (#32607306)

Who gets the repair contract ??

An easier fix? (1)

ngc5194 (847747) | more than 4 years ago | (#32607336)

Okay, liquid mirrors are cool but point straight up. Why not use a pair of flat mirrors to reflect the night sky into the spinning liquid mirror? Yeah, there would be some loss due to the imperfect reflectivity of the flat mirrors, but if liquid mirrors are so awesome, then just make them a little bigger to compensate.

Re:An easier fix? (1)

bfmorgan (839462) | more than 4 years ago | (#32607424)

This might work or be cost effective for small (up to 10 inch) flat quarter wave mirrors, but as you increase the diameter of these flat mirrors the glass substrate needed to stabilize the first surface mirror will be cost prohibitive.

Wobble wobble (3, Insightful)

blair1q (305137) | more than 4 years ago | (#32607446)

Seems to me that liquid mirrors would be orders of magnitude more sensitive to vibrations than solid ones. (Experiement: fill a glass with water; tap the glass; which has a greater amplitude, the ripples on the surface of the water, or the ripples on the surface of the glass?)

And rotating something large and heavy with a motor, moreso while simultaneously manipulating its surface with several dozen actuators, is a huge source of vibrations.

Step two (1)

wonkavader (605434) | more than 4 years ago | (#32607480)

Step one, manage the forces on a liquid to make a constant bowl -- this allows you to make a telescope and point it anywhere you want.

Step two, manipulate that bowl to alter the parabola. No more adjustable mirrors on solar collection systems, for starters, but this also allows you to direct sunlight on a quickly moving target, like a solar powered space elevator crawler. This gets particularly interesting in space. It allows you to focus sunlight on a satellite, or an object on the ground. A small mirror could charge up the batteries on a satellite, with a wide focal point, and a big one could burn tiny little holes in even the fastest moving target. A big enough lens could do the same gag on people's heads on the ground. Not sure how big it would have to be accomplish that through the atmosphere, though.

Imagine a 200-sq foot mylar fixed mirror doing a crappy job of focusing sunlight on a fixed position high-quality adaptive mirror, which was in turn capable to directing that light down to a few receiver stations on the rotating planet below, constantly compensating for the movement of the receiver.

Only one problem? I think they forgot something. (1)

clone53421 (1310749) | more than 4 years ago | (#32607490)

The key problem in this situation is that the bowl will always have to point straight up.

That, and the fact that mercury is an extremely toxic and hazardous element that has to be carefully handled and disposed of. Accidentally disperse some into the air (splatter) and you could face a very costly cleanup. In short, mercury is a little bit beyond something your average hobbyist should be playing with – not that it would likely deter them, unfortunately.

Re:Only one problem? I think they forgot something (2, Informative)

geekoid (135745) | more than 4 years ago | (#32607578)

Oh please. You need a good dose, and constant exposure. Otherwise your body will purge it. Don't drink it, but don't drink motor oil either.

Just be careful. You average hobbyist has no problems with it.

why not use it in space? (1)

Rooked_One (591287) | more than 4 years ago | (#32607662)

Yes, there will be the earths gravity, but the temp of space would freeze it? Then you have an awesome replacement for the Hubble's lens, if it needs to be upgraded (not from what I've seen though).

Or a whole new telescope all together.

Re:why not use it in space? (1)

Quartinus (1678656) | more than 4 years ago | (#32607838)

Yes, there will be the earths gravity, but the temp of space would freeze it?

*wince*

Transparent liquids? (0)

Anonymous Coward | more than 4 years ago | (#32607686)

Hey, aren't there any optical liquids whose refractive index would depend on electromagnetic field strength?
Imagine a liquid-filled lens for photography, that could be zoomed or focused with no moving parts, perhaps
even reconfigured on the run...

Gyroscopic forces (1)

Culture20 (968837) | more than 4 years ago | (#32607798)

The key problem in this situation is that the bowl will always have to point straight up.

Not if it's at the bottom of a tube in a centrifuge. Of course, spinning the end and dealing with the gyroscopic forces is a new problem, but you can't have everything. Assuming you can figure that out, you could take snapshots every X microseconds (whenever you're pointing at something you want).

Re:Gyroscopic forces (1)

goodmanj (234846) | more than 4 years ago | (#32607866)

Unfortunately, exposure times for astrophotography need to be seconds to an hour long, even with modern digital imaging.

Re:Gyroscopic forces (1)

Culture20 (968837) | more than 4 years ago | (#32607958)

Unfortunately, exposure times for astrophotography need to be seconds to an hour long, even with modern digital imaging.

What if we built this large wooden badger?

abringing (1)

Onymous Coward (97719) | more than 4 years ago | (#32607856)

Rather, that should be spelled a-bringin'.

MIT's Technology Review is annal-ma-lyzin' a team's success in combatin' problems with a-bringin' liquid mirrors and such t'the pract'cal applicationin's of the astronomy.

Herculean project (1)

IceFoot (256699) | more than 4 years ago | (#32607940)

...ferromagnetic liquid coated with a metal-like film... very strong magnetic fields... non-linear problems of control...produced... liquid mirror just five centimeters across with ninety-one actuators cycling at one Kilohertz and the ability to linearize the response of the liquid.

Yikes! That is ONE TOUGH PROJECT. Sure am glad I'm not working on it! *sigh of relief*

Liquid mirrors (1)

etudiant (45264) | more than 4 years ago | (#32607954)

Is this not a very expensive way to solve a problem that could be addressed much more simply by just using a large flat mirror to capture the view that we want the telescope to look at?
We do know how to make very reflective large flat surfaces as well as how to point them accurately. The mirror can stay flat on the ground, only the flat reflector moves.
Seen that all the objects are at infinity, any distortions introduced by the reflection should be easy to eliminate.

Zero G Applications (0)

Anonymous Coward | more than 4 years ago | (#32607978)

I know i'm an idiot but why not use this is Zero G? I'm sure with a decent set of thrusters you could make a bowl rotate and point in the right direction plus have enough acceleration to simulate gravity on earth (thus solving the always point up problem). I bet mercury is a lot lighter then the mirrors on hubble...

Re:Zero G Applications (1)

IceFoot (256699) | more than 4 years ago | (#32608070)

Because you need gravity to create the perfectly-shaped mirror surface on the rotating bowl of mercury. On Earth, that's easy. In zero g, no gravity.

I'm sorry, your grant application has not been approved.

Big CCD (1)

HaeMaker (221642) | more than 4 years ago | (#32607990)

So why are we still using mirrors? Why not a big CCD?

Why does it have to be liquid? (1)

nicksan (1078613) | more than 4 years ago | (#32608054)

It would seem a relatively simpler matter to stretch a thin mylar membrane over a frame, like a drum head, apply a partial vacuum to introduce the basic curvature and then control the surface with a combination of loudspeaker-like actuators, operating at frequencies designed to create standing waves of arbitrary shape according to the needs of an adaptive optics control system. This would have the advantages: lightweight, easy to assemble, use of off-the-shelf speaker technology, very high response time, relatively low power requirements, etc. What's not to like?
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