Please Register or Log in to view the hidden image! One day my dream of seeing huge telescope mirrors constructed in space might be a reality. Reflector dishes perhaps thousands of kilometres in diameter with near perfect curvature for focusing faint traces of light from other Earths orbiting distant suns. We will be able to look at hundreds of planets not unlike our own. Will the first observed Alien plant life be green or will some other chemical process not involving chlorophyl be employed. Blue trees perhaps? Will we be able to make out such tiny details as herds moving across open savannah? Depends on the scale of the mirror. Zero gravity opens up a whole new realm of possibilities for mirror construction. On Earth many clever techniques must be developed to build larger reflectors. From motor controlled segmented surfaces to ultralight materials. All to contend with distortion from gravity and temperature changes. In space these problems do not exist. Launching mirrors subjects them to even greater stress as they must be built to withstand the high acceleration. Hubble is not very big. Its main advantage is a clear line of sight devoid of atmospheric distortion. Only with industry in space can we put together a truly grand engineering miracle. Without gravity liquids naturally form perfect spheres. A liquid metal bubble can be made by following the art of glassblowing. It could be done in open void. Simply charge up a lump of metal such as silver with enough amps so that it melts. Heat will dissipate very slowly without convection or conduction available to take it into the environment. Radiating heat will eventually return solidity but only after the work is complete. A tube is inserted and a measured quantity of hydrogen gas pumped inside to turn the liquid into a perfect bubble. Perhaps only a millimetre or less thick. Remove the tube and spin the bubble of silver using magnets until centripetal force flattens the bubble and achieves the correct curvature for our needs. It will maintain rotational speed until a countering force is applied. Eventually the bubble returns to a solid and can be cut carefully into two identical halves. Two perfect dishes. Polishing which usually takes years can be achieved in minutes by spraying on a surface coat that adheres uniformly. All this requires is existing technology. The size of the dishes depends on the size of the initial mass used. There is theoretically no limit to scale. You could build a mirror to any diameter your quantity of construction material and industrial infrastructure allows. The pictures would be light gathered images of great detail quite agreeable to the human eye. Much like Hubble images but far more power. The largest reflector currently planned is something along the lines of 4 metres. Space built mirrors like the one described above could easily be 400 or even 4000 metres in diameter. Aswell as being able to look deeper into space than ever before we would be able to search out other Earths among neighbouring stars. Possibly even locate intelligent life. The detail would be intense. Wouldn't it be something to view another civilisation going about its buisness. We might not like what we find. Perhaps there is no life among the local stars inhabiting this spiral arm section of the Milky Way. Thats a lonely thought to contend with. On the other hand the sheer strangeness of things not remotely human but posessing intellect might be very frightening. We may even find another eye in their sky looking directly back at us.
Wrong. The temperature changes in space are, in a word, extreme. A kilometer scale mirror would also experience significant tidal warping. The weak surface tension of liquid metals will not support bubbles like this. Silver is diamagnetic. Two perfect non-paraboloids. You say this as if it were easy. In a word, no. You seem to be having trouble separating the concept of "resolution" from the concept of "light gathering area." The most important quality of an instrument used to detect distant planets is resolution. Resolution is a measure of the smallest features discernable in an image, and follows from the diffraction of light. Current plans for telescopes like the NGST and TPF are based on the concept of a space-borne optical interferometer. There will be several small telescopes, widely separated, which will together achieve a resolution equivalent to a mirror the diameter of the earth. There is no need to build a kilometer-scale space-borne mirror, which, despite your ignorance, would be impossible with existing technology. - Warren
I beg to differChrooty. Quote. "Wrong. The temperature changes in space are, in a word, extreme. A kilometer scale mirror would also experience significant tidal warping." "I would be interested in seeing the false assumptions this theory is based upon. It is only commonsense to place such a dish well out of the elliptic plane far away from the gravitational influence of the Earth moon system and other bodies. At a similar orbital distance to Saturn solar flares would not cause significant temperature fluctuations. You are grasping at straws." Quote. "The weak surface tension of liquid metals will not support bubbles like this." Have you tried it? In the absence of any serious opposing forces, even a weak surface tension will suffice. Whatever alloy is used would be suitable. quote "Silver is diamagnetic." All objects have a degree of magnetism. I did state silver only as an example. The actual material used would most likely be an alloy composed of various metals. A small amount of Iron in the mix would suffice. Magnetic manipulation is only one possible method of making a sphere spin anyway. Simply blowing on it is another. You are nitpicking. Quote. "Two perfect non-paraboloids." Two perfect anyshapeyouwannas. Like spinning clay its as much an art as a science. Use your imagination. quote: "You say this as if it were easy." Polishing a surface in space is a piece of cake. I'll ask my engineering friend John Fraz to give an explanation to you. quote: All this requires is existing technology. "In a word, no." In a word yes, its doable with off the shelf technology old chap. quote: "You seem to be having trouble separating the concept of "resolution" from the concept of "light gathering area." The most important quality of an instrument used to detect distant planets is resolution. Resolution is a measure of the smallest features discernable in an image, and follows from the diffraction of light." For which you need the most perfect diffraction possible. Ie a perfect mirror rather than something grinded into shape over many years down here and still crap. "Current plans for telescopes like the NGST and TPF are based on the concept of a space-borne optical interferometer. There will be several small telescopes, widely separated, which will together achieve a resolution equivalent to a mirror the diameter of the earth. There is no need to build a kilometer-scale space-borne mirror, which, despite your ignorance, would be impossible with existing technology." Interferometers are not as good as a single large mirror. There is no need to waste time on lots of tiny little mirrors when it is simpler to construct one large one. Despite your ignorance the technology has been around for decades. - me
Re: I beg to differChrooty. What is the elliptic plane? Perhaps you meant ecliptic? I never said solar flares are the cause of temperature fluctuations. The side of an object facing the Sun is hundreds of degrees warmer than the side of an object facing space, flare or no. Regardless of your assertion that I am "grasping at straws," I am in fact pointing out obvious and serious errors in your little pet idea. What makes you so sure? Have YOU tried it? Ah, blowing on it... right. I fail to see how a spinning ellipsoid bubble could produce a paraboloid. Think about it for a bit. Please do. Why, then, young whipper-snapper, are space-enabled nations not currently funding work on building kilometer-scale mirrors from giant bubbles of silver in space? Care to speculate on the reason? Ah, that's right. You truly DON'T understand resolution -- as I suspected. Resolution has nothing to do with the perfection of the optical element, and everything to do with its aperture. Please look up the Dawe's limit and derivation thereof. Interferometers are just as good as a single large reflector, at least in terms of resolution. In what way do you assert that interferometers are "not as good?" And I have to argue quite strongly with your assertion that building a single big one is easier than building many small ones. Point of fact, the difficulty required to construct ANYTHING generally increases much more rapidly than the scale. A kilometer-scale mirror is much, much more difficult, and much, much more expensive to construct than are an array of small reflectors with the same surface area. Despite your ignorance, the reason it's not being done is because it is infeasible on so many levels. It would be a tremendous and stupid waste of money to even attempt to construct a kilometer-scale mirror in space -- with existing technology. - Warren
Because of the scale of technological and manufacturing barriers, more and more of the new telescopes are being built with multiple, small mirrors fitted together to make one. It is far easier to make, transport, and put into place these small mirrors than trying to handle 1 large, single mirror of the same size. Several telescopes and radio scopes around the world have been networked at one time or another to increase base width and resolution as opposed to a single telescope. This is exactly the principal behind the VLA only on a broader scale. In the testing phase, which I have not heard how it worked out, are foil based reflectors for space telescopes. The idea, was to be able to put out a low cost reflector that could be manipulated to some degree for enhancement. Should this prove feasiable then it would not be beyond our ability to set several up across the solar system for a VLA type setup. The idea was were to go next after the currently planned NGT scope missions have been completed. As this is just testing to see the feasiablity of the concept there is no telling how this will turn out or what problems might have to be over come, if they can.
"What is the elliptic plane? Perhaps you meant ecliptic?" Resorting to spelling errors so soon. How sad. I had hoped you were a more worthy conversationalist. Oh well, I'd better address your response. Quote "Regardless of your assertion that I am "grasping at straws," I am in fact pointing out obvious and serious errors in your little pet idea." Hardly very serious. At several AU the sun is just another star in the sky. You assumed I was thinking of an orbital mirror when I was not. Therefore the error only exists in your head. A head which I suspect is full of errors. I wrote Whatever alloy is used would be suitable. quote: "What makes you so sure? Have YOU tried it?" Stop and think. If it wasn't suitable then it wouldn't be used. Think hard. quote: "I fail to see how a spinning ellipsoid bubble could produce a paraboloid. Think about it for a bit." Yes, you think about it for a bit. I wrote Polishing a surface in space is a piece of cake. I'll ask my engineering friend John Fraz to give an explanation to you. Quote "Please do." I'm awaiting a reply. John did write earlier: There is a simple way of making parabolic shapes. Fill a cup/glass of water,then swirl the water with a spoon. You will then see that the water in the glass rises on the outer and lower in the middle.Thats a parrabolic shape. The faster you spin it, the smaller the focal ratio. The slower you spin it, the longer the focal ratio and more magnification. This is how to make Huge Parrabolic Mirrors, using liquid mercury and a large spinning container. The liquid mercury & container is spun at a precise rate, to give a certain focal ratio. The mirror is always a liquid parabolic mirror. Me again. In a word yes, its doable with off the shelf technology old chap. Quote. "Why, then, young whipper-snapper, are space-enabled nations not currently funding work on building kilometer-scale mirrors from giant bubbles of silver in space? Care to speculate on the reason?" Trying to fob me off as a conspiraliar. Tragic. Such a waste of a mind. We don't have the launch technology available to get heavy industrial infrastructure into space. All the Saturn V's were scrapped years ago old chap. The technology exists, but not in space. The material for a giant mirror would have to be mined from asteroid resources. Theres no hope of carrying it onboard a big firework. Mining space resources is still a few years away. Stay with us. This is a conjectural topic. Like space elevators. It's concievable but nobody will be doing it for some time. Quote. "Interferometers are just as good as a single large reflector, at least in terms of resolution." Lots of small eyes are better than one big eye. Spiders must have good eyesight then. Much better than us poor optically deficient humans. LOL. Quote. "And I have to argue quite strongly with your assertion that building a single big one is easier than building many small ones." Strongly noted. Quote. "Point of fact, the difficulty required to construct ANYTHING generally increases much more rapidly than the scale." Generally. Quote. "A kilometer-scale mirror is much, much more difficult, and much, much more expensive to construct than are an array of small reflectors with the same surface area." I strongly disagree. Quote. "Despite your ignorance, the reason it's not being done is because it is infeasible on so many levels. It would be a tremendous and stupid waste of money to even attempt to construct a kilometer-scale mirror in space -- with existing technology." Despite your ignorance, the reason it's not being done is because it is a futuristic idea. Landing men on the Moon was a stupid waste of money with existing technology. So was the ISS. Responding to this thread is a tremendously stupid waste of time by your reckoning and yet you have done so. Humans often do tremendously stupid and wasteful things. That reasoning doesn't dismiss concepts or provide any argument as to their validity as workable engineering feats. - me.
Spelling errors can be misunderstood as real errors. The faster you learn to proofread your responses, the faster we'll learn to take you seriously. Oh really? Would you care to make a calculation of the flux received by a 1 km radius mirror at 2 AU from the Sun? If you don't, I will. Please Register or Log in to view the hidden image! That's exactly my point -- there aren't any that are suitable. That hardly qualifies as a response. Point of fact, a piece of an ellipsoid is never parabolic. Ok, who on earth has not already heard this idea? I hope you've passed a few college courses and will understand that the geometry of a pan of mercury in the presence of a gravitational field is wholly different than a giant bubble in the absence of a gravitational field. Hey, slow the fuck up here -- wait a minute. First you say: That's a powerful statement. Not just existing technology, but off-the-shelf technology. But then you retract it completely and say this: Sooooo... what you're saying then, fuckwit, is that IT CAN'T BE DONE WITH EXISTING TECHNOLOGY?!?!? Holy premise retraction, Batman! Please Register or Log in to view the hidden image! This anecdote is not an argument. You have still not dealt with the fact that interferometers have the same resolving power as a single reflector of the same baseline. I already asked you once: please explain to me why an array of small mirrors is "not as good" as a single large one. Hey, but wait again -- you keep saying that's it's doable with existing off the shelf-technology, but now you're saying (again) that it's not. Care to actually make up your mind on the issue? I'm waiting. - Warren
Nitpicking spelling mistakes, trying to make me out as a conspiracy nut, appealing to authority by boasting your education credentials and finally direct insults. As you are so determined to shout me down and 'win' the grand prize of most obnoxious person in this debate, I will grant you your wish. The topic was interesting but you are not. Life is too short to waste on you. I stand by my statement that the technology exists. We simply don't have the launch capacity to place said technology in deep space. Just as it doesn't exist for large interferometry arrays. Although it might become possible far sooner than for the large dish. We know how to get stuff into space but no heavy launchers have been built. I can't think of a simpler way to say it so chalk yourself up a victory if you still can't understand. This was supposed to be a friendly discussion on large dishes constructed in space. I wrote the first post straight off the top of my head and admit its not a fully researched and heavily funded space program. It was an idea. I also admit to not being a professional scientist. Never claimed I was. I wanted some input as to how my very rough idea 'might' work. I concede you the thread. Talk to yourself now.
nice going chroot! not only did he leave the thread, appearently he left the entire forum as well http://www.sciforums.com/showthread.php?s=&threadid=13958 :m: but look whats new!!!!:m:
Now, aside from the juvenile insults and all... We could conceivably create in the future mirrors a thousand kilometres across, without significant warping due to temperature extremes. How? There are three things I thought of in moments. 1) The mirror ir constructed of small tiles controlled by a computer. 2) The mirror is merely a thin reflective film, also controlled by computer. 3) The mirror is composed of several large mirrors placed a great distance apart. I'm sure those who have studied more astrophysics can think of more methods. Saying "that'll never fly" is the kind of pathetic drivel I would expect from the bureaucrats of the science world who try to slow down progress. Those of you without imagination, who can only say "that'll never fly", please stick to simple number-crunching threads. As for new construction methods in space, there is a very interesting new method involving sound. Some students discovered that in microgravity, you can create just about any shape using soundwaves. You get a container, speakers at the ends, and put inside your material to be formed into a shape. Free of Earth's gravity, the material is shaped only by the sound. So far all experiments have worked quite well, and the idea has basicaly opened up whole new ideas for space engineering.
