h a l f b a k e r yRenovating the wheel
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As an alternative to carrying rocket fuel, launch a satellite by repelling it magnetically. Create a powerful magnetic field which is focused into a narrow vertical beam over which a small metallic satellite is positioned.
questions i cant answer but would like some input:
can a magnetic
field even be shaped like this? if so, does it still lose strength further from its source?
can an object achieve orbit by simple slow vertical ascention without attaining escape velocity?
NASA Magnetic Launching System
http://www.sussex.a...oct99/article1.html
NASA Advanced Space Transportation Programme [Brummo, Oct 17 2004, last modified Oct 21 2004]
Magnetic Propulsion and Space Travel
http://www.physics....135-2/06/space.html
[Brummo, Oct 17 2004, last modified Oct 21 2004]
Electromagnetic launch technology symposium
http://www.emlsymposium.org/
Conference on the subject [xxxppp1, Oct 14 2005]
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Magnetic fields are inversely proportional to the square of the distance. You would need outrageous amounts of energy to affect an object miles up in the air.
But, yes, slow vertical ascension works, as long as you have enough upward force to counteract the downward accelleration due to gravity.
Escape velocity is only really relevant for ballistic projectiles which get an initial accelleration and then "coast" the rest of the way (like the space shuttle). If they are not going fast enough by the time they start to "coast" they will not escape.
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At first I thought this to be an unlikely idea, but searching google, it turns out it's already being baked (researched at least) by NASA.
Although, in their case, it is only for getting the space craft off the ground. |
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It would be nice if the magnetic launching device didnt have to be as physically long as the area it influences, as described in the nasa articles. I was hoping the magnetic field could be funelled out into space and focused entirely on any object intersecting its path (much like laser light emanating in a straight line). Is that non-sensical? |
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Sadly, magnetic fields are not projected like lasers: the magnetic field is tied to the object creating it. The field consists of imaginary "lines of magnetic flux" which must form a closed loop passing through the object (electromagnetic coil or permanent magnet) creating the field. Don't forget that the satellite would have to have a strong on-board magnetic field as well, either permanent or generated as needed. You have to have two opposing magnetic fields to generate magnetic repulsion. The NASA system accomplishes this by carrying permanent magnets on the underside of the train. Shorted loops of wire are embedded in the track. As the train moves down the track, the magnetic field from it's on-board magnets moves across the loops. This causes current flow in the loops. This current in turn generates a magnetic field of its own, of opposite direction to the magnetic field which created the current. Thus you have two opposing magnetic fields, and repulsion lifts the train off the track. The inverse square law referenced by DeathNinja is the reason that such maglev type systems work. At the short distances in use for such systems, a small magnet can do lots of heavy lifting. Also, such system use a specialized arrangement of magnets known as a Hallbach Array, which "focuses" the magnetic field strength on one side of the array. |
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Hmm. I understand about the nasa system carrying on-board permanent magnetic material to generate the opposing force, but Im not so convinced that the magnetic lines themselves couldnt be focused in a useful shape. If the magnetic field forms a closed loop passing through the object creating it, couldnt you still reflect/refract that field into a conical shape? As a beginning thought, semiconducting materials reflect incoming imaginary flux lines, causing magnetic objects to repel themselves over the surface of the material. Also, the inverse square law mentioned only applies in situations where the field is expanding outward, like a flashlight or a match? It doesnt apply to focused systems, like a spotlight. In theory, couldnt the closed loops be manipulated into a magnetic spotlight? |
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If you could figure out how to make a magnetic spotlight, the world would be your oyster.
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You might want to do a search for "Magnetospheric Plasma Propulsion". It is still not the thing you're asking for, but it seems pretty cool: |
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"Magnetospheric Plasma Propulsion (M2P2) seeks the creation of a magnetic wall or bubble (i.e. a magnetosphere) attached to a spacecraft that will intercept the solar wind and thereby provide high-speed propulsion with little expenditure of propellant" |
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This is kind of old, you know. Arthur C. Clarke proposed something like this in the '50s. |
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There are lots of ways to use electromagnetic forces to accelerate stuff linearly, but none works quite like you suggest. |
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One thats easy to understand is a solenoid: a coil of wire through which you pass DC current. Turn it on, and metallic objects within it are attracted towards its center. Solenoids are generally used for small things like moving flaps on model airplanes. With a big solenoid, though, you can turn it off just as the object reaches the center, and it acts as a sort of gun. Not a very good one, but it works. This is also known as a single-stage coilgun. |
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The next logical step is to use multiple coils. Use many short coils, each of which is turned off by a high-speed electronic switch as the projectile passes through it, so that only the coild in front of it are attracting it at any time. This is what people are normally referring to when they use the phrase "coil gun." |
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My favorite electromagnetic launcher, though is the railgun. Its dead simple in concept: Shove a conducting metal slug in between two rails. Current flows between the rails through the slug, and the Lorenz force propels the slug out. All you need to do is shove a whole lot of current through the rails. In practice, its harder to do than it sounds. Still, engineers have succeeded at propelling bits of metal to rather ridiculous velocities using the things. |
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NASA has actually toyed with the idea of using railguns (and perhaps also of using coilguns) to launch small satellites into low-earth orbit. But there are a few problems: |
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1 - A gun barrel must be a great deal shorter than the distance over which a rocket accelerates. That means that in order to reach the same speed that a rocket does, the satellite must be accelerated very, very rapidly. Sensitive electronics may not like g-forces very much. |
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2 - Sensitive electronics may not like intense and rapidly changing magnetic fields generated by such devices. |
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3 - Think conservation of energy. Eventually you're ending up with orbital gravitational and kinetic energy. This net final energy can be carried at least partway up with a rocket in its fuel. Unlike a rocket, a bullet needs all of its final energy to be stored in its initial kinetic energy and nothing else. That means that it must travel at much higher velocities than a rocket. At higher velocities, atmospheric drag is much greater (proportional to the square of the velocity), which necessitates even HIGHER velocities. Its something of a vicious circle. You CAN eventually win, but only by sending the thing at some ungodly velocity. And then think of all the energy lost in the form of heat due to that drag (and the temperature that your satellite will reach). Its inefficient. That and sensitive electronics may not like superheated plasma. |
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So, your idea IS partially baked (serious people are doing serious research), but, so far, there are some fundamental problems with the approach. |
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Short of cheap and abundant Antimatter protons, electromagnetic rail launch offers cheap, easy to use fuel (electricity), and much higher effectiveness in making the most of that energy. Especially, since a maglev catapulting a missile doesn't waste 99 percent of its mass on fuel. Major cost savings is the result of using electricity to accelerate a rocket to supersonic or hypersonic speeds from a mountain. |
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Heat shields are routinely used on spacecraft returning from orbital speeds of 18,000 mph and using maglev rail rockets requires a heat shield on the way up as well as back to earth. |
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Given a Rocket Rail of two miles vertical or longer using maglev technology, flights to orbit are perhaps 100 times cheaper, less risky, and can carry more cargo, more often to space. |
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Mountains, rather than Beaches, offer a natural advantage in positioning Electro Magnetic Rocket Rail
and its likely merger with rocket propulsion. On this planet, the atmosphere puts a significant damper on this technology. |
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Casinos, Hotels, mining operations and new industries can gain much using Rocket Rail Maglev. Tourist space offering spectacular adventures and universal vistas with the comfort of a resort for Architects, Astronomers, Conventioneers, Engineers, Explorers, Investors, Developers and people stand to gain by making access to space cheaper and realistic for public and private. |
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Magnetic propultion would only help the craft reach enough speed for orbit or escape, but additional propultion/velocity gain would be required. There's a reason meteors burn up and shine when they fall to Earth! Anything launched fast enough from the ground (to get into orbit or escape earth's gravity) would unfortunately burn up as it passed through the atmosphere on its way out toward space. |
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A rail gun, say 5000 feet tall, could easily propel a small sattelite into orbit. (This is nothing more than a powerful magnetic field along a bar of metal.) Acceleration could be "feathered" so that G forces are kept below a destructive level. Problem is, at 5000 feet, there is too much atmosphere, and the sattelite would be glowing hot as it streaked into space. If it could be launched from 10,000-15,000 feet in the mountains it would make a huge difference. |
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My question is, if we've got magnetically charged satellites up in the sky, strong enough to be repelled by gravity, mightn't they attract metal objects with the right charge to them, causing stuff to rise up into the air stuck to the magnets untitl too much stuff gathers and it all comes crashing back to earth? Won't your idea doom us all?!?!?! |
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If we ever produce something with a
magnetic charge that repels gravity, this
will indeed be a grave concern. |
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// something with a magnetic charge that repels gravity // |
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Grave concern ? Bloody useful, more like ! |
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I've said it before, and I'll say it again: helium balloons carrying railguns are the only answer. Actually I may not have said it before, but will start saying it now. |
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The array of balloons could have a wire dangling down to earth by which the onboard capacitors for the railgun is charged. Actually, with such a wire, the balloons might be able to charge up the gun on the differntial between earth and sky. The balloons would hover at the point of neutral buoyancy. The satellite would be lifted up to the array with more balloons. I am not posting this as a new idea because it is already around here somewhere. |
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// by which the onboard capacitors for the railgun is charged // |
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Presumably from induced currents from the geomagnetic field ? Anything else would be silly. |
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// balloons would hover at the point of neutral buoyancy. // |
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Sorry, we are dazzled by the blinding flash of the obvious ... |
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In reference to the slow vertical ascention comments. |
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Yes, if you've a way of doing it, slow vertical ascention is much more efficient, due to reduced atmospheric friction, however there is a problem. Once you reach a suitable height and let go, it'll just fall back to earth, unless you're so far out you're geostationary. There are some complexities here I'm sure you don't appreciate, ie the vectors involved with "slowly lifting" a satellite. As you raise the object, you'll have to give it lateral thrust just to keep it overhead, as you're essentially adding to it's rotational speed. This is something we don't really appreciate, cause we rarely lift things very far. It's similar to coreolis forces. |
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You need a good deal of lateral velocity to put the "orbit" in the phrase "being in orbit". However it would still be more efficient to slowly raise your satellite with a smaller final rocket stage attached, that would fire once atmospheric drag wasn't a factor, giving you the necessary orbit velocity. |
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