Electromagnetic Propulsion

[vidar]

I can see there is a problem with designing interstellar ships at hundreds of tonns that should travel <br />at speed at c/10 or more. The propulsion needed must be enormous. <br /><br />However, supposing that a probe, at a few hundred kilos is required as pioneers, the propulsion can be much simpler. I was thinking more in the way of use of electromagnetism and gravity. I am quite fascinated by the use of transforming electromagnetism into thrust. That is done quite effective by the electromotor and in the magnetic levitation train, Maglev, which can reach over 400 km/h. Similar system could be interesting for launching rockets. <br /><br />I cannot think of a complete electronic, non-mechanic, way of propulsion. However, when accepting exploding chemical, or nukes, in a rocket chamber, it should be acceptable with a magnetic plate hammering in the rear of the rocket. I think that can be done by simply placing a magnet close to the backside, and an electromagnet behind the magnet that alternative shifting between + and – polarity. The magnet will then vibrate, i.e. alternative pushing the hull forward and getting back in place. It can even function as steering if the el.mag. pushes a little to one side. <br /><br />The transformation of energy would then be; heat (nuke), motion (liquid), electricity (dynamo), and thrust (el.mag hammer). <br /><br />I would very much like feed back on the idea. <br />Has it been designed previously? Will it work? If not, why?<br />

 

[nacnud]

Look up F=ma, you need to push on something to move. There doesn't seem to be anything you are pushing against in your idea. That or I missed the point <img src="/images/icons/smile.gif" />

 

[no_way]

<blockquote><font class="small">In reply to:</font><hr /><p>“Next I had a very light iron chariot constructed. In a few months, when all my devices were complete, I climbed onto my worthy chariot. You may ask what it was all for. Well, the angel had told me in my dream that if I wanted to acquire the perfect knowledge I desired, I would have to go to the Moon. There I would find Adam’s paradise and the Tree of Knowledge. As soon as I had tasted its fruit, my mind would be enlightened with all the truths a person could know. That is the voyage for which I built my chariot.<br /><br />“Finally, I climbed aboard and, when I was securely settled on the seat, I tossed the magnetic ball high into the air. The chariot I had built was more massive in the middle than at the ends; it was perfectly balanced because the middle rose faster than the extremities. When I had risen to the point that the magnet was drawing me to, I seized the magnetic ball and tossed it into the air again.”<p><hr /></p></p></blockquote><br /><br />Look up Elijah’s magnet by Cyrano de Bergerac <img src="/images/icons/smile.gif" /><br /><br />

 

[vidar]

I am sorry that I have not made the point clear. I should have been better in computer drawing. I picture tells more than words.<br /><br />Imagine a large hammer (piston) beating at the back of a ship. For each stroke the hammer pushes the ship forwards (acceleration). The hammer is fastened to the hull and strikes when the el.mags polarity is the opposite of the magnet at the rear of the hull. The hammer pulls back each time the polarities are the same, but do not hit any part of the ship and do not give the ship backwards thrust. <br /><br />The magnet should cover the most of the rear end of the ship’s hull. It should be formed as a bowl and not be entirely flat, to give room for steering by hitting a little to the side. The el.mags surface (hammer/piston) should be just as large and fit perfectly into the magnets surface.<br /><br />I suppose there will be some backwards thrust too. But I thing the forward thrust would be much greater, which in sum gives a total of forward acceleration (a).<br /><br />The whole engine should be capsulated. It is a closed system that only provide, thrust, noise and heat. It should not be open to let dust or moist in.<br />

 

[vidar]

Well yeah. <br />It is a great dream.<br />But I do not think we find The Tree of Knowledge or Arthur C Clarks monolith on the moon.<br /><br />I must admit that I think the hammering magnet is a little brutal and not as energy efficient that I want it. A purely magnetic thrust would be much better. That is what they have managed with the mag-lev train. Such a construction on the moon would provide any vessel a ‘flying start’. Remember, there is no air resistance and only 1/6 G there.<br /><br />I am quite certain that there is a way to push a rocket in space merely by use of electro magnetism. I can not really imagine the effect if the electro magnet did not push a hammer, but permanently was set to the same polarity as the fixed magnet. Would el.mag push the magnet/ship forward in constant force and thereby give the ship a constant acceleration (a)?<br />

 

[nacnud]

<font color="yellow">I suppose there will be some backwards thrust too. But I thing the forward thrust would be much greater, which in sum gives a total of forward acceleration (a). <br /><br /><font color="white">Er... no. The max impulse force might be different but the total force would be the same for both motions. The ship would just sit there, throbbing.<br /><br />Think about this, which weights more <br /><br />1) a lorry load of canaries that are sitting on their perches or <br /><br />2) a lorry load of canaries that are flying.<br /><br /><br /></font></font>

 

[drwayne]

In rocketry, the equation F = ma is actually not applicable much of the time, or even correct. The correct form is<br /><br />f = dp/dt<br /><br />where p is the momentum, and dp/dt is the time rate of the change of momentum. Note that if the mass is constant, this reduces to<br /><br />f = d/dt(mv) = m(dv/dt) = ma<br /><br />But, in the case of an engine, the mass is not a constant, so the original form applies. In space, in general you must throw something overboard, give it momentum in one direction, so that by conservation of momentum, you move in the opposite direction. You are not,strictly speaking, pushing against anything.<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[nacnud]

Yeah, I was looking at the problem from the centre of mass of the system, propellant and rocket. Perhaps not the best way to describe whats going on.

 

[vidar]

Then I will try describing the idea in an other way.<br /><br />Imagine sitting on your knees in the small lorry, after letting the canaries free. You have a great sledgehammer that you swing over your head and hit the back of the lorry. It moves a little forward, wouldn’t it? Before it stops, you manage to make another swing with the hammer and hit it again. Once again the lorry gains speed, and your swing did not make it stop, would it? The speed is accumulating and the wagon accelerates.<br /><br /><br />I think the idea of the el.mag hammer is indifferent to the idea of the sledgehammer lorry. <br /><br />A main difference though, is that in space there is no resistance of air, and the rocket has no resistance from wheels or planet gravity. It will not loose the gained velocity provided by the strokes.<br /><br />

 

[grooble]

Wouldn' t the hammer swinging backwards do something with gravity that negates any push it might deliver?

 

[no_way]

Just some elementary physics, explanation of Newton's third:<br /><blockquote><font class="small">In reply to:</font><hr /><p>In the case of internal forces, a force on one part of a system will be countered by a reaction force on another part of the system so that an isolated system cannot by any means exert a net force on the system as a whole. A system cannot "bootstrap" itself into motion with purely internal forces - to achieve a net force and an acceleration, it must interact with an object external to itself. <p><hr /></p></p></blockquote><br /><br />In other words, you have to have something to push against in space to move. For rockets, its the propellant that the rocket is "pushing" against. Your magnetic hammer may bang all it wants but it will remain in relatively constrained part of space <img src="/images/icons/smile.gif" /> <br />Read Cyrano's iron boat with magnetic ball idea that i linked above and try to think about it why it doesnt get one to moon.

 

[cuddlyrocket]

No, it won't work. It's an enclosed system and there is no net external force, so it won't accelerate. All that happens is that the rest of the probe moves in the opposite direction to your magnet (although not by as much if it's heavier). The centre of mass stays in the same place.<br /><br />Basically, how are you going to get your magnet to return to its original position? Something must exert a force on it to do so, and that something is connected to the rest of the probe, which will therefore be moved.<br /><br />The example of the hammer is the truck is a good one. To bring the hammer back, you have to exert a force on it to move it. Unless the individual moves, he would have to brace himself on the floor of the truck, which will move the truck in a manner that cancels out the effect of the hammer.

 

[drwayne]

Actually, the truck/train example is a classic physics/dynamics problem. You can not propel a train in this fashion.<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[vidar]

Can you please tell me about the ‘classic’ truck/train example, and why it does not work?<br />I still think it is possible to move a wagon while sitting in it.<br />

 

[no_way]

<blockquote><font class="small">In reply to:</font><hr /><p>it is possible to move a wagon while sitting in it. <p><hr /></p></p></blockquote><br />Yes but this has got to do with various forms of friction, and ultimately you are pushing yourself against the ground. In space there's nothing to push against.

 

[drwayne]

Actually, the other explanations here pretty much sum it up. Unless a system has an external force acting on it, you can not create motion.<br /><br />When the hammer strikes the train, it exerts a foce on the train. BUT, the train also exerts a force that is equal and opposite on the hammer (and by extension the train). There is no net force at the interrface to drive motion.<br /><br />The danger in a dynamics problem in examining forces is that you do not account for all forces acting in the problem. This happens to many. You should always have a final check on your though process that says, for a given system, is there a net external force acting on it. If there is not, and you are accelerating, then you have done something wrong.<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[ehs40]

this is a good idea and may no work on earth but once we return to the moon we will need to be as energy efficent as possibly and because we all know the moon has little gravity this could work on the moon as a launch to mars

 

[nacnud]

<img src="/images/icons/rolleyes.gif" />

 

[tomnackid]

<p>From Wikipedia:<br /><br />Starwisp is a hypothetical unmanned interstellar probe design proposed by Robert L. Forward. It utilizes beam-powered propulsion in the form of a maser driving a solar sail.<br /><br />The Starwisp probe would consist of a mesh of extremely fine wires about a kilometer across, with the wires spaced the same distance apart as the wavelength of the microwaves that will be used to push it. Light weight is the key feature of Starwisp; the wire mesh would have a mass of 12 grams, and the remainder of the probe's microcircuitry and sensors would mass 4 grams for a total mass of only 16 grams. Constructing such a delicate probe would be a significant challenge. One proposed method would be to "paint" the probe and its circuitry onto an enormous sheet of plastic which degrades when exposed to ultraviolet light, and then wait for the sheet to evaporate away under the assault of solar UV after it has been deployed in space.<br /><br />Using a microwave laser producing 10 gigawatts of power, Starwisp could be accelerated at 115 Gs (1130 m/s²) and reach 20% of the speed of light in only a matter of days. Since masers cannot be easily focused at long ranges, Starwisp could not be driven much faster than this. The probe would cruise without power at 20% c for decades until it finally approaches the target star, at which point the maser which launched it would again target its beam on Starwisp. This would be done when the Starwisp was about 80% of the way to its destination, so that the maser beam and Starwisp would arrive there at the same time. At such extreme long range the maser would be unable to provide any propulsion, but Starwisp would be able to use its wire sail to collect and convert some of the microwave energy into electricity to operate its sensors and transmit the data it collects back home. Starwisp would not slow down at the target star, performing a high-speed flyby mission instead.<br /><br /><br />For the whole article go to:</p>

 

[vidar]

I will try to explain the elmag hammer principle in another way.<br /><br />An overblown balloon flies forward, when the back end is opened. It is not because the streaming air pushes at the air outside. It is not like a stream at a wall that pushes an engine from the wall. It is because the air that is pressed forwards inside the balloon does not meet a counterforce at the back. <br /><br />Most rocket engines works at such an ‘overblown balloon’ principle. In the engine chamber, the burning chemical liquid fuel expands when ignited and explodes into gas molecules. The molecules hammer at the back side of the rocket. This provides forward thrust. Such constant ‘blowing up of the balloon’ makes constant forward thrust of a rocket. That is also why it works in vacuum. It is a common misunderstanding that the tail of fire of a rocket is the power to the thrust. Most of the tail is in fact wasted energy.<br /><br />There is no doubt that the gas principle works on rockets and that it is the hitting of molecules at the backside of it that moves it forward.<br />Therefore I think it is worth testing if an elmag hammer/piston could work as well in space.<br />

 

[nacnud]

<p>No<br /><br />If you push the hammer away once then it would propel you forwards but if you try to take the hammer with you it won’t work<br /><br />Here is an (bad) sketch. <br />COM = Centre of Mass<br /><br />At time=0<br />……………………………………..(COM)<br />……………………………..[Hammer Spaceship]<br /><br />At time=t<br />……………………………………..(COM)<br />[Hammer]………………………………………………………………[Spaceship]<br />…………………………………………………………………………..->V<br /><br />If the hammer and the spaceship are still joined a time=t then you have to take the common centre of mass as the reference frame and that hasn’t moved.<br /></p>

 

[vidar]

I am not interested in dropping the hammer after the first stroke. I was more thinking of letting it come along and repeat the beats at a rate of 1000 Hz. The beat of the hammer must therefore provide greater force than what is necessary to drag it along. I think the much more massive ship, set in motion, can do that without stopping. I also think that the generator can provide sufficient energy to set the ship in accelerating motion.<br /><br />Remember, there is no 1 G (10 m/s^2 counter-acceleration) to overcome. There is no air friction to fight or mechanical friction, like in wheels, to struggle with. It is free floating and need far less energy for motion than on earth.<br />

 

[no_way]

<blockquote><font class="small">In reply to:</font><hr /><p>Remember, there is no 1 G .. to overcome. There is no air friction to fight or mechanical friction<p><hr /></p></p></blockquote><br />Oh yes but there's couple basic laws of physic to overcome that you this far seem to be ignoring. Re-read Newtons laws first and try to understand them. <br /><br />Additionally, there are couple in-depth pages on the web that explain why various perpetuum mobiles wont work, and also why various "propellantless rockets" wont work. And i can tell you before you get to it, converting angular momentum to linera momentum wont work either.

 

[nacnud]

<font color="yellow">I am not interested in dropping the hammer after the first stroke.<br /><br /><font color="white">Then the ship is just going to sit there buzzing at 1khz, except there is no sound is space so you won't hear it <img src="/images/icons/tongue.gif" /> <br /></font></font>

 

[vidar]

A problem with Newton theories is that they were the fundamental once, explaining very simple systems. His theories were made 250 years ago. I do not think he could imagine the technologies of today, and thereby did not think very advanced. He kept fighting gravity, air resistance, and frictions of mechanics. I do not think he could imagine the realities of space. The laws showed to be too simple for the previous centuries technologies, and they still are.<br /><br />I am no skater. But please tell my why I can stand with both feet on a skateboard, and with quick pushes forwards with my legs; I am able to make that board and myself moving forwards, - repeatable. Newton’s laws might say I can not, but anyone can do it themselves if they try.<br /><br />Skip that law and just do it.