Space highway

grooble · Mar 21, 2005

Would it be possible to build a highway of powerful magnets to pull a ship to a destination? I know the magnets would have to be big, so that the magnet isn't pulled to the ship instead. Also, can you somehow negate the magnetism of a magnet, so that once it pulls, it can be shut down somehow? I'll post an image of what i mean.

grooble · Mar 21, 2005

As the ship nears the magnet pair, the magnets are switched off to allow the ship to coast past. They are in pairs as i imagine the ship would be pulled along the middle and not straight into a magnet. Computers could control the magnetism strength so that the ship can be kept in alignment. I don't know what sort of speeds would be reached, it's just an idea, and i don't know what the benefits could be.

grooble · Mar 21, 2005

image. And thinking about it, this would work with the space cannon, in order to SLOW down payloads, crew ships so they don't smash into the moon at incredible speeds.

nacnud · Mar 21, 2005

I don't think it will work unless you can reboost the magnets, remember Newton’s third law, every action has an equal opposite reaction.

grooble · Mar 21, 2005

Maybe the magnets could have solar power and small thrusters.

najab · Mar 21, 2005

Also, how would you keep the magnets from drifting around when they're not in use?

severian · Mar 21, 2005

Umm, well most space elevator designs use magnets to pull the capsule up along the stalk. In a way, you could have a big long tether running from the moon, through the central Earth-moon lagrange point, into the Earths upper atmosphere, anchored in a similar way to a space tether. Of course, then you would also be talking about a single piece of material (probably largely superconducting magnets) over 50,000 km long, which would be quite an engineering project. Free floating magnets would need to have something to anchor them, although use of high ISP propulsion over time could actually make it possible. Since there would be many of the magnets in space, the individual push each one gave would be relatively small, and if the traffic level was low, ion propulsion might be able to keep them in the correct position. However, the second you ask them to give large boosts, or do to do so regularly, they would start floating off. As for the floating around in orbit thing, again high isp propulsion could possibly keep them in a line, although I'm not sure how feasible that would be. Maybe you just have to wait for them to re-align before you send something through

vogon13 · Mar 21, 2005

Reaction forces on magnets need to be conteracted. Probably with thrusters larger than that needed to accelerate payload. And now that we are at this point, why bother with the magnets? <div class="Discussion_UserSignature"> TPTB went to Dallas and all I got was Plucked !!So many people, so few recipes !!Let's clean up this stinkhole !! </div>

najab · Mar 22, 2005

>...a big long tether running from the moon, through the central Earth-moon lagrange point, into the Earths upper atmosphere, anchored in a similar way to a space tether. Of course, then you would also be talking about a single piece of material (probably largely superconducting magnets) over 50,000 km long...The distance From the Earth to the Moon, is over 384,000km.

yurkin · Mar 22, 2005

There’s really no point in stretching the magnets out from here to the moon. Just put them all at LEO and at EM-L1. A series of circular electro-magnets in LEO powered by a space based nuclear reactor. This space ship passing through the magnets could be easily accelerated to the moon. At EM-L1 there would be another series of circular, nuclear, electro-magnets to catch the space ship by accelerating it to orbital velocity at that distance. The magnets would need station keeping since each “launch” would knock them backwards but in LEO this shouldn’t be too difficult. The EM-L1 station would be more of challenge to build and maintain. But the one can still work without the other.

vogon13 · Mar 22, 2005

I think if you measure the reaction forces, the fuel to station keep the magnets would be sufficient to propel the ship in the first place. Somewhere, your system has to conserve momentum. Unless I'm missing something here......... <div class="Discussion_UserSignature"> TPTB went to Dallas and all I got was Plucked !!So many people, so few recipes !!Let's clean up this stinkhole !! </div>

yurkin · Mar 23, 2005

the fuel to station keep the magnets would be sufficient to propel the ship in the first place. Yes that would be correct. The advantage would be that the ship would not need an engine. A lot of small engines on the magnets would be easier then building huge engines on each ship launched. But there’s not much point in such a system unless you have a lot of traffic from here to the moon.

rpmath · Mar 25, 2005

There’s really no point in stretching the magnets out from here to the moon. Just put them all at LEO and at EM-L1. LEO looks like a good point to build such a system. You can just launch a cheap ship to the orbital height, like Space Ship One, and let the system accelerate it to orbital speed. The station orbit will be a little lowered due to momentum exchange with the ship, but it could be slowly re-raised with ion rockets or other high ISP thrusters. To return, the ship can be accelerated in the opposite direction to return part of the momentum it gained, and reduce the amount of thrust the ion rockets must need. The ship itself would not need a very good heat shield, but it would be wise to have a capsule with heat shield rated to orbital speed, just in case the system fails, you will loose the cheap ship, but not the astronauts or expensive cargo. I think at L1 they are not needed, you can launch a ship from LEO to the Moon and put the magnets on Moon surface. You will need the Moon ones to land there using or not L1. They will be easy to build with lunar material (well… after there are some mining operations there) and easy to keep in place: just stick them to the ground. A series of circular electro-magnets in LEO powered by a space based nuclear reactor. This space ship passing through the magnets could be easily accelerated to the moon. At EM-L1 there would be another series of circular, nuclear, electro-magnets to catch the space ship by accelerating it to orbital velocity at that distance. I think the nuclear powered will be a political problem… Solar cells may be a solution, but they reduce the time window when you can launch: To have sunlight in a thousands of kilometers path, you need to launch near sunrise. If this must match the time where your location crosses the plane of the station orbit, and the time the fi

meteo · Mar 25, 2005

I think if you measure the reaction forces, the fuel to station keep the magnets would be sufficient to propel the ship in the first place. Somewhere, your system has to conserve momentum. Unless I'm missing something here......... What if there were equal amounts of space ship momentum traveling through the magnets in opposite directions? ie send one ship to the moon and have one come back shortly after. That should solve the problem of the magnets being moved out of place by reaction forces since the system would be designed so that reaction forces cancel out.

nexium · Mar 26, 2005

My guess is metro has the best idea. We build a million of the accellerating magnets. Each (of many) space craft uses as many as are lined up properly for accellerating, for direction change, and decellerating. That way the magnets and the space craft only need to make minor course and attitude adjustments except when one drifts to a location where it won't be useful long term or collision is likely with a planet, moon, asteroid or comet. The accelerating magnets could perhaps be built in pairs a kilometer apart with the superconducting current being switched from one to the other, to switch off the magnet at the correct instant. The main hazzard is possible scraping when a space craft passes though the hole and the speed difference is perhaps 10 kilometers per second. Neil

meteo · Mar 26, 2005

The main hazzard is possible scraping when a space craft passes though the hole and the speed difference is perhaps 10 kilometers per second. Neil That's a good point; if the magnets seperation from the ship was too far the magnets wouldn't be doing much, can't be much less that a foot (SWAG, I'm thinking maglev's). I really don't like the idea of flying a space ship through that small of a hole. It would seem this has to be a docking sort of thing. Magnets and mass have to be uniform within the space ship otherwise your say if your ship is accelerated yaw-wise your going to smack the tube at 10km/s. I So the ship has to be physically connected in some way, unless the tube has some way of keeping the ship from rotatinging (intellgently accelerating the ship more on certain sides when neccessary). A much better way of have canceling out the reaction forces and having the ship physically connected would be to set the tube rotating, and have it capable of lauches out of both ends. pi + x(2pi) radian rotation then launch out of opposite side This system would only lauch ships (physical connection neccesarry and hence the need to dock) so you would have to decelerate ships with aerocaputre or thrusters or something. However, the system would stay put if you planned the rotation right and seems much more plausable.

grooble · Mar 28, 2005

Yeah the guns are probably better on the moon. What is escape velocity on the moon? What is the lowest speed you could have a cargo container go from the moon to a landing in the ocean?

yurkin · Mar 28, 2005

Steve The mass will go forward, but the rail gun will go backwards. Right the mass go forwards to the moon the rail gun goes backwards. (m*V)1=(m*V)2. But, if you fired the “mass” vessel in the direction of the rail gun’s orbit, then the rail gun’s radial velocity would decrease. This would cause it to drop into an elliptical orbit whose apogee is at the attitude that you fired the mass and at the opposite side of the orbit. Travel half an orbit and you will reach the second apogee. At that location, fire a “mass” ballast in the direction opposite of the rail gun’s orbit. This will cause an increase in your orbital velocity which will increase your orbital velocity. If the momentum of the vessel and ballast is the same, and they were fired in opposite directions, at opposite sides of an orbit, there would be no change in the final orbit of the rail gun. It is just conservation of momentum. <img src="/images/icons/smile.gif" /> Meteo That's a good point; if the magnets seperation from the ship was too far the magnets wouldn't be doing much, can't be much less that a foot (SWAG, I'm thinking maglev's). I really don't like the idea of flying a space ship through that small of a hole. It would seem this has to be a docking sort of thing. It all depends on how much energy you put into the system. A maglev train only generates enough magnetic flux to elevate the train a foot; actually I think it’s less then that. But if you pumped more juice into the magnets and those magnets were larger you could elevate the train as high as you wanted. The problem is it’s not a linear relationship. Elevating a train 2 feet would take many times more electricity then elevating that same train 1 foot. Using the system described I would guess you would need at least twenty feet on all sides of it. In order to do that you would need

nexium · Aug 21, 2005

Hi steve: You need to make a lot of unlikely assumptions for the escape velosity to change with the ratios of the mass which is rarely the same as the ratio of the surface gravities. 2.4 kps however may be the escape velosity from the moon's surface in some direction. Escape velosity toward Earth or the sun is logically less than escape velosity toward the North star. The mass of the moon is only about 2% of the mass of the Earth not 1/6 th of the mass of Earth. Neil

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