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Maglev launch

Posted by: Garnetstar - Thu Sep 11, 2003 1:24 am
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Maglev launch 
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Post Maglev launch   Posted on: Thu Sep 11, 2003 1:24 am
It seems that one trick that can be turned with today's technology is to use a Maglev track for launch. It could be especially efficient if it were used to bring an air-breathing hydrogen ramjet up to speed. The ramjet could in turn serve as the "second stage," giving way to a self-contained rocket outside the atmosphere. Does anyone see any problem other than initial cost (I estimate you'd need a Maglev track a kilometer long) that would prevent this from being viable?


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Post    Posted on: Thu Sep 11, 2003 5:57 am
Maglevs seem to be the forgotten launch technology. People are always clamboring over how great space elevators are because they don't require you to carry fuel along with your payload but neither do railguns necessarily and they don't require a cable that's 60,000 miles long. *steps off soapbox.* In any case, I was wondering if it might be possible to build a maglev launcher like a bridge across several stationary platforms at sea. Not sure if you could keep it stable or if it would be cheaper finding a long stretch of land somewhere. :?:


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Post Made a nice little drawing   Posted on: Thu Sep 11, 2003 10:43 pm
Made a nice little drawing of a maglev launch.. :D
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Post    Posted on: Thu Sep 18, 2003 1:56 am
That drawing looks plausible--including the "exit ramp."


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Post    Posted on: Fri Sep 19, 2003 12:13 am
You know, I have always thought that some sort of sloped track would be a great way to lauch any sort of rocket. And I don't think that it would neccearily have to use Mag-Lev technology. The rocket would buitd up momentum as it traveled down the ramp till it reached a point where it would initialize it's rocket boosters, just like in Voyager4D's example.

The only thing I havent really figured out is how to get the rocket to the top of the ramp. I mean, we are talking quite a few tons here! You would have to use some sort of mega durable elevator contraption to get it even 100 feet up! Unless of course you built it on a hill...but you would still have to get it up there some how. Probably using mega durable simi-trucks that can go up hill caarring 20+ tons of space craft....

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Post    Posted on: Fri Sep 19, 2003 12:41 am
Alternatively, one could dig a tunnel into the earth. However, to get up good speed within a short distance, Maglev is probably the best currently available technique. I'm also thinking of the next stage being a hydrogen ramjet, to take advantage of the weight reduction obtained using an air-breathing engine with a very light fuel. Since jet engines won't get you much above 30 km, the top stage would be a rocket.
The ramjet, of course, doesn't function until accelerated to a high speed. That's where the Maglev track comes in handy--it means we don't have to carry another type of engine aloft just to get the ramjet going. The very successful SR-71 Blackbird uses a hybrid engine--turbines to get up the speed and pure ramjet at high speeds. But an X-Prize entry would be better off if it didn't need to carry the weight of the turbines.
I've calculated that a 1 km Maglev track can accelerate an appropriate sized vehicle to about 300 m/s, (a very nice speed, efficient for a ramjet and just shy of the speed of sound at sea level), provided it could be supplied with a current upwards of 200 000 A, about 40 times that used in a subway train. Handling that kind of current might prove the biggest practical difficulty.


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Post    Posted on: Fri Sep 19, 2003 12:42 am
Alternatively, one could dig a tunnel into the earth. However, to get up good speed within a short distance, Maglev is probably the best currently available technique. I'm also thinking of the next stage being a hydrogen ramjet, to take advantage of the weight reduction obtained using an air-breathing engine with a very light fuel. Since jet engines won't get you much above 30 km, the top stage would be a rocket.
The ramjet, of course, doesn't function until accelerated to a high speed. That's where the Maglev track comes in handy--it means we don't have to carry another type of engine aloft just to get the ramjet going. The very successful SR-71 Blackbird uses a hybrid engine--turbines to get up the speed and pure ramjet at high speeds. But an X-Prize entry would be better off if it didn't need to carry the weight of the turbines.
I've calculated that a 1 km Maglev track can accelerate an appropriate sized vehicle to about 300 m/s, (a very nice speed, efficient for a ramjet and just shy of the speed of sound at sea level), provided it could be supplied with a current upwards of 200 000 A, about 40 times that used in a subway train. Handling that kind of current might prove the biggest practical difficulty.


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Post    Posted on: Wed Oct 29, 2003 1:34 pm
Even if you didn't use the maglev system, the launch cradle will still remain on the ground, so any number of propulsion systems could be utilized. Jet's, rockets, maglev, or just plain electric motors. As long as the launch cradle achieves the velocity needed for the payload's ramjets, or more likely scramjets to takeover. However, you have to remember that however you accelerate your craft, the energy used has to be bought. The beauty of the space elevator is that, following the initial spend, very little additional cash input is required.

I do like the idea of magnetic rail launches though. It's the romantic inside of me. If I'm to visit orbit, I want it to be a ride, not a trip in an elevator.

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Post    Posted on: Wed Oct 29, 2003 9:30 pm
The maglev launch idea seems to be a great idea, but when the vehicle/rocket will go from +-45 degrees vertical down to 90 degrees up, a change of 135 degrees in a very short moment.
Isn't it creating a too large pressure for the people inside the vehicle with that accelerating speed and almost a full vertical U turn ?
At low speed taking a looping in a roller coaster can create already a large pressure... are there numbers or is there information available about this ?


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Post    Posted on: Thu Oct 30, 2003 2:46 am
I would not recommend that big a change of direction. Rather, the launch track could consist of a circular arc with a radius of 2-3 km, but an actual length of 1-1.5 km. A tighter turn would produce too much centripetal acceleration. Consider: a = v^2/r. Substituting v = 300 m/s (a nice speed for firing up a ramjet) and r = 2000 m, we get an acceleration of 45 m/s, ~ 4.5 g. However, seeing that people are very free to hand over money to take upward of 5 g at amusement parks, I don't think that X-Prize contestants need be too conservative on g-force. Get Shirley Muldowney to drive it for you!


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Post    Posted on: Thu Oct 30, 2003 3:34 am
4,5G's (of lateral acceleration) would be far too much to any modern orbital rocket design. The rocket with that much sideways acceleration at full load would need to be quite a bit sturdier than anything now flying.


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Post    Posted on: Thu Oct 30, 2003 8:06 am
Quote:
don't think that X-Prize contestants need be too conservative on g-force.


Some people will indeed ignor that, but I think most older people and people with medical problems will not be able to use it, so this idea isn't that good at all for the x-prize, the goal is to make space open for "everyone" and not beeing a ride in a roller coaster with +-5G.

But if the tickets would be cheaper compared to normal vehicles, then yes I could be one of the people paying for a ticket, cause an extra roller coaster adventure is never that bad ;) as long as we return "safe" back to earth.

But for the future we don't need a system like this, but a safe, comfortable, useable for everyone, cheap, ... way of accesing space.
So a combination of the best of all.


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Post    Posted on: Sat Nov 01, 2003 6:48 pm
But even at my advanced age, a good kick is fun. Last summer my sister dragged me to an amusement part, after not being near one for 30 years. Shall we say. . . the rides have advanced a little in that time? I was all shook up but I loved it and I would do it again. I think you might be able to charge a higher price for the high-g ride! (Provided it's at least reasonably safe, of course)

The other objection is more serious--there is no structure currently available for a WINGED vehicle that could take 4.5 g laterally. That doesn't make it impossible, but the mechanical engineering challenges would be formidable. I'm trying to avoid the other alternative: a VERTICAL maglev track a mile high, which would present equally severe engineering (and economic!) challenges.


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Post    Posted on: Sun Nov 02, 2003 10:05 am
The wings could be deployable after the horizontal to vertical transition. Swing wing, like some military fighter jet, with only some small control surfaces at the beginning. Feasible? Yeah, I know, more mechanics, more systems, more chance of failure, more redundancy, more safety equipment, more weight, more cost, less payload, less efficiency. But, like all things, with a little engineering, possible.

I think the Maglev will be more suited to offworld launches. The moon for instance. Should a habitat be built there, the advantages are enormous for maglev launch systems. The amount of sunlight up there is greater due to there being no atmosphere, so solar collectors could produce nice quantities of energy. And less energy would be required due to the lack of any atmospheric friction, (oh, there goes the need for wings), and the escape velocity is far reduced.


Just need to get there.

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Post    Posted on: Sun Nov 02, 2003 12:19 pm
I think building the track mostly underground is the way to go here, digging is cheaper than vertical building :)


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