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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 factored in earth's spin   Posted on: Mon Jan 29, 2007 7:12 pm
Added the 465 m/s into your equations there, and that ended up with about a 40% reduction in required fuel if the assumptions used in the original set of equations are held the same.

m0=887
m0-100=787
787/1302= .601598=60.15%

That isn't too bad for a track with rather low acceleration. I will have to see what maxxing out the accel at about 7gs would do for humans, or assume 10gs for unmanned cargo ships.

One doesn't have to acheive orbital velocity out of the railgun, just give it enough of a boost to be cost effective.

I guess the ultimate arbitor of whether the whole "boost" idea is worthwhile is the cost of fuel versus the costs of the launcher. This is, I know, something of a simplification, but the essence of the question.

ah well, lunch hour is over.

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Post    Posted on: Mon Jan 29, 2007 9:29 pm
Since a ground launched rocket at the equator would enjoy the same benefit of the Earth's rotation, rather than add the 465 m/s into the velocity supplied by the magnetic launch, you should subtract that number from the total DeltaV needed to reach orbit in both cases. To be more precise, I calculated the exact velocity for a circular orbit at 300 km altitude from information available in wikipedia. It is the square root of u/a where u is the standard gravitational parameter of Earth (basically the universal gravitational constant times the mass of the Earth = 398,600) and a is the radius of the orbit measured from the center of the Earth (Equatorial radius of the Earth = 6,378.137 km, plus 300 = 6,678.137). SQRT(398,600/6,678.137) = 7.725755951 km/s (I’ll round it to 7.726). The DeltaV needed to get up to that speed from the equator of the rotating Earth is only 7.726 -0.465 or 7.261 km/s. Adding an assumed 2.0 km/s for air drag and gravity losses (based on the chart at http://www.pma.caltech.edu/~chirata/deltav.html) means we need to get 9.261 km/s to reach orbit. Subtracting out 0.7 for the velocity gotten from the rail and 0.2 advantage from starting at 2 km altitude, means the rail launched rocket only needs 8.361. When I plug 9.261 and 8.361 into the Excel rocket equation, I get 32% less propellant needed for the magnetic launch (if the exhaust velocity is 3.5 km/s). The savings is only 26% if the rocket has an exhaust velocity of 4.5 km/s. A LOX/LH2 engine can give 4.5 km/s in a vacuum, but no rocket engine can do that well at sea level air pressure.

But it isn't really so simple. The DeltaV calculated by the rocket equation is just what you would get starting in a weightless vacuum at zero speed and burning that much fuel. The amount of additional propellant you waste due to gravity and air drag to actually get to orbit from the ground depends highly on things like launch trajectory, acceleration rate, and aerodynamic efficiency of the vehicle. Ideally you would want to launch almost horizontally, but the atmosphere prevents that so you have to launch close to straight up, then turn a corner and accelerate horizontally up to orbital speed. The exact angle you launch at, how high you go before turning the corner, and how sharply you turn the corner makes a world of difference in how much propellant you waste getting out of the atmosphere! And I am not even considering how the exhaust velocity of the engine increases as outside air pressure decreases during the flight. A higher acceleration, lower drag vehicle on the most efficient trajectory will get to orbit with only a little more propellant than would be required to accelerate from a dead stop in a weightless vacuum up to 7.261 km/s. A worst case, absurd example of the other extreme is a rocket with only 1.0 G acceleration which never goes anywhere; it just hovers until it runs out of fuel! So there are a host of engineering and operational details we are totally ignoring that are actually far more important that the choice between a magnetic rail and a conventional rocket powered first stage.


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Post    Posted on: Tue Jan 30, 2007 3:03 pm
campbelp2002 wrote:
Since a ground launched rocket at the equator would enjoy the same benefit of the Earth's rotation, rather than add the 465 m/s into the velocity supplied by the magnetic launch, you should subtract that number from the total DeltaV needed to reach orbit in both cases.
[message truncated for brevity--js]


Once again, good points. This is precisely the kind of stuff I had hoped to soak up by reading here.

Here is something else to consider:

http://www.navytimes.com/news/2007/01/aprailgun070117/

[begin excerpt]


[i]A flashy demonstration of the futuristic and comparatively inexpensive rail gun weapon Tuesday at the Naval Surface Warfare Center had Navy brass smiling. The weapon, which was successfully tested in October at the King George County, Va., base, fires nonexplosive projectiles at incredible speeds, using electricity rather than gunpowder.

The technology could increase the striking range of Navy ships more than tenfold by the year 2020. “It’s pretty amazing capability, and it went off without a hitch,â€

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Post    Posted on: Mon Feb 05, 2007 1:16 pm
From time to time I am thinking about the possibility to accelerate an object to less than 27,500 km/h before it leaves the maglev.

This might be done either if the object leaves the maglev earlier or if it is heavier.

If it is done then an engine might be added that later adds the velocity not got by the maglev.

Regarding the heat discussed for the original case of acceleration up to 27,500 km/h - what about using heat to apply VAPAK once an altitude of around 10 km is reached?

Where might be the critical value of speed got by maglev at which VAPAK no longer could be applied?



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Post    Posted on: Mon Feb 19, 2007 7:33 pm
Just this moment I remember another technology where there is a NIAC study about maglev could be a component of.

The NiAC study is about the idea that a vehicle located in orbit permanently could temporaryly go to lower altitudes to catch a payload from an airplane or so.

Launchpoint Technologies' concept perhaps could be used to launch the 100 kg-payloads to a lower orbit or suborbital but to an altitude where the vehicle located in orbit permanently could catch it.

And since the payloads are that light and supposedly relatively small the concpet might be an opportunity to test the catch-concept by down-scaled prototypes.

I remember to have initated a thread about the NIAC study in 2004 or 2005.



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Post    Posted on: Tue Feb 20, 2007 9:08 am
Regarding a maglev on the Moon: Could it be used for suborbital transportation across the Moon somehow? The gravity is much less there and the container could have a crushable part or something like airbags.

What about it?



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Post    Posted on: Tue Feb 20, 2007 9:43 am
One thing to think about is the huge EM pulse that is produced every time one of these things is fired. Normally the frequencies that are produced are relatively low frequency and so predominantly produce magnetic fields rather than electric fields which require lots of screening for electronic equipment. Magnetic fields normally pass through non-ferrous materials so any screening will need to have an iron content.

Not sure whether there is a lot of iron on the moon that can be extracted, if not then it would have to be transported from Earth. I think I am right in saying that most light weight alloys commonly used in the space industry do not contain iron, although I am not completely sure this is the case.

As an aside the EM pulse was a problem when a magnetic launcher was being considered for use on aircraft carriers to launch planes. The pulse would effect the electronics on the plane.

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Post    Posted on: Tue Mar 06, 2007 6:46 pm
Andy Hill wrote:
One thing to think about is the huge EM pulse that is produced every time one of these things is fired. Normally the frequencies that are produced are relatively low frequency and so predominantly produce magnetic fields rather than electric fields which require lots of screening for electronic equipment. Magnetic fields normally pass through non-ferrous materials so any screening will need to have an iron content.

Not sure whether there is a lot of iron on the moon that can be extracted, if not then it would have to be transported from Earth. I think I am right in saying that most light weight alloys commonly used in the space industry do not contain iron, although I am not completely sure this is the case.

As an aside the EM pulse was a problem when a magnetic launcher was being considered for use on aircraft carriers to launch planes. The pulse would effect the electronics on the plane.


The iron content in most of the free floating asteroids is quite high, so even if iron were rare on the moon, iron wouldn't be a problem.

As for the EM problem, that is yet another hurdle for such a rail launcher.

It would be irrelevant if the launch vehicle was simply a container and had no real electronics. Low orbit "catches" of such things would be very doable, as was pointed out.

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Post    Posted on: Tue Mar 06, 2007 6:59 pm
A rail gun can't launch directly into low Earth orbit because to do so requires a path parallel the the Earth's surface. As long as the projectile is moving under the influence of gravity only, with no thrust or drag, then it will describe a closed, repeating path. It will come back to the same location that it came from, and it will arrive there going in the same direction and at the same speed as it left there on the previous orbit. If that place is the muzzle of a rail gun on the ground, or even the point where the projectile left the atmosphere, then unless it has onboard propulsion it must of necessity reenter before completing one orbit no matter how fast it was going at launch. Unless it was launched with escape velocity, to the Moon or whatever.


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Post    Posted on: Tue Mar 06, 2007 7:32 pm
James Summers wrote:
As for the EM problem, that is yet another hurdle for such a rail launcher.

It would be irrelevant if the launch vehicle was simply a container and had no real electronics. Low orbit "catches" of such things would be very doable, as was pointed out.


It would be a problem for any avionics or guidance equipment used for course correction and would play havoc with things like solenoids used to open/shut valves in any propulsion system.

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Post    Posted on: Sun Jul 29, 2007 11:20 am
hi im new here and i was surprised to find people talking about an idea ive had for a few years lol i dont have the math skills some of you have but tell me what u think of my idea. ive read a the entire thread and others have talked about using maglev launchers at higher altitudes but they have been around a mile in altitude, and you have shown that the atmospher at that altitude would still be to dence for maglev to be viable.

now for my idea lol

take a location like Mt Elbert in Colorado it is 2.73 miles in elevation now build a maglev track in a vacume going down the slope of a nearby mountain and up the side of mt elbert. yes i know the cost would probably be crazy lol and use this method to bring a craft equiped with scramjet engines up to mach 7 the needed speed for them to engage. and use the scram jets to reach orbital velocity.

Projections for the top speed of a scramjet engine (without additional oxidiser input) vary between Mach 12 and Mach 24 (orbital velocity), but the X-30 research gave Mach 17 due to combustion rate issues.

now i know some more work is needed to reach this speed with scram jets but once its reached and the track could be built for a reasonable price or be proven to be worth the cost wouldnt this be a viable option just tryin to add to the conversation


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Post    Posted on: Mon Jul 30, 2007 1:49 pm
I believe 2.73 miles is way too low for a mach 7 scramjet. That is only a little a little over 14,000 feet. Most private planes can fly higher than that. I think altitudes above 50,000 feet are needed to get thin enough air. The SR-71 for example flew at Mach 3 at 70,000 feet. That is over 13 miles high.


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Post    Posted on: Wed Aug 01, 2007 10:46 am
re iron on the moon, here is a link to a pdf about making magnets from regolith.. http://isru.msfc.nasa.gov/lib/Documents ... MRS-NR.pdf

Apparently moon regolith has enough magnetic properties to be manipulated magnetically:
http://www.lpi.usra.edu/meetings/lpsc2007/pdf/1662.pdf

also I heard somewhere that a small fraction of moon regolith is basically pure iron, so it could be extracted by some sort of simple magnetic sorting

(ps I didnt examine those pdf closely so I hope I wasnt missing the point on either)


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Post    Posted on: Wed Aug 01, 2007 11:06 am
The equqipment to handle the regolith is looking as if a lunar maglev might be based on it.

On the other hand I am not sure if a torus is required since on the Moon there is a vacuum and only the magents of the maglev are required.

The idea to make a lunar maglev from lunar iron is very good but what about the equipment required? If that equipment is as heavy as the equipment of the lunar maglev then the components of the lunar maglev should be carried from Earth it seems to me at present.

...



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Post    Posted on: Wed Aug 01, 2007 11:42 am
um.. yes. I was jumping in a bit out of context on just the iron comment.

Also those links werent as relevant as I thought. the magnets from regolith one was more enthusiastic about mars. Still, lots of mention of iron on the moon.

You might as well send any initial device from earth since even a small mass driver could send a massive tonnage into orbit per year. The problem is finding the power for it. Finding a way to manufacture acres of solar cells from moon resources would probably make a much larger difference.

I wonder how small a massdriver could be made.. one idea I had was to launch tiny magnetised iron particles, and use their magnetic proprties to allow them to clump in orbit. Possibly you could send them on a path where they would reliably burn up in the earths atmosphere if not collected.


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