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Costs of a Railgun system.

Posted by: James Summers - Thu Jan 11, 2007 6:50 pm
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Costs of a Railgun system. 
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Post    Posted on: Tue Feb 13, 2007 10:47 pm
Has anyone followed the recent US Navy experiments with rail guns? They plan to equip ships with operational rail guns instead of traditional guns from 2020, and have just made some tests with a 3.2kg projectile that they shot at a target with 8MJ of energy (that makes about 2236 m/s exit velocity). Their target is 8 times as much energy, though I'm not sure if the projectile mass will be the same; and apparently one thing that's holding them back is capacitor supply. Other than that, apparently they're quite happy with the cost effectiveness (at least from the point of view of getting ordnance somewhere).

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Post    Posted on: Tue Feb 20, 2007 8:08 pm
I read that article on Navy rail guns with a lot of interest, and probably posted something on it here.

The problem with capacitors on a ship is space, from what I understand. One has to fit everything within the confines of a hull.

Not so much of a problem with ground facilities.

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Post update to hypacc   Posted on: Tue Feb 27, 2007 7:26 pm
I have recenly updated my design for a rocket acclerator as the basis for cheap orbital access. take a look at my site www.hypacc.com and click the animations button for a quick explination. I am looking for comments and get the feeling I might get more than I bargined for here! The site is a bit rough and I do tend to get on my soap box a bit.


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Post    Posted on: Tue Feb 27, 2007 9:05 pm
The problem I have with all these orbital gun ideas is that you need orbital velocity parallel to the ground but the gun fires straight up, or much closer to straight up than to horizontal. A rocket can "turn a corner" and apply most of its thrust horizontally but a gun can't since all the acceleration takes place at ground level. It would work well for escape, as in "From the Earth to the Moon", but how could it ever put something in LEO?


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Post    Posted on: Wed Feb 28, 2007 9:53 pm
campbelp2002 wrote:
The problem I have with all these orbital gun ideas is that you need orbital velocity parallel to the ground but the gun fires straight up, or much closer to straight up than to horizontal.


That's an important point. It's actually possible to reach stable orbits like that, but only very limited orbital parameters (where your instantaneous velocity vector happens to be aligned with the projectile's flight path). However, there are a few ways to mitigate the problem, and the good thing is you can use them all together:

1) Use a projectile with its own propulsion system to make an orbital correction maneuver (say for circularization). This was planned e.g. in the HARP project.
2) Fire in an oblique angle so that the flight path of the projectile near its apex is close to your intended orbit. I know of one serious railgun project where the firing angle would be about 30° from horizontal only.
3) Rather than Verne's Columbiad that could hit the Moon only once every 18 years, mount the gun on a movable structure. Of course that limits the size somewhat but we're anyway talking nano- pico- or femtosats here.

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Post Re: update to hypacc   Posted on: Tue Mar 06, 2007 6:50 pm
scott taylor wrote:
I have recenly updated my design for a rocket acclerator as the basis for cheap orbital access. take a look at my site www.hypacc.com and click the animations button for a quick explination. I am looking for comments and get the feeling I might get more than I bargined for here! The site is a bit rough and I do tend to get on my soap box a bit.


I read that site.

Interesting idea and one I wish I had the money to fund a feasibility study along with and small test mock up.

Give me another 20 years... ;^)

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Post    Posted on: Fri May 04, 2007 10:39 pm
Might help to look for submerged karst tunnels like what folks skydive into...


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Post Navy Rail guns   Posted on: Sun Jul 01, 2007 9:24 am
A comment on the question above about navy rails guns. First most don't use caps because getting the 1000000 or more amps is too hard. They use Compulsators http://en.wikipedia.org/wiki/Compulsator. Coil guns, big ones anyway would use them too.

The biggest problem by far is rail wear. These currents turn the sliding contacts into plasma and erode the rails. Finding a material thats strong enough and can handle the erosion is hard. Remember that there are HUGE forces pushing the rails apart.

Also don't forget that this is for a gun with a 1-5kg projectile. Scaling this up to 1000+kg is something we just can't do right now.

Personally I think the general category of mass drivers will not be that economic within atmospheres (note: I did not say imposable).


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Post Re: Navy Rail guns   Posted on: Sun Jul 01, 2007 11:52 am
delt0r wrote:
A comment on the question above about navy rails guns. First most don't use caps because getting the 1000000 or more amps is too hard. They use Compulsators http://en.wikipedia.org/wiki/Compulsator. Coil guns, big ones anyway would use them too.

The biggest problem by far is rail wear. These currents turn the sliding contacts into plasma and erode the rails. Finding a material thats strong enough and can handle the erosion is hard. Remember that there are HUGE forces pushing the rails apart.

Also don't forget that this is for a gun with a 1-5kg projectile. Scaling this up to 1000+kg is something we just can't do right now.

Personally I think the general category of mass drivers will not be that economic within atmospheres (note: I did not say imposable).


I agree that an earth's surface to orbit railgun system for any real payload is not going to happen soon if at all, but I think the railgun concept would be good for escaping other planetary bodies, for example a surface mounted railgun on the moon (or somewhere with a low escape velocity) to fire samples or payload back to earth.

Also you could conceivably use a railgun system to drive an airbreathing vehicle past the speed of sound so that no take-off turbojets are required. In a rocket based combined cycle spaceplane system the main problem (which is usually overcome with using turbojets too, one more system = tons of wasted mass) is that you have to run the rocket motors to take off. If you used a railgun to accelerate the vehicle to a velocity at which the ram/scramjets could work then you could do-away with the takeoff turbines.


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Post    Posted on: Fri Sep 14, 2007 1:04 pm
I think this thread pretty much has convinced me of the un-economicalness of such things for now.

Maybe the company trying to build one will work, but I will be placing my bets (literally) elsewhere.

I do see some applicability for places like the moon where both the lack of atmosphere and reduced gravity will make such a thing FAR more feasible, but that is, sadly, a looooong way away.

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