Author Topic: Navy rail gun breaches atmosphere  (Read 11186 times)

Offline kevin-rf

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Re: Navy rail gun breaches atmosphere
« Reply #20 on: 01/19/2007 10:42 PM »
and the tomahawks just take up space in the launch tubes on attack subs? They can get in close, fire and get out, a surface ship lacks stealth and needs a fleet to back it up. The LCS is an interesting concept, swarm the enemy with several small low cost ships spreading there resources thin and lauch a massive bombardment from them.

Might be a dumb question, but if a section of the slug was Al, is there enough energy in the impact to vaporize and ignite it?
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Offline TyMoore

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Re: Navy rail gun breaches atmosphere
« Reply #21 on: 01/20/2007 12:22 AM »
O.K., let's do some basic physics. There is a lot of really good information on the current Naval gun system: the Mk 45/54 Caliber 5 inch gun system at:

http://www.globalsecurity.org/military/systems/ship/systems/mk-45.htm

The muzzle energy of this system is 10-18 Megajoules (10 MJ for the Mk45/Mod 4, and 18 MJ for a more advanced unit with longer barrell and probably different propellant.) Project weight is probably somewhere in the neighborhood of 50-70 Kg (110 lb to 154 lb.) This gun system has a 'regular' range of 13 nautical miles, but with extended range ammunition (advanced rocket boosted, GPS guided munitions) this can be extended to 40 n.m.

Running some numbers for the Mk45:

Since KE=1/2*m*v^2 then rearranging to solve for "v" we get:

v=sqrt(2*KE/m)

For a projectile mass of 50 kg, muzzle energy of 18 MJ, we can expect to get about

v=848.5 m/s or about 2780 ft/s (a little slower than a 30-06 rifle bullet for you hunters out there!)

One of the number's 'tossed out' was Mach 5 projectile. Using this number as a WAG let's run some numbers.

Since Mach 5 at sea level is about 5*1043 ft/s=5215 ft/s. Let's use a muzzle velocity of 1 statute mile per second, 5280 ft/s, or 1600 m/s for metric buffs.

Let's look at a 20kg projectile of depleted uranium (this will be a dart about 5 cm in diameter with a 6 degree cone half angle and about 60 cm long (about 2 feet.) With a muzzle velocity of 1600 m/s, this project will have a muzzle energy of about:

KE=1/2*20kg*(1600m/s)^2

KE=25.6 Megajoules or about 70% more than the muzzle energy of the much heavier MK 45 shell.

This thing would definately pack a wallop! Incidently the "other" reason for choosing depleted urainum in armor defeating rounds has nothing to do with its density. It is that uranium metal is naturally pyrophoric--which means it burns spontaneously on contact with air when finely divided into powder. Well the impact of a highly energetic but very dense projectile will create jets of material that spalls of the penetrator as it flows through the steel armour. This jets of material will finely divide into microscopic droplets, which almost instantly burn in air. The net result is a catastrophic explosion inside whatever is penetrated all because of kinetic energy and pyrophoric chemicals. Inserting a pin of aluminum in the middle probably won't add too much to this, but I'm pretty sure it would burn just fine if it were a jacket.

Larger, faster projectiles are certainly possible and likely, especially if the Navy want's to go for guided munitions.

The problem is acceleration--rather too much of it. A rail gun projectile will accelerate pretty close to 100,000 g's which is about 10 times the g load of a conventional projectile: this means more difficult to engineer electronics with probably less capability. Longer barrels can help alleivate this, but that makes the weapon less compact. It's an interesting concept...

Offline Polecat

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Re: Navy rail gun breaches atmosphere
« Reply #22 on: 01/21/2007 05:23 AM »
Maybe China was responding to this ;)

Offline simonbp

Re: Navy rail gun breaches atmosphere
« Reply #23 on: 01/21/2007 07:14 PM »
Quote
TyMoore - 19/1/2007  7:22 PM

The problem is acceleration--rather too much of it. A rail gun projectile will accelerate pretty close to 100,000 g's which is about 10 times the g load of a conventional projectile: this means more difficult to engineer electronics with probably less capability. Longer barrels can help alleivate this, but that makes the weapon less compact. It's an interesting concept...

I know some people a specialty soldering company here in Huntsville (whose main business is Army and NASA missiles) who are working on integrating the chip die directly on the PCB, specifically for high-G applications...

Simon ;)

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Re: Navy rail gun breaches atmosphere
« Reply #24 on: 01/21/2007 07:49 PM »
Where there's a will and a government contract, there's a way.

Offline stargazer777

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Re: Navy rail gun breaches atmosphere
« Reply #25 on: 01/22/2007 12:20 AM »
Thanks Chris.  You should also check out the latest Aviation Week lead story on this topic:  http://www.aviationweek.com/aw/generic/story_generic.jsp?channel=awst&id=news/aw012207p1.xml

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