Navy Debuts New Railgun That Launches Shells at Mach 7 630
Jeremiah Cornelius writes: "The U.S. Navy's new railgun technology, developed by General Atomics, uses the Lorentz force in a type of linear, electric motor to hurl a 23-pound projectile at speeds exceeding Mach 7 — in excess of 5,000 mph. The weapon has a range of 100 miles and doesn't require explosive warheads. 'The electromagnetic railgun represents an incredible new offensive capability for the U.S. Navy,' says Rear Adm. Bryant Fuller, the Navy's chief engineer. 'This capability will allow us to effectively counter a wide range of threats at a relatively low cost, while keeping our ships and sailors safer by removing the need to carry as many high-explosive weapons.' Sea trials begin aboard an experimental Navy catamaran, the USNS Millinocket, in 2016."
IANA Physicist, So... (Score:4, Interesting)
...Can someone who is explain where the big fiery explosion out of the railgun is coming from, if this thing is electromagnetically driven?
Re:IANA Physicist, So... (Score:2, Interesting)
So you need an incredible amount of current in a very short time to get an effect like this.
It's not entirely clear what the advantage of a railgun would be, it's very hard on the cannon. Psychology, I guess. It's an inert piece of metal that can't be jammed and is probably hard to spot on radar too.
Is anything actually burning? (Score:5, Interesting)
Actually, do we know that there's any burning going on at all? I believe the light from a fire is not directly emitted by the chemical reaction, it's a result of the combustion gasses glowing from the heat. In which case just heating even an inert gas sufficiently will cause it to glow similarly. And the immense high-speed compression from a mach-7 projectile traveling down a confined tube should generate plenty of heat.
Difficult to defend against (Score:5, Interesting)
Perhaps one of the big benefits of a naval railgun is that it's so difficult to defend against. Old-fashioned anti-ship missiles can be disabled or destroyed by the defending ship's close-in defenses [wikipedia.org]. This is because the incoming missile is filled with sensitive electronics, guidance systems, explosives, fuel, turbojet engines, stabilizing fins, etc, and is very likely to be damaged or destroyed if hit by a 20mm round from the defending ship's CIWS missile defenses.
However, how do you shoot down a hunk of metal traveling at mach 7 toward your ship? It wouldn't make any difference if you hit it with a 20mm round from the goalkeeper [wikipedia.org] or phalanx [wikipedia.org]. The projectile would just keep flying toward the ship and strike it anyways. Besides, how would you even hit something which is so small and traveling at mach 7.
It doesn't seem there would be any good defense against this.
Re:HOT HOT HOT! (Score:5, Interesting)
I suspect it's compression rather than friction doing most of the heating. Much like an orbital reentry vehicle - the gas within the shockwave starts to glow long before it contacts the vehicle itself.
Re:Power? (Score:5, Interesting)
Energy is not the issue – it is the rate of fire. Diesel engines power the supper capacitors, they discharge to fire the gun, and then fill them up again. I have read that this cycle might be measured in minutes instead of seconds. How big of an issue that it will be is a big question.
That depends on how many capacitor banks you've got, yes? Or possibly the sustained power output of the generators, though that's perhaps more of an issue for sustained firing. (Naval ships are pretty big; you can fit a lot of capacitors and generators in there.)
What I'm impressed at is that they can fire the railgun multiple times instead of needing to strip it down and rebuild it each time. That was always the problem with the early railguns; they'd be fine firing once but after that would be so burned up from the currents that they'd be unable to take a second shot on any reasonable timescale. They were cool, but not practical weapons. I'm guessing that that must've been solved, and the result is that pure kinetic weaponry starts to make sense again for ship-level encounters.
Re:WTF? (Score:4, Interesting)
Re:So... (Score:5, Interesting)
I found it interesting to describe by calculating kinetic energy. A stabbing ~ 185 joules. A gunshot of 45 caliber ACP round ~ 702 joules. A 1 ton vehicle going 100mph ~ 1 megajoule. A giant truck about to hit a series of tubes ~ 30 Megajoules. The kinetic energy of this railgun as it leaves the muzzle ~ 30.9 Megajoules.
Re:Incom.... (Score:5, Interesting)
Smaller diameter projectiles have more drag per unit mass and slow down faster due to air resistance. It's called their ballistic coefficient.
The practice for howitzer-like weapons like railguns is to fire their projectiles in a high arc to get them out of thick atmosphere as fast as possible to reduce air friction. They still won't hit their target at anything like their muzzle velocity even after they recover some kinetic energy on the way back down to target from the top of their parabolic arc.
The ballistically efficient shells from the late-model 15" US Naval rifles had a muzzle velocity of about 3500 feet/second and a flight time to target at maximum range (25 miles or so) of a couple of minutes. Their velocity at impact was half that of their muzzle velocity. I don't see these railgun projectiles achieving anything like that performance as drag increases roughly as the square of velocity and their ballistic coefficient will be a lot less.
Re:IANA Physicist, So... (Score:5, Interesting)
OK, hot, yes, but wouldn't they need something combustible to actually erupt into flame? Or what am I missing?
I think this is what's going on: when something is burning, the flame you see is just glowing hot air, heated by the energy from the combustion. The flame is not part of the combustion, just the side effect. In this video you see glowing hot air heated by compression and possibly the shock wave from the projectile. Same result, but the energy source is different.
If you've seen a meteor (streak of light in the sky at night, or a visible fireball with a trail if you're really, really lucky), the principle is the same, nothing is burning. The heat come from compression of the air in front of it, and the light you see is from the superheated air in its wake (and a little from the glowing meteorite).
Re:IANA Physicist, So... (Score:4, Interesting)
traditional aircraft carriers and these will get a lot smaller as drones take place of manned strike craft,
I also believe aircraft carriers will get smaller but not for the reasons you state. I believe that they will get smaller because there will be a greater reliance on vertical lift aircraft, helicopters and tilt-wings. I also believe that aircraft will get faster and have longer range, allowing for lesser reliance on carriers. The politics of flying through nations that might not like to get involved would be solved with aircraft that fly high enough to be considered orbital, and therefore technically in outer space, and therefore flying above "airspace".
Much of that is more about the "how" of shrinking aircraft carriers, the "why" is more about economics. Current carriers are big, slow, and very expensive which makes them easy and tempting targets. For the price of one US Navy aircraft carrier the Navy could have four amphibious assault ships, either choice capable of carrying 80+ aircraft. The amphibious assault ships get cheaper by the dozen but the aircraft carriers cannot, there are only a dozen afloat at any given time which makes economies of scale difficult.
Part of what makes aircraft carriers so expensive is the power plant, nuclear power is expensive. It looks like newer, smaller, safer, reactors which will allow for putting nuclear power in smaller ships, removing the range advantage of the larger aircraft carrier. Addition of jet fuel production systems on board means that they will not need to have oilers come by as often for supplies.
Smaller, faster, cheaper, and still capable of long term missions would be a great alternative to the super carriers we have now. Easier to defend against cannon fire and missiles, due to smaller size. If one is lost or damaged in battle then the reduction in fighting capability is reduced.
I believe your description of sea battles are accurate. The cannon fire is not fast or accurate enough to compete with missiles. Rail guns increase the rate of fire, reduce the weight of the ammunition, and reduce the cost, making it a very good alternative to current missiles and cannons. The range and accuracy of the rail guns might not yet compare to that of the missiles but are still a leap in improvement over cannons.