Oh, wait. We're preparing for the last war or even the one before that, all over again.

How does this help in the world of asymmetric warfare, failed states, nukes in container ships, and Stuxnet? (I'll bet the Maginot Line was pretty cool technology in its day as well.)

Definitely. Hidden tunnels with high speed trains to bring ammunition and personnel at any point in no time; hidden turrets in the forest that emerge from the ground; dragon teeth and minefields prevent tanks from going through.

Unfortunately big brass love big weapons, big bombers, big ships, big guns; never mind if they're useless nowadays in a world of guerilla and IEDs. The future is not the F22, it's a slow and cheap remote controlled drone with a propeller.

It's a slow but highly efficient autonomous drone with GPS and a terrain map.

http://en.wikipedia.org/wiki/Mark_48_torpedo

I think the main advantage for rail guns are that they allow a much higher volume of fire and faster time to engage more targets. It just happens to use cheaper ammo - I'm sure the gun will be much more expensive to make than a standard machined barrel.

But a part of the point is that they could in theory.

they certainly would still spend whatever money it takes though: Mark 48 torpedos are a cool $1M to $3.5M.

This would be dandy for blowing up a submarine or major warship which costs a lot more. This might also be viable for "demonstrating" your capabilities one or several times. Sinking a major merchant marine fleet this way wouldn't be cost effective.

It just happens to use cheaper ammo - I'm sure the gun will be much more expensive to make than a standard machined barrel.

With a 200 mile stand-off range, a much more expensive gun would still make sense. The extreme range would make such a weapon more survivable. There would also be applications for land to shore fire support.

And what's the "rail gun" for nation building - how would serious money spent on R&D help us create a stable, democratic Afghanistan?

I fear we're stuck in the "meta" version of "if all you have is a hammer": in terms of budget, all we have, in international relations, is the Defense Department. It has its uses, but its effectiveness is increasingly limited, not by dollars, but by our vision.

On the serious note, they didn't specify the weight of the projectile, and this is quite important factor. Comparison of the energy delivered at the target range to the energy delivered by the conventional winged missile would be useful as well.

Blog of the guy who build portable supersonic railgun at home (in Russian): http://railgun.org.ua/ Check out his video page: http://railgun.org.ua/video/

What you want is 20 minute strike with less warning than existing ICBMs. And also banned. The nuclear weapons reduction and restriction of weaponization of space treaties are some of the successful treaties with regard to controlling weapons that anyone, let alone the United States has been involved with. Violating said treaty will bring ridicule and anger to whoever breaks it, and a non-miniscule chance of the other major nuclear powers launching all their nukes.

ICBMs are too expensive to use to deliver conventional explosives or kinetic kill projectiles. Forget bioweapons and toxins, they're not any deadlier than cluster bombs.

The power of an explosion follows an inverse square law, so you can destroy something with 1/4 the explosive if you can get twice as close to it.

If you could drop thousands of 25 lb bomb equivalent devices an hour with GPS accuracy at a city, you could wreck it's infrastructure in a few weeks.

I believe prompt global strike (and similar schemes) to be highly unstabalizing and to be avoided at all costs. The global suspicion (with a country with 2000k+ nukes none the less) would be suffocating. If the USA employed such a system, the moment you acted as anything less than a white knight, the world be up in arms. And justly. Your friends (the UK and Canada and Australia) would start edging away. And then you're truly fucked. (Canadian).

According to that logic, Canada should already have that attitude to the US, since most of their population is inside aircraft range...

Airplanes [edit: and rocket artilleri, for that matter] in range is functionally the same thing as such a strike capacity, but cheaper.

There is no reaction from Canada and won't be; see the democratic peace theory.

When people discuss the weaponization of space in terms of the treaties, implying ignorance because it isn't about basic physics doesn't provide any constructive input, and is frankly just needlessly hostile. These treaties are about weapons in a military sense, with the ultimate issue being the presence of nuclear weapons in orbit. I don't think it would be news to anyone that the whole business is inherently dangerous and that anything in orbit can come down anywhere on earth with little warning.

And no, I seriously doubt our political leadership really understands this at a gut level. You might even find some people in such positions that could pay lip service to the idea, but still don't really get it. You don't even need "nukes", which, frankly, are redundant pretty quickly and would only add a psychological scare factor.

That seems more like pure conjecture than anything clear.

http://www.google.com/search?q=2*33megajoules/(2500+m/s)^2+i...

http://www.google.com/search?q=2*33megajoules/(7+*+speed+of+...

There's an unfortunate focus in the admiral's comments on ship-to-ship warfare, which really isn't something we get a lot of nowadays.

What's deliberately not mentioned is how useful this might be for shooting down a missile at launch. It is, as they say, hard to hit a bullet with a bullet. But hitting a bullet with a much faster bullet...

With a missile coming toward you at Mach 2-3 you don't want to be shooting subsonic cannon shells at it.

The rail gun ammunition is much smaller so you can carry much more of it and make a much more mobile gun turret because it doesn't need to store tonnes of shells or have a feed back to a magazine.

Current destroyer's gun: http://en.wikipedia.org/wiki/5%22/54_caliber_Mark_45_gun

Iowa Class gun: http://en.wikipedia.org/wiki/16%22/50_caliber_Mark_7_gun

The article says "Indeed, a railgun could be used to inflict just such harm on another vessel.", which is true, it could be used for this purpose, but they would not be sinking money into this just for that.

I'd expect that most projectiles decay exponentially toward a terminal velocity, so the impact of shooting a bullet faster is negligible when it's going to be in flight for 6 minutes. Anyone know whether that's true for long range projectile weapons these days?

I guess I can spend my time worrying about other things!

edit: obviously would have to be slower then these for the sake of any fragile cargo (including people)...

"The extension of this technology [rail guns] to the muzzle velocities ( 7500 m/s) and energies ( 10 GJ) needed for the direct launch of payloads into orbit is very challenging, but may not be impossible."

[1] http://research.lifeboat.com/ieee.em.pdf

Assuming:

Launch Speed: 17,180 mph (Speed of Space Station) [1]

Launch Acceleration: 25g (Based on my understanding of what humans can survive) EDIT [2]

Just using that as a rough estimate and Wolfram Alpha we get 242,250 meters, or about 150 miles.

http://www.wolframalpha.com/input/?i=17,239.2+mph+/25+gs

http://www.wolframalpha.com/input/?i=31.434+seconds+at+17,23...

Please feel free to check my math and yell at me.

[1] http://en.wikipedia.org/wiki/International_Space_Station

[2] cperciva [http://news.ycombinator.com/item?id=1993399] used 3g. Based on that you would have to multiply the launch distance by (25/3) and get 2,018,750 meters, about 1,250 miles. Again please correct me if I got something wrong.

Anyway, aren't you forgetting that most of the time is spent at a lower speed, so that you want to integrate the acceleration rather than simply multiplying by the escape velocity?

d = 1/2 at^2, where t = escape velocity / 3 G?

http://www.wolframalpha.com/input/?i=escape+velocity+%2F+3gs t = 6.3 min

http://www.wolframalpha.com/input/?i=distance+travelled+in+6... d = 2100 km (1300 miles)

While we're at it, I'm not sure what we really should be using for escape velocity. We should probably account for the deceleration after we leave the muzzle while still in the atmosphere. And if we presume a surface mounted rail gun, we'd probably want the escape velocity for a launch aimed just above the horizon, which involves more of this.[1]

Or if we're somehow presuming vertical, we'd want the escape from that height. But if vertical, we'd have to account for the extra gravitational force on the passengers, unless this is already accounted for in the human limits. In any case, I'm not sure that the speed of the Space Station (or the surface velocity I used above) really makes sense here.

[1] I vaguely recall that ignoring air resistance, the velocity is the same regardless of direction, but I don't have confidence in this, and my quick searching hasn't turned up anything definitive. Is this possibly right?

Think of it this way: if you were approaching Earth from space and wanted to enter orbit with the ISS, you need to reach a speed, e.g. 17,600. The speed is the same no matter where you are coming from, such as from the Earth's surface.

On the equator, if you take off east, you already have about 1,000 mph working with you. If you take off west, you need to get an extra 1,000 mph. Towards the poles, the (dis)advantage lessens.

Details aside, the overall conclusion remains that rail guns are not likely to be a useful means of propelling squishy cargo like humans into space.

For cargo a railgun a few miles long would probably be enough, but designing a missile which can survive surface air densities while travelling at orbital velocities would be very difficult.

That said for human payloads you'd need a really long track, tens or hundreds of kilometers. I wouldn't want to live near the launch end. (edit: to get a useful amount of speed; still assuming rockets to get us the rest of the way)

Rockets turn sideways because when you're in orbit, you're moving sideways.

And yes, since the first half of the tunnel is sloping downwards you are using a large fraction of g to accelerate the slug/projectile, thus reducing the power requirements.

Its an engineering problem, not a physics problem.

Unfortunately a project of this scale is beyond the largest organizations that exist today, nation-states. Maybe later?

When the day comes for the need of a super-structure to be built in orbit, this technology will likely be used. This or a space elevator. Getting far enough away from our own gravity well will free us from this rock.

I think our government should build such a launch accelerator in the desert somewhere. (Tilted at 45 degrees or so, to get a cargo drone out of the atmosphere and give it a big boost towards orbital velocity.) The ability to place bulk cargo into orbit would give the US a tremendous economic advantage. (Selling solar power satellites, colonization of Mars...)

A ram accelerator is probably more practical in any case.

Just how long does the shielding have to withstand high temps? We already solve a much harder problem with reentry of orbital vehicles. The problem here is much simpler, as we don't actually want to shed most of the velocity. In fact, we want to lose as little of our kinetic energy as possible. If ablative shielding can handle reentry, it can handle launch. AFAIK, the mass ratio for reentry shielding is quite good.

The rail gun cargo is going in the opposite direction - you start in the thick air at a speed greater than orbital velocity. It's been years since I could grind through the numbers, but it makes a big difference

This speaks to my point. In launch accelerator mode, you want to dissipate as little energy as possible. In reentry mode, you want to dump the majority of a big honking chunk of kinetic energy.

I'm sure there are all sorts of optimizations to consider. How about a mostly vertical trajectory, with most of the horizontal velocity provided by lasers heating a heat-exchanger?

By keeping the trajectory mostly vertical, one can avoid most of the lower atmosphere by stationing the opening to the atmosphere miles above the surface. This also limits the downrange danger-zone for falling malfunctioning cargo pods. Additionally, it makes the cargo pods easier to target with the lasers, since the powered flight would be entirely in the upper atmosphere. It would also make the rocket nozzles easier to design.

The first half (logistics benefits) is a good statement. The rephrasing the the second half is bogus.

Joules are joules the world over. If the enemy fire hits the caps full of joules, it ain't gonna be good for the good guys even if there are no conventional explosives involved.

If, on the other hand, you take out a magazine, you liberate an amount of energy equal to all the shots the ship is capable of taking ALL AT ONCE.

The energy necessary to fire all those shots is probably still on board, but it is likely in the form of a nuclear pile in the reactor, which is shielded up the wazoo. Even if the ship is running a conventional generator, diesel fuel doesn't have a tendency to explode in quite the same way as gunpowder.

Even more so if the energy is coming from a fission reactor. Since the energy source is comparatively more compact and can be protected with armor more effectively.

My question: does it actually have practical utility as a weapon of war for the modern US Navy? This seems like fighting the last war -- this is about building a weapon that goes on giant ships, when the new war is all about information and special forces strikes.

So I guess they're hoping that they can bring back gunboat diplomacy in a form more suited to the 21st century. And if they're aiming for ranges of two to three hundred miles, I guess that theoretically means that no part of the UK would be entirely safe except maybe Birmingham, and that's mostly because nobody wants to go there even to blow it up.

The one they plan to deploy is supposed to go something like mach 20 and have a ballistic trajectory. Not something you could destroy a city with, but it'll make a bigger bang than an 8-inch shell.

"Now they just have to figure out the Quad Damage and it's going to be insta-gibs on any target!"