We were launching hypersonic bricks at Mach 5, Mach 6

[DSE]

http://defensetech.org/2011/04/14/we-were-launching-hypersonic-bricks-at-mach-5-mach-6/

Here’s an exclusive Defense Tech video giving you an update on General Atomics’ high-speed railgun project. Last summer, General Atomics and Boeing tested a high-speed sabot round to replace the “hypersonic bricks” (which tended to tumble out of control) that the company had been firing from the gun, says General Atomics’ Tom Hurn. The sabot round went seven kilometers downrange after punching through a 1/8-inch thick steel plate. General Atomics officials estimate that they could install the weapon on a DDG-51 class destroyer by the end of the decade, according to Hurn.

 

[sferrin]

20+ years ago they were digging 6" deep craters in solid aluminum with small plastic "bullets" and now they're "punching through" 1/8" plates? Is there a typo in there somewhere? ???

 

[TomS]

Couple of points. That plate was near the muzzle, which means the round was still intact and aerodynamic after that -- those lexan slugs tended to vaporize on impact with just about anything. Second, going seven kilometers at zero elevation suggests it retained a hellacious amount of velocity after going through that plate (how much depends on the height of bore, obviously, but a large number). I'd guess the plate wasn't a target so much as a witness plate and possibly a sabot stripper in the event the round didn't separate as designed.

 

[sferrin]

Couple of points. That plate was near the muzzle, which means the round was still intact and aerodynamic after that -- those lexan slugs tended to vaporize on impact with just about anything. Second, going seven kilometers at zero elevation suggests it retained a hellacious amount of velocity after going through that plate (how much depends on the height of bore, obviously, but a large number). I'd guess the plate wasn't a target so much as a witness plate and possibly a sabot stripper in the event the round didn't separate as designed.

Re: the lexan pellet, I wonder how far it would travel through the air before their was nothing left.

 

[bobbymike]

Future of warfare, hypersonic for attack, directed energy for defense. Who is going to get there first?

 

[seruriermarshal]

I can't access the video , anybody send it to youtube ?



thanks

 

[sferrin]

Having looked at the video I don't see the point. If they're talking about mounting a gun that fires the projectile shown at 1.6km/sec they could get better than that from an L44/M829 (Abrams tank gun/round combo) right off the shelf. ???

 

[bobbymike]

Having looked at the video I don't see the point. If they're talking about mounting a gun that fires the projectile shown at 1.6km/sec they could get better than that from an L44/M829 (Abrams tank gun/round combo) right off the shelf. ???

Watched it again didn't realize the "shot" was basically modern tank gun velocity. I can only think 1) It can be scaled up in power and therefore speed and range; 2) It would still be worth it not having to carry "gunpowder" for a traditional cannon ???

 

[pathology_doc]

2) It would still be worth it not having to carry "gunpowder" for a traditional cannon ???

No more magazines! (It's electrically driven.) No more explosive shells! (The kinetic energy yield takes care of that.)

Bottom line: No more Jutland battlecruiser embarrassments!

But will that offensive weapon still be able to make over-the-horizon shots, the sort that arc down and smash through the deck before ripping into a ship's guts? Or will it just fire straight over their heads?

As for directed energy weapons - hmm, will we go back to missiles turned out in shiny aluminium, to reflect as much of that back as possible? No, thanks - I'll take Goalkeeper or better with ten thousand immediate-use rounds, and mount at least two on a destroyer, four on a cruiser, six on a carrier... Western ships simply do not have enough guns.

 

[Dragon029]

An update from the Navy:

The U.S. Naval Research Laboratory Materials Testing Facility announced that it has fired its electromagnetic railgun 1000 times and reached a materials testing milestone toward the deployment on warships.

http://www.tomsguide.com/us/us-navy-railgun-warship-weapon-military,news-13053.html

What I found rather interesting:

"The Navy railgun is rumored to accelerated a 7-pound projectile to a speed of 2.4 km/s or 5400 mph. However, rumor has it that velocities of up to 3.5 km/s have been achieved."

At 3.5km/s, that's over Mach 10 which ain't bad.

If that's true, it'll finally answer this:

Having looked at the video I don't see the point. If they're talking about mounting a gun that fires the projectile shown at 1.6km/sec they could get better than that from an L44/M829 (Abrams tank gun/round combo) right off the shelf. ???

 

[Rickshaw]

2) It would still be worth it not having to carry "gunpowder" for a traditional cannon ???

No more magazines! (It's electrically driven.) No more explosive shells! (The kinetic energy yield takes care of that.)

No more magazines? Where do they store the "shells"/projectiles? How well does it do with firing a HE round? Afterall, tanks fire far more HE than they do AT as the main role of the tank is, despite what the turret-heads claim, still supporting infantry.

Bottom line: No more Jutland battlecruiser embarrassments!

Overly optimistic. There really isn't much difference between a capacitor exploding and a magazine explosion.

 

[Creative]

Speaking of hypersonic, whatever happened to Scramfire?

 

[TomS]

No more magazines? Where do they store the "shells"/projectiles? How well does it do with firing a HE round? Afterall, tanks fire far more HE than they do AT as the main role of the tank is, despite what the turret-heads claim, still supporting infantry.

At the impact velocities anticipated by typical major-caliber railguns, HE truly isn't needed. KE submunition (multi-dart) rounds can provide area coverage with better terminal effects than HE fragmentation rounds.

 

[Rickshaw]

No more magazines? Where do they store the "shells"/projectiles? How well does it do with firing a HE round? Afterall, tanks fire far more HE than they do AT as the main role of the tank is, despite what the turret-heads claim, still supporting infantry.

At the impact velocities anticipated by typical major-caliber railguns, HE truly isn't needed. KE submunition (multi-dart) rounds can provide area coverage with better terminal effects than HE fragmentation rounds.

The amount of kinetic energy in a 20mm solid piece of metal travelling at Mach 5 or 6 will not equal the amount of chemical energy and the kinetic energy of the subsequent shell splinters of a 120+mm HE round. How long between shots for these weapons? How long does it take to charge the capacitors?

 

[pathology_doc]

No more magazines? Where do they store the "shells"/projectiles? How well does it do with firing a HE round? Afterall, tanks fire far more HE than they do AT as the main role of the tank is, despite what the turret-heads claim, still supporting infantry.

Terminology - magazines store propellant powder charges; shell rooms store shells.

Overly optimistic. There really isn't much difference between a capacitor exploding and a magazine explosion.

This makes no sense; a capacitor stores only electrical energy, with no inherent explosive capability. Sure if your dielectric is oil it will burn, and bits will fly everywhere, but how can there be an explosion beyond the effect of the shell which strikes it?

Set off a whole lot of propellant charges at once, however, and...

In a naval application, your targets are SSMs, ASMs, aircraft, and other ships. The first three will be vulnerable to a hit from a sufficiently large Mach 6 kinetic projectile; the latter will mostly be vulnerable in direct line of sight (the extremely flat trajectory may be a problem in firing just over the horizon). I suspect point-defence and anti-surface applications will demand different sizes of 'gun', just as they do with chemical projectiles.

 

[TomS]

This makes no sense; a capacitor stores only electrical energy, with no inherent explosive capability. Sure if your dielectric is oil it will burn, and bits will fly everywhere, but how can there be an explosion beyond the effect of the shell which strikes it?

No, this is a real thing. Overload or short a capacity, and it will explode as parts of the capacitor simply vaporize due to the rapid heating from current flowing rapidly through the material. Large capacitors can be quite impressive when they do this.

And it's worse because the more likely power source for a railgun isn't a classical dielectric capacitor but a compulsator, which is basically a flywheel motor-generator optimized for high-density energy storage and rapid discharge. Break one of those while it's spinning and it's going to fail rather catastrophically. Fortunately, they won't have to be kept spun up for long, but it's still a legitimate concern.


Edited to fix some nasty typos

 

[Rickshaw]

No more magazines? Where do they store the "shells"/projectiles? How well does it do with firing a HE round? Afterall, tanks fire far more HE than they do AT as the main role of the tank is, despite what the turret-heads claim, still supporting infantry.

Terminology - magazines store propellant powder charges; shell rooms store shells.

Naval terminology perhaps. Army terminology is different.

Overly optimistic. There really isn't much difference between a capacitor exploding and a magazine explosion.

This makes no sense; a capacitor stores only electrical energy, with no inherent explosive capability. Sure if your dielectric is oil it will burn, and bits will fly everywhere, but how can there be an explosion beyond the effect of the shell which strikes it?

See TomS's reply. Capacitors explode. While one a small scale this is what happens - http://www.youtube.com/watch?v=kjhoePUJ8Vg

Set off a whole lot of propellant charges at once, however, and...

Propellant charge explosions can be compensated for and suppressed. Capacitor explosions can't be, as far as I am aware.

In a naval application, your targets are SSMs, ASMs, aircraft, and other ships. The first three will be vulnerable to a hit from a sufficiently large Mach 6 kinetic projectile; the latter will mostly be vulnerable in direct line of sight (the extremely flat trajectory may be a problem in firing just over the horizon). I suspect point-defence and anti-surface applications will demand different sizes of 'gun', just as they do with chemical projectiles.

However, I wasn't talking about naval applications and it wasn't clear that you were. However, the problem remains you take a hit in your capacitor bank, its going to have similar effects to taking a hit in the magazine. All that electrical energy has to go somewhere and its usually converted into heat and light.

 

[pathology_doc]

My understanding was that actual deployment was being talked about in naval terms. Apologies for the confusion.

Capacitor explosion in the vid looks like a deliberate imposition of a gross electrical overload, a very different kettle of fish from a kinetic strike, which would perforate the dielectric and cause a local discharge across the plates. What happens next would depend on the kinetic and chemical-explosive effect of the shell - if the capacitor broke up from the hit, the arcing might be over a broad enough surface area to discharge safely. I suspect the model equivalent of the case we're discussing is a three inch high capacitor loaded in the millifarad range, being perforated by a high-explosive bullet.

At least with a capacitor bank on a warship, one could theoretically distribute it out very low in the vessel, unlikely to be hit by anything that wouldn't sink the ship outright - as opposed to a magazine which has to be concentrated in the vicinity of the gun(s) it services. A mine or torpedo might then set it off, but chances are that will break the ship's back and do for it anyway.

How you'd fit that much storage and generating capacity into a tank is another matter. If you use e.g. a generator powered by the gas turbine in an Abrams, you are surely going to do horrible things to the fuel economy.

 

[RP1]

How you'd fit that much storage and generating capacity into a tank is another matter. If you use e.g. a generator powered by the gas turbine in an Abrams, you are surely going to do horrible things to the fuel economy.

Minor note that there is a device called the Compulsator developed for precisely this. It all fits quite nicely, but is large compared with capacitor banks. However, as TomS noted, rotating storage devices need to withstand a rotor failure - which will usually be included in the unit weight as additional casing thickness.

Capacitors have to be protected against penetration not just because of the effects on the energised capacitor, but also on the penetrating fragment - which can become very hot very fast. The analogy usually given is to drop a spanner into a submarine battery compartment and watch what happens.

Of course, the ESS can be low, but that increases the length of the high power cables to the gun itself, which are heavy anyway, let alone with any fragment protection. Note that some studies suggested 0.5-1.0 tonne/m for a protected propulsion cable on IFEP ships.

RP1