Cheap and simple AT weapon

[mandelkubb]

The exhaust doesn't have to be straight to the rear, you could have multiple exhausts at an angle rearwards (ATGMs generally work this way since the guidance cable and tracking devices are mounted in the rear of the missile). On the other hand, you would lose energy this way, and need more fuel for the rocket motor. Damned if you do, damned if you don't.

 

[mike wightman]

What about at higher TLs?
Could thase things be miniaturised to the size of, say, snub pistol or shotgun rounds?

 

[Badbru]

Yeah... they called it an accellerator rifle

Sorry Sigg just being cheeky

 

[mandelkubb]

Originally posted by Straybow:
Do you really want to be 30m back in the direct line of thrust&#151a stream of thousand-degree gasses going at least Mach 5?

>Poof<

You could mount a small shield to protect the operator's face from the gasses, like the german WW2 Panzerschreck:

 

[mike wightman]

I was thinking of something that could be used to penetrate high tech combat armour and BattleDress (and lower tech APCs and the like

).
Or a development of the gauss rifle that fires scramjet rounds?

 

[Straybow]

Panzerschreck is a decidedly low velocity munition. ATGMs are subsonic iirc. A supersonic missile is a different beast, but depending on application might still have low enough thrust that operator is in no danger (eg, Stinger).

A hypervelocity missile must reach max velocity ASAP, and 30m is closer than you think.

 

[Todg]

Originally posted by Straybow:
100 m is when the thruster ignites. It would probably take another couple hundred meters to accelerate to full v.

100m is probably way too m uch. The Javelin only goes a few meters from the launcher before lighting. I'd say the SLOSAT is probably about the same, with full speed achieved at more like 25 meters (look at the stats for the Sprint missile, or even LOSAT. Those things get up to speed very quickly)

I'll see if I can find exact acceleration figures but primive systems like the LAW manage to accelerate up to full speed while still within the launch tube (~1m).

 

[mandelkubb]

Originally posted by Straybow:
Panzerschreck is a decidedly low velocity munition.

But the Panzerschreck fires a rocket that's still burning when it exits the tube, hence the need for a shield.

Maybe it won't be enough with a shield, it was just an idea.


A hypervelocity missile must reach max velocity ASAP, and 30m is closer than you think.

The AT-4 LAW has a minimum firing distance (due to the arming devices) of 30 meters. If you fire a something from 30 - 50 meters (IIRC), you are advised to take cover immediately after firing.

As I said, a small ejection charge (enough to throw the rocket about 30 meters) will make the weapon lighter and lower the time from firing to impact, but might be somewhat unpleasant for an unprotected operator.

There is also a question on how hard you can accelerate the penetrator, maybe it's easier to have a somewhat lower acceleration (and lower signature) from 30-150 meters (I'm assuming max V at 150 m) than a higher acceleration from 100-150 meters?

 

[mandelkubb]

Originally posted by Corejob:
The Javelin only goes a few meters from the launcher before lighting.


But that's a subsonic system, right? And, as I mentioned in an earler post, the exhausts on ATGMs are usually angled outwards becuase the rear of the missile is filled with guidance stuff.



I'll see if I can find exact acceleration figures but primive systems like the LAW manage to accelerate up to full speed while still within the launch tube (~1m).

But that's a subsonic system. Launch velocity is about 300 m/s, fine for short distances with a HEAT warhead, pretty much useles for longer distances and KE penetrators.

 

[Straybow]

Wha? No way. If the LAW achieved maximum speed within the tube it would be a shell, not a rocket/missile. The recoil would be punishing, which is not the case (by far).

Things like Pschreck and LAW accelerate through most of the flight profile. They need only be going fast enough for directional stability on exiting the tube. They use shaped charge so that warhead performance is independent of momentum or KE.

/me does some math in his head, tries again on calculator

35kg LOSAT achieving full 1500 m/s in 25m would require 45k m/s² or (to mix units thoroughly and ignore the initial mass of propellant) about 175 tons of thrust, and I don't think that is possible.

 

[Todg]

Originally posted by Straybow:
Wha? No way. If the LAW achieved maximum speed within the tube it would be a shell, not a rocket/missile. The recoil would be punishing, which is not the case (by far).

The M72 does in fact burn all of it's propellant in the tube. It is not a shell, it is a rocket, but one with a very short burn time. I've fired more than a few. Unlike TV and movies, there's no tail flare. When you press the trigger, you hear a BANG! and off it goes.

Take a look in Jane's Infantry Weapons if you don't believe me. Here's what it says:

"The rocket motor is designed to insure that all of the propellant is fully burnt before the rocket leave the the launcher, even under Arctic conditions where the propellant burns more slowly."

Some other references:

http://www.adtdl.army.mil/cgi-bin/atdl.dll/fm/3-23.25/ch2.htm
http://www.sasrogues.bravepages.com/law.html
http://www.isayeret.com/weapons/rockets/law/law.htm

 

[Todg]

Originally posted by mandelkubb:
The AT-4 LAW has a minimum firing distance (due to the arming devices) of 30 meters. If you fire a something from 30 - 50 meters (IIRC), you are advised to take cover immediately after firing.

Rioght, but the AT-4 is a HEAT rocket with an explosibe warhead. The arming dstance is to protect the firer from the blast of his own rocket. In the case of a KE penetrator, there won't be the same concern.

The limiting factor will be how fast the rocket accelerates. The KE rocket may not have sufficient velocity at short ranges to penetrate all armor.

 

[Todg]

SLOSAT is coming!

After looking up data on LOSAT to see how viable SLOSAT really is, it turns out the army is already developing something very much like our SLOSAT for deployment within the next 10 years.

The Compact Kinetic Energy Missile (CKEM) is a long rod, hyper-velocity anti-tank round for the Army's Future Combat System.

It's statistics are close to the proposed SLOSAT, although it is heavier at 22.5 kilos and is guided, bringing up the cost.

The performance data is what is interesting:

Missile length: 1.22 meters
Missile mass: 22.5 kilos
Minimum range: 200m
Maximum range: 6-10km
max velocity: mach 6.5
Terminal energy: 10MJ

The CKEM is initially supposed to reach maximum velocity at 400 meters in the first iteration, and 200m in later versions.

It should be noted that our own SLOSAT doesn't carry guidance and doesn't have a 6-10km range requirement, so it would seem very much within the realm of the achievable. Certainly, the acceleration required is within reason, given the CKEM's performance requirements. Not surprising, since the 1960s era Sprint missile was capable of 150 Gs of acceleration.

The CKEM was succesfully tested 28 Jan 2004.

 

[Todg]

Originally posted by Straybow:
Do you really want to be 30m back in the direct line of thrust&#151a stream of thousand-degree gasses going at least Mach 5?

30m is a long way and you'd be surprised how quickly backblast dissipates. Many soft launched missiles travel no more than 5 or 10 meters from the user before the rocket motor ignites. True, these aren't KE missiles, but you aren't going to need 100m.

Here's a video of a Javelin test firing:

http://guntech.com/media/Javelin2.mov

LOSAT does kick out a lot more junk, but a lightweight shield is enough to protect the occupants of the launch platform. A soft launch of 20-30 meters will be more than sufficient to protect the firer from thermal effects of the motor.

 

[kaladorn]

The interesting thing in the paper-scissors-thermonuclear_device category is that modern reactive armour systems are developing capabilities (as are modern armours) to effectively defeat kinetic kill warheads.

So I suspect it will continue to be a game of who gets in the right place and gets off the first accurate shot.

 

[Todg]

Originally posted by kaladorn:
The interesting thing in the paper-scissors-thermonuclear_device category is that modern reactive armour systems are developing capabilities (as are modern armours) to effectively defeat kinetic kill warheads.

Manufacturers of ERA (explosive reactive armor) have been claiming the ability to defeat KE rounds since the mid 1980s, but only in very special cases and only against small caliber rounds. Specifically, long rod penetrators are very difficult to defeat because the same characteristics that give them low cDs also makes them resistant to explosive shockwaves.

Modern armors are another mtter. Appliqué armors like Chobham rely on 'defense in depth' to trap and redirect KE. As a consequency, they are thick. Not a problem on an MBT, but a suit of battledress will be limited because it has to allow for human range of motion.

It should also be noted that the LOSAT has a huge energy advantage over conventional guns. The 120mm gun on the M1A2 is an 8-11 MJ gun (depending on range). The LOSAT delivers 40MJ of kinetic energy. To counter that kind of KE, ERA would have to deliver a high fraction of that energy to the incoming warhead, and since reactive armor is not highly directional, the total energy of the reactive plate would have to be orders of magnitude higher - not a good thing for the vehicle being protected.

The future of ERA against KE threats is something called Momentum Transfer Armor. It utilizes rods fired perpendicular to incoming KE rounds. Traveller would probably consider this point defense and not armor at all.

An interesting brief on reactive armor concepts can be found at:

http://www.arl.army.mil/wmrd/Tech/re-both.pdf

 

[Straybow]

Eh... why was I thinking LAW was a closed tube?? Anyway, those links say LAW is a mere 475 fps (145 m/s), which requires far lower acceleration.

200m to accelerate to 1500m/s would take 5625m/s²
Accelerating to 1500m/s at 150 gee would take 750m, 300 gee would take 375m. Perhaps the 200m LOSAT minimum range is not full velocity, but a lesser velocity that achieves the minimum design effectiveness.

 

[Todg]

Actually, the specs are for CKEM, which is supposed to accelerate up to speed within 400 meters in the first iteration, and withinh 200 in the second. The 150 G acceleration was for Sprint, a missile using 1950s technology (and tested in the early 1960s).

Also, note that a gun can accelerate a projectile to 1500 mps over a distance of about 3 meters. Certainly a rocket, being an open system, is different. But apparently those types of accelerations are possible since that is the design spec for CKEM.

(Don't ask me. I'm no rocket scientist. I'm just going by what ATK, Lockheed and the Army have published.)

 

[mandelkubb]

Originally posted by Corejob:
Rioght, but the AT-4 is a HEAT rocket with an explosibe warhead. The arming dstance is to protect the firer from the blast of his own rocket. In the case of a KE penetrator, there won't be the same concern.

Correct, I was just trying to put the "30 meters from something unpleasant" (HEAT blast or rocket ignition) in perspective.

 

[Straybow]

Yes, and a 900mps rifle bullet is accelerated at 67500 gee. The aid of tube designed to contain the combustion products is required. I guess the question is, can the rate of burn by itself (funneled through a supersonic nozzle) generate 1% of the thrust?

Phrased that way, it doesn't sound unreasonable.