So I Drew A Tank, Need Commenatary

[Ra]

Basically what the title says. For some of the more military-minded folks, I need to know how (im)practical this beast is.



Background: the Enforcer Mk. II is being designed for my own little sci-fi universe, for the Earth Union Marine Corps. It's basically a huge railgun on treads, with a small tritium-fusion powerplant to make it go.

Note, I didn't put this in MAP because I didn't see it warranting a permenant thread.
- Ra

[frigidmagi]

A railgun with treads isn't all that impractial, although it is likey you will have a bit of collatieral damage. Treads are quite practial has well.

However I need weight, height, gun range, operation range, ammo and crew requirements to make a real judgement on wheter it is a good weapons system.

Tritium-fusion is outside of my knowledge base so can't help ya.

[Comrade Tortoise]

In addition to general dimensions like height width and mass, operational range etc, I need to know two things, Power generation, and how the FUCK you are absoring the recoil from that railgun?

[Hotfoot]

Fusion reactors inside of tanks can cause issues, but depending on the tech level, it should be okay.

Just keep in mind that this will make the tank amazingly hot on thermal sensors.

[The Cleric]

Recoil is going to be a hell problem, especially with the treads coming up in the back. If you make them like this "\" as opposed to "/" you might have some more stability.

[Ra]

OK, I might be a little guilty of compensation with the main gun.

For dimensions, the vehicle is slightly larger than a modern tank. At minimum, she's 3 meters tall, 11-12 meters long (with gun), 8-9 meters long (body), and about six meters 4.2 m wide.

Weight, I really couldn't say, but I'd guess around 70 metric tons. She could be much heavier with the powerplant and such, or advanced future materials and armor could make her a little lighter.

The tank is for the 2300 timeframe, if that helps. The fusion powerplant I assumed would be needed for any railgun-based main weapon, let alone the two laser AP turrets.

The main gun is in the 140 to 150 mm range. Barrel velocity would probably be about mach 3 to 4, but I could lower it if that's a little overpowered. What's the Abrams' muzzel velocity?

Anyway, Most Union "railguns" are merely electromagnetic guns with a similar, if slightly higher, muzzle velocity to modern firearms. The actual hypervelocity weapons are mainly used as artillery pieces.

As for power, tritium-fusion is simply normal nuclear fusion with tritium instead of deuterium or light hygrogen. The tank will more than likely have a highly advanced cooling system to reduce thermal emissions.

Hope all this helps.
- Ra

[Hotfoot]

Actually, you wouldn't need a fusion reactor for a railgun or lasers unless you planned on supplying the tank with near-infinite power for both. High-capacity batteries or "fuel cells" or somesuch would do the job just as easily. Fusion power is actually a rather large and cumbersome process compared to fission power. Also consider that Tritium is radioactive, as this will create additional potential shielding issues.

For something set as near in the future as a hundred years, I would expect only that large vehicles, such as big airplanes or large naval vessels, would be fusion-powered. Of course that depends entirely on how rapidly your setting develops technology, which is author fiat.

Concerning the speed of the projectile, 140-150mm projectiles at mach 4-5 is more than a little excessive. Assuming iron as the base material (the slug would need to have some iron or otherwise magnetic material in it to work, and this gives us a lower limit) and just working on the assumption of a 150mm sphere, density of 7870, area of:

(4(pi)r3)/3
(4(pi)0.075^3)/3 ~= 0.001767 m3

7870 * 0.001767 ~= 13.9 kg

That is how much a solid iron slug fired from this railgun will weigh. If you make it look more like a traditional bullet or something, it's going to be more massive.

I'm going to make a raw guess and say your barrel is 3 meters from breech to muzzle. Feel free to correct me if I'm off by too much.

Accelerating a 13.9 kg slug from 0m/s to 330*5 = 1650 m/s over the space of 3 meters will require the following acceleration:

1650^2 = 0^2 + 2a(3-0)
2722500 = 6a
453750 = a
a = 453,750 m/s^2

The total time between shot starting to accelerate and leaving the muzzle is found here:
1650 = 453750*t
t = 1650/453750
t ~= 0.0036 seconds

The amount of force required for this acceleration is as follows:
F=ma
F = 453750*13.9
F = 6307125

6,307,125 Newtons is not precisely a trivial amount of force. To more accurately depict the amount of recoil involved, this following equation may help. Let's assume the tank is 100 metric tons, rather than 70.

F/m=a
6307125/100000 = 63.07125
a = ~63 m/s^2

To determine what speed the tank would accelerate to in the opposite direction (disregarding for the moment traction and such), we go back to the v(f) = v(i) + at equation.

v(f) = 0 + 63*0.0036

v(f) ~= 0.229 m/s

To put it in perspective:

(0.229 * 60 * 60)/1000 ~= 0.8247 kph

Naturally, the lighter the tank, the worse recoil will be, and the same if your choose a heavier round, like a uranium-cored sabot or something similar. Also, recoil goes up as you make the barrel shorter. Other factors, such as torque, will also present themselves as you turn the barrel in other directions.

Modern tanks, IIRC, use something like 20kg projectiles fired at roughly 350-450m/s.

[Ra]

I see now. I'll change the powerplant to a quantum capacitor of some kind, and reduce the muzzle velocity to about 500 m/s at maximum. Thankfully, I had actually designed the rather long barrel with recoil reduction in mind, not just the linear acceleration factor.

The tank-killer round is going to be a tungsten or, alternatively, a DU sabot round, with probably an iron or superconductant polymer armature. So yes, it was going to be very massive. Just for reference, the other rounds will be a frag round for clearing bunkers, a plasma-generating successor to the HEAT round, and a sonic concussion shell, probably for general purpose AP and building destruction.

Thanks for the input, everyone. I want to produce a vehicle that is within reason, and this helps immensely. I'm also considering redesigning the rear of the tread system somewhat. The original exposure in the rear was inspired by the similar feature on the Abrams, but if the machine would benefit by shifting the center of mass to the rear, that will do just fine.
- Ra

[Hotfoot]

By the way, if you're going for penetration, larger bore size shouldn't really be entirely a major concern. A 10-30mm bolt accelerated to higher speeds will likely be preferable to a 140-150mm slug accelerated to 500m/s.

[Ra]

OK. What would the energy requirement be for, say, a 20 mm or 40 mm railgun with the same kinetic power as the big 150 mm railgun? Would it be about the same, or does energy cost go up a lot for higher velocities?
- Ra

[The Cleric]

Moved to Sci-Fi. This is most certainly not spam.

[Ra]

Thanks.

Now, time for other specs.

The tank has a crew of two to three; a driver, gunner, and tank commander. Since the main gun is auto-loaded and both AP weapons are automated, the need for a loader/machine gunner is eliminated. Even so, the commander's hatch has a SAW-type weapon stowed away inside the turret, since a fancy-pants DE weapon won't work in every situation; the Marines prefer to always have a low-tech backup available.

Land speed is about 100 mph. While the tank is very heavy, it can still outrun anything we have today.

Armor is the one thing I'm still up in the air about. I am, however, musing a composite multi-layer armor, despite the fact that I could easily have things like electric armor. I'm not fond of electric armor, however, because of high EM emissions. In this setting, EM detection is rather common for both space and land warfare.

For sensors, the Enforcer has IR, Image Intensification, Acoustic sensors, and a passive EM scanner. The EM scanners can both detect vehicle EM emissions, and in a special mode, human heartbeats (like the device from Rainbow Six). There is also a laser rangefinder, of course. Basically all the tools a modern tank has, plus the EM and acoustic scanner suite.

To counter enemy scanners, the Enforcer has IR-absorbant shielding to cover the vehicle itself and its occupants, as well as a cooling system for the treads, although a vehicle is damn near impossible to cloak from IR. The tank also has a smokescreen device and flares for defeating IR.

The Enforcer is also designed to produce a minimal radar and EM signature, and run as quiet as possible. Basically, you can only hear the grass or dirt crunching under its treads.
- Ra

[Caz]

Thanks.

Now, time for other specs.


Land speed is about 100 mph. While the tank is very heavy, it can still outrun anything we have today.

- Ra

I'm curious as to how you've designed the tread system so that it can safely manouvre at that speed.

[Ra]

Actually, that should have probably read 100 kph. My bad. Even so, I'll tone it down to about 80 kph, to be on the safe side.
- Ra

[Shroom Man 777]

Top speed doesn't have to factor in maneuvering or some such. Heck, it could be from a tank gunning it at a straight line, going downhill.

And maybe, if you equip the shells with rockets, you won't have to bother much with making the railguns too powerful that their recoil will rip the turret off. After a while, the rockets ignite and further accelerate the shells. Heck, they could even maneuver the shells and stuff. The Ruskies already have a tank-fired missiles.

A plasma-based cloaking system could hide away your electric armor's EM emissions.

[Ra]

Ooh, all great ideas!

I especially like the idea of a guided RP Shell. Basically the best elements of a guided ATM and a DU penetrator all in one.

On OZ, I rated the Enforcer's speed as 85 kph, but it would have to go faster in order to compete with antigravs. I wouldn't see 100 mph as being unreasonable when the vehicle goes all out.

Regarding the plasma cloak, I might use that as well, making it kinda like with the Nod stealth tank. It would "decloak" to fire, but remain virtually undetectable.

BTW, wasn't the plasma cloak also equipped on your Teminator tank?

[Hotfoot]

A plasma-based cloaking system could hide away your electric armor's EM emissions.

While this is sci-fi, I should like to point out that plasma is a highly energetic state of matter, and as such not exactly optimal towards, well, hiding anything.

Gyrojet rounds are a possibility, though one has to wonder what the difference is between a gyrojet and a kinetic kill missile.

Railguns on a tank aren't a bad idea, it's just that you have to remember that there are still physical limits on them. The best part of railguns is the potentially higher ammo capacity and the (generally) inert nature of the ammo. Drawbacks include high-powered magnetic fields at the time of firing (for the love of god give the crew plastic or at least magnetically unreactive ones), and a need for power source.

[Robert Walper]

Correct me if I'm wrong, but aren't rail guns free from recoil as well since they use a magnetic field the accelerate the projectile?

I just watched a episode on TV talking about future plans to put them on navy craft, although the primary problem is power supply.

[Hotfoot]

Nope, the myth of zero recoil railguns is just that, a myth. Take two highly polar magnets, find the same poles, and push them together, or find two opposite poles and try to keep them apart. Forces are clearly applied as per normal, it's just that the force is applied in a way that seems magical because it's not through direct contact.

The only thing that helps with recoil is that acceleration is somewhat more spread out over the course of the firing process, but that's a relatively minor concern.

[Robert Walper]

Nope, the myth of zero recoil railguns is just that, a myth. Take two highly polar magnets, find the same poles, and push them together, or find two opposite poles and try to keep them apart. Forces are clearly applied as per normal, it's just that the force is applied in a way that seems magical because it's not through direct contact.

The only thing that helps with recoil is that acceleration is somewhat more spread out over the course of the firing process, but that's a relatively minor concern.

Is this a matter of the projectile's resistance to the magnetic field and the speed at which it's accelerated, imparting the 'recoil' to the tank?

[Hotfoot]

The easiest way to think about it is that the Magentic field of the railgun is providing push on the projectile, and the projectile's inertia, or resistance to change in velocity, is similarly pushing back on the tank.

If you go back to the example of the astronaut throwing a rock during a spacewalk, you can get the basic idea. Now just replace physical force with magnetic force.

What's interesting to note is that all physical reactions for things we consider to be "kinetic" are in fact a direct link to the electromagnetic force. The reason matter doesn't pass through other matter is because negatively charged electron shells on the outside of the atom will repel shells from other atoms far before they come into contact, and this force is amazingly strong, hence why solid matter will tend to shatter before allowing atoms to get close enough to "touch".

[Robert Walper]

The easiest way to think about it is that the Magentic field of the railgun is providing push on the projectile, and the projectile's inertia, or resistance to change in velocity, is similarly pushing back on the tank.

If you go back to the example of the astronaut throwing a rock during a spacewalk, you can get the basic idea. Now just replace physical force with magnetic force.

What's interesting to note is that all physical reactions for things we consider to be "kinetic" are in fact a direct link to the electromagnetic force. The reason matter doesn't pass through other matter is because negatively charged electron shells on the outside of the atom will repel shells from other atoms far before they come into contact, and this force is amazingly strong, hence why solid matter will tend to shatter before allowing atoms to get close enough to "touch".

This is actually very interesting and educational stuff. Thanks.

[Shroom Man 777]

A plasma-based cloaking system could hide away your electric armor's EM emissions.

While this is sci-fi, I should like to point out that plasma is a highly energetic state of matter, and as such not exactly optimal towards, well, hiding anything.

http://bbs.stardestroyer.net/viewtopic.php?t=80966

Wrong[/Arnie]

Gyrojet rounds are a possibility, though one has to wonder what the difference is between a gyrojet and a kinetic kill missile.

Nothing. It's just that instead of having the railgun throw the bullet harder (thus giving out more recoil), the gyrojet can do the accelerating.

Railguns on a tank aren't a bad idea, it's just that you have to remember that there are still physical limits on them. The best part of railguns is the potentially higher ammo capacity and the (generally) inert nature of the ammo. Drawbacks include high-powered magnetic fields at the time of firing (for the love of god give the crew plastic or at least magnetically unreactive ones), and a need for power source.

Hence the gyrojets. The railguns still have a recoil limit.

[Hotfoot]

http://bbs.stardestroyer.net/viewtopic.php?t=80966

Wrong[/Arnie]

Microwave radiation shielding isn't exactly useful for tank warfare. We're talking about thermal energy, which is somewhat more energetic than radio or microwave. The issue being discussed here is heat signatures, and plasma itself is a source of heat. Planes don't worry about it as much because they fly very high in the atmosphere, giving the thermal energy a long time to disperse. However, in the range of <10km, thermal signatures can very much be used to find tanks that are attempting to hide. Lighting up a hot plasma shield is only going to exacerbate the problem, and it certainly won't provide protection from the visible spectrum. A cold plasma wouldn't provide much additional heat, but it also wouldn't shield against existing heat.

The only practical application of a such a device for a tank would be as a defensive weapon against EMP devices.

Nothing. It's just that instead of having the railgun throw the bullet harder (thus giving out more recoil), the gyrojet can do the accelerating.

And missiles tend to have guidance systems, plus large amounts of fuel in order to accelerate. Also, with a gyrojet, you have the issue of a minimum effective range.

Hence the gyrojets. The railguns still have a recoil limit.

Gyrojets, however, remove several of the advantages given by the railgun design. Fuel means the possibility of ammo cooking off is still very real, and ammo is going to be much more expensive. Even if it's a dumbfire rocket, that's still more expensive than a simple iron slug with a DU core. Additionally, it will need control surfaces in order to accelerate properly, and depending on how it's designed, might even require some sort of guidance system (which would need some way to survive the electromagnetic force applied at launch).

[Shroom Man 777]

The plasma is at room temperature, as Admiral Vlad says. And it hides you from radar (but you yourself can't use radar too). So you'll have to use passive sensors, or active sensors that stick out of the plasma field.

Which is perfectly fine, as Ra's tank is supposed to work against enemies with fancier sensors and crap.

So, the plasma is not hot. It's room temperature.
It hides you from radar (and maybe other fancy pants stuff), which the enemy would use (perhaps heavily).
It also helps mask the massive emissions your giant railgun makes.
You can see the enemy look for you with their radar, thanks to your passive sensors.
You blow them away, and they won't know what hit them.

Perfect!