Ranged Weapons
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ID: 4239


August 31, 2007, 6:40 pm

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Fission Cannon


Think of it as a nuclear machine-gun…

The Fission Cannon appears as normal capital-class railgun, either mounted internally - usually forward-facing, or in a large turret.  Due to the relative fragility of the railgun, the internal mounting, with it’s greater potential for armoring is more common.

Full Item Description

The Fission Cannon is a generally a standard capital-ship railgun modified to fire a special projectile.  This projectile is a large slug of transuranic matter as well as softer dampening materials (the exact formulation is classified) that is sufficiently unstable to initiate nuclear ignition upon impact with an enemy ship. Yields vary, but being a pure fission device, is generally limited to sub-megaton. 

The ammunition is highly unstable and has a very short half-life, so ships using this weapon system also need to be installed with a purpose-built reactor that produces the necessary material.  The exact composition of the slugs can be varied to take into account various conditions, targets, etc. 

The weapon system, supply infrastructure and breeder reactor all need to be heavily rad shielded and armored against battle damage.  Very large ships, such as the Ballista class battleship, may deploy multiple breeder reactors.

Tactical Employment

These systems are best used against armored warships, as thin-skinned ships might not provide enough resistance to cause the slugs to properly compress.  In those cases, the rounds do little more damage then standard depleted uranium or osmium slugs - punching completely through the vessel.

They are most lethal against moderately armored ships, as the projectiles may punch fully through one layer of armor and then detonate when they strike the other layer on the way out, causing an internal nuclear detonation.

Against heavily armored ships, generally those with more then 1 meter of hard armor, the rounds surface detonate, destroying any external structures within hundreds of meters and biting deep into the armor.

Other options are to fire rounds with varying velocities to allow for collisions or time on target strikes.   It is possible with a sufficiently accurate system to have projectiles strike each-other, causing a detonation without striking an enemy ship.  This could be used to attack groups of smaller vessels such as fighters, which are too small and unpredictable to directly target.

Due to the sub-light velocity of the projectiles, they are considered a short range weapon and it is highly unsuitable for planetary bombardments against worlds with signficant atmospheres.  Detonation is affected adversely both by loss of mass due to atmospheric friction, and loss of velocity.

In its effective performance environment, short-range ship to ship combat, the rapid cycle time of modern capital ship railgun allied to the nuclear payload allows an unprecedented amount of energy being delivered to enemy targets.

One advantage of this system is it allows for reactor energy to be stored (short term!) in the unstable nuclear slugs. As a result, a smaller ship can match the firepower of larger ships whose weapons feed directly from current reactor output.  Batteries and capacitor systems can produce similar capabilities, but these generally cannot store energy with the same density as nuclear materials.

And yes, if antimatter is commonly available, this system would be superseded.

This idea was inspired by descriptions of ships in the TTA series of books.  They mentioned the weapon Nuclear Pellet Launcher without any details on one actually was. So this is my take.

Ballista class warship

The Ballista was the first warship class built after the development of the Fission Cannon that was specifically designed around this weapon system.

The Ballista has a long, slender profile, with a simple configuration.  The front two-thirds of the vessle comprise six fission cannons arranged radially around the ship’s primary axis with thick armored shrouding. The primary sensors are also present in raised blisters on port and starboard sides of the bow.  The aft third of the ship is devoted to the engines, main powerplant, and the three breeder reactors used to supply the main armament with ammuniton.  In addition, three heavily armored pods attached to the main hull by thick nacelles contain the command and control systems, sensors, secondary armament and crew quarters.  All three of these pods are detachable and can navigate independantly.  The command and control unit is able to operate the ship even when detached.

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Comments ( 10 )
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Voted manfred
August 31, 2007, 16:51
Nuclear weapons should take out quite a bite out of any ship. Now that _is_ really a big gun!

One thing I would seriously add are the fakes - you can bet there will be countermeasures, and shooting numerous fake rounds gives more chances to the real things to do the job. Of course, fake rounds doesn't mean they have to be duds - they could also be explosive (just the regular kind), or carry small electromagnetic pulse generators, on the off chance they hit something important. Plus the many bugs that will trace the enemy ship should it escape, etc. There is no limit what can be shot at the enemy. :)
Voted Siren no Orakio
August 31, 2007, 17:12
FWIW - Yes, this will work, with technology right now. No, Radiation Is Not Quite As Much A Hazard As You Think. U-235 has a half life measured in the gigayear. It is stable enough to produce at home, send it out, and won't blow till impact - Which can be its own trigger mechanism, as you noted. A plug of uranium is left able to slide free from back to front, ultrahigh speed impact will take care of the rest.

Power -can- be drawn from such a nuclear pile, but it's not a real smart engineering decision - The reactor decisions would interfere with quick access to ammo.

What is a hazard, very much so, is producing the ammo. Uranium is toxic and will spontaneously ignite. Underwater. It is Bad Stuff!!!(TM)(R)(C) You do not want to work with it. Osmium is worse. MUCH worse. Microgram quantities are lethally toxic.
August 31, 2007, 18:47
Heh, so make sure the reactor is not under life support - no O2.

Perhaps I underestimated how small the projectials could be without using overly exotic artificial elements.
Siren no Orakio
September 1, 2007, 0:41
From Wikipedia:

The isotope 239Pu is a key fissile component in nuclear weapons, due to its ease of fissioning and availability. The critical mass for an unreflected sphere of plutonium is 16 kg, but through the use of a neutron-reflecting tamper the pit of plutonium in a fission bomb is reduced to 10 kg, which is a sphere with a diameter of 10 cm.

A shell of Pu will have a functional fissile life of over a millenium. Happy blamming~
Voted Chaosmark
August 31, 2007, 17:24
So basically, the worst job on the ship is cleaning a plugged fission cannon barrel?
August 31, 2007, 18:49
That *would* be bad, since the round may already be close to detonation.

Might be smarter to jettison the barrel...
Voted Cheka Man
September 2, 2007, 10:23
Some civilations would make slaves/criminals produce the ammuntion for this.
February 3, 2014, 13:26
And smart ones would just use robots :)


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