Forum adverts like this one are shown to any user who is not logged in. Join us by filling out a tiny 3 field form and you will get your own, free, dakka user account which gives a good range of benefits to you: No adverts like this in the forums anymore. Times and dates in your local timezone. Full tracking of what you have read so you can skip to your first unread post, easily see what has changed since you last logged in, and easily see what is new at a glance. Email notifications for threads you want to watch closely. Being a part of the oldest wargaming community on the net. If you are already a member then feel free to login now.

Erm, I'll admit I'm no astrophysicist, so I don't know the reality here, but my knowledge of the "Nova Cannon" is that its destructiveness is essentially the same as a star going nova, making them highly-effective AoE weapons in space battles.

Two questions arise.

First, these things are never used near anything important, right? Like, planets, other starships, and it has a range measured in light(unit of time) right? Because a star going nova, to my knowledge, has a destructiveness that annihilates entire planets in its own system, so these vessels would effectively have to fight entire battles on their own in the empty regions of space between star systems to avoid unnecessarily destroying their own fleet and whatever planet's being fought over. Yes, that does imply these ships would essentially be interceptors for things like Ork Roks, Tau fleets, other space threats that don't travel through the Warp, and. well, if we're being honest, entire Tyranid hive fleets since I'm pretty sure there's no biological adaptation possible to survive a star going nova in close proximity.

Second, why is this not the Imperium's default Exterminatus weapon?

Nowhere near so big.

BFG rulebook says:
A nova cannon is a huge weapon, normally mounted in the prow of a ship so that the recoil it generates can be compensated for by the vessel's engines. It fires a projectile at incredible velocity, using graviometric impellers to accelerate it to close to light speed. The projectile implodes at a preset distance after firing, unleashing a force more potent than a dozen plasma bombs.

So big? Yeah.
Probably overkill for Exterminatus, energy intensive, finicky, and difficult to use-prow mounted and no momentum to counter recoil.
Not to mention explosive would explode early, due to friction.

 Farseer Anath'lan wrote:
Nowhere near so big.

BFG rulebook says:
A nova cannon is a huge weapon, normally mounted in the prow of a ship so that the recoil it generates can be compensated for by the vessel's engines. It fires a projectile at incredible velocity, using graviometric impellers to accelerate it to close to light speed. The projectile implodes at a preset distance after firing, unleashing a force more potent than a dozen plasma bombs.

So big? Yeah.
Probably overkill for Exterminatus, energy intensive, finicky, and difficult to use-prow mounted and no momentum to counter recoil.
Not to mention explosive would explode early, due to friction.

...If it fires its projectiles at speeds close to light speed, there's really no reason to make the projectile explode, too.

Because depending on exactly how close to lightspeed it gets its projectile, it's going to utterly destroy any starship it touches, probably leave a crater in a planet deep enough you can see the mantle, and given how momentum works in space, you damned well had better not miss your target for fear of blowing up something later on that you actually don't want to. Making the projectile blow up with a self-destruct mechanism probably would just turn it into a shotgun of destruction instead of a bullet.

If it gets its projectile up to "Oh-My-God Particle" velocities, it has a serious potential to obliterate planets with enough destructive force that other planets in the same system are also devastated by the effects.

Also the word for what would happen when it entered the atmosphere is not "friction" it's "nuclear fusion." If you throw a baseball at 90% lightspeed in an atmosphere, it literally causes a nuclear explosion that destroys a city.

Literally, this thing could cause an entire planet to explode into plasma in a flash brighter than the Sun.

And does the Imperium really have so much trouble steering their battleships they can't aim directly toward something the size of a planet?

The Nova Cannon despite its name does not make a star go nova. In the Gothic War (as per the BFG rulebook), it took the combined firepower of 3 Blackstone Fortresses to make a star go nova.

The Nova Cannon fires a shell to an effective range of 150cm in BFG scale which is 1cm = 1000km.

From the novel Warriors of Ultramar, which is consistent with the BFG scale:

Travelling at close to five thousand kilometres per second, the shell closed the gap between the foes in a little under twenty-five seconds.

p. 152, Warriors of Ultramar

25 seconds at 5000km/s means the targets were at 125,000 km range or 125cm in BFG tabletop scale, well within the range of a Nova Cannon.

Iracundus wrote:
The Nova Cannon despite its name does not make a star go nova. In the Gothic War (as per the BFG rulebook), it took the combined firepower of 3 Blackstone Fortresses to make a star go nova.

The Nova Cannon fires a shell to an effective range of 150cm in BFG scale which is 1cm = 1000km.

From the novel Warriors of Ultramar, which is consistent with the BFG scale:

Travelling at close to five thousand kilometres per second, the shell closed the gap between the foes in a little under twenty-five seconds.

p. 152, Warriors of Ultramar

25 seconds at 5000km/s means the targets were at 125,000 km range or 125cm in BFG tabletop scale, well within the range of a Nova Cannon.

So... NOT close to the speed of light then?

And I didn't think it made a star go nova or even suggest it. I heard years ago it got its name because the blast radius of the projectile and destructiveness within was similar to a star going nova.

How big is the blast radius, anyways? I heard "a dozen plasma bombs" but that doesn't tell me anything without knowing how many tens of thousands of kilometers in radius a plasma bomb's detonation covers.

 Pouncey wrote:

Iracundus wrote:
The Nova Cannon despite its name does not make a star go nova. In the Gothic War (as per the BFG rulebook), it took the combined firepower of 3 Blackstone Fortresses to make a star go nova.

The Nova Cannon fires a shell to an effective range of 150cm in BFG scale which is 1cm = 1000km.

From the novel Warriors of Ultramar, which is consistent with the BFG scale:

Travelling at close to five thousand kilometres per second, the shell closed the gap between the foes in a little under twenty-five seconds.

p. 152, Warriors of Ultramar

25 seconds at 5000km/s means the targets were at 125,000 km range or 125cm in BFG tabletop scale, well within the range of a Nova Cannon.

So... NOT close to the speed of light then?

And I didn't think it made a star go nova or even suggest it. I heard years ago it got its name because the blast radius of the projectile and destructiveness within was similar to a star going nova.

How big is the blast radius, anyways? I heard "a dozen plasma bombs" but that doesn't tell me anything without knowing how many tens of thousands of kilometers in radius a plasma bomb's detonation covers.

The speed of light is 299,792 km/s.

The blast template is 5cm in diameter so that is 5,000 km in diameter. The inner hole of greatest damage is 1.2cm diameter so 1,200 km diameter.

Iracundus wrote:
The speed of light is 299,792 km/s.

Personally I round it and say "roughly 300,000 km/s" but yes, there is a big difference between 299 and 5.

The blast template is 5cm in diameter so that is 5,000 km in diameter. The inner hole of greatest damage is 1.2cm diameter so 1,200 km diameter.

So they're blowing up a volume way smaller than Earth every time it fires?

That's not exactly an AoE weapon for space battles.

 Pouncey wrote:
...If it fires its projectiles at speeds close to light speed, there's really no reason to make the projectile explode, too.

"It sounds cool tho" - GW

It's certainly an area of effect weapon, but in ground terms it's the equivalent of a tank's High Explosive shell rather than the equivalent of a Tactical Nuke. The energy 'released*' may travel thousands of km in the unopposed vacuum of space but the actual damage inflicted on anything contacted is not particularly impressive.

* due to the description saying IMplosion instead of EXplosion I've always interpreted it as being a mega-gravity warhead that inflicts damage by yanking nearby objects.

As to the question about Exterminatus: The Imperium's 'standard' form of Exterminatus is the virus bomb, a warhead which kills every living thing on a planet whilst leaving it's material resources intact for later reclamation for the glory of the God-Emperor and even that is only done as a matter of last resort. Blasting planets to atoms is theft from the Emperor.

The name is hyperbole.

Star cannons do not fire stars either.

 Kid_Kyoto wrote:
The name is hyperbole.

Star cannons do not fire stars either.

Blackstone fortresses are not black, not made of stone and they move.

At least the Planet Killer actually kills planets

 Pouncey wrote:

Iracundus wrote:
The speed of light is 299,792 km/s.

Personally I round it and say "roughly 300,000 km/s" but yes, there is a big difference between 299 and 5.

The blast template is 5cm in diameter so that is 5,000 km in diameter. The inner hole of greatest damage is 1.2cm diameter so 1,200 km diameter.

So they're blowing up a volume way smaller than Earth every time it fires?

That's not exactly an AoE weapon for space battles.

for a fleet, no.
for a destroyer squadron in close formation, it can take out several ships at once.


the explosion as well as speed on light is required because whilst a kinetic projectile could kill a ship, it would also have to hit it directly, which is damn hard at several light seconds range. Just getting a shell within a few thousand kilometers is fairly easy.

 n0t_u wrote:

 Pouncey wrote:
...If it fires its projectiles at speeds close to light speed, there's really no reason to make the projectile explode, too.

"It sounds cool tho" - GW

Fun fact - in the Only War RPG, it's possible to put a bayonet on your flamer. It's then possible to make that bayonet a chain-knife.

One way or the other, the Imperium's going to get ya, and they're going to make sure you don't get back up again. Given some of the foes they face, it's really not an unreasonable position. I wouldn't want to be the Imperial Admiral that hits a giant ominous Necron ship with a projectile traveling at near light speed only to watch it shrug it off because Necron bullcrap physics.

Admiral Tooreasonablius wrote:We should have had them explode! Why didn't we have them ex -

locarno24 wrote:

 Pouncey wrote:

Iracundus wrote:
The speed of light is 299,792 km/s.

Personally I round it and say "roughly 300,000 km/s" but yes, there is a big difference between 299 and 5.

The blast template is 5cm in diameter so that is 5,000 km in diameter. The inner hole of greatest damage is 1.2cm diameter so 1,200 km diameter.

So they're blowing up a volume way smaller than Earth every time it fires?

That's not exactly an AoE weapon for space battles.

for a fleet, no.
for a destroyer squadron in close formation, it can take out several ships at once.


the explosion as well as speed on light is required because whilst a kinetic projectile could kill a ship, it would also have to hit it directly, which is damn hard at several light seconds range. Just getting a shell within a few thousand kilometers is fairly easy.

Easier than having to hit the target directly or at the very least get even closer to hitting the target directly (some of the Imperium's weapon batteries are area of effect but not to an appreciable tabletop extent). The maximum effective range of Imperial weapon batteries is 60cm which is 60,000 km using BFG scale. However the need to time the detonation of the Nova Cannon shell is also why Eldar holofields work against those hits. If the timing is off, the shell has already hurtled off at 5,000km/s and the resulting explosion can be partially or entirely off target. The tabletop is also an abstraction of 3D space so even if the template is "on" the target Eldar ship, it may actually be far above or below. All this is why the Eldar holofield save still works.