Is this laser cannon really that big?

[Ejidoth]

Originally Posted by Kraydak

I couldn't actually remember if it was Damage=E or D=E^(1/2), but either way, it scales wrong. Vaporizing stuff takes E=mass (chemical binding energy) or for large enough objects, which is relevant for lasers of this scale in space, E=mass^(5/3), the gravitational binding energy. It really bugs me when people use the mass^(1/3) to estimate the hp of the Earth, a mountain range or a large asteroid, for example.

This is possibly why laser damages appear to be the cube root of their energy output.

Anyway, the issue you're having, I think, is that the GURPS rules for breaking/killing something assume you just have to blow a huge hole through it, and the rules for disintegration are sort of tacked on (that is, it takes somewhere between two and ten times 'breaking' damage to disintegrate something, but this is probably less realistically true for sufficiently huge objects.) It really does work for most purposes, though.

[Anthony]

A SM+14 major battery has a beam output of 300 gigajoules, equivalent to 71 tons of TNT. There's some scaling issues there (based on the explosions rules, it should do 4,500d damage, not 1,500d damage), but the explosion rules don't actually scale properly at high levels, so disagreement with the explosions rules is fine (and yes, Spaceships beam weapons scale with the 1/3 power of beam energy).

[DouglasCole]

Originally Posted by Kraydak

One of the examples of why hp=mass^(1/3) doesn't really work well, especially if damage is supposed to scale with energy linearly.

Fortunately, damage is not supposed to scale with energy linearly. It scales as sqrt(energy) for impact projectiles, and cube root (energy) for explosions and energy weapons that tend to vaporize stuff, IIRC.

[sir_pudding]

Originally Posted by Kraydak

I couldn't actually remember if it was Damage=E or D=E^(1/2), but either way, it scales wrong. Vaporizing stuff takes E=mass (chemical binding energy) or for large enough objects, which is relevant for lasers of this scale in space, E=mass^(5/3), the gravitational binding energy. It really bugs me when people use the mass^(1/3) to estimate the hp of the Earth, a mountain range or a large asteroid, for example.

It doesn't require anything near the gravitational binding energy to render a planet, mountain range, or asteroid completely useless as a planet, mountain range or asteroid for most characters. A human corpse with 200 points of arrow damage doesn't stop being a human corpse, it isn't a person in any meaningful way. -6XHP is probably a gameable abstraction for "rendered irreparably destroyed".

[Kraydak]

Originally Posted by DouglasCole

Fortunately, damage is not supposed to scale with energy linearly. It scales as sqrt(energy) for impact projectiles, and cube root (energy) for explosions and energy weapons that tend to vaporize stuff, IIRC.

I admit to having misremembered the damage/energy relation for guns, but note that explosives to damage as sqrt(energy), given that damage scales with sqrt(explosive weight).

At the scale we are talking here (100 tons), the difference between a 1/3 power and a 1/2 power is a 1/6 power, here about a factor of 10. Not negligible at all. GURPS scaling works sorta-ok for single attacks on targets of less than a ton (1000^(1/6)=3) in mass, but go much over a ton or allow for multiple attacks and the scaling goes crazy. There is a reason GURPS battleships have absurdly low HP.

Unfortunately, GURPS damage doesn't actually effectively scale with sqrt(energy) as it scales linearly with the number of shots. 10 shots of our laser are doing 10X the damage and so apparently dumping 100X the energy of a single shot into the target.

[Polydamas]

Originally Posted by Kraydak

I couldn't actually remember if it was Damage=E or D=E^(1/2), but either way, it scales wrong. Vaporizing stuff takes E=mass (chemical binding energy) or for large enough objects, which is relevant for lasers of this scale in space, E=mass^(5/3), the gravitational binding energy. It really bugs me when people use the mass^(1/3) to estimate the hp of the Earth, a mountain range or a large asteroid, for example.

Damage isn't mostly about vaporizing things, but about disabling and destroying them. 90% of the time, the targets of damage in GURPS are creatures or human-scale artifacts. So complaining that a straight HP vs. damage comparison doesn't perfectly model the energy required to vaporize a mass of rock so thoroughly that it will never fall back together is missing the point IMHO.

You might search these forums for a suggested HP model for warships by David Pulver circa 2005.

[panton41]

Originally Posted by sir_pudding

It doesn't require anything near the gravitational binding energy to render a planet, mountain range, or asteroid completely useless as a planet, mountain range or asteroid for most characters. A human corpse with 200 points of arrow damage doesn't stop being a human corpse, it isn't a person in any meaningful way. -6XHP is probably a gameable abstraction for "rendered irreparably destroyed".

In other words, if you take that 7.62mm Gatling gun and put 10,000 rounds into my poor, defenseless Toyota Echo the end result will just be a Toyota Echo with 10,000 (or fewer) holes in it. It's worthless as anything except scrap metal, but it's probably still roughly car-shaped.