Planet cracker

[sir_pudding]

Originally Posted by JHDude

I assume "kinetic kill" means smashing some other celestial object into it. The race has focused almost all of it's research efforts into energy manipulation, so they're not exactly inclined to chuck a moon at it if they already have beams at their disposal. Besides, the original targets for the weapons were actually hollowed-out planetships, which usually had enough firepower to take out objects like that.

You don't need a moon. A old junked spacecraft will do.

[Fred Brackin]

Originally Posted by sir_pudding

You don't need a moon. A old junked spacecraft will do.

To actually splatter the planet it needs to be a big spacecraft. On the order of miles of diameter even at .99C.

Now, if you only want to kill people it doesn't need to be nearly so big. It probably doesn't need to be going that close to C either.

[sir_pudding]

Originally Posted by Fred Brackin

To actually splatter the planet it needs to be a big spacecraft. On the order of miles of diameter even at .99C.

In real life or in GURPS?

[Fred Brackin]

Originally Posted by sir_pudding

In real life or in GURPS?

"Splatter" was used as shorthand for "make a new, long term asteroid belt". That's where the multiple miles in diameter at .99C comes from.

Doing enough HP to take the Earth down to automatic death is difficult to calculate. You don't know if the Earth has Unkillable I or Damage Reduction just for a start. It might have bought it out of it's experience pts after the Permian or KT boundary events.

If you wonder, yes, I am being sarcastic about giving inanimate objects HT scores and having them make death checks.

[jason taylor]

I should think that the most important elements in game terms would be how much space the weapon takes up, how much space is left in the platform for armor, secondary armament, etc. Because if a weapon is so big that it can destroy a planet, figuring out how much damage points it can cause is academic. Though it may be a fun exercise for those with a bent that way.

An exception might be if planet-crackers are fighting each other and each is well armored enough for calculations of damage to have an actual effect on game play.

[JHDude]

The planet cracker was designed by the aliens to take out another race's battleship (which was made from a hollowed-out planet). Of course, the enemy planet-ship was also shielded, so I was wondering if I wanted to re-create that scenario for some players, what all would be involved for the ships (both firing and receiving).

And, yes, the planet-cracking ships are massive.

Celjabba, where did you find that number? I'd be interested in reading that article :)

[sir_pudding]

Originally Posted by Fred Brackin

"Splatter" was used as shorthand for "make a new, long term asteroid belt". That's where the multiple miles in diameter at .99C comes from.

You don't need to explode the planet to render it uninhabitable.

[MattStriker]

Mind if I slightly hijack this thread with a question about the equivalent toy from my own scifi setting:

The Excalibur Device projects a spherical field of hyperspatial energy. Any mass caught inside the field when it triggers (requires several hours to fully charge) is violently ripped into hyperspace. Because of the way hyperspace works in that setting, matter can't exist there for long and is ejected back...in highly destabilized form. It arrives as a mass of random particles, roughly half regular matter and half anti-matter.

So what takes place next is basically an anti-matter explosion with a size depending on the amount of mass converted.

This is where I get into some maths trouble.

I'm trying to come up with an approximate radius for the field that would make sense in that it'd reliably wipe out a planet (and subject the entire system to a lethal burst of radiation) but not significantly endanger systems over 5 LY away.

I've got as far as to dig up the volume-of-a-sphere formula (been a while), find the density of an earth-type planet's inner core (15g/cm³) and the energy density of an annihilation reaction (9e16 J/kg).

That's when the numbers involved got a little overwhelming :P.

Anybody here want to have some fun with that idea?

[Edges]

Originally Posted by MattStriker

Mind if I slightly hijack this thread with a question about the equivalent toy from my own scifi setting:

The Excalibur Device projects a spherical field of hyperspatial energy. Any mass caught inside the field when it triggers (requires several hours to fully charge) is violently ripped into hyperspace. Because of the way hyperspace works in that setting, matter can't exist there for long and is ejected back...in highly destabilized form. It arrives as a mass of random particles, roughly half regular matter and half anti-matter.

So what takes place next is basically an anti-matter explosion with a size depending on the amount of mass converted.

This is where I get into some maths trouble.

I'm trying to come up with an approximate radius for the field that would make sense in that it'd reliably wipe out a planet (and subject the entire system to a lethal burst of radiation) but not significantly endanger systems over 5 LY away.

I've got as far as to dig up the volume-of-a-sphere formula (been a while), find the density of an earth-type planet's inner core (15g/cm³) and the energy density of an annihilation reaction (9e16 J/kg).

That's when the numbers involved got a little overwhelming :P.

Anybody here want to have some fun with that idea?

I get a sphere around 6.5 km in diameter at the core of the earth if transformed into antimatter would destroy the earth assuming your core density is correct (I know your antimatter reaction number is) and the death star guys in the post #6 link got their number right.

After a quick search, some estimates for core density are a little lower (12.6-13g/cm^3). So 6.5 km should be plenty.

[lwcamp]

Originally Posted by sir_pudding

In real life or in GURPS?

Just for reference, in the thread that you link to the relativistic spacecraft would have a kinetic energy of 3.6E22 J (if I did the math right). From the ever useful Atomic Rocket boom table
http://www.projectrho.com/rocket/rocket3x1.html , about 1/6 of the way down the page
that's about an order of magnitude less energy than the Chicxulub event that ended the dinosaurs. It would cause a lot of consternation to the people living there, but would not really damage an earth-like planet.

With four orders of magnitude more energy, you could remove all of an earth-like planet's atmosphere. For five orders of magnitude more energy, you could turn all of earth's oceans into steam. Six orders of magnitude more energy allows you to melt the earth's crust, making the entire earth molten. It would take nine orders of magnitude more energy to blast the earth into gravitationally unbound rubble.

Luke