Space - Crush Pressure

[Kimbo]

Two related questions:

(1) What is the crush pressure of a space ship?
and
(2) At what depth inside a gas giant, would that atmospheric pressure be reached?

Taken together, these two questions become: How far down inside a gas giant can I fly my spaceship before it implodes like a sinking-submarine in a WWII movie?

I realize this question might be highly hypothetical and thus arbitrary. "A spaceship can withstand as much pressure as it is designed to withstand. If its specs say 50 atmospheres, then it is good to 50." Okay, but what is a believable, reasonable, number for that upper pressure (crush limit)?

Probably, the answer to this question will be complex - an equation of multiple variables. For instance, Tech Level probably plays a role. (The Millenium Falcon probably can withstand higher pressures than our 1970's Apollo spaceships). What else is part of the equation? Size? Armor? Shape (Streamlined vs. Not)?

The second part of the question also most certainly depends on variables - the size, diameter, mass, and density of the particular Gas Giant. A generic formula works fine, but in this case, the specific gas giant I am considering is roughly 5 times the size of Jupiter, or a mass 1650xEarth, with Diameter 14xEarth, and Surface Gravity of 8.4G.

Lastly, a third related question: (3) Supposing an acceleration of 1.4G on a streamlined hull, how long (assume terminal velocity) would it take to fall to this hypothetical crush depth?

That is, suppose a 10G Contragravity Lifter malfunctioned, or was only working at 70% efficiency (only canceling 7G above a world with 8.4G, thus net downward force of 1.4G), how long would the ship's Mechanic have (while the ship is falling) to fix the Contragravity Lifter before the atmospheric pressure crushes them? Seconds? Minutes?

Thanks in advance!

[vicky_molokh]

Crush depth (in yards) = dDR × 150 / L.

dDR is precisely that, while L is the length of the hull in hundreds of feet.

That's for water under Terran conditions.

Divide crush depth by 33 to get pressure in atmospheres.

[cosmicfish]

Originally Posted by Kimbo

(1) What is the crush pressure of a space ship?

To paraphrase Futurama, "Somewhere between zero and one!" Seriously, vicky has the formula from Vehicles (I think!) and that will tell you for more rugged and futuristic ships.

Originally Posted by Kimbo

(2) At what depth inside a gas giant, would that atmospheric pressure be reached?

This is pretty complicated, and will vary between gas giants. If it is important to you, there are charts for some planets (Jupiter at least) that show experimental data. Personally, I would handwave it.

Originally Posted by Kimbo

(3) Supposing an acceleration of 1.4G on a streamlined hull, how long (assume terminal velocity) would it take to fall to this hypothetical crush depth?

This is also depends on the density (not just strength) of the vessel in question - the ship has to be dense enough to sink in that high-pressure atmosphere!

You could determine all this with some not trivial math, but is there a reason not to just handwave it? It is a lot of work for a very specific set of circumstances.

[malloyd]

Originally Posted by Kimbo

I realize this question might be highly hypothetical and thus arbitrary. "A spaceship can withstand as much pressure as it is designed to withstand. If its specs say 50 atmospheres, then it is good to 50." Okay, but what is a believable, reasonable, number for that upper pressure (crush limit)?

Honestly, not much. Maybe not even 1. In most settings spaceships aren't *supposed* to be diving into oceans or gas giants, they're for flying around in space. There's no reason to design them for more than highest pressure atmosphere they will encounter minus the interior pressure.

(The Millenium Falcon probably can withstand higher pressures than our 1970's Apollo spaceships).

Actually, I bet Apollo will withstand more. It's much more symmetric, and designed to take pretty substantial reentry stresses the Falcon would never need to worry about.

Lastly, a third related question: (3) Supposing an acceleration of 1.4G on a streamlined hull, how long (assume terminal velocity) would it take to fall to this hypothetical crush depth?

Fall *from where*? A spacecraft in orbit won't fall, ever. A vessel on contragravity lift just above its crush depth when the generator goes out is doomed in seconds. But why the hell would you be hanging around in the atmosphere of a gas giant on contragravity lift anyway?

That is, suppose a 10G Contragravity Lifter malfunctioned, or was only working at 70% efficiency (only canceling 7G above a world with 8.4G, thus net downward force of 1.4G), how long would the ship's Mechanic have (while the ship is falling) to fix the Contragravity Lifter before the atmospheric pressure crushes them?

If you are far enough down in the atmosphere of a gas giant to be feeling 8.4 G, you're way past the crush depth of anything not designed as a dedicated gas giant probe *already*, and were crushed well before the contragravity problem came up.

[Anthony]

Originally Posted by malloyd

If you are far enough down in the atmosphere of a gas giant to be feeling 8.4 G, you're way past the crush depth of anything not designed as a dedicated gas giant probe *already*, and were crushed well before the contragravity problem came up.

Nah, it could be a superjovian; a 3-4 Jupiter mass giant would have that much at its cloudtops.

[Pomphis]

G:Atlantis p.73 has more detailed rules for crush depth which also consider the vehicle´s shape.

[David Johnston2]

Originally Posted by malloyd

Honestly, not much. Maybe not even 1. In most settings spaceships aren't *supposed* to be diving into oceans or gas giants, they're for flying around in space. There's no reason to design them for more than highest pressure atmosphere they will encounter minus the interior pressure..

Assuming that they are armoured to take missile hits they probably have decent compression resistance. So yes there's a reason.

[fifiste]

Originally Posted by Kimbo

(1) What is the crush pressure of a space ship?
and
(2) At what depth inside a gas giant, would that atmospheric pressure be reached?

I hope those are inspired by a hilarious British tv series called Hyperdrive.

[Agemegos]

Originally Posted by David Johnston2

Assuming that they are armoured to take missile hits they probably have decent compression resistance. So yes there's a reason.

If the armour a monolithic block of strong, tough material, maybe. But ablative or refractory material that resists energy weapons, or spaced and stuffed Whipple shields that resist hypervelocity penetrators, don't necessarily withstand steady pressure, and even massive-plate armour might have overlapped or flexible joints to interrupt the propagation of cracks and shockwaves—spaceship armour might be tiles.

And then there is shape. Even if the armour is the pressure hull, it'll only be designed to withstand one atmosphere of pressure difference, which means little need to shape it like a bathyscaphe.

[cosmicfish]

Originally Posted by Brett

If the armour a monolithic block of strong, tough material, maybe. But ablative or refractory material that resists energy weapons, or spaced and stuffed Whipple shields that resist hypervelocity penetrators, don't necessarily withstand steady pressure, and even massive-plate armour might have overlapped or flexible joints to interrupt the propagation of cracks and shockwaves—spaceship armour might be tiles.

And then there is shape. Even if the armour is the pressure hull, it'll only be designed to withstand one atmosphere of pressure difference, which means little need to shape it like a bathyscaphe.

All of which is valid but almost all of which is beyond the resolution of most GURPS. While some of this might make for interesting (if extremely narrow) optional rules (or part of the never-gonna-happen Vehicles 4E!) it is more detail than most people will want or can even apply to ships not designed to specify these details.