crazy_cat
Adventurer
This is clearly a very complex problem - I think we're going to need to wave a bigger hand at it
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Scifi science question
- Thread starter garrowolf
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tomBitonti
Hero
Googling "spherical pressure hull limit"
LEEAMITe: The Transport Vehicle
ScienceDirect - Marine Structures : An overview of buckling and ultimate strength of spherical pressure hull under external pressure
The first gives some nice equations, with this perhaps the most useful:
Pe = 1.22 e (t/r)^2
Pe = elastic buclking pressure
e = module of elasticity
t = spherical shell thickness
r = radius to shell midsurface
There is a second limit equation ... probably worth running numbers through that, too,
to see if there is a different limit which is reached.
For a number of materials:
Elastic Properties and Young Modulus for some Materials
Structural Steel: 200 GPa
Silicon Carbide: 450 GPa
Tungsten Carbide: 450 - 650 GPa
Diamond: 1,050 - 1,200 GPa
Is a diamond sphere practical? I have no idea, but lets plug in some numbers.
e set to 1x10^3 GPa for diamond
t = 1m (arbitrarily)
r = 5m (arbitrarily)
Pe = 1.22 * 1x10^3 GPa * (1/5)^2
= 1.22 * (1/25) * 10^3 * GPa
= 0.05 * 10^3 GPa
= 5 * 10 GPa
That gets us nicely into the middle of the gas layer (which ends at 10
* 10 GPa, the gas transitions to a liquid metal, at a depth of 10,000
kilometers.
If you increase that by a factory of 100 ... then you are well above
the pressure at the transition, and can enter the metallic region.
Still a problem of temperature.
I *think* I read that the gas layer is transparent. Not really sure,
but I don't think the metal layer would be transparent.
Now, that is for an ideal sphere of solid diamond! 1m thickness and
5m radius seems to give you about 8m of interial space (diameter),
about 25 feet across.
That is an unbroken sphere, too! Maybe it runs off an special
"projection" engine that allows the machinery to be permanently
installed in the center of the sphere. Putting in passengers seems to
be a problem ...
(Edit: Putting carbon in a high temperature high pressure bath of atomic hydrogen seems to be a short lived experiment ... as well, if the reaction can be avoided, hydrogen infiltration would seem to be a problem.)
LEEAMITe: The Transport Vehicle
ScienceDirect - Marine Structures : An overview of buckling and ultimate strength of spherical pressure hull under external pressure
The first gives some nice equations, with this perhaps the most useful:
Pe = 1.22 e (t/r)^2
Pe = elastic buclking pressure
e = module of elasticity
t = spherical shell thickness
r = radius to shell midsurface
There is a second limit equation ... probably worth running numbers through that, too,
to see if there is a different limit which is reached.
For a number of materials:
Elastic Properties and Young Modulus for some Materials
Structural Steel: 200 GPa
Silicon Carbide: 450 GPa
Tungsten Carbide: 450 - 650 GPa
Diamond: 1,050 - 1,200 GPa
Is a diamond sphere practical? I have no idea, but lets plug in some numbers.
e set to 1x10^3 GPa for diamond
t = 1m (arbitrarily)
r = 5m (arbitrarily)
Pe = 1.22 * 1x10^3 GPa * (1/5)^2
= 1.22 * (1/25) * 10^3 * GPa
= 0.05 * 10^3 GPa
= 5 * 10 GPa
That gets us nicely into the middle of the gas layer (which ends at 10
* 10 GPa, the gas transitions to a liquid metal, at a depth of 10,000
kilometers.
If you increase that by a factory of 100 ... then you are well above
the pressure at the transition, and can enter the metallic region.
Still a problem of temperature.
I *think* I read that the gas layer is transparent. Not really sure,
but I don't think the metal layer would be transparent.
Now, that is for an ideal sphere of solid diamond! 1m thickness and
5m radius seems to give you about 8m of interial space (diameter),
about 25 feet across.
That is an unbroken sphere, too! Maybe it runs off an special
"projection" engine that allows the machinery to be permanently
installed in the center of the sphere. Putting in passengers seems to
be a problem ...
(Edit: Putting carbon in a high temperature high pressure bath of atomic hydrogen seems to be a short lived experiment ... as well, if the reaction can be avoided, hydrogen infiltration would seem to be a problem.)
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Yes, well, depending on your sci-fi, you're probably transparent aluminum, duranium alloy, or some other form of unobtanium.
One effect that I was thinking would occur is that since the deflector field would be redirecting force at right angles to the axis of the ship then it would reduce the actual pressure against the hull. Therefore the hull pressure that the ship would actually encounter would be a lot less. Then the technology of just an extremely strong hull would be sufficient. The technology of the previous tech level involved lots of underwater colonies and high pressure submarines. The special spaceships designed to travel in gas giants would have some of those features built in.
Hmmmm actually the complexity of the problem could work in the other direction. If it is too complex to be easy to figure out then I can say whatever I want and people would be none the wiser.
I was thinking resisting 100,000 bars of pressure would allow the ship to go deep into the liquid layer but maybe that is too much. that would still be above the metallic hydrogen level.
Temperature would be an interesting issue. The field would be reducing the density of the liquids and gases at the ship's hull causing them to "boil" away from the hull. Effectively this would increase the motion of the gas and heat it so it would keep the coldest part away from the hull.
It would be dangerous to use a rocket in a gas giant but it would probably produce a super cavitation effect and push the ship away from the area of thrust very quickly. Then the explosions would direct their force upward in the direction of least resistance. It would be good for fast movement but another system would be needed for slower movement. Perhaps a gravitic drive would be good here since you would need something like it to act as a ballast system.
It may not even need to go that deep anyway since there would be so much accessible gas in the upper atmosphere.
Then there is the question of weapons. A beam weapon would cause damage at the point of firing. Maybe a gravitic drive torpedo so that all the damage is at the target.
Hmmmm actually the complexity of the problem could work in the other direction. If it is too complex to be easy to figure out then I can say whatever I want and people would be none the wiser.
I was thinking resisting 100,000 bars of pressure would allow the ship to go deep into the liquid layer but maybe that is too much. that would still be above the metallic hydrogen level.
Temperature would be an interesting issue. The field would be reducing the density of the liquids and gases at the ship's hull causing them to "boil" away from the hull. Effectively this would increase the motion of the gas and heat it so it would keep the coldest part away from the hull.
It would be dangerous to use a rocket in a gas giant but it would probably produce a super cavitation effect and push the ship away from the area of thrust very quickly. Then the explosions would direct their force upward in the direction of least resistance. It would be good for fast movement but another system would be needed for slower movement. Perhaps a gravitic drive would be good here since you would need something like it to act as a ballast system.
It may not even need to go that deep anyway since there would be so much accessible gas in the upper atmosphere.
Then there is the question of weapons. A beam weapon would cause damage at the point of firing. Maybe a gravitic drive torpedo so that all the damage is at the target.
Well, your usual "deflector field" is a nod to the fact that space is not really a vacuum, and that hitting even a grain of dust at near or super-light speeds is problematic. As such, these things are usually described as being oriented forwards, sweeping away or blocking incoming material from forward motion - they don't protect the sides, top, bottom, or rear.
Well, that depends on how your machinery works. The Trek-style inertial dampers are essentially gravity generators. They exert forces, but don't change the mass of an object - so the density of the material remains the same.
Reducing the mass of objects is a whole other kettle of fish.
Cavitation is the creation of voids in a fluid medium, and the immediate implosion of those voids (generally due to pressure). Cavitation doesn't generally push the vehicle away - more often the overall effect is drag, slowing the vehicle down.
Setting off a rocket in a thick hydrogen atmosphere, and having the hydrogen explode, would not be "cavitation" in the normal sense. Mind you, you don't expect a hydrogen atmosphere to explode in any event - if you had any oxygen present to burn the hydrogen, it would already have burned off - the atmosphere is what's left over. Without an oxidant, no boom.
Whether a beam weapon causes damage at the point of firing, or would simply be attenuated, depends on what it is a beam of, and the composition of the atmosphere. The atmosphere may be largely transparent to certain wavelengths of light, for example.
Pbartender
First Post
"Unobtanium", which, in all honesty, works just as well for the original problem... Remember that you're playing science FICTION just as much as you are playing SCIENCE fiction.
I presume your setting has force field generators at least used for defense against stray meteorites and the friction generated from atmospheric entries while traveling at 100g of acceleration? Why not use those instead? In the context of most sci-fi settings a "force field" is simply a bubble-like barrier of energy that prevents most matter and some types of energy from passing through.
If your ships already have one, it's just a matter of retuning the ship's protective force fields to keep out molecular gasses and then pumping in enough energy for those fields to withstand the forces generated by the excessive pressures.
Voila! A bit of pseudo-scientific techno-babble about rerouting power from the auxiliary systems to the force field generators, and you're golden... And hopefully the force field will hold long enough.
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RainOfSteel
Explorer
The force of pressure in a gas giant's atmosphere at any altitude is the result of the planet's total gravitational field exerted across it's entire atmosphere.
Coming along in a ship, diving down into the atmosphere of the gas giant, and putting up a localized gravitational exception to prevent yourself from being dragged down to the Gas Giant's core is not going to change the pressure because all the gas immediately outside your ship's gravity field still has just as much pressure and still pushes down on the gas inside your ship's gravity field all the way to the hull.
The ship's tiny little gravity field is not going to negate the pressure of the entire rest of the atmosphere, unless the ship can generate a gravity field the size of the gas giant, in which case the ship has a weapon of mass destruction handy.
I would say that the gravity field keeps a ship at whatever altitude you want, but it had better have a hull that can withstand the full pressure of the atmospheric depth where it wants to dive.
Coming along in a ship, diving down into the atmosphere of the gas giant, and putting up a localized gravitational exception to prevent yourself from being dragged down to the Gas Giant's core is not going to change the pressure because all the gas immediately outside your ship's gravity field still has just as much pressure and still pushes down on the gas inside your ship's gravity field all the way to the hull.
The ship's tiny little gravity field is not going to negate the pressure of the entire rest of the atmosphere, unless the ship can generate a gravity field the size of the gas giant, in which case the ship has a weapon of mass destruction handy.
I would say that the gravity field keeps a ship at whatever altitude you want, but it had better have a hull that can withstand the full pressure of the atmospheric depth where it wants to dive.
MarkB
Legend
One problem you're dealing with is that your accelerative field needs to be far more controlled and constrained in the anti-pressure application.
When used as an inertial compensator, it can be applied equally across the whole of the ship's interior, and only needs to provide acceleration in one direction at any one time.
Used as a pressure-compensator, it must not operate on any internal volume of the ship (or that volume will be just as greatly compressed as it would from the outside, simply in a different direction) - instead, it must project outwards from just beyond the surface of the vessel, and must radiate away from the hull at every point, acting in lots of different directions at once.
Those factors will require a completely different configuration than the inertial compensation system, and one which may well not be capable of the same level of power.
Yes, that's kind of my point. A shell of pure diamond, as far as I am concerned, counts as an "exotic material" - if you're going to that point, just say your hull is superstrong, and be done with it. If it works for classic sci-fi author Larry Niven, it works for your game, too
