Starships underwater

[asmodeus]

Starships are of course sealed against vacuum and the environment. So they function in a liquid environment although they are not specifically designed for that. Furthermore, even the "unarmoured" ships are fitted with a decent amount of armour to protect against radiation, rocks, etc. found in space. Warships are usually fitted with more. It seems that this armour should help the ship withstand higher amounts of pressure.

Ok, so how far underwater can a starship go before it either begins to leak or implode? In space it would be dealing with 0 pressure, but underwater the pressure gets very high very fast. Does the amount of armour effect the highest pressure it can withstand? Will the drives operate? What about directional control?

On earth the pressure at sea level (1 atmosphere) is 1kg/cm2 (14.7 psi) and increases by 1 atmosphere every 10 meters (33 feet). I think most naval submarines can withstand no more than 30 - 65 atmospheres (300m - 650m) depending on the design. Beyond that special deep diving units are needed. I think there are currently a number of small scientific units and ROVs that can withstand up to 150 atmospheres (~1.5km). I think there is even 1 or 2 (in the world) that can reach maybe 650 atmospheres which is enough to reach most (but still not all) of the earth's ocean floors.

 

[Spinward Scout]

Also remember that a starship that can skim a Gas Giant for fuel or hide in a Gas Giant atmosphere has to be able to withstand the pressures of at least the top layer of the GGs atmosphere. They speculate that the core of a Gas Giant could be a diamond from all of the pressure and heat.

Later,

Scout

 

[Malenfant]

Plus the underwater pressure depends on (a) the world's gravity and (b) the density of the liquid. On Earth, the highest pressure is 11 km down in Challenger Deep (at the base of the Marianas Trench), which is at about 1100 atmospheres. A manned submersible has been down there - once - and even then apparently the very thick porthole cracked a bit

. But that consisted basically of a very thick, cramped pressure sphere that had a couple of people in, and the rest of the sub was tech, ballast, and other equipment - see here for some details.

I don't actually know much about how large submarines withstand high pressure. Assuming the insides are pressurised to 1 atm, presumably it's down to the strength of the hull material. Traveller hull materials are presumably pretty strong and resistant to tension and compression (especially the superdense hulls), and grav drives and thruster plates presumably work under water too so they should be able to get around at least.

But what about the other things like portholes, windows, intakes, etc? I don't think they'd be too resistant to handling going deep underwater at high pressure, without significant modification.

 

[Malenfant]

One more thing to consider is that a spacecraft underwater would be completely blind. There's no reason for it to carry sonar (sound doesn't travel in space, after all), and water severely limits EM transmission so radar and ladar are right out. The only sensor it could rely on is a neutrino sensor to detect nearby fusion reactors - a densitometer might work to some extent, though it'd be confused by the currents and density gradients and other stuff carried in the water.

 

[mike wightman]

Not completely blind
They can switch their headlights on and use TV cameras.
It works for the subs sent down to look at the Titanic on the Discovery channel.

 

[Malenfant]

Yeah, but headlights and TV cameras only show what's happening within about 10 metres of the ship, tops. By "blind" I meant that they're not going to be able to see a stealthy nuclear-fission powered sub (do fission reactors emit neutrinos?) sneaking up a few hundred metres behind them unless they can figure out what they're seeing on the densitometer...

 

[mike wightman]

Yes, fission reactors emit neutrinos.
According to this anyway

 

[BrennanHawkwood]

GT:Starships actually touches on this. IIRC, a starship has to be totally compartmentalized and have at least Very Good streamlining for it to be able to submerge. GT:Starships does include an Underwater Sensor Suit that can be added to a starship that is specifically designed to be able to operate this way.

 

[Malenfant]

Originally posted by Sigg Oddra:
Yes, fission reactors emit neutrinos.
According to this anyway

Aha. I suspected they would. Presumably they emit less neutrinos than fusion reactors though. But the neutrino levels should still be high enough above background to detect them with a neutrino sensor, especially if within a few km.

 

[mike wightman]

There's an interesting article about SDB's fighting underwater, with HG and Striker compatible rules additions, in JTAS 22. Written byMarcus L Rowland.

 

[far-trader]

And TA#8 available from this very site also offers some rules (T20 mostly) on streamlining requirements, speed, and depth.

 

[graden1]

Originally posted by Sir Dameon Toth:
Also remember that a starship that can skim a Gas Giant for fuel or hide in a Gas Giant atmosphere has to be able to withstand the pressures of at least the top layer of the GGs atmosphere. They speculate that the core of a Gas Giant could be a diamond from all of the pressure and heat.

Later,

Scout

True, but they don't have to skim very deep--hence the term "skimming". The reason that this maneuver only requires partial streamlining is because the ships performing it only experience pressures equivalent to "very thin" atmospheres.

XO

 

[vutpakdi]

Originally posted by Malenfant:
One more thing to consider is that a spacecraft underwater would be completely blind. There's no reason for it to carry sonar (sound doesn't travel in space, after all), and water severely limits EM transmission so radar and ladar are right out.

If memory serves me, there have been experiments on using blue-green lasers underwater for detection (lidar) and communication. The average starship probably wouldn't have blue-green lasers as part of the their sensor suite, but I could see them being available as an option for SDBs built for a world with a significant water percentage.

Ron

 

[CarlP]

>True, but they don't have to skim very
>deep--hence the term "skimming". The reason that
>this maneuver only requires partial streamlining
>is because the ships performing it only
>experience pressures equivalent to "very thin"
>atmospheres.


Hmmm. Wasn't there a reference to system defense boats hiding inside of gas giants in the hopes of ambushing invading ships when they tried to refuel? In that case, the SDBs would have to be able to withstand quite a bit more pressure, and could probably handle an aquatic environment.

 

[Flynn]

I'd suggest treating pressure damage as standard physical damage to the ship, and letting the ship's AR drop the pressure's damage off. SDBs are more highly rated in terms of AR than, say, merchant vessels, so they can go deeper and wait longer at those greater depths without any undue strain on their structural integrity.

For those looking for a game mechanics option in T20, anyway,
Flynn

 

[Malenfant]

Originally posted by Ron Vutpakdi:
If memory serves me, there have been experiments on using blue-green lasers underwater for detection (lidar) and communication. The average starship probably wouldn't have blue-green lasers as part of the their sensor suite, but I could see them being available as an option for SDBs built for a world with a significant water percentage.[/QB]

Blue-green lasers have the longest range in water of the visible wavelengths, but it's still greatly attenuated (especially when you consider the laser has to hit a target and bounce back)

 

[mike wightman]

Stick a battlefield meson gun in a sub and watch those spaceships explode/implode

 

[asmodeus]

Determining if the ship will float should be pretty straight forward. If it weighs less than the volume of liquid that it displaces, then it will float.

IIRC on Earth fresh water weights 1kg per liter. So a ship displacing 1350 kl (100dt) would float in fresh water if it weighed less then 1,350,000 kg (1350 metric tons). Ocean water is of course more dense, but commonly 1.024 kg (it varies based on temp and depth and such). So maybe the ship would have to weight less than 1382 tons.

So this would depend on the weight/density of the particular liquid. I guess if it were in a gas that was very dense it might float too. Deep in the atmosphere of a gg maybe, but pressure would probably be so great that it would crush it. Still there could be a naturaly boyancy point.

 

[The Oz]

Originally posted by CarlP:

Hmmm. Wasn't there a reference to system defense boats hiding inside of gas giants in the hopes of ambushing invading ships when they tried to refuel? In that case, the SDBs would have to be able to withstand quite a bit more pressure, and could probably handle an aquatic environment.

Yes, there was. There was also an adventure published in the old JTAS where an SDB under computer control was running around sinking ships on a waterworld.

I personally would not allow a starship to operate underwater unless it had been specifically designed and equipped for underwater operations. Something designed to operate in space and atmospheres is not necessarily built to operate immersed in liquid.

 

[SlightlyLyons]

Well the one problem I could see are presure seals that rely on positeve enternal presure to hold, remember starships are designed to keep air in not water out. However I se no reason a ship couldn't be equiped to function under water, and perhapse bolt a Sonar and a MAD suit onto it's hull or one of those BlueGreen lasers if it expects to travel to a water world, it would muck with your streamlineing a bit but do you realy think a starship will be fast underwater. Heck, you could use an off the shelf TL7 helicopter diping sonar and boom mounted MAD. Stick some Torps in the missile tubes and rock and roll.