Starships Underwater

[alex_greene]

It's a technomagical handwavium to allow non-aerodynamic objects to fly and hover with no visible means of support; it's conveniently been brought forward to TL8, along with Jump drive at TL9, even though technically grav and FTL could easily belong up there with the TL 18 "sufficiently advanced technology."

Not really. No more so that Jump Drives. Reactionless M drives are the staple for Trav Stellar level tech like Jump drives.

Well, technically, by what we currently know of the laws of physics reactionless M-drives, J-drives and grav can't be made to work at any tech level (we're hoping NASA can prove that wrong, but it's still early days yet on that score ...).

Lowering grav to TL 8 (leading to practical fusion reactors and M-drives) and J-drive to TL 9 is a convenient fiction - the setting doesn't have pattern replicators, force fields, teleporters, ship shields or tractor beams, but TL9 is just futuristic enough that the characters can fly around in spaceships equipped with reactionless M-drives and grav plates so they can walk on the decks while the ship is in transit through space, but still with enough verisimilitude to have recognisable technologies such as kettles for boiling water, microwave ovens for heating food, refrigerators and freezers, ration packs, 2D screens and, these days, laptops, smartphones and wifi communications.

Heck, these ships could even still have newspapers and magazines made with paper with actual ink printed on them, letters you write with a biro on a sheet of paper and actual paper books instead of eReaders.

 

[F33D]

Well, technically, by what we currently know of the laws of physics reactionless M-drives, J-drives and grav can't be made to work at any tech level (we're hoping NASA can prove that wrong, but it's still early days yet on that score ...).

Actually, IF (and no one has a CLUE about this except maybe some A.F. types who aren't talking) we can create gravity fields, reactionless drives are easy peasy. 8)

 

[alex_greene]

Well, technically, by what we currently know of the laws of physics reactionless M-drives, J-drives and grav can't be made to work at any tech level (we're hoping NASA can prove that wrong, but it's still early days yet on that score ...).

Actually, IF (and no one has a CLUE about this except maybe some A.F. types who aren't talking) we can create gravity fields, reactionless drives are easy peasy. 8)

Exactly. And once we get grav and reactionless drives, the need for ballast tanks in a submersible vessel would be reduced at the lower stellar tech levels, and eliminated at the higher ones.

 

[F33D]

Well, technically, by what we currently know of the laws of physics reactionless M-drives, J-drives and grav can't be made to work at any tech level (we're hoping NASA can prove that wrong, but it's still early days yet on that score ...).

Actually, IF (and no one has a CLUE about this except maybe some A.F. types who aren't talking) we can create gravity fields, reactionless drives are easy peasy. 8)

Exactly. And once we get grav and reactionless drives, the need for ballast tanks in a submersible vessel would be reduced at the lower stellar tech levels, and eliminated at the higher ones.

True since gravity is unchanged by the presence/absence of water.

 

[Wil Mireu]

True since gravity is unchanged by the presence/absence of water.

Buoyancy, however, is not.

There's a few things at work here. "Gravitics" is contragrav, thruster plates, and what generates gravity inside the ship.

I think we can generally assume that whatever generates gravity inside the ship is a pseudoforce like centrifugal force - it doesn't exist outside the ship - otherwise grav plates will be attracting matter from all around the ship as if there was a 1G field there (which plainly doesn't happen).

If contragrav is involved in moving the ship (as it could be in FF&S and I think in GT?), then the ship's buoyancy in both water and atmospheres will change. Effectively, if you reduce the mass of the ship to a very low value, it should takeoff like a balloon because it is now much less dense than the surrounding air. You could then use more conventional thrusters with far less fuel since they're not pushing anywhere near the same mass (e.g. if you reduce the effective mass of a space shuttle to the mass of the car, that's a huge fuel saving!).

If AG doesn't work like that and the effective mass of the ship stays the same, then it's essentially a conventional drive that doesn't use fuel, and buoyancy won't be affected (I do wonder how 'superdense armour' will affect a ship's buoyancy though).

 

[SSWarlock]

(I do wonder how 'superdense armour' will affect a ship's buoyancy though).

Extremely negatively, one would think. What has a greater chance of floating, a feather or the equivalent volume of a neutron star? Assuming the fluid in question is distilled water in a 1G environment, that is.

 

[F33D]

True since gravity is unchanged by the presence/absence of water.

Buoyancy, however, is not.

Correct.

There's a few things at work here. "Gravitics" is contragrav, thruster plates, and what generates gravity inside the ship.

Actually not totally correct. Thruster plates are MT not MgT. MT doesn't use Grav M-drives.

I think we can generally assume that whatever generates gravity inside the ship is a pseudoforce like centrifugal force - it doesn't exist outside the ship - otherwise grav plates will be attracting matter from all around the ship as if there was a 1G field there (which plainly doesn't happen).

Not necessarily. If you can create local and finite field. Also, if you create a "drive" field outside the ship, the whole ship free falls in that direction. Those inside the ship would not feel it as the ship is moving at the same direction/rate.

 

[rust]

Also, if you create a "drive" field outside the ship, the whole ship free falls in that direction.

The problem underwater would be to prevent the water in
front of the ship from free falling towards the field, too, be-
cause otherwise the field would create a water current with
the same strength as used for the ship's movement, but in
the opposite direction.

 

[F33D]

Also, if you create a "drive" field outside the ship, the whole ship free falls in that direction.

The problem underwater would be to prevent the water in
front of the ship from free falling towards the field, too, be-
cause otherwise the field would create a water current with
the same strength as used for the ship's movement, but in
the opposite direction.

As one creates "one way" fields inside the ship for artificial grav (q.v. multi-decked ships) , it would work the same way for the "drives"...

 

[Wil Mireu]

Actually not totally correct. Thruster plates are MT not MgT. MT doesn't use Grav M-drives.

page 52 of MGT High Guard claims otherwise: "The gravitic drive is the standard for spacecraft throughout the Imperium, combining efficiency with moderately high thrust." (in the "Manoeuvre Drive" section). I was unable to find any further explanation or elaboration elsewhere, but that is what it says there at least.

I think we can generally assume that whatever generates gravity inside the ship is a pseudoforce like centrifugal force - it doesn't exist outside the ship - otherwise grav plates will be attracting matter from all around the ship as if there was a 1G field there (which plainly doesn't happen).

Not necessarily. If you can create local and finite field.

I think it is generally the sanest option. I'm talking solely about the artificial gravity generated inside the ship by the internal deck plates here - if the field extended to objects beyond the ship, then they would be attracted to it as if the ship was a mass generating a 1G field, which means that when a ship jumps in then an essentially point-sized object with the mass of the Earth just arrived, and that would cause all sorts of fun things to happen to nearby objects (spaceships, stations, planets, etc).

Also, if you create a "drive" field outside the ship, the whole ship free falls in that direction. Those inside the ship would not feel it as the ship is moving at the same direction/rate.

If you assume that a reactionless drive is an alcubierre-type drive that warps the space in front and behind the ship, then sure - I don't think any version of Traveller has assumed that though. TNE's FF&S, which provides probably the most detailed explanation, said that they work via a "force generated by the drive [that pushes] on the actual Thruster Plates on the ship itself, propelling it through space and achieving a true reactionless drive" (FF&S p73), which is acknowledged as being very unrealistic but Hey, It's Space Opera (TM).

 

[F33D]

page 52 of MGT High Guard claims otherwise: "The gravitic drive is the standard for spacecraft throughout the Imperium, combining efficiency with moderately high thrust." (in the "Manoeuvre Drive" section). I was unable to find any further explanation or elaboration elsewhere, but that is what it says there at least.

Sorry, sloppy wording on my part. MT's Thrust plates aren't Grav drives. (they are described in detail in that system). In MT Grav drives only work well deep inside a Grav well.

If you assume that a reactionless drive is an alcubierre-type drive that warps the space in front and behind the ship, then sure - I don't think any version of Traveller has assumed that though.

Actually, MgT is the 1st. It doesn't use the tech used in MT or any other version (per the description in MGT books) and it does use Grav deep space M-drive (CT & MT didn't). So, my explanation fits with the way it works in this rule system. Actually, it would be a field that could be around any part of the ship.