Lanthanum Grid in Carried Craft?

[Gray Lensman]

Just how big is that Jump Bubble?

Hmmm.... couldn't get the image in.

http://www.travellerrpg.com/CotI/Gallery/index.php?n=1024

from Supp 8: Library Data A-M page 16 by W.H. Keith

 

[BlackBat242]

And where is the grid on that ship?

Oh, yeah... CT didn't have grids... Marc's JATS retcon attempt notwithstanding.

 

[robject]

I mean pick one:
Fuel used all at once or not
Misjumps
Jump Diameters
Hull Grid or not
Ect, Ect, Ect.

BLEH

That's what T5 was faced with - how to use the given concepts in useful ways. Not that jump is the only tricky issue, but there's always been questions.

T5's solution is to let designers pick a grid or a bubble, and to give each one different pluses and minuses.

 

[DaveChase]

I remember that discussion from over a year ago. Has it been decided yet for T5?

Dave Chase

 

[robject]

I remember that discussion from over a year ago. Has it been decided yet for T5?

Dave Chase

I'm sure the discussion is far from over, but FFE (i.e. Marc) has consistently sidestepped some technical aspects for the sake of interesting design options. I call this the FFE Position because it's intended to be a resolution of issues for Traveller in general, though of course the direct beneficiary is T5.

Bubble vs Grid (FFE)

The jump bubble is cheap and useful for dispersed structures, or when a ship's mission might vary by tonnage, and can be disrupted by debris entering its jump field. The jump grid costs more, conforms the jump field to the hull, can't be disrupted by debris, but can't be installed on dispersed structures and are difficult to repair.

The jump field is not composed of jump fuel. All jump fuel is burned by the powerplant, up front, very quickly, to kick-start the jump drive.

Drop tanks only need grids if they're carried on ships using a jump grid.

Other Jump (and other non-jump) Issues

As far as other issues go (when and how the fuel is used, how misjumps happen, jump diameters and masking, fighter effectiveness, how droptanks work and why other refuel methods don't, ship computers vs robots, the ANNIC NOVA, ship bridge size, power plant inefficiency, Virus, the Xboat and Xboat routes, and a dozen-plus other things) Marc makes the FFE Position based on where he wants to go with Traveller, effectively ending many controversies -- within the T5 sphere of things at least.

 

[BraselC5048]

I did some math on the subject, and I got some pretty interesting results. If the ship is surrounded by either a layer or a sphere of hydrogen gas, its possible to caculate the pressure of the bubble. I used a 6000 ton ship, about 117 meters long. I also assumed a Jump-1 uses 500 tons of fuel for the bubble.
If the hydrogen is at a temperature of 0 degrees C, a 1 meter thick layer would produce a pressure of 488 atmospheres, and essentially crush the ship.

If its at the temperature of liquid nitrogen, the pressure's 137 atmospheres, still enough to crush the ship.
A 10 meter thick layer at that temperature gives you a pressure of 13 atmospheres, which it's possible to design a ship to withstand (mabye), but the ship would weigh a ton, and it isn't really practical for normal ships.

If it's 'a bubble of boiling hydrogen', or very very cold, a 10 meter thick layer is a pressure of 3.75 atmospheres, which, for when I went and caculated structure, would just barely crush the ship. A 60 meter thick layer at that temperature would probebly work up to a jump-3 (but the ship's only 117 meters long).

A 200 meter radius bubble at 0 degres C gives a pressure of .167 atmospheres. So a bubble (or an ovel) is pretty much required.

That is, if most of the hydrogen goes into the bubble. And if the gas laws apply to the hydrogen bubble.

 

[Gray Lensman]

I'm sure the discussion is far from over, but FFE (i.e. Marc) has consistently sidestepped some technical aspects for the sake of interesting design options.

Bubble vs Grid (FFE)

Or.... there could be more than 1 version of jump drive (after all several differerent races came up with it right (damn, my fingers are fat today).

OOPS did I say that (not the part in parentheses).

 

[HG_B]

As far as other issues go (when and how the fuel is used, how misjumps happen, jump diameters and masking, fighter effectiveness, how droptanks work and why other refuel methods don't, ship computers vs robots, the ANNIC NOVA, ship bridge size, power plant inefficiency, Virus, the Xboat and Xboat routes, and a dozen-plus other things) Marc makes the FFE Position based on where he wants to go with Traveller, effectively ending many controversies -- within the T5 sphere of things at least.

So, it sounds like the T5 rules are far from complete or, they will leave gaping holes, once again...

 

[Gray Lensman]

So, it sounds like the T5 rules are far from complete or, they will leave gaping holes, once again...

Here, let me correct that for you ..... ONCE AGAIN...

 

[DaveChase]

I did some math on the subject, and I got some pretty interesting results. If the ship is surrounded by either a layer or a sphere of hydrogen gas, its possible to caculate the pressure of the bubble. I used a 6000 ton ship, about 117 meters long. I also assumed a Jump-1 uses 500 tons of fuel for the bubble.

6000 ton ship needs 600 ton fuel for a J1

If the hydrogen is at a temperature of 0 degrees C, a 1 meter thick layer would produce a pressure of 488 atmospheres, and essentially crush the ship.

...

Is this assuming Zero-G or in a gravity for these figures?

Also why the set meter thick figures?

Dave Chase

 

[atpollard]

I did some math on the subject, and I got some pretty interesting results. If the ship is surrounded by either a layer or a sphere of hydrogen gas, its possible to caculate the pressure of the bubble. I used a 6000 ton ship, about 117 meters long. I also assumed a Jump-1 uses 500 tons of fuel for the bubble.
If the hydrogen is at a temperature of 0 degrees C, a 1 meter thick layer would produce a pressure of 488 atmospheres, and essentially crush the ship.

If its at the temperature of liquid nitrogen, the pressure's 137 atmospheres, still enough to crush the ship.
A 10 meter thick layer at that temperature gives you a pressure of 13 atmospheres, which it's possible to design a ship to withstand (mabye), but the ship would weigh a ton, and it isn't really practical for normal ships.

If it's 'a bubble of boiling hydrogen', or very very cold, a 10 meter thick layer is a pressure of 3.75 atmospheres, which, for when I went and caculated structure, would just barely crush the ship. A 60 meter thick layer at that temperature would probebly work up to a jump-3 (but the ship's only 117 meters long).

A 200 meter radius bubble at 0 degres C gives a pressure of .167 atmospheres. So a bubble (or an ovel) is pretty much required.

That is, if most of the hydrogen goes into the bubble. And if the gas laws apply to the hydrogen bubble.

Hydrogen is lighter than air, so a 1 meter thick layer of H2 gas should weigh less than a 1 meter thick layer of air ... and the 25+ mile thick layer of air over the earth is not crushing me right now.

 

[far-trader]

I'm expecting the calculation was done for the volume of LH required for the jump, and that volume compressed into a 1m thick layer over the hull will give you the pressure. Not maths I want to do so I'm just taking that as correct. As for why 1m thick, I'm pretty sure that's the presumed thickness noted in the rules, something along the lines of jump space being held at bay about a meter off the hull, permitting one to carefully crawl along the hull while in jump space. There's also something basic (but the memory is foggy) about the reason we aren't crushed like beer cans under a mile or several of air. Something about being part of the same air equalizing the pressure, which you won't have with a substantial pressure outside the hull of a spaceship maintaining 1 atm of pressure, or less.

That said, Traveller ships, even unarmoured ones, can withstand a few atm of pressure in canon. There are no restrictions on world ATM type so they can all handle Dense at least. And there are iirc mentions of submersible operations permitted, though not at great depth.

 

[BraselC5048]

6000 ton ship needs 600 ton fuel for a J1


Is this assuming Zero-G or in a gravity for these figures?

Also why the set meter thick figures?

Dave Chase

I assumed 100 tons of fuel was used in the power plant to generate the power, and the rest was used for the jump bubble. I think the gas laws apply the same regardless of gravity. The reason the pressure is so high is becacuse a huge amount of hydrogen is squeezed into a small space; think a compressed air tank.
Up to about 3.5 atmospheres is much of an issue, but more then that an you really need to beef up the ship's sturcture.
A 1-meter thick layer around the ship only comes out to 850 dtons. And since the hydrogen fuel is stored as a liqued, and liquids can't be compressed, the jump bubble has to have a volume (in dtons) at least the of the tonnage of the fuel used in the bubble.
However, a .6 meter thick layer around the ship would hold 500 tons of hydrogen as a liquid, with a very low pressure, so you don't have to worry about crusing the ship. But, it can't have a temperature of more then 20 kelvins (-423 degress F), and 0 kelvins is absolute zero. A that temperature, you have to worry about issues such a hullmetal becoming very brittle, keeping the ship warm, and whatnot. Fortunitly, you can just assume that jumpspace takes away enough heat to keep the hydorgen liquid.
That also means that anyone who goes outside will freeze to death very fast.

The way I handle it is that a ship's in a bubble of hydrogen gas, with a dimameter a couple times the length of the ship. If there's a hole in your ship, that compartment fills with hydrogen from the bubble, with no more effects then a hole in the ship in normal space would have. You can go outside as long as you're wearing a vacc suit, and even lauch small craft (as long as they stay very close to the ship). Haven't decided yet what happens if you touch the outer boundry, but either you bunce off, or you're in your own universe. One makes missile lauching drills easier, the other makes burrial in space easier.
It also looks kind of like an auroa, when looking at in from on board the ship, and is kind of pretty.