Citizens of the Imperium

Citizens of the Imperium (http://www.travellerrpg.com/CotI/Discuss/index.php)
-   Imperial Research Station (http://www.travellerrpg.com/CotI/Discuss/forumdisplay.php?f=54)
-   -   Air rafts / grav cars (http://www.travellerrpg.com/CotI/Discuss/showthread.php?t=25451)

Enoki October 27th, 2011 12:50 AM

Air rafts / grav cars
 
Can these (assuming they are suitably enclosed) operate under water? I mean, they can operate in space. SDB's are noted in CT Supplement 7 Traders and Gunboats these are noted as being submersible.

Now, I'm assuming an enclosed, pressurized model of air raft that doesn't require vac suits.

BlackBat242 October 27th, 2011 01:56 AM

Vacuum doesn't short out grids and electrical/electronic circuits & components, water (especially salt water) does.

Find an enclosed grav vehicle rated for corrosive atmospheres and I'll say it can go underwater... as will any grav-capable craft designed for water use.

Dragoner October 27th, 2011 02:23 AM

James Bond type speeder. :devil:

Andrew Boulton October 27th, 2011 11:59 AM

Maybe, but not that deep - they probably couldn't cope with more than 2 atmos of pressure.

Carlobrand February 17th, 2012 03:18 AM

There's a world of difference between keeping in air and keeping out water. If you lean on Striker, your space-capable boats and ships have a minimum armor value equal to about a foot of steel, which makes them at least as tough as a modern sub, if not a bit tougher. (That's not to say they have foot-thick steel walls - only that their hull construction has equivalent resistance to penetration, likely to prevent damage due to micrometeors and orbital space junk.) The maximum depths of modern naval subs is as much as 500 to 700 meters.

However, I don't know anyone ever suggesting an air/raft was that tough. The MegaTrav version is the only one detailed enough to draw conclusions from. It had a skin that could stop a pistol round and slow a rifle round down enough to give you a fair chance at surviving if it hit you, if I recall - appreciable but not overwhelming. A passenger cabin of that strength could possibly get down to about 100 meters depth - assuming it was entirely enclosed in the material. (The WW-II Japanese Midget Sub, with 8mm steel walls, could manage a maximum depth of 100 meters.)

Given the more common portrayal of the vehicle as including some sort of windows, I'd agree that it could not handle more than a couple or three atmospheres pressure difference - which is only about 10 or 20 meters of depth. That's not even deep enough to avoid getting tossed about by bad weather, so keep your Dramamine handy.

So, ship's boat, yes - assuming you're going with the reactionless drive convention and can find some way to dump your fusion plant's heat without flash-boiling a mass of water everywhere you go. Air/raft, mostly no, unless you're just tourist-jaunting down a few meters to see the local reefs or you have one specially designed for 100-meter dives.

Of course, you could build something designed to both go deep and fly to orbit on grav generators, but then it's a flying sub, not a submersible air/raft - and expensive.

aramis February 17th, 2012 04:01 AM

The MT air/raft has armor 4G... bonded superdense equivalent to 1cm of steel.
The minimum spaceworthy is AV 8... equivalent to 2cm of steel... for one-use stuff (like rockets) or AV40 (equivalent to 33cm of steel) for reusable hulls.

atpollard February 17th, 2012 09:34 AM

Quote:

Originally Posted by aramis (Post 389650)
The MT air/raft has armor 4G... bonded superdense equivalent to 1cm of steel.
The minimum spaceworthy is AV 8... equivalent to 2cm of steel... for one-use stuff (like rockets) or AV40 (equivalent to 33cm of steel) for reusable hulls.

Am I the only one who finds those numbers strange?
(You quoted them correctly.)

I mean Bono designed a Saturn Application Single Stage To Orbit (SASSTO) reusable spacecraft made out of an old Saturn upper stage. A Saturn Rocket's fuel tank (90% of the craft) is a lot thinner than 33 cm of steel or even 2 cm of steel ... The 345,000 gallon lox tank is a 2219-T87 aluminum alloy cylinder with ellipsoidal upper and lower bulkheads. The skin thickness is decreased in eight steps from 0.64 cm at the aft section to 0.48 cm at the forward section. Since it is aluminium, a steel tank of equal strength would be about 2/3 as thick (but twice as heavy).

Deep space radiation protection is the only thing that I can think of that might require that much armor - so any craft operating inside the Van Allen Radiation Belt (like low earth orbit) should be able to get by with AV 8 (or possibly even a lot less).

aramis February 17th, 2012 09:28 PM

I don't disagree, Arthur...
I'd say AV1 should be sufficient for single use - except that MT armor doubles as structure, while the Saturn V has some structure - figure out the structure mass and the skin mass, and sum them, then rework the thickness equivalent.

Carlobrand February 18th, 2012 01:33 AM

Classic Traveller Book 2 envisioned interplanetary craft able to move under constant 1g to 6g thrust, moving from planet from planet by accelerating continuously to midpoint and then decelerating constantly from there until arrival. Makes for a nice quick trip, but even something like an Earth-to-Moon jaunt at 1g meant peak velocities of 60,000 meters per second - and it gets a LOT worse for those flights out to the local gas giants. At those speeds, accidentally smacking your ship into a stray orbiting pebble is like getting hit by a tank round. Worse, perhaps: if I understand the physics right, the pebble becomes a high-temperature plasma under that kind of impact (as does a bit of your hull), interacting with your hull rather like a small shaped charge. By comparison, the M1 tank's cannon hits muzzle velocities of a bit under 1600 meters per second.

I'm guessing the developers might have had that in mind when deciding spacecraft hulls were as strong as they say. I'm not sure even these hulls would survive some of the potential impact speeds, but it's a game, not reality, so I'm content with the approximation.

As far as I can see, there's nothing wrong with the thin-hulled stuff doing orbital work or coasting slowly from planet to planet. After all, our Voyager series did just fine without needing 2cm or 33cm steel walls.

Enoki February 18th, 2012 01:38 AM

Quote:

Originally Posted by Carlobrand (Post 389679)
Classic Traveller Book 2 envisioned interplanetary craft able to move under constant 1g to 6g thrust, moving from planet from planet by accelerating continuously to midpoint and then decelerating constantly from there until arrival. Makes for a nice quick trip, but even something like an Earth-to-Moon jaunt at 1g meant peak velocities of 60,000 meters per second - and it gets a LOT worse for those flights out to the local gas giants. At those speeds, accidentally smacking your ship into a stray orbiting pebble is like getting hit by a tank round. Worse, perhaps: if I understand the physics right, the pebble becomes a high-temperature plasma under that kind of impact (as does a bit of your hull), interacting with your hull rather like a small shaped charge. By comparison, the M1 tank's cannon hits muzzle velocities of a bit under 1600 meters per second.

I'm guessing the developers might have had that in mind when deciding spacecraft hulls were as strong as they say. I'm not sure even these hulls would survive some of the potential impact speeds, but it's a game, not reality, so I'm content with the approximation.

As far as I can see, there's nothing wrong with the thin-hulled stuff doing orbital work or coasting slowly from planet to planet. After all, our Voyager series did just fine without needing 2cm or 33cm steel walls.


Actually, if you have a jump capable ship and fuel processors it is often quicker to just make an inter-system jump to the outer planets as it is quicker than going slower-than-light.......


All times are GMT -4. The time now is 05:01 PM.

Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2020, Jelsoft Enterprises Ltd.
Copyright (c) 2010-2013, Far Future Enterprises. All Rights Reserved.