Air rafts / grav cars

[Enoki]

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]

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]

James Bond type speeder. :devil:

 

[Andrew Boulton]

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

 

[Carlobrand]

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]

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]

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]

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]

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]

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.......

 

[aramis]

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.......

Jupiter is borderline... 778Gm
Earth at 150Gm
For a range of 628-928Gm

628E9m=0.5AT^2
A=10 so
125.6E9=T^2
354401≅T (sec)≅98:26:40.9 (H:M:S) Closest Separation

928Gm=0.5AT^2
430813.≅T (sec)≅119:40:13.2 (H:M:S) Furthest separation

Keeping in mind that Jumps are 168 hours... Jupiter IS faster by 1G than by jump. Saturn is faster by 3G+ than by Jump, and I think J2 is about breakeven.

 

[Carlobrand]

It depends.

Book 2 envisions "neighbor worlds" 1 1/2 to 2 1/2 days out at 1g, so those are clearly normal space jaunts. It envisions gas giants 5 1/2 to 7 days out at 1g (drawing on our best-known real-universe example, which may or may not be the true norm, but it will do). There might be other locations farther out that are worthy of a visit: an Oort Cloud research station, for example. Whether it's worthwhile to jump-1 out there depends on circumstances. For ships capable of only jump-1 an in-system jump to refuel is pointless, and that Oort base had better have fuel for you or you'd end up spending time hunting down an ice comet for fuel. For ships capable of better than 1g, it could be faster just to normal-space it; a 6-g warship can cover a lot of ground fast, so to speak. However, for some ships it would make good sense.

Of course, this is Sci-Fi. If you want to excite imagination, then you want a few places that don't conform to norms. Imagine a long-established settlement in the scattered remnants of an Oort cloud around some black hole, research stations studying the hole from various angles, and asteroid cities whose economy is based on collecting and exporting contra-terrene matter created in the ancient super-nova explosion that produced the hole. The various places are so far apart that in-system jumps (around the fringes!) are the most practical way to get from place to place - in fact, travelling around too fast in normal space without really, really good radar might just get you killed.

Or, you could imagine an entirely robotic industrial facility on the dark side of a planet tidally-locked around a massive blue-white supergiant, mining precious lanthanum and drawing on the massive power of the star itself via solar collectors on the day side for free energy, the world so deep in the star's gravity well that you have to go out a billion kilometers to reach safe jump distance.