[Spaceships] Orion space drive: launch from underwater?

[Fred Brackin]

Originally Posted by Agemegos

G'day!

Does anyone know whether an external pulsed nuclear spaceship could be launched from underwater? My guess would be that the force from the first pulse below and the inertia of the water above would crush any possible craft.

What if a subaquatic civilisation floated their spacecraft to the surface and then lit off a nuke underneath. If the ship were big enough and the nuke small enough, could this put them into the air intact? If they are using non-fission-initiated advanced fusion, how bad is the radioactive contamination?

As most Orion proposals start with "assume a viable pusher plate" it is very difficult to make assumptions about what the acceptable level of stress would be.

Spaceships assumes a 2G Orion drive but as this would be the average accel over a period of time, peak accel would be far higher. An Orion spaceship would have to be _very_ rugged in any event. Spaceships requires a dDR 50 (DR500) rear hull.

Still, there's no reason not to float to the surface.

If your propellant bombs are pure fusion with no fissiles or fissionables the only source of contaminants will be neutron activated elements in the water or pieces of your pusher plate ablating away.

Hydrogen and oxygen do not become radioactive when hit be neutrons but I can't tell you about sodium or chlorine. Gawd only knows what your pusher plate is made of or how much of it you lose with each explosion.

[Ulzgoroth]

Originally Posted by Fred Brackin

If your propellant bombs are pure fusion with no fissiles or fissionables the only source of contaminants will be neutron activated elements in the water or pieces of your pusher plate ablating away.

Also, importantly, the neutron-bombarded remains of the bomb itself.

[Fred Brackin]

Originally Posted by Ulzgoroth

Also, importantly, the neutron-bombarded remains of the bomb itself.

If you don't do something stupid that's pretty avoidable.

You probably do still want a dense metal for an outer casing just to help hold things together a little longer with inertia but even lead would do. Perhaps tungsten if you wanted to avoid chemical pollution.

Both have been used in modern thermonuclear bombs. You can gain more explosive power (50% more) by using even depleted uranium but that would be where the great majority of fallout from modern bombs comes from. Use lead for the outer casing (tamper) and you have what's called a "clean" bomb. Use uranium and it's called "dirty" but is twice as powerful.

[Ulzgoroth]

Originally Posted by Fred Brackin

If you don't do something stupid that's pretty avoidable.

You probably do still want a dense metal for an outer casing just to help hold things together a little longer with inertia but even lead would do. Perhaps tungsten if you wanted to avoid chemical pollution.

Both have been used in modern thermonuclear bombs. You can gain more explosive power (50% more) by using even depleted uranium but that would be where the great majority of fallout from modern bombs comes from. Use lead for the outer casing (tamper) and you have what's called a "clean" bomb. Use uranium and it's called "dirty" but is twice as powerful.

I don't see how this avoids leaving the neutron-bombarded remains of the bomb.

Irradiated lead or irradiated tungsten still fit that description.

[Fred Brackin]

Originally Posted by Ulzgoroth

I don't see how this avoids leaving the neutron-bombarded remains of the bomb.

Irradiated lead or irradiated tungsten still fit that description.

Nope, If being hit by neutrons does not make a substance radioactive (and this is quite common) they you can't call it a radioactive contaminant.

Radiatioactivity isn't like being tainted by Original Sin.

[Anthony]

Originally Posted by Fred Brackin

Nope, If being hit by neutrons does not make a substance radioactive (and this is quite common) they you can't call it a radioactive contaminant.

Though fast neutrons may cause heavy elements to break up. Pb-206 can absorb a neutron and turn to Pb-207 without any radiation, but if it splits up both halves will be extremely neutron-heavy and thus radioactive.

[Agemegos]

Thanks everybody. I'm trying to make an adventure that is agnostic as to whether setting is superscience or not, and what sort of spaceship tech is in use, while wasting the fewest possible words on enumerating technological contingencies. The adventure is going to need

1. a branch in which the greeblies can launch their ship from the seabed (which Star Wars, Star Trek, and Lensman pseudotech would all allow);
2. a branch in which they can do final assembly underwater, but have to float the ship to the surface and launch from there;
3. a branch in which they have to launch the ship from above the surface, and therefore would have to work in environment suits and with waldoes to build a facility on a pontoon and assemble the ship on that;
4. and a branch in which the ship cannot be launched.

I reckoned that external pulsed nuclear drive technology would go in the third branch, but wanted to make sure.

[lwcamp]

Originally Posted by Fred Brackin

Nope, If being hit by neutrons does not make a substance radioactive (and this is quite common) they you can't call it a radioactive contaminant.

Radiatioactivity isn't like being tainted by Original Sin.

Tungsten contains five stable isotopes: W-180, W-182, W-183, W-184, and W-186. Neutron capture by W-180 leaves you with W-181, with a 121 day half life (and which normally decays via electron capture to stable Ta-181, so it will only give off x-rays and thus is not that bad). Neutron capture on W-182 and W-183 just gives you another stable iostope of tungsten. Neutron capture by W-184 gives W-185, with a 75 day half-life that beta decays to stable Re-185. Neutron capture by W-186 gives W-187, with a half-life of 1 day which beta decays to stable Re-187. So neutron bombardment of tungsten will give rise to some residual activity. A more complete analysis would look at neutron capture cross sections and the energy spectrum of neutrons within the tungsten shell.

Brett didn't specify what form of fusion is being used, but D-T fusion produces neutrons with 14 MeV of energy - this is really quite energetic and can lead to various nuclear spallation processes as well, such as having the neutron knocking off another neutron or proton or alpha particle. These can make make other radioactive particles, which can be the head end of a decay chain of several isotopes before you reach something stable.

Lead will be similar in general scope to tungsten, although different in the particulars.

Luke

[Agemegos]

Originally Posted by lwcamp

Brett didn't specify what form of fusion is being used

Indeed not. I'm trying to cover all possible bases. For what it's worth, D-T seems most plausible. But you might use an expensive and bulky aneutronic launch unit to lob the spacecraft to a safe altitude where its cheap and cheerful D-T pulse units would be not to much of a problem.