[Spaceships] Orion space drive: launch from underwater?

[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?

[RogerBW]

I can't think of a good reason to try to launch from underwater rather than going to the surface first. (Compare SLBMs - obviously they don't want to destroy the launching submarine, but even so they tend to pop up to the surface, align themselves correctly, then ignite the main engine.)

But a surface launch should be fine. Either pop it up in a gas bubble like an SLBM, or build an expendable launching raft to hold the engine clear of the water for the first shot.

Contamination will depend on the fusion device, but neutron irradiation is generally bad news.

[Astromancer]

Frankly, with an Orion drive I'd support a launch from high orbit. I can't see anyone wanting to put up with the radioactive pollution.

That said, just because a launch from underwater isn't in anyway desirable does not mean it is impossible. I suppose that if launching from underwater was a necessity in your case, it would work. But there would be complications.

[Flyndaran]

Still, it sounds like the performance would be horrible, and nukes aren't cheap. Better to have a more conventional launch system if only to pop it into the air a bit.

[Sciencezam]

First, let it be known that this is a terrible idea, and best avoided at all possible costs.

Launching it from underwater depends on how deep you launch it from. If you do it too deep, the initial blast will create a massive bubble in the ocean. This is pretty much the worst possible thing, as then there's water above you and even more to your sides that really, really wants to get back to where it used to be. Water pressure is bad, but the collapse of a cavitation bubble is terrible.

If you do it closer to the surface you might still end up sending your ship careening into a wall of water, as the ship conveniently prevents the water above it from getting pushed aside by the blast. This is also bad, but how well a spaceship can take speeding headfirst into water depends on how much water you've got and what your spaceship's made out of. I don't see it going well, either way-possibly survivable, maybe, but this is the kind of abuse that makes engineers cry.

The radiation situation is more or less the same as that of a subsurface or surface water blast, though there's going to be more of them. Being in water means direct radiation from the blast is much less of a problem-water provides better shielding than air-but fallout is going to be even more of a pain. If you're going to do this, do it on a day with low wind, in the middle of an ocean gyre, and hundreds if not thousands of kilometers from anything you care about.

Land-based Orion crafts have a much more straightforward fallout situation, and some of the research done back in the cold war showed that they could get fallout to acceptably low levels if the launch took place from a metal disk sprayed with some oil. In the ocean, that's not going to help you-it'd keep ocean floor from becoming fallout, but water and the things in it are going to still be a problem.

[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.