Could we use antimatter-based propulsion to visit alien worlds?

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Well, At least it worked well enough in Hollywood to become the technological motivator for "The Hunt for Red October".

Not sure if they would tell us if there really is some ultra-quiet sub sneaking around in "quite mode" with that drive when the mission requires it, then using props to go to and from the mission location.
Nov 19, 2021
That's magnetohydrodynamic thrust. You set up a channel full of conductive fluid with a vertical magnetic field, run an electric current horizontally and the fluid will shoot out the back. You need an awful lot of current for the magnets and for the horizontal current. I would guess there would be a lot of electrolysis happening. In salt water that creates chlorine gas and sodium hydroxide along with hydrogen and oxygen. Probably not good corrosion wise.
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May 14, 2021
If there are any, they would likely not even have propellers. As seen on multi-screw vessels. A trailing shaft would be quite noisy and a stopped-and-locked shaft is really bad, so any sub more stealthy than the nukes we have would not have propellors.
I am not saying that I think there are real magnetohydrodynamic thruster subs in operation, but I do think you guys are throwing up imagined obsticles that good engineering could overcome.

Regarding propellers, I would expect a "stealth sub" to still have them to get to its mission location fast and efficiently. Going into stealth mode would not require that the props be locked and thus cavitate - they could be allowed to free-wheel. But, that would probably still make a bit of bearing noise. So, better solution is a prop with blades that feather. Yes, flat blades would be less efficient than cupped blades during use. But, compound blades (2 blades that can swivel into a position to act as a single cupped blade) might be able to address that problem, too. And there could be deployable cowlings to shield a stopped prop from water flow. There is a lot of money that has gone into making subs quiet, so I suspect that mundane things like prop and bearing noise were thoroughly addressed along with the more exotic things like the magnetohydrodynamic thruster technology.

Regarding electrolysis, are you sure there would be actual bubble production? Both oxygen and chlorine are soluable in water and get produced at the electrodes as individual atoms, so rather immediately in-solution until they can coalesce into bubbles. With a rapid flow, do bubbles actually form? When I did electroysis of salt water (at low current) in a pot, the bubbles formed slowly. So, not clear on what the bubble formation would really be in a high thrust design.

As for corrosion, I am sure our military budget is large enough to gold or platinum plate whatever might need it.
Jul 6, 2021
The electromagnetic generator was, I believe, an idea I read in the ‘70s that they could use an EM field to force seawater through chutes on a submarine using the moving water as propulsion, would make virtually no noise. We see how well that worked, they still make propellers.
But they did use the idea in a movie on a Russian submarine...

May 14, 2021
This was an article I remembered reading back in the ‘70s in Science Digest. So, the other day after my previous post, I read the Wikipedia article ‘Magnetohydrodynamic drive’, and, yes, problems include excessive noise (I believe seawater turbulence) and electrolysis. A small amount of current will generate a small amount of electrolysis, but, this is an extreme magnetic field. This drive would require extreme amounts of energy, which is not available, as the drive isn’t all that efficient.
The biggest problem is the magnetic signature on a sub that wants no magnetic field to elude those magnetic seeking torpedoes.
The state of the art of subs even in my time in the Navy in the 70s was when rigged for quiet, the subs were quiet enough that there was permitted no extraneous noise, certain equipment was shut down, most pumps were sound isolated in three axes, walking around with quiet shoes only if absolutely necessary, personnel not on watch were in there bunks, whispering only, no talking. That’s hard to beat.

A shaft stopped and locked certainly makes for insane noise and vibration, but, a trailing shaft still makes a lesser noise, mostly water turbulence, but since the drive turbine also turns, it would overheat, thus a small amount of steam would still be admitted to the turbine to keep it ‘cool’, another source of noise.


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