Whilst noodling about other things, my brain wandered to travel between the stars in a fantasy universe. tl;dr version, change the substance of the etheral plane into a liquid, apply magnets and current, generate thrust.

    Whilst noodling about other things, my brain wandered to travel between the stars in a fantasy universe. tl;dr version, change the substance of the etheral plane into a liquid, apply magnets and current, generate thrust.

Yes, there is Starfinder. Yes, there is Spelljammer. (I love Spelljammer).

I don't want helm and NPC magic-users to be the engine. I need a system that a Thief can drive.

I thought that maybe a Magnetohydrodynamic drive would fit the bill, assuming a few things.

One, the ethereal plane exists and works in typical D&D fashion.
Two, that stuff is very conductive under the right conditions, but not all the time.
Three, reverse works easily.

So, the engine is essentially a jet powered by a completely inert, non-detectable substance (ether) being manipulated to produce thrust.

If a psionicist can give shape to ether in the form of protoplasm, there is a way to remove the non-electromagnetic pressure that makes ether inert and undetectable.

The engine, then, uses a device (because magic) that doesn't give physical shape to ether, it merely strips away the non-magnetic pressure on it. When this denatured ether interacts with magnets and electricity, it produces thrust.

The device that converts ether would need to be available to both ends of the tube to have reverse. In non-magical places, a psionic character could serve in place of the device to slowly limp the ship along to a place where magic will work.

Now, I'm thinking about psionic engineers.
I know what you're going to say, Captain, and I've already made the adjustment.

https://en.wikipedia.org/wiki/Lorentz_ether_theory