[Spaceships] Perpetual Motion?

[Mailanka]

Originally Posted by acrosome

I'm missing your point, there. Can you dumb it down?

Sure!

Chemical Refinery (TL7): Different types are possible, but
the most common spacecraft type processes ice or water into
hydrogen and oxygen for rocket fuel or reaction mass.

You're not creating rocket fuel out of nothing. You're taking ice or water, and refining it into rocket fuel. So you couldn't strictly have a perpetual motion machine, because you'll run out of (usable) water or ice. I suppose in your specific case, you might be able to trap the water being burned by the fuel cell for the purposes of making fuel-cell fuel, and then feed it to the refinery to make more fuel-cell fuel. I suppose that's what you mean by a perpetual motion machine?