[Spaceships] Reactionless Drives, Pseudovelocity, and NOT breaking a setting (much)

[Ulzgoroth]

Originally Posted by malloyd

Depends on how you violate physics when you toggle the drive - if you keep your momentum or energy through a toggle, you of course are moving toward the center of the planet infinitely fast when you reach zero mass, which exceeds your pseudovelocity speed limit by a lot.

I don't know why you've decided that pseudovelocity drives mean you have zero mass.

Originally Posted by malloyd

The simplest way is to imagine you have a generator, attach a long rod perpendicular to the shaft and glue the reactionless engine to the tip. Power it with the output of the generator. If there is some speed at which the tip of the rod moves at which the output of the generator exceeds the power consumption of the drive, you have net energy creation. If there isn't you destroy energy. Since the rod can be arbitrarily short, a top speed limit won't help. If you add in relativity, the breakeven power requirement for the reactionless thruster turns out to be the same as for a photon drive. If you insist on pseudovelocity, the drive can't move the rod at all, which is functionally identical to the inertialess condition, and essentially useless as a drive, since you can never move again once you encounter a free atom.

So, no, the rod can't be arbitrarily short because generators and reactionless drives are not usually arbitrarily small (but I don't see how a speed limit would help anyway). And the 'how can a pseudovelocity ship move in a universe where vacuum isn't absolute' is not a hard problem.

If all you were going for is that an otherwise physics-compliant reactionless drive that can impart more kinetic energy on itself than it consumes energy input allows a perpetual motion generator, I'd agree. But 'reactionless motion' includes a variety of things that won't play nice with your generator at all.

Originally Posted by malloyd

Physics is highly interconnected, there really is no way to make miracle SF propulsion systems - whether they're reactionless thrust, FTL, or just superefficient drives - useful only for propulsion. There are always severe side effects, and if you are going to have to ignore them eventually it might as well be from the start rather than trying to come up with some sort of justification that pushes them somewhere you can't see them but somebody else can find them and surprise you with them.

You claimed a specific consequence.

Originally Posted by malloyd

So what kind of energy are you imagining which is not convertible into kinetic energy?

Taking out the rest of the italicized condition really changes the statement.

Even supposing that your reactionless drive is used as a high-power perpetual-motion generator, if your only way of using it to produce a relativistic projectile is using that power to run a rocket, it's not really more of a problem than a conversion power plant of the same output would be.