[Spaceships] Your preferences regarding plausible/playable Reactionless Drives

[vicky_molokh]

Greetings, all!

Reactionless Drives are obviously considered TL^. However, either to satisfy physics buffs, defend against munchkins, and just to avoid inconsistencies and unwanted uses/consequences, GMs often prefer to carefully select the way reactionless drives work.

AtomicRocket/ProjectRho mentions the problem with 'realistic' reactionless drives being de-facto fancy Photon Drives. The alternative is to use some sort of special frame of reference. Question #1 for the experts and Space GMs: what are the consequences of doing it with a universal frame of reference, butchering relativity?

The other option is to tie the reference frame to the mass within a certain volume. With a small enough volume, this gives us weaponized Tractor Beams/Spheres, which may or may not be what you want. However, I'm looking at a different idea:

The sphere of volume is increased, until its total mass, excluding the spaceship, is so large that as a result of the 'Reactionless' Drive's work, the mass gains an acceleration relative to the spaceship of less than one Planck length per Planck time. In other technobabble, the universe allows a 'reactionless' drive due to 'rounding errors'. This probably butchers Quantum Mechanics, but might have fewer consequences for the game world, since the differences might be written off as humans misunderstanding QM.

Finally, there was some talk of a project named for the ST drive, i.e. Warp Drive. How hard is to playabilitate/plausibilitate it to acceptable levels?

Awaiting comments and a discussion.
Thanks in advance