Space is hard, and making a spaceship engine powerful enough to do interesting things requires an absolutely bonkers amount of energy. I know that lots of authors (including me) think of trying to get around the issue by making reactionless drives, but those have the issue of allowing ships to accelerate to arbitrary velocities and destroy planets. I had a slightly different idea.
I've heard that theoretically, we can have a non-physics violating warp drive as long as it can't get above the speed of light. So what if someone invents a warp drive, but one which can only generate "virtual" velocity relative to the ship's "true" reference frame; and only up to a certain relative velocity, like, say, 50 km/s.
If you have a ship in orbit of Earth, and it uses its warp drive to travel at 90% of the speed of light for one minute away from earth, then when the drive shuts off the 0.9c velocity vanishes, and the ship is left with only the velocity it possessed while orbiting earth.
If two ships are stationary relative to each other, and one turns on its drive and attempts to ram the other, the instant they touch the warp bubble collapses and the two ships are left kissing without having damaged or imparted kinetic energy to the other, since they didn't have any relative kinetic energy to begin with.
If a ship wants to get actual velocity without expending fuel, it can do so by using its drive to hover above the surface of a massive object, like a planet, and using its gravity to increase its true velocity, until it shuts off its drive and shoots off like a rock from a slingshot. The caveats are that you can't get a true velocity any higher than your drive's maximum speed (because otherwise you crash into the planet), and you need to be able to slow down at the other end of your trip (because the drive can't cancel your true velocity.)
You can't use the drive to extract infinite energy from a gravity well by lifting an object above the surface and then dropping it through a generator, because raising an object through a gravity well requires additional energy equal to the potential energy gained by the lifted object.
EDIT: It's been pointed out that #3 and #4 contradict each other, since you could hover above a planet to build up 'true' velocity, and then drop into a generator with much greater energy than just the potential energy of the fall. My solution to this is that getting up to a certain 'virtual' velocity requires at least as much energy as the kinetic energy of the mass of the ship traveling at the same 'true' velocity. Though this brings up the issue that the energy would then have to GO somewhere once the drive is shut off, which might be hazardous, as a 20-ton craft going at 50 km/s would have to get rid of an amount of stored energy equal to half of Hiroshima.
My question is: Does this break the universe/physics? How? Does it make sense?
EDIT: Numbered bullet points.