I get the idea of expanding and narrowing grids but how would that be accomplished. And also i do not think the spaceship will actually travel that fast, it will act more as a teleportation device since it travels so fast that measuring time is useless. The way to cheat gravity and speed is to reduce the drag of air. If there was a system that propels air particles away from the spaceship/airplane, it would continue to build speed infinitely because there would be no drag so the only slowdown would be the limit of the engine. I think U.F.O's work on this principle.