Let's say you're on a spaceship and you can accelerate to a speed very close to c. As your own time seems to slow down (relative to slow moving observers), your mass also increases. I know that mass increases in the sense that one requires more energy to give the same acceleration, but does this also mean that your impulse increases ? I assume so. So, if your spaceship would crash into something when you're close to c, it would seem as impulse was violated because (assuming you slow down enough), the mass becomes close to the rest mass again? In that case, would one have to consider a relativistic version of the conservation of impulse?