I agree with everything except this: > Still not true. YOU have rest mass ant therefore the faster you go, the more of the energy used for momentum transfer wi

I agree with everything except this: > Still not true. YOU have rest mass ant therefore the faster you go, the more of the energy used for momentum transfer will be converted to relativistic mass, thus preventing you from ever approaching the speed of light in any frame of reference Rest vs relativistic mass only exists from the outside observers perspective. The traveler doesn't see any change in it's own mass. On a ship traveling near the speed of light, people walking around won't have to spend extra energy to move in the direction of ships motion. Relativistic mass just accounts for the energy being spent to accelerate that doesn't result in an increase in velocity (and thus momentum) from an external perspective. > Ultimately, even a reactionless drive would be limited by the human physique - it takes about 3½ months to accelerate to 30% light speed at 1g constant acceleration. So unless inertia negation devices are invented, that sets the practical lower limit for any interstellar travel time. This is a really good point! This means the Andromeda galaxy could be only 30 years of travel away. The primary point I am trying to make is that "FTL" isn't important for interstellar travel if a reactionless drive gives us most of the benefits we need (getting to other stars within human lifespans). Honestly I don't think either reactionless or FTL drives are actually possible, so generation ships or ships full of human popsicles coasting most of the way are most likely how we will get to other stars.