Energy requirements for a relativity "launcher" I read about an interesting concept for space travel in the book "the Millennial Project: colonizing the galaxy in eight easy steps". Unfortunately, I forgot what exactly the author called it, and so have dubbed it a "relativity launcher". It was basically a method of rapid travel between vast distances in space, using the old concept of going at relativistic speeds to 'slow down' the time involved in travel. It was based on building incredibly large, star-powered rail guns. The "shuttle" carrying the passengers from point A to point B would be aimed precisely at the "barrel" of their end destination, then "fired" ( or more accurately slowly accelerated) out of the gun/launcher (point A). Eventually, it would "land" right in the barrel of the gun/launcher at point B, which would then use electromagnetic forces to slowly bring it to a stop. Now, this might incite debate about the group dynamics of creating interstellar societies, the psychology of passengers dealing with everything else aging after they stop, etc. but please set these aside for now so that I can ask the main question. Also understand that I wish I was smart enough to answer it myself, but am unfortunately far too ignorant of mathematics, science, and physics to so. The question (preceded by the necessary assumptions) is this: Assume the device was built near a star that was more or less identical in every way to our own sun., Assume the device had no replenishment of energy from any other source. Assume the energy extraction method from the star is 50 percent efficient. Assume that it was firing payloads at relativistic speeds that would make a distance of one billion light years traversible in just one year of time for any passengers. Approximately How much mass could be shot out before entirely consuming the energy of the star?