Every time this topic comes up somebody suggests constant acceleration, and every time somebody has to point out that even if you don’t want to decelerate the r

Every time this topic comes up somebody suggests constant acceleration, and every time somebody has to point out that even if you don’t want to decelerate the relativistic rocket equation is still a very harsh mistress. Remember you don’t just have to carry the fuel to accelerate your payload, you have to accelerate the fuel as well. You may say, “Oh, but I could use a laser to accelerate my craft, that way I don’t need to carry the fuel on board,” and the amount of energy required is still going to be a hell of a lot more than you think.