I've heard that a spacecraft could never exceed the speed of light because it's (relativistic) mass quickly approaches infinity and therefore there could never create a big enough rocket to propel it faster and faster.
I'm 99% sure this is a stupid question, but I'll ask it anyway :). Theoretically if a spacecraft had unlimited fuel (by travelling through a nebula picking up hydrogen/oxygen and whatever else it needed as a propellant), couldn't it actually break the speed of light?
Yes I know it gets harder and harder to accelerate the craft because it gets more and more massive (relativistically speaking), but as the craft and propellant tanks get more and more massive so does the thrust right? 1 million pounds of propellant exploding out the back gives 1 million pounds of thrust at Newtonian speeds. As the spacecraft gets heavier and heavier, the thrust would also get more and more massive would it not? In that way more massive mass is countered by more massive thrust. If not, why is the reaction mass any different to the rest of the spacecraft's mass?