If special relativity is taken into account, the following equation can be derived for a relativistic rocket, with Δ Δ v again standing for the rocket's final velocity (after expelling all its reaction mass and being reduced to a rest mass of m 1 ) in the inertial frame of reference where the rocket started at rest (with the rest mass including fuel being m 0 initially), and c standing for the speed of light in vacuum: m 0 m 1 = [ 1 + Δ Δ v c 1 − − Δ Δ v c ] c 2 v e