Imagine two space ships each with thrusters that can accelerate them .1c or .3c almost instantly. The velocity addition formula indicates that if one space ship applied the .1c thruster 3 times then if c is estimated to be 300,000,000 m/s the velocity of the ship after the accelerations the ship will be approximately 87,669,903 m/s. Which is less than the 90,000,000 m/s which would have been achieved using the .3c thruster. So does this mean that the energy needed to go .1c in space < (energy needed to go .3c in space)/3? Also given the formula (u + v) / (1 + ((u*v)/(c*c))) Is it saying it is more expensive to try to go .1c then .4c or .4c then .1c than go .2c then .3c or .3c then .2c (because u + v = .5c in both cases, but the u * v = .04c with the .1c and the .4c, but .06c with the .2c and the .3c) but you would achieve a higher velocity?