I know how to figure out how much energy is needed to acclerate to a certain speed. What I don't know is how much energy is needed to maintain that speed. For example. I was watching the first Trek movie the other day, and Kirk orders the Enterprise to go to .5 light speed. So the Enterperise goes from 0 to 150M meters per second in like 5 seconds. I wondered how much force would be needed to do that, so I calculated: F = M * A The ship has a mass of 200,000 metric tons, so 200,000,000 kg * acceleration, which going from 0 to .5 light in 5 seconds would be 30,000,000 meters per second per second (i hope that's right). That gave me 6*10^15 Newtons (damn!) I then tried to see what this would be in joules, so I next calculated the distance traveled, using: Distance = .5*Acceleration*Time^2 .5*30,000,000*(5^2) That gave me 375,000,000 meters. To then calculate joules, I used W(joules) = Force * Distance 6*10^15 * 375,000,000 That gave me 2.25*10^24 joules of energy needed to accelerate a 200,000 metric ton object to .5 light speed in 5 seconds (please correct me if I'm wrong). My question, how many joules per second is needed to maintain that speed? This is not homework. I'm just a nerd.