So... there came a question up in another board which I can't answer... and perhaps you can give me an answer. First of all there's the equation for kinetic energy: Ekin = 1/2 m v² Which effectively means that the amount of energy needed for constant acceleration rises lineary to the velocity. Or: To accelerate from 0 to 1 m/s takes less energy than from 1 m/s to 2 m/s. So far, so good. But unfortunately, spacecraft, such as the Space Shuttle, show a different behavior. Actually I'd expect a starting Shuttle to have the max G right after takeoff and acceleration dropping steadily from then on. Here's a chart I found and it shows that acceleration is steadily RISING during the second half of the flight: http://www.russellwestbrook.com/launch.jpg [Broken] Why? A couple of ideas of mine: - The longer the flight, the lighter the mass of the spacecraft, but since v² is the determining part of the equation, I wouldn't expect the mass change, unless it's somewhere in the vicinity of gigantic, to have such profound impact on the accel. - Is perhaps the horizontal flight path at fault? During lift off, the Shuttle has to accelerate against earth's gravity, but when it's flying horizontally, thanks to centrifugal forces there's less to none gravity to compensate. But I'm still not very sure. I hope you can help me solve this riddle.