Editing Rocket (section)

====Oberth effect====
{{Main|Oberth effect}}
One subtle feature of rockets relates to energy. A rocket stage, while carrying a given load, is capable of giving a particular [[delta-v]]. This delta-v means that the speed increases (or decreases) by a particular amount, independent of the initial speed. However, because [[kinetic energy]] is a square law on speed, this means that the faster the rocket is travelling before the burn the more [[orbital energy]] it gains or loses.

This fact is used in interplanetary travel. It means that the amount of delta-v to reach other planets, over and above that to reach escape velocity can be much less if the delta-v is applied when the rocket is travelling at high speeds, close to the Earth or other planetary surface; whereas waiting until the rocket has slowed at altitude multiplies up the effort required to achieve the desired trajectory.