What escape velocity actually describes
Escape velocity is the speed needed to leave a body's gravitational influence without further propulsion, under an idealised model. It depends on the body's mass and the starting distance from its centre. It is not a universal speed limit, and a powered spacecraft can gain energy gradually rather than receiving one instant push.
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Enough energy for an unbound path
In a simplified model with one spherical gravitating body and no atmosphere, escape speed is the speed needed to reach indefinitely far away without additional propulsion.
It depends on the body's mass and the starting distance from its centre. Near Earth's surface, the ideal value is about 11.2 kilometres per second.
The definition assumes that propulsion stops after the initial speed is supplied. A rocket that continues firing can add energy along its path instead of receiving all the required energy in one moment.
- More massive bodies require greater escape speed at the same distance.
- Starting farther away lowers the required speed.
- Atmospheric resistance and other bodies complicate real missions.
Escape does not mean gravity suddenly becomes zero at a boundary. The spacecraft has enough energy not to return under the simplified gravitational model.