Escape Velocity - Misconception

Misconception

Escape velocity is sometimes misunderstood to be the speed a powered vehicle, such as a rocket, must reach to leave orbit and travel through outer space. The quoted escape velocity is commonly the escape velocity at a planet's surface, but it actually decreases with altitude. It is the speed above which an object will depart on a ballistic trajectory, i.e. in free-fall, and never fall back to the surface nor assume a closed orbit. Such an object is said to "escape" the gravity of the planet.

A vehicle with a propulsion system can continue to gain energy and travel away from the planet, in any direction, at a speed lower than escape velocity so long as it is under propulsion. If the vehicle's speed is below its current escape velocity and the propulsion is removed, the vehicle will assume a closed orbit or fall back to the surface. If its speed is at or above the escape velocity and the propulsion is removed, it has enough kinetic energy to "escape" and will neither orbit nor fall back to the surface.