What is the Delta-V

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The measure of the energy needed to transfer from one orbit to another, or the difficulty of carrying out a space mission, is the delta-v: the velocity change, or boost, needed to achieve the required new trajectory. The delta-v necessary to achieve low Earth orbit is 8 km/s (5 miles/sec); to go from low Earth orbit to Earth-escape velocity (achieve an orbit around the Sun, free of the Earth's gravity) requires an extra 3.2 km/s (2 miles/sec). The delta-v to achieve geostationary orbit from low Earth orbit is 3.6 km/s (2.25 miles). The most accessible asteroids have a delta-v as low as 4 km/s (2.5 miles/sec).