Definitions

characteristic velocity

Mission characteristic velocity

The mission characteristic velocity (also mission velocity or characteristic velocity) is an important parameter describing space missions. It is the total velocity change needed (the sum of all maneuvers) to accomplish the mission, typically given in km/s. To achieve low earth orbit it is approximately 8 km/s, while to escape from Earth needs 11.2 km/s, both ideal minimus figures for neglecting various inefficiencies that typically range from 10% to 20%. For the Apollo lunar landings with return to Earth it was of the order of 20 km/s.

Because the mass ratio required for a given mission is exponential in the mission velocity divided by the effective exhaust velocity of the rocket propulsion system, high mission velocities rapidly become extremely expensive for chemical rockets, so that the mission velocity, along with the payload, is a key parameter in assessing the overall difficulty of a given mission. Missions that would at first appear to be infeasible due to high mission velocity can sometimes be done by means of various tricks, such as gravity assist encounters with planets along the way, aerobraking, staging to intermediate bases, etc. Some of these have been described in the large literature of astronautics, e.g. Arthur C Clarke's Interplanetary Flight, and many others.

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