Mission Characteristic Velocity

Mission Characteristic Velocity

In astrodynamics and the aerospace industry, a delta-v budget (literally "change in velocity budget") is an estimate of the total delta-v required for the various propulsive tasks and orbital maneuvers over one or more phases of a space mission. Delta-v is a scalar quantity. Delta-v budget is the total of all changes in speed made by the propulsion system during the mission.

Delta-v is a particularly useful measure since it is independent of the mass of the space vehicle. For example, while more thrust, fuel, etc. will be needed to transfer a larger communication satellite from low Earth orbit to geosynchronous orbit, the delta-v required is the same. Also delta-v is additive, as contrasted to rocket burn time, the latter having greater effect later in the mission when more fuel has been used up.

Tables of the delta-v required to move between different space venues are useful in the conceptual planning of space missions. In the absence of an atmosphere, the delta-v is typically the same for changes in orbit in either direction; in particular, gaining and losing speed cost an equal effort. An atmosphere can be used to slow a spacecraft by aerodynamic braking.

A typical delta-v budget might enumerate various classes of maneuvers, delta-v per maneuver, and number of each maneuver required over the life of the mission, and simply sum the total delta-v, much like a typical financial budget. Because the delta-v needed to achieve the mission usually varies with the relative position of the gravitating bodies, launch windows are often calculated from porkchop plots that show delta-v plotted against the launch time.