For other uses, see Delta-v (disambiguation).
Delta-v (literally "change in velocity"), symbolised as Δv and pronounced delta-vee, as used in spacecraft flight dynamics, is a measure of the impulse that is needed to perform a maneuver such as launch from, or landing on a planet or moon, or in-space orbital maneuver. It is a scalar that has the units of speed. As used in this context, it is not the same as the physical change in velocity of the vehicle.
Delta-v is proportional to the thrust per unit mass, and burn time of a vehicle's rocket engines, and is used to determine the mass of propellant required for the given maneuver through the Tsiolkovsky rocket equation.