In orbital mechanics, what does delta-V represent?

• A. The required change in velocity to perform a maneuver.
• B. The current velocity of the spacecraft in its orbit.
• C. The rate of change of speed over time.
• D. The velocity of Earth relative to the spacecraft.

Answer: (A)

Delta-V is the amount of velocity change required to perform a maneuver. It’s the impulse you must impart to the spacecraft to move from its current trajectory to the new one, expressed as the magnitude of the velocity change (often in meters per second). It represents the difference between the velocity vector before the burn and after the burn, not the spacecraft’s current velocity itself. It’s also not the rate at which speed changes—that’s acceleration. And it isn’t Earth’s motion relative to the spacecraft. Delta-V is the planning quantity that tells you how much propulsion you need to achieve the desired orbital change, and it’s what you use to estimate propellant needs via the rocket equation.