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Delta-v, meaning delta velocity and symbolized as Δv, is a measure of a spacecraft's ability to change it's trajectory (the path it will take in the future). Delta velocity in simple terms means 'the change in speed' It is measured by a unit of speed, usually meters per second (m/s).#
Factors that go into calculating delta-v are:
- The mass of the spacecraft.
- The amount of gravity in which the spacecraft currently finds itself.
- The thrust and efficienty of the engine.
- The amount of fuel the spacecraft has.
As an example of how delta-v is used, we can imagine a goal: flying a spacecraft into low Earth orbit. (In simple words, getting a rocket to spin around the Earth). We would first calculate how much delta-v will be required for that journey. Then, with the factors in the above list, we can calculate how much delta-v our spacecraft would need to go on that journey. Like if a person were to drive his car from point A to point B, he'd need to know how much fuel he needs in his car first. But in rocket science, using delta-v is much more relevant, as we have to completely design our spacecraft, including all factors mentioned above.
To reach Low Earth orbit, (LEO) our spacecraft would need roughly 10,000 m/s of delta-v.
Delta-v can be seen a budget, because if our spacecraft were to use up the 10,000 m/s of delta-v, it wouldn't be able to complete its journey to low Earth orbit.
Delta-v is calculated using this integral equation: