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This answer is to clear up the confusion on "is gravity/air resistance included?" Say you've got an engine in free fall in the atmosphere. You're going 200m/s now and you'll be going 600m/s when you hit the ground ~40 seconds later. Your engine has 600m/s of delta-v which can be imparted over X seconds with a certain specific impulse. Note: I'll be ...


It assumes no gravity and no air resistance. For ascent from Earth's surface to LEO, it's typical to expend around 9.4 km/s of ∆v, to reach a final orbital speed of around 7.8 km/s. Most of the loss, around 1400-1500 m/s, is in fighting gravity, with around 100-200 m/s lost to air drag -- the exact numbers vary with the characteristics of the launch ...


It doesn't assume anything about your environment, but rather simply indicates what your engines can do. If gravity is a factor some of your delta-v is used to counter gravity rather than actually accelerating your rocket.


Supplemental answer: Here are the relevant equations and discussion from Sutton, 4th edition.


Specific impulse is a measure of the fuel efficiency of a rocket engine. It’s established by the design of the engine, not by the size of the rocket. Specific impulse of multiple stages is definitely never added together. For a very rough analogy, imagine a car that gets 30 miles to a gallon of gas. Ten of them driving in a convoy do not achieve 300 miles ...

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