How does the Oberth effect work?
In: Physics
Just to be clear to anyone, the Oberth effect is that when you are at the periapsis of your orbit, spending fuel is more efficient, than spending it at the apoapsis.
This is because the fuel has potential energy, that transforms into kinetic energy, when it’s getting closer to the gravitational center it’s orbiting. By spending fuel, when more of the fuel’s energy is kinetic, the rocket gains more kinetic energy total from spending fuel. EDIT: I forgot to add that rocket engines have a maximum speed, at which they propel spent fuel outwards, and because of that can make use of the “faster” fuel in a lower orbit, because the difference in velocity of the fuel is larger.
You can also see that it has to be this way, because of thermodynamics. Energy can’t be destroyed, only transferred or changed. The exhaust from the fuel is either in a high orbit or a low orbit, depending on where it has been spent.
Fuel in a higher orbit obviously has more energy, so it has to give less to the rocket.
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