Q: How does the Oberth Effect work, and where does the extra energy come from? Why is it better for a rocket to fire at the lowest point in its orbit?
If the original speed is W, and the rocket speeds up by ΔV, then the change in energy is: . This is a basic rule of thumb in rocket science; if you’re going to fire your rocket, fire it at the lowest point in its orbit. Conservation of momentum says that the momentum of the rocket and fuel before burning is the same as the momentum afterward. The energy before the burn is and the energy afterward, from the rocket and the fuel parcel, is . Rather than being a magical extra boost when a rocket is traveling fast, it’s just a cute and fortunate distribution of energy.