A rocket is intended to leave the earth's gravitational field. The fuel in its main engine is little less than the amount that is necessary, and an auxillary engine, only capable of operating for a short time, has to be used as well.
When is it best to fire the auxillary engine: at take-off, or when the the rocket has nearly stopped w.r.t earth, or does it not matter?
Please share if you like it!!!!