Hello, I will be thankful if you could explain what appears to me as a paradox. We know that a satellite on a circular orbit, let say around the earth, has a uniform speed given by v=√(GM/r0). Now I would like to accelerate the satellite by keeping it on the same circular orbit r0. The only way to achieve this should be to "simulate" a higher gravitational field. As far as the Einstein's equivalence principle (EEP) is true, a mechanical acceleration is equivalent to a gravitational acceleration (http://www.einstein-online.info/spotlights/equivalence_principle), therefore we should be able to simulate a higher gravitational field with the thrust of the satellite's engine. Unfortunately the experiment, and the orbital mechanics, show that any mechanical thrust applied to the satellite, whatever its intensity and its direction, will transform the circular trajectory into an elliptic one. Therefore the mechanical acceleration is not equivalent to a gravitational acceleration, and then the EEP seems to be invalid. Note that the space-time box needed for this experiment might be as small as one meter large, as far as it includes the center of gravity of the satellite, and this preserves the locality necessary to apply the EEP. Can you help with this ?