Einstein's theory of relativity will be put to the test in a micro-gravitational environment by Atomic Clock Ensemble in Space (ACES), European Space Agency (Esa) mission developed in cooperation with the French Space Agency (CNES). It is scheduled to be installed in 2013 on board the International Space Station (ISS). The space will be studied by a new kind of atomic clock (Pharao) which will yield data accuracy much higher than what is attainable under earth’s gravitation. Theoretical physics, metrology and atomic clock design are all starters to benefit from this joint venture. Our wish is that ACES includes the Allais eclipse effect in his application domain. This effect is related to an unexplained deviation of the plane of oscillation of the pendulum during solar eclipse. Pharao, called a "cesium fountain clock", would provide a unique way to search a possible variation of the constant G in an eclipse framework. Frequency comparisons between distant clocks both space to-ground and ground-to-ground would allow, during the eclipse time interval, to discover if the gravitational potential and velocity of the ground stations are still constant, if the equivalence principle contains a flaw.