Evaluation of a proposed test of the weak equivalence principle using Earth-orbiting bodies in high-speed co-rotation: re-establishing the physical bases

Test masses coupled by weak mechanical suspensions are sensitive to differential forces such as the force due to a possible violation of the equivalence principle (EP). If in addition they are put in rapid rotation, the differential signal is modulated at high frequency, which is beneficial for noise reduction. Galileo Galilei (GG) is a proposed space experiment for testing the equivalence principle to 1 part in 10(17) based on these concepts. A recent paper by Jafry and Weinberger (1998 Class. Quantum Grav. 15 481-500) claims that GG can only reach 10(-14). We show that the analysis of this paper is flawed (by several orders of magnitude) because of two misconceptions: one on the physical nature of mechanical damping and the other on active control methods for the stabilization of spinning bodies.