Testing newtonian gravity in space: a null 3-body experiment

A space experiment to measure G and test for the equivalence principle should use a pure dynamical system of bodies dominated by their mutual gravitational interaction. We show that a system of 3 bodies in the equilateral triangular configuration allows to perform a null experiment as far as the equivalence principle is concerned. The experiment is less sensitive to perturbations which are present in the space laboratory and are known to limit small force experiments. Moreover, it contains an external check. Distance measurements to an accuracy of about 1 μ can provide the difference Δα between different materials to 1 part in 106. The measurement of the absolute value of G does not have the advantages of the null experiment. However, it has become more and more important to improve the present poor accuracy in the value of this fundamental physical constant; the accuracy achievable with this experiment is limited to 10-5, mainly because of electrostatic perturbations and gravity gradient effects from the space laboratory. This would be much better than results obtained so far in ground based Cavendish experiments