"Galileo Galilei-GG": design, requirements, error budget and significance of the ground prototype

"Galileo Galilei-GG" is a proposed experiment in low orbit around the Earth aiming to test the equivalence principle to the level of 1 part in 10(17) at room temperature. A unique feature of GG, which is pivotal to achieve high accuracy at room temperature, is fast rotation in supercritical regime around the symmetry axis of the test cylinders, with very weak coupling in the plane perpendicular to it. Another unique feature of GG is the possibility to fly 2 concentric pairs of test cylinders, the outer pair being made of the same material for detection of spurious effects. GG was originally designed for an equatorial orbit. The much lower launching cost for higher inclinations has made it worth redesigning the experiment for a sun-synchronous orbit. We report the main conclusions of this study, which confirms the feasibility of the original goal of the mission also at high inclination, and conclude by stressing the significance of the ground based prototype of the apparatus proposed for space. (C) 2003 Published by Elsevier B.V.