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  • "Galileo Galilei (GG)" : A Small Satellite for a High Accuracy Test of the Equivalence Principle

    Paper ID



    • A.M. Nobili
    • D. Bramanti
    • G. Catastini
    • E. Polacco
    • A. Anselmi
    • S. Portigliotti
    • A. Lenti


    Università di Pisa






    1 A high accuracy test of the Equivalence Principle, through a test of the Universality of Free Fall, would be of great value for the Physics of next century. Space offers two advantages: a signal about a factor of a thousand bigger than on Earth and the absence of weight. '‘Galileo Galilei” (GG) is a small space mission under study with the financial support of ASI (Agenzia Spaziale Italiana). GG is a small (~ 250 kg), low Earth satellite stabilized by spin (at 5 Hz) and equipped with PEEP thrusters for partial drag compensation. The main novelty is to have mechanically suspended, rotating test bodies and sensors so as to modulate the signal at higher frequency and reduce the impact of “1//” noise. The advantages of fast spin are numerous: a high frequency signal, supercritical rotation of the test bodies which behave almost like free rotors hence aligning on one another very precisely, many “dangerous” perturbations DC (nearby mass anomalies, parasitic capacitances, patch effects, non uniform thermal expansion at room temperature).... Dissipation in the rotating system is known to generate unstable whirl motions; however, losses are low, instabilities grow very slowly and can be damped with small electrostatic capacitors rotating with the system. Another major advantage of the mechanical suspensions is that the test masses are electrically grounded, thus eliminating the major effect of electrostatic charging. At the current level of investigation (Pre-Phase-A) [1, 2] a sensitivity of 1 part in 1017 appears within the reach of GG. A prototype for ground testing is under construction in the laboratories of LABEN in Florence.