The “Galileo Galilei” (GG) project: Testing the Equivalence Principle in space and on Earth (original) (raw)
2000, Advances in Space Research
GALILEO GALILEI" (GG) is a proposal for a small, low orbit satellite devoted to testing the Equivalence Principle (EP) of Galileo, Newton and Einstein to 1 part in 10 17 . At the end of 1997 GG has been selected and funded by ASI (Agenzia Spaziale Italiana) for a 1-year Phase A study. The main novelty of GG is that the concentric hollow test cylinders whose relative motion (in the plane perpendicular to the spin axis) would be affected by an EP violation, spin together with the read-out capacitance sensors placed in between them. The nominal spin rate is 2 Hz, and this is the frequency at which the putative EP violation signal is modulated by the sensors. As compared to other experiments the modulation frequency is increased by more than a factor 10 4 , thus reducing 1/f (low frequency) electronic and mechanical noise. GG will have FEEP ion thrusters for drag compensation. The required amount of propellant is of a few grams only. The experiment works at room temperature. To demonstrate the feasibility of the space experiment a payload prototype for EP testing on the ground (GGG -GG on the Ground) is under development in the laboratories of Laben. The challenge in this field is to fly an experiment able to improve by many orders of magnitude the current best ground sensitivity (≅10 -12 ). This requires spurious relative motions of the test bodies to be greatly reduced, leaving them essentially motionless. Doing that with more than one pair of bodies appears to be an unnecessary complication. This is why GG is now proposed with a single pair of test masses. Information, research papers and photographs of the ground apparatus are available on the Web (http://tycho.dm.unipi.it/nobili/ ggproject.html).
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