Dynamical response of the Galileo Galilei on the ground rotor to test the equivalence principle: Theory, simulation, and experiment. II. The rejection of common mode forces

"Galileo Galilei on the ground" (GGG) is a fast rotating differential accelerometer designed to test the equivalence principle (EP). Its sensitivity to differential effects, such as the effect of an EP violation, depends crucially on the capability of the accelerometer to reject all effects acting in common mode. By applying the theoretical and simulation methods reported in Part I of this work, and tested therein against experimental data, we predict the occurrence of an enhanced common mode rejection of the GGG accelerometer. We demonstrate that the best rejection of common mode disturbances can be tuned in a controlled way by varying the spin frequency of the GGG rotor. (c) 2006 American Institute of Physics

Radiometer effect in the mu SCOPE space mission

Space experiments to test the Equivalence Principle (EP) are affected by a systematic radiometer effect having the same signature as the target signal. In [PhRvD 63 (2001) 101101(R)] we have investigated this effect for the three proposed experiments currently under study by space agencies: muSCOPE, STEP and GG, setting the requirements to be met-on temperature gradients at the level of the test masses-for each experiment to reach its goal. We have now re-examined the radiometer effect in the case of muSCOPE and carried out a quantitative comparative analysis, on this issue, with the proposed heliocentric LISA mission for the detection of gravity waves. We find that, even assuming that the muSCOPE spacecraft and payload be built to meet all the challenging requirements of LISA, temperature gradients along its test masses would still make the radiometer effect larger than the target signal of an EP violation because of flying in the low geocentric orbit required for EP testing. We find no way to separate with certainty the radiometer systematic disturbance from the signal. muSCOPE is designed to fly a second accelerometer whose test masses have the same composition, in order to separate out systematic effects which-not being composition dependent like the signal-must be detected by both accelerometers. We point out that this accelerometer is in fact insensitive to the radiometer effect, just as it is to an EP violation signal, and therefore even having it onboard will not allow this disturbance to be separated out. muSCOPE is under construction and it is scheduled to fly in 2004. If it will detect a signal to the expected level, it will be impossible to establish with certainty whether it is due to the well known classical radiometer effect or else to a violation of the equivalence principle-which would invalidate General Relativity. The option to increase the rotation speed of the spacecraft (now set at about 10(-3) Hz) so as to average out the temperature gradients which generate the radiometer effect, is allowed in the GG design, not in that of STEP and muSCOPE. (C) 2002 Elsevier Science B.V. All rights reserved

Tidal effects in space experiments to test the equivalence principle: implications on the experiment design

Experiments to test the equivalence principle (EP) in low Earth orbit require to detect the effects of an extremely small non-classical differential acceleration between test masses of different composition. In all proposed experiments the test masses are concentric coaxial cylinders, so as to reduce classical tidal effects which are differential too. Perfect centring being impossible, tidal effects need to be carefully investigated as they impose severe constraints on the basic features of the experiment design. The present analysis shows that with free flying (uncoupled) test masses an EP violation signal could be detected if the initial conditions of the masses were finely adjusted for them to remain at a fixed distance relative to each other while orbiting around the Earth. However, such an experiment is severely limited by non-gravitational effects. If the test cylinders are weakly coupled in 2D in the plane perpendicular to their symmetry axis (close to the orbit plane), while rapidly spinning around it, a position of relative equilibrium is provided by physical laws which makes tidal effects widely separated from the signal. Weak coupling in ID along the symmetry axis (to lie and slowly rotate in the orbit plane) is viable but less advantageous. (C) 2003 Published by Elsevier B.V

"Galileo Galilei (GG) on the Ground-GGG": experimental results and perspectives

The GGG differential accelerometer is made of concentric coaxial test cylinders weakly coupled in the horizontal plane and spinning in supercritical regime around their symmetry axis. GGG is built as a full scale ground based prototype for the proposed "Galileo Galilei-GG" space experiment aiming to test the equivalence principle (EP) to 10(-17) at room temperature. We report measured Q values of 95000 at 1.4 Hz, and expect even better ones at typical spin frequencies of a few Hz. An EP violation signal in the field of the Sun would appear as a low frequency displacement in the horizontal plane of the laboratory, and it can be separated out from a much larger whirl motion of the test masses at their natural differential frequency. So far we have managed to reduce the amplitude of this whirl to about 0.1 mum. We discuss how to improve these results in view of the very high accuracy GG experiment in space, and/or to reach a 10(-13) sensitivity in the lab which would allow us to either confirm or rule out recent predictions of violation to this level. (C) 2003 Published by Elsevier B.

Abatement of Thermal Noise due to Internal Damping in 2D Oscillators with Rapidly Rotating Test Masses

Mechanical oscillators can be sensitive to very small forces. Low frequency effects are up-converted to higher frequency by rotating the oscillator. We show that for 2-dimensional oscillators rotating at frequency much higher than the signal the thermal noise force due to internal losses and competing with it is abated as the square root of the rotation frequency. We also show that rotation at frequency much higher than the natural one is possible if the oscillator has 2 degrees of freedom, and describe how this property applies also to torsion balances. In addition, in the 2D oscillator the signal is up-converted above resonance without being attenuated as in the 1D case, thus relaxing requirements on the read out. This work indicates that proof masses weakly coupled in 2D and rapidly rotating can play a major role in very small force physics experiments

"Galileo Galilei" (GG) a small satellite to test the equivalence principle of Galileo, Newton and Einstein RID G-3742-2010 RID A-1966-2009 RID G-5658-2011

"Galileo Galilei" (GG) is a small satellite designed to fly in low Earth orbit with the goal of testing the Equivalence Principle-which is at the basis of the General Theory of Relativity-to 1 part in 10(17). If successful, it would improve current laboratory results by 4 orders of magnitude. A confirmation would strongly constrain theories; proof of violation is believed to lead to a scientific revolution. The experiment design allows it to be carried out at ambient temperature inside a small 1-axis stabilized satellite (250 kg total mass). GG is under investigation at Phase A-2 level by ASI (Agenzia Spaziale Italiana) at Thales Alenia Space in Torino, while a laboratory prototype (known as GGG) is operational at INFN laboratories in Pisa, supported by INFN (Istituto Nazionale di fisica Nucleare) and ASI. A final study report will be published in 2009