Fabrizio De Marchi

Torsion pendulum revisited

We present an analysis of the motion of a simple torsion pendulum and we describe how, with straightforward extensions to the usual basic dynamical model, we succeed in explaining some unexpected features we found in our data, like the modulation of the torsion mode at a higher frequency and the frequency splitting of the swinging motion. Comparison with observed values yields estimates for the misalignment angles and other parameters of the model.

Constraining the Nordtvedt parameter with the BepiColombo Radioscience experiment

BepiColombo is a joint ESA/JAXA mission to Mercury with challenging objectives regarding geophysics, geodesy, and fundamental physics. The Mercury Orbiter Radioscience Experiment (MORE) is one of the on-board experiments, including three different but linked experiments: gravimetry, rotation, and relativity. The aim of the relativity experiment is the measurement of the post-Newtonian parameters. Thanks to accurate tracking between Earth and spacecraft, the results are expected to be very precise. However, the outcomes of the experiment strictly depend on our “knowledge” about solar system: ephemerides; number of bodies (planets, satellites, and asteroids); and their masses. In this paper we describe a semianalytic model used to perform a covariance analysis to quantify the effects on the relativity experiment, due to the uncertainties of Solar System bodies’ parameters. In particular, our attention is focused on the Nordtvedt parameter η used to parametrize the strong equivalence principle violation. After our analysis we estimated σ½η� ⪅ 4.5 × 10 −5 , which is about 1 order of magnitude larger than the “ideal” case where masses of planets and asteroids have no errors. The current value, obtained from ground-based experiments and lunar laser ranging measurements, is σ½η� ≈ 4.4 × 10 −4 . Therefore, we conclude that, even in the presence of uncertainties on Solar System parameters, the measurement of η by MORE can improve the current precision of about 1 order of magnitude.

Testing the Strong Equivalence Principle with spacecraft ranging towards the nearby Lagrangian points

General relativity is supported by great experimental evidence. Yet there is a lot of interest in precisely setting its limits with on going and future experiments. A question to answer is about the validity of the Strong Equivalence Principle. Ground experiments and Lunar Laser Ranging have provided the best upper limit on the Nordtvedt parameter

“Quasi-complete” mechanical model for a double torsion pendulum

\sigma[\eta]=4.4\times 10^{-4}

Space tests of the strong equivalence principle: BepiColombo and the Sun–Earth Lagrangian points opportunity

. With the future planetary mission BepiColombo, this parameter will be further improved by at least an order of magnitude. In this paper we envisage yet another possible testing environment with spacecraft ranging towards the nearby Sun-Earth collinear Lagrangian points. Neglecting errors in planetary masses and ephemerides, we forecast

PETER: a torsion pendulum facility to study small forces/torques on free falling instrumented masses

\sigma[\eta]=6.4\,(2.0)\times10^{-4}

Optimizing the Earth?LISA ?rendezvous?

(5 yr integration time) via ranging towards

Modulation of LISA free-fall orbits due to the Earth?Moon system

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Effects of interplanetary dust on the LISA drag-free constellation

in a realistic (optimistic) scenario depending on current (future) range capabilities and knowledge of the Earths ephemerides. A combined measurement,

Analysis of the residual force noise for the LISA Technology Package

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