arXiv subjects

Thibault Damour

Publications and source records attributed to Thibault Damour.

218 records · Page 13Linked to original sources

arXiv1994

Orbital Tests of Relativistic Gravity using Artificial Satellites

We reexamine non-Einsteinian effects observable in the orbital motion of low-orbit artificial Earth satellites. The motivations for doing so are twofold: (i) recent theoretical studies suggest that the correct theory of gravity might contain a scalar contribution which has been reduced to a small value by the effect of the cosmological expansion; (ii) presently developed space technologies should soon give access to a new generation of satellites endowed with drag-free systems and tracked in three dimensions at the centimeter level. Our analysis suggests that such data could measure two independent combinations of the Eddington parameters (beta - 1) and (gamma - 1) at the 10^-4 level and probe the time variability of Newton's "constant" at the d(ln G)/dt ~ 10^-13 yr^-1 level. These tests would provide well-needed complements to the results of the Lunar Laser Ranging experiment, and of the presently planned experiments aiming at measuring (gamma -1). In view of the strong demands they make on the level of non- gravitational perturbations, these tests might require a dedicated mission consisting of an optimized passive drag-free satellite.

gr-qc↗

arXiv1993

Testing for Preferred-Frame Effects in Gravity with Artificial Earth Satellites

As gravity is a long-range force, one might a priori expect the Universe's global matter distribution to select a preferred rest frame for local gravitational physics. At the post-Newtonian approximation, two parameters suffice to describe the phenomenology of preferred-frame effects. One of them has already been very tightly constrained (|alpha_2| < 4 x 10^-7, 90% C.L.), but the present bound on the other one is much weaker (|alpha_1| < 5 x 10^-4, 90% C.L.). It is pointed out that the observation of particular orbits of artificial Earth satellites has the potential of improving the alpha_1 limits by a couple of orders of magnitude, thanks to the appearance of small divisors which enhance the corresponding preferred-frame effects. There is a discrete set of inclinations which lead to arbitrarily small divisors, while, among zero-inclination (equatorial) orbits, geostationary ones are near optimal. The main alpha_1-induced effects are: (i) a complex secular evolution of the eccentricity vector of the orbit, describable as the vectorial sum of several independent rotations; and (ii) a yearly oscillation in the longitude of the satellite.

gr-qc↗