A new test of gravitational redshift using Galileo satellites: The GREAT experiment

Abstract We present the result of the analysis of the GREAT (Galileo gravitational Redshifttest with Eccentric sATellites) experiment. An elliptic orbitinduces a periodic modulation of the fractional frequency difference between a ground clockand the satellite clock, partly due to the gravitational redshift, while the good stability of Galileo clocksallows one to test this periodic modulation to a high level of accuracy. GSAT0201 and GSAT0202, with their large eccentricity and on-board H- maser clocks, are perfect candidates to perform this test. Satellite laser rangingdata allows us to partly decorrelatethe orbit perturbations from the clockerrors. By analyzing several years of Galileo tracking data, we have been able to improve the Gravity probeA test (1976) of the gravitational redshiftby a factor of 5.6, providing, to our knowledge, the first reported improvement since more than 40 years.