Galileo Launch and Reprovisioning Satellites as Gravity Probes
According to GPS World:
Together with Sytèmes de Référence Temps Espace (SYRTE, or Time-Space Reference Systems department) of the Observatoire de Paris and the Center of Applied Space Technology and Microgravity (ZARM) at the University of Bremen, ESA has explored taking advantage of the combination of Dorena’s and Milesa’s eccentricity (about 0.15 in the corrected orbits), the passive hydrogen maser (PHM) on-board clocks’ high accuracy-stability (~10−14 per day), and high orbital precision to perform a measurement of the gravitational redshift.
The redshift or Einstein shift is a process by which electromagnetic radiation originating from a source that is in a gravitational field is reduced in frequency, or redshifted, when observed in a region of a weaker gravitational field. The three organizations believe that the two satellites can help measure this effect with a superior accuracy compared to today’s state of the art, based on Gravity Probe A, an experiment performed in 1976.