ИСТИНА

The effect of the gravitational time dilation, or the gravitational redshift, is a cornerstoneof general relativity and a direct consequence of the Einstein Equivalence Principle (EEP). Precise measurements of the gravitational redshift have become a powerful tool for testing general relativity and thus finding hints towards the “new physics”. The two most accurate redshift tests to date were performed by the NASA/SAO Gravity Probe A rocket mission and the European GREAT experiment with the Galileo 5 6 satellites, which resulted in redshift measurement accuracies of 1.4×10−4 and (2.5−3.1)×10−5, respectively. We report on new results of testing the EEP using the Spektr-R satellite of the RadioAstron space VLBI mission whichoperatedfrom2011to2019. The experiment benefitted from the spacecraft’s ultra-stable on-board hydrogen maser (Allan deviation of 2×10−15 at 3600 s), its highly eccentric orbit (e ∼ 0.95) and a relatively long data accumulation time. The ground support for the experiment was provided by the two tracking stations of the RadioAstron mission, in Russia and the United States, the European VLBI network (EVN), and a number of geodetic observatories worldwide. In our presentation we will give an update on the current data processing results and discuss prospects for reaching the design accuracy of ∼ 2×10−5.