ИСТИНА

The gravitational time dilation effect not only forms the experimental basis of general relativity but also finds its way to applications in satellite navigation, chronometric geodesy and many others. Therefore, testing this effect with an ever increased accuracy is important not only for fundamental physics but also for applied sciences. Experimental studies of gravitation using spacecrafts are complicated by the necessity of separating tiny gravitational effects from much larger contributions due to nonrelativistic and relativistic Doppler, ionospheric and tropospheric phenomena, instrumental noise, etc. Compensation of such effects becomes possible with data acquisition systems using concurrent frequency measurements of 1- and 2-way radio links as well as satellite laser ranging. We discuss the compensation schemes used by the GP-A [1] and ACES [2] missions as well as our own approach developed for the RadioAstron spacecraft [3].We also give a status update of the gravitational redshift experiment with RadioAstron using the developed technique. [1] Vessot, R. F. C. et al. Phys. Rev. Let. 45, 2081 (1980) [2] Hess, M. P. et al. Acta Astronautica 69, 929 (2011) [3] Biriukov, A. et al. Ast. Rep.58, 783 (2014)