ИСТИНА

RadioAstron satellite admits in principle a testing the gravitational redshift effect with an accuracy of better than 10^{-5}. It is better the result of Gravity Probe A mission at least an order of magnitude. However, RadioAstron's communications and frequency transfer system is not adapted for a direct application of the non relativistic Doppler and troposphere compensation scheme used in the Gravity Probe A experiment. This results in a degradation of the redshift test accuracy to approximately at the level 0.01. We discuss two approaches to overcome this difficulty and present preliminary results based on data obtained during special observing sessions scheduled for testing the new techniques