Gravitational redshift test of EEP with RadioAstron from near Earth to the distance of the Moon

Abstract The Einstein Equivalence Principle (EEP) is a cornerstone of general relativity and predicts the existence gravitational redshift. We report on new results measuring this shift with RadioAstron, space VLBI spacecraft launched into an evolving high eccentricity orbit around Earth geocentric distances reaching 353,000km. ground tracking stations at Pushchino, Russia, Green Bank, USA, were each equipped hydrogen maser frequency standard allowing possible violation predicted redshift, in form parameter ε, to be measured. By alternating between RadioAstron’s referencing modes during dedicated sessions 2015 2017, recorded downlink frequencies can essentially corrected for non-relativistic Doppler shift. analysis using Doppler-tracking measurements made these find ε = (2.1 ± 3.3) × 10−4. also discuss prospects uncertainty order 10−5 instead time-domain recordings signals envision how 10−7 might future mission.