The cronos hydrogen maser clock redshift experiment on Radioastron Original Research Article

The Radioastron satellite, having a highly elliptical orbit with a period of 28 hours and a mission duration of more than 3 years, offers the interesting possibility of a redshift experiment. The Space Hydrogen Maser, recently introduced as a new instrument on the satellite in order to be used as local oscillator for the Space VLBI, can in fact be tracked in frequency from the ground stations, implementing only minor modifications in the originally planned frequency transfer system. The modified system allows also the measurements of the geometric and ionospheric Doppler shifts. An analysis of the best strategy for achieving the highest measurement precision is presented. The analysis takes into account the maser frequency stability, its environmental sensitivities, and the other known sources of noise. The error budget of the experiment is established.