This was a modification of the Molniya-1 satellite to test deep space radio-based tracking methods for the Soviet Lunar program.

The Soviet manned lunar programs needed to test new tracking methods - how to translate doppler and location readings into orbital parameters quickly in order to make maneuvers in lunar and translunar orbit. To investigate this Ryazanskiy modified a Molniya-1 spacecraft with measuring systems in place of the retransmitter. This Molniya-Yu was used to confirm new methods of orbital measurement.