The spacecraft carried a set of solid-state oscillators that had been programmed to reproduce the notes of "The Internationale", so that it could be broadcast live to the 23rd Congress of the Communist Party of the Soviet Union. During a rehearsal on the night of 3 April, the playback went well, but the following morning, controllers discovered a missing note and played the previous night's tape to the assembled gathering at the Congress — claiming it was a live broadcast from the Moon.