Mastering Morse code requires a great deal of practice in both  
sending and receiving.  
Cosmonaut Valentina Tereshkova, first
woman in space, listens as Cosmonaut Yuri Gagarin sends.

Early Russian Cosmonauts were trained to communicate in
Morse code as a backup to their AM voice mode of operation.  
The Russian spacecraft from that era relied heavily on
shortwave radio, the quality of which, is dependent on
favorable atmospheric conditions.  When shortwave radio
conditions were poor, the cosmonauts had to abandon their
AM voice mode and switch to Morse code which is more
readable through static and weak signal conditions.