ESA - Pedro Duque's diary from space https://www.esa.int/Science_Exploration/Human_and_Robotic_Exploration/Cervantes_Mission/Pedro_Duque_s_diary_from_space

"...But the other day I was with my Soyuz instructor and I saw he was preparing the books for the flight, and he was attaching a ballpoint pen with a string for us to write once we were in orbit. Seeing my astonishment, he told me the Russians have always used ballpoint pens in space."