In 1976, he was chosen from a pool of 500 Polish military pilots to take part in the Interkosmos space programme. The group of candidates, who initially were not informed what they were being selected and psychologically tested for, was narrowed down to 120, then just five, and eventually from an elite selection of only several pilots Hermaszewski was finally picked with Zenon Jankowski as his backup to participate in the Soyuz 30 mission. For a period of almost two years, they underwent extensive training for theoretical expertise, physical endurance, and resistance to mental stress (among various other factors) at the Yuri Gagarin Cosmonaut Training Center in Star City, near Moscow. Besides training in weightless conditions, psychological trials took place as well with candidates at one point having to complete 998 tests in one day.