Concurrently with his part-time research activities, he joined the Swiss Air Transport School in Zürich and became an airline pilot in 1974, assigned as a DC-9 pilot for Swissair. At the end of 1976, he accepted a Fellowship at the European Space Agency’s (ESA) Space Science Department at Noordwijk, Netherlands, where he worked as a research scientist in various airborne infrared astronomy programs. In July 1978, he was selected by ESA as a member of the first group of European astronauts. Under agreement between ESA and NASA, he joined NASA Astronaut Group 9 selected in May 1980 for astronaut training as a mission specialist. Unlike colleague Wubbo Ockels—who withdrew from training to focus on Spacelab and remained an ESA payload specialist—Nicollier became a mission specialist, the first non-American to become a full-time NASA astronaut.