Which astronaut flew on more space missions, Piers Sellers or Jean-Jacques Favier?
Piers Sellers: Piers John Sellers OBE (11 April 1955 – 23 December 2016) was a British-American meteorologist, NASA astronaut and Director of the Earth Science Division at NASA/GSFC. Piers Sellers:  He was a veteran of three space shuttle missions. Jean-Jacques Favier: Jean-Jacques Favier (Born April 13, 1949) is a French engineer and a former CNES astronaut who flew aboard the STS-78 NASA Space Shuttle mission. Jean-Jacques Favier:  Favier was due to fly aboard the Columbia mission in 2003, but later signed out of the mission.
Piers John Sellers