Astronaut Group 6 (the 'XS-11') was announced by NASA on August 11, 1967, the second group of scientist-astronauts. Only five of the eleven were given formal assignments in the Apollo Program, and these were all non-flying. Assignments for the group were delayed by the requirement to spend a full year at UPT to become qualified as jet pilots (as were the Group 4 scientists before them). This requirement for scientists to be trained as jet pilots was eventually lifted with the creation of the Mission Specialist position in the Shuttle Program. The seven members of Group 6 who stayed with the program after Apollo went on to form the core of Shuttle Mission Specialists, accomplishing a total of 15 flights.
A chart showing Group 6 assignments in relation to other astronaut groups up through the Apollo era. This shows how Group 6 scientists earned their nickname "XS-11", with all eleven members being "excess" to the program.