due to Shepard's previous position as head of the astronaut office. Shepard would be later reassigned to command Apollo 14 by the Office of Manned Spaceflight director George Mueller, against Slayton's wishes, who felt that Shepard needed additional training time. After the postal covers scandal during the Apollo 15 mission, Slayton reassigned the crew to non-flying jobs, effectively ending their astronaut careers. Slayton supported keeping Joe Engle as the lunar module pilot on Apollo 17, but was pressured by NASA management to replace him with Jack Schmitt, a scientist-astronaut. Return to flight status While grounded, Slayton took several measures to attempt to be restored to flight status, including regularly exercising, taking vitamins, quitting cigarette smoking and coffee and reducing his consumption of alcoholic beverages. In 1970 his palpitations became more frequent and he started taking experimental daily doses of quinidine, a crystalline alkaloid. This treatment was successful, but concerned that taking medication would still disqualify him from solo flying, Slayton stopped taking it against doctors orders. After a decade of seeing doctors around the world, in 1971 Slayton was examined at the Mayo Clinic after a long period without heart fibrillation, and was determined to not have a coronary condition. On March 13, 1972, NASA announced that Slayton had returned to flight status. Apollo–Soyuz flight In February 1973, Slayton was assigned to the Apollo–Soyuz Test Project (ASTP) as a docking module pilot, along with commander Thomas Stafford and command module pilot Vance Brand. The American crew began a two-year training program, which included learning the Russian language and making trips to the Yuri Gagarin Cosmonaut Training Center in the USSR. He remained in a managerial role throughout the Skylab program, and resigned as Director of Flight Crew Operations in February 1974 in preparation for his upcoming flight. The Apollo and Soyuz spacecraft both launched on July 15, 1975. On July 17, the two craft rendezvoused in orbit and the American astronauts conducted crew transfers with cosmonauts Alexei Leonov and Valeri Kubasov. At the end of the flight, an erroneous switch setting led to noxious nitrogen tetroxide fumes from the command module's RCS thrusters being sucked into the cabin during landing and the crew was hospitalized as a precaution in Honolulu, Hawaii, for two weeks. During hospitalization, a lesion was discovered on Slayton's lung and removed. It was determined to be benign, but he would have likely been grounded from ASTP