It was planned that some of the astronauts would first make a ballistic flight powered by a Redstone rocket. Slayton’s flight MR-6 (Mercury-Redstone 6), the fourth launch of a manned Mercury spacecraft, was scheduled for fall 1961.
After the successful orbits of the Earth by Soviet cosmonauts Yuri Gagarin and German Titov, the number of suborbital Redstone flights was reduced to three, which would have made Slayton the first American in Earth orbit. However, when the Redstone flights of Alan Shepard and Virgil Grissom were successful, the third manned Mercury flight was supposed to take an Atlas rocket into orbit. On November 29, 1961, John Glenn and Slayton were announced as crews for MA-6 and MA-7.
Deke Slayton would have called his flight Delta 7, but he didn’t get to go into space. Due to a heart problem, which NASA had known about since 1959, Slayton was denied fitness to fly on March 15, 1962. Instead of his replacement Walter Schirra, Scott Carpenter flew the MA-7 mission on May 24, 1962, which he called Aurora 7, and Schirra flew MA-8 mission on October 30, 1962.
Slayton initially took part in astronaut training and medical examinations, but took on more and more administrative tasks within NASA. He was appointed Coordinator of Astronaut Activities and headed the newly established Astronaut Office for Projects Mercury, Gemini and Apollo. In 1963, during a restructuring of NASA, he became deputy director of Flight Crew Operations and from 1966 its director.
Deke Slayton was responsible for assigning astronauts to specific Gemini and Apollo missions. It was he who decided who piloted which spaceship and who was allowed to set foot on the moon.
In the meantime, Deke Slayton did everything he could to possibly return to active astronaut status: he did daily exercises, gave up smoking and drinking coffee, and reduced alcohol consumption. His heart problem disappeared in the summer of 1970, and after extensive examinations he was certified as fully fit for manned space travel in March 1972. On February 9, 1973, Slayton, along with Tom Stafford and Vance Brand, was assigned to the Apollo-Soyuz Test Project, the first American-Soviet rendezvous in space.
The flight took place from July 15 to July 24, 1975. At 51, he was the oldest space newcomer to date. The Apollo spacecraft docked to Soyuz 19 in Earth orbit, and the astronauts and cosmonauts were able to transfer from one spacecraft to the other via the docking module. Deke Slayton spent an hour and 35 minutes aboard the Soyuz. A catastrophe almost occurred when the Apollo spacecraft returned. After the parachutes were deployed manually, the attitude control jets ignited and toxic gases flowed into the landing capsule through an equalization valve. Fortunately, the three astronauts were not injured.
The Apollo Soyuz Test Project (ASTP) was the last flight of an Apollo spacecraft, and NASA focused on the new Space Shuttle. From December 1975, Slayton was director of the Approach and Landing Tests (ALT) program for the Shuttle Enterprise in California.
After this project ended in November 1977, he was manager of the Orbital Flight Training Program until February 1982 and prepared the first six flights of the Space Shuttle. Slayton was also responsible for ferrying the shuttle using a converted Boeing 747.
Deke Slayton retired from NASA on February 27, 1982. He married a second time on October 8, 1983.
Deke Slayton died of a brain tumor on June 13, 1993 in League City at the age of 69.