The Mercury 7 astronaut who spent sixteen years waiting for his first spaceflight

History · Published 3 October 2026 Swipe more like this →

In short: Donald K. Deke Slayton was a member of the original Mercury 7, yet he was grounded just months before his scheduled mission due to a heart irregularity. He spent over a decade managing his peers before finally securing medical clearance and launching into orbit in 1975 at age fifty-one.

Selected in April 1959 as one of the original Mercury 7 astronauts, Slayton was initially slated to pilot the second American orbital mission. However, flight surgeons had identified a minor heart condition known as idiopathic atrial fibrillation as early as mid-1959. While initially deemed non-interfering, the medical assessment shifted in February 1962. Doctors concluded that despite the low risk of the condition manifesting during a short flight, the lack of data on spaceflight's impact on the heart necessitated his removal from flight status on March 15, 1962.

Grounded from both spaceflight and solo high-performance jet operations, Slayton pivoted to a critical administrative role. As coordinator of astronaut activities and later as director of flight crew operations, he became the architect of the American astronaut corps. He established a rotation system for crew assignments and oversaw the selection of multiple astronaut groups for the Gemini, Apollo, and Skylab programs. His peers, including Eugene Cernan, regarded him as a trusted godfather figure who managed the corps with fairness and deep professional respect.

Slayton never abandoned his ambition to fly. He maintained a rigorous regimen of exercise, diet, and vitamins, hoping for medical reinstatement. His persistence paid off in March 1972 when cardiac specialists cleared him for flight. Assigned to the Apollo-Soyuz Test Project, he spent two years training, which included intensive study of the Russian language. On July 15, 1975, he finally reached space, docking with the Soviet Soyuz 19. Following his nine-day mission, he transitioned to managing the space shuttle's atmospheric and orbital test programs, retiring from NASA in 1982 after a career defined by resilience.

The mission itself was not without peril. During the Apollo capsule's descent, a valve left inadvertently open allowed toxic nitrogen tetroxide to enter the cabin. Slayton and his crewmates suffered pulmonary issues, requiring two weeks of hospitalization. A subsequent chest X-ray revealed a spot on Slayton's lung, though surgery confirmed the growth was benign. This final chapter of his NASA career underscored the unpredictable nature of early space exploration, a field Slayton helped shape from the ground for over a decade before finally claiming his place among the stars.

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