and Genie missiles, and later tested the stall-spin characteristics of the F-105. In 1958, he helped test Britain's first supersonic fighter, the English Electric P1B Lightning. NASA career Mercury Seven In January 1959, Slayton was selected as one of the candidates for NASA's Project Mercury, the first U.S. crewed space flight program. Despite his initial lack of interest in spaceflight, he agreed to pursue astronaut selection. After an initial interview at the temporary NASA headquarters in the Dolley Madison House in Washington, D.C., Slayton was psychologically and physically tested at the Lovelace Clinic in Albuquerque, New Mexico, along with fellow future astronauts Scott Carpenter and Jim Lovell. On April 2, 1959, Slayton was notified of his selection as an astronaut. He moved his family from Edwards Air Force Base to a housing development near Fort Eustis, where he was neighbors with fellow Mercury Seven astronauts Gus Grissom and Wally Schirra. After he began at NASA, Slayton was assigned to the development of the Convair Atlas LV-3B. In 1959, during a centrifuge training course, he underwent an electrocardiogram that found that he had erratic heart activity. He received further medical evaluation at Brooks Air Force Base and was diagnosed with idiopathic atrial fibrillation, but he was considered healthy enough to continue flying. During the uncrewed Mercury-Atlas 4 orbital spaceflight, he worked at the tracking station in Bermuda. He was selected for the second American crewed orbital mission, Mercury-Atlas 7, which he intended to name Delta 7. In early 1962, NASA Administrator James Webb opened an investigation into Slayton's atrial fibrillation. On March 15, 1962, two months prior to the launch of Delta 7, Slayton was medically disqualified from the flight and replaced on the mission by Scott Carpenter. Initially, Slayton's ineligibility was only for his assigned mission, and he attempted to improve his health by exercising more regularly and abstaining from alcohol. NASA leadership determined that Slayton was still at risk for atrial fibrillation and removed his eligibility to fly any of the remaining Mercury missions. Flight doctors recommended a cardiac catheterization to determine if he had a congenital condition, but NASA management rejected the proposal because of the risks of the operation. NASA management After being grounded by NASA, Slayton was selected in early 1962 to serve as the senior manager of the astronaut office. One of his first roles was to select the Group 2 astronauts, and the new