It’s hard to comprehend just how much preparation goes into spaceflight missions – especially those with a crew. For every minute spent in space, an untold number of hours is spent on the ground calculating, designing, building, testing and simulating. And the Mercury was the project on which these procedures began. After modeling on basic computers and countless heat, drop, spin-tunnel and wind-tunnel tests, the design for the cone-shaped, blunt-nosed Mercury capsule was finished. It had a light but strong titanium outer layer, and a thick heat-resistant aluminum shield designed to burn away during reentry to Earth. At 21,000 feet it would deploy a parachute to stabilize its descent, and another at 10,000 feet to slow it down for landing. This obsession with scrupulousness extended to all parts of the project, and would become a central feature of NASA’s culture. Almost every system of the Mercury capsule, from its mechanics to electrics, had at least one backup. Every unit of the craft and every system on the ground was tested dozens of times more than strictly required by the mission. This meticulous eye for safety, strength and reliability was also reflected in the recruitment and training of the Mercury’s human crew – the first astronauts. At first it was difficult to know whom they should hire – this job had never been done before, so there were no established job descriptions or requirements. But in December 1958, President Eisenhower ruled that only US test pilots could apply. This made sense for a number of reasons. These men were the best pilots around, in charge of testing newly designed aircraft for flaws. They were used to highly stressful working conditions, and could keep their cool while operating complex cockpits. Most of all, though, they were desensitized to death – in 1952, the mortality rate for US test pilots was 25 percent. Aside from test pilot credentials, the Mercury’s job requirements included 1,500 hours of flying time, superb physical condition, a bachelor’s degree in engineering or equivalent and a height no greater than 5 feet 11 inches, to allow the men to fit inside the tiny capsule. There were 110 men in the country who met these requirements; seventy applied. Through a grueling selection process that included long interviews, psychological scrutiny, medical exams and fitness tests, this group was whittled down to seven future astronauts, called the Mercury Seven. They were Scott Carpenter, Gordon Cooper, John Glenn, Virgil Grissom, Walter Schirra, Alan Shepard and Donald Slayton. No one expected all seven to survive Project Mercury.