The Mercury missions were America's first manned spaceflight missions. They took place from 1961 to 1963. The goals of the program were to put an astronaut in orbit and achieve spaceflight lasting longer than 24 hours safely. Alan Shepard, Gus Grissom, John Glenn, Scott Carpenter, Wally Schirra, Gordon Cooper and Deke Slayton were the seven astronauts chosen for the program, but Deke Slayton was grounded for medical reasons.
Each Mercury mission had a specific call sign ending in the number seven in order to commemorate the seven astronauts and seven planned missions. Freedom 7 and Liberty Bell 7 were the first two missions, for which Shepard and Grissom flew suborbital paths to test the equipment. John Glenn took Friendship 7 into orbit for nearly five hours, and Scott Carpenter followed up in Aurora 7. Wally Schirra's Sigma 7 stayed in orbit for more than nine hours, and Gordon Cooper's Faith 7 was America's first spaceflight lasting longer than 24 hours.
Project Mercury led directly to Project Gemini, which used a two-person capsule to test longer term spaceflight missions as well as extravehicular activity and docking techniques that would be necessary to reach the moon. While the United States spent much of Project Gemini lagging behind the Russians in the Space Race, NASA pulled ahead and ultimately landed the first man on the moon.