John Glenn was not popular with the other astronauts. Glenn was the backup pilot for Shepard and Grissom on the first two manned Project Mercury flights, the sub-orbital missions Mercury-Redstone 3 and Mercury-Redstone 4. Glenn was selected for Mercury-Atlas 6, NASA's first manned orbital flight, with Carpenter as his backup. Putting a man in orbit would achieve one of Project Mercury's most important goals. Shepard and Grissom had named their spacecraft "Freedom 7" and "Liberty Bell 7". The numeral 7 had originally been the production number of Shepard's spacecraft, but had come to represent the Mercury 7. Glenn named his spacecraft, number
John Glenn 55-minute flight. He carried a note on the flight which read, "I am a stranger. I come in peace. Take me to your leader and there will be a massive reward for you in eternity" in several languages, in case he landed near southern Pacific Ocean islands. The original procedure called for Glenn to exit through the top hatch, but he was uncomfortably warm and decided that egress through the side hatch would be faster. During the flight, he endured 7.8 G of acceleration and traveled at about . The flight took Glenn to a maximum altitude (apogee) of about