Mercury astronaut John Glenn speaks during the "On Shoulders of Giants" program celebrating 50 years of Americans in orbit, an era which began with Glenn's MA-6 mission on Feb. 20, 1962. The event was conducted in the Rocket Garden at the Kennedy Space Center Visitor Complex in Florida a few miles from the launch pad where Glenn and Scott Carpenter took flight in Mercury spacecraft. Glenn's launch aboard an Atlas rocket took with it the hopes of an entire nation and ushered in a new era of space travel that eventually led to Americans walking on the moon by the end of the 1960s. Glenn soon was followed into orbit by Scott Carpenter, Walter Schirra and Gordon Cooper. Their fellow Mercury astronauts Alan Shepard and Virgil "Gus" Grissom flew earlier suborbital flights. Deke Slayton, a member of NASA's original Mercury 7 astronauts, was grounded by a medical condition until the Apollo-Soyuz Test Project in 1975.