John Glenn's passing on December 8, 2016 means that the first seven American astronauts chosen to lead the fledging US space program in 1959 are now dead. This crew of military aviators, known as the "Mercury 7," proved that spaceflight was possible, and paved the way for the pioneering US trips to the moon. He was 95 years old.

Here is a list of the other "Mercury 7" astronauts:

-Alan Shepard was the first American to go into space aboard the Freedom 7 spacecraft. He later commanded the Apollo 14 in 1971. Shepard died in 1998 from leukemia.

-'Gus' Grissom, Ed White and Roger Chaffee were killed in 1967 in a fire during a launch pad test ahead of the planned Apollo 1 mission, which Grissom was slated to command.

-Scott Carpenter was the second American to orbit the Earth. He died in 2004 of heart failure at the age of 77.

-Walter M. Schirra, Jr. became the first man to fly aboard all three of the United States' first three human space projects the Mercury, Gemini and Apollo missions. Schirra died in 2007 at the age of 84.

-Donald K. 'Deke' Slayton was unable to fly in the 1960's because of an erratic heart rate. He became NASA's director of Flight Crew Operations. Slayton died of a brain tumor in 1993, at the age of 69.

-Gordon Cooper flew on the final Mercury mission and became the last US astronaut to fly alone in space. He died in 2004 of heart failure at the age of 77.

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