The space shuttle has launched 134 times during its 30 years of service, and in that time it has ferried more than 540 astronauts into space. Each one of those astronauts is a prime specimen of humanity and has made their own unique contributions, but a few space travelers stand out from the rest.

1. Robert Crippen

Even before Robert Crippen piloted the first flight of the space shuttle program, he had put together an impressive resume with NASA. He was a member of the astronaut support crew for Skylab missions and for the 1975 Apollo-Soyuz Test Project, which was the last Apollo mission, and the first joint U.S./Soviet space flight. In addition to the first shuttle flight, he commanded the shuttle on three missions in the 1980s: He presided over the first five-person crew, STS-7, flew with the first female American astronaut in space, Sally Ride, on STS-41-C and commandeered the first seven-person crew (STS-41-G). He spent 23 days in space over the course of his four shuttle missions.

2. John Young

John Young had already been in space four times by the time he was chosen to become the commander of the first space shuttle mission. He went on to be the commander of another space shuttle mission STS-9 in 1983, which carried the first Spacelab module. Additionally, he was the ninth person to walk on the moon (as commander of the Apollo 16 mission in 1972), and he is one of only three people who has been to the moon twice. When he retired in 2004, he had spent a total of 34 days in space.

3. Sally Ride

Sally Ride was already a notable American physicist before she began her rather unorthodox path to becoming a space shuttle astronaut. Ride found her way to the shuttle by being one of 8,000 people to answer a NASA application advertisement in a newspaper. In August 1979, she completed one year of training, and then performed as an on-orbit capsule communicator (CAPCOM) on the STS-2 and STS-3 missions. On June 18, 1983, she became the first American woman in space as a crewmember on Challenger for STS-7.

4. Guy Bluford

Before becoming the first African-American in space on Challenger mission STS-8, Guy Bluford was an engineer and a retired colonel from the United States Air Force. He participated in four space shuttle flights between 1983 and 1992. In addition to his STS-8 flight, he flew on the Spacelab-equipped STS-61-A mission, and two Department of Defense-dedicated missions, STS-39, and STS-53. He retired in 1993, having logged more than 28 days in space.

5. Kathryn Sullivan

In 1984, mission specialist Kathryn Sullivan became the first American woman to walk in space (STS-41 G). She was a crewmember on three space shuttle missions (STS-41G, STS-31 and STS-45), and logged 22 days in space.

6. John Glenn

One of the pioneers of space exploration, John Glenn was the fifth person in space and the first person to orbit the Earth, aboard Friendship 7 on February 20, 1962. He went on to have a long career in NASA, and in 1998 he was asked to be a part of the space shuttle Discovery mission (STS-95). He was 77 at the time, setting the record of oldest person to go into space. This also made him the third seated politician to fly in space (he was serving as a U.S. senator from Ohio at the time). Glenn logged a total of nine days in space during his NASA career.

7. Bruce McCandless II

If you're impressed by John Glenn's feat of orbiting around the Earth, you'll be blown away by Bruce McCandless II's main claim to fame: In 1984, he became the first human to orbit Earth without a spacecraft. He made the trip wearing just his Manned Maneuvering Unit, that jetpacklike device astronauts use on spacewalks. As a mission specialist on two space shuttle missions (STS-41-B and STS-31), he logged more than 312 hours in space.

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