PHOENIX (AP) -- Retired astronaut Mark Kelly entered the race Tuesday to finish John McCain's term in the U.S. Senate, looking to join a small club of space explorers who have served in the U.S. Capitol.
Kelly and his twin brother, Scott Kelly, joined NASA in 1996 after flying combat missions in the U.S. Navy. Mark Kelly flew his first of four space missions on the shuttle Endeavor in 2001 and commanded a mission on Endeavor in 2011, according to his campaign biography. He's spent more than 50 days in space.
Here's a look at some of the other astronauts who've turned to public office:
JOHN GLENN -- The first American to orbit the Earth, Glenn was later elected to the U.S. Senate from Ohio and served four terms. He was a Democrat who worked to block the spread of weapons of mass destruction and was chairman of the Government Affairs Committee, according to his NASA biography. In 1998, while still a senator, he became the oldest person to go to space at age 77. He was involved with tests on the aging process during a nine-day mission on the Space Shutter Discovery. He died in 2016 at 95.
HARRISON "JACK" SCHMITT -- The former Republican senator from New Mexico flew on Apollo 17 and was the 12th and last man to walk on the moon in 1972, according to the U.S. Geological Survey, where he worked as a geologist in Flagstaff, Arizona before joining NASA as a scientist-astronaut. Schmitt was elected to the Senate in 1976 and was the top Republican on the subcommittee overseeing space. He was defeated in his re-election bid six years later. He is 83.
JACK SWIGERT -- Swigert is the man responsible for one of the most famous lines in NASA history: "Houston, we've had a problem here." He was a backup pilot for the 1970 Apollo 13 mission and was swapped in a few days before the flight when Ken Mattingly was exposed to measles. Swigert, a Republican, was elected to represent the 6th Congressional District of Colorado but died in 1982 before taking office. He was 51.