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In 1962 Mr Glenn became the first American in orbit in a Friendship 7 capsule that took five hours to circle the Earth three times before crash-landing into the Caribbean.
Today the 77-year-old astronaut and his six crew mates aboard the Space Shuttle Discovery glided safely into the Kennedy Space Centre in Florida at 0903 local time (1703 GMT).
They had travelled more than 3.6 million miles in space, making 135 laps of the globe.
In high spirits
Nasa's official reason for allowing Mr Glenn to return to space was to compare the effects of microgravity with the ageing process.
But some critics said the trip was a publicity stunt to revive public interest in the space program.
This includes the construction of a $60-billion international space station, a project that will involve 12 countries and will begin with the launch of the first module in December.
Nasa's chief doctor, Philip Stepaniak, said Mr Glenn and the other crew members were all doing better than expected and described Mr Glenn as being animated and in high spirits.
He was able to walk unaided down the steps before being reunited with his wife, two children and grandsons.
Mr Glenn even found the energy to call out on the communications link moments after landing, "I want to reprise a statement that I made a long, long time ago, except this time it is: One-G and I feel fine."
He was recalling his previous trip to space when, on blast-off, he said "Zero-G, and I feel fine."
Message from president
Nasa had put Edwards Air Base in California on stand-by in case of bad weather on the east coast.
In the event the shuttle made a perfectly smooth landing.
President Bill Clinton saw the mission blast off nine days ago. A few hours before Discovery's return, the president sent the senator an email congratulating him on a successful mission.
"We are very proud of you and the entire crew, and a little jealous," it read. "Back on Earth we're having a lot of fun with your adventure."
Other crew members included the first Spaniard in space, Pedro Duque, and the only woman on board, Japanese astronaut Chiaki Mukai.
Ten days later John Glenn was feted by thousands of Americans during a ticker-tape parade - his second - in New York's "Canyon of Heroes" in lower Manhattan.
The police officer who drove Mr Glenn through the parade in a 1952 convertible was the son of the man who drove the space hero 36 years before.
Mr Glenn's first ticker-tape parade after his Mercury flight is considered the largest ever in New York.
It was attended by a record four million people, and an estimated 3,474 tons of confetti and ticker-tape rained down along a seven mile (11 km) route.
Mr Glenn retired as Democrat Senator for Ohio in January 1999. That same year Nasa renamed its Lewis Research Center the Glenn Research Center.
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