Washington Correspondent Tom Carver: A great place for old folks

But American hero John Glenn, the oldest man in space, would not mind extending the nine-day mission.

"I wish it could last another week," said the 77-year-old astronaut, who, in 1962, became the first American to orbit the earth.

Mr Glenn even joked about returning to space to open a retirement home.

He said, from on board Discovery: "You just float across the room, there is no such thing as broken hips or anything like that.

"If you have trouble sleeping at night, that's no problem, as you have another night coming up in not more than 45 minutes."

But 78-year-old Annie Glenn, the astronaut's wife of 55 years, does not envisage retiring to space.

She said: "As far as I'm concerned, there are going to be no more other flights."

John Glenn's 1962 space capsule

Mr Glenn joined the six-member crew of Discovery to act as a guinea-pig to help scientists with their geriatric experiments, including assessing the effects of weightlessness on the body.

Mr Glenn has even swallowed a radio transmitter to monitor his body temperature.

Astronauts - both old and young - lose bone and muscle mass in the weightlessness of space, just like elderly people do on earth.

Scientists hope to use the results of the tests carried out on Mr Glenn for research into the ageing process.

But for Mr Glenn the flight means much more than a scientific experiment. He described his return to space as a "terrific" experience, a dream coming true.