It was 36 years ago that Glenn thrilled his country by catching up with the Soviet Union in the space race. Since then he has become a Democratic senator representing Ohio. Yesterday he declared he was ready to go, confessing to "a real sense of deja vu."
"Needless to say, I'm excited to be back and I'm honoured and I'm privileged," he said. "The important thing is the opportunity that this gives to take us in some new directions in research."
The particular focus of the research will be on ageing, and the effects of space travel on an older body.
Glenn exercises daily and lifts weights, but his body has 36 more years of wear and tear than when it last experienced the extreme forces of blast- off on 20 February, 1962. Doctors will study the effect of weightlessness on Glenn's bones and immune system, and his ability to bounce back afterwards.
Nasa approved Glenn's appointment to become a payload specialist on the Shuttle Discovery for a flight tentatively set for October. "I see this as another adventure into the unknown," Glenn said.
Since he flew into the unknown for the first time, Nasa also has 36 more years of space expertise, but that doesn't translate into a hazard-free mission. One space expert said, "Probably there's as much risk today flying the Shuttle as there was then because (in 1962) Glenn had an escape rocket that there isn't on the orbiter. And I wouldn't want to go through the training he would have to go through."
Even so, Glenn lobbied Nasa extensively to get it to consider using him for geriatric research, helping to connect the space agency's researchers with scientists eager for the information that tests in weightlessness might provide about human ageing.
The tests are "scientific research on the process of getting older, which we're all concerned about," said John Logsdon, of George Washington University.
"What is happening is they've decided to make Glenn the subject of those experiments, not making up the experiment so he can fly," he said. "I think that's an important distinction."Reuse content