In 1962, Mr Glenn was the first American to orbit the Earth and became a national hero. His presence on Discovery fired the imagination of the world. More than 250,000 people gathered around Kennedy Space Centre to watch the launch. From VIP seats inside the base, President Bill Clinton and a host of Hollywood stars saw the mission blast off. Mr Glenn has been taking part in a series of experiments, including assessing the effects of weightlessness on the body.
Scientists hope to use the results of the experiments for research into the ageing process.
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