Return to space.

The first American astronaut to orbit Earth in 1962 is about to blast back into orbit. Tile big difference: The 10-day space voyage will make John Glenn, now 77, tile oldest human ever to travel in space.

Glenn became a national hero After circling the planet three times during a five-hour ride strapped inside a 2.7-by-2.1-meter (9-by-7-ft) capsule atop the experimental rocket Mercury (right). "Tile first time I went up we were just trying to figure out: Can we do this thing or not?" Glenn recently told TV-network CNN. Now Glenn is preparing to board the space shuttle Discovery, scheduled to launch on October 29. Glenn will be a guinea pig for research on how microgravity (near-zero gravity) affects the body of an older person. Astronauts in space suffer from a host of ailments--loss of bone and muscle mass, disturbed sleep patterns, and balance disorders--that are common among the elderly on Earth. NASA hopes Glenn's mission will help scientists unlock the keys to the process of aging. Glenn thinks his voyage might pave the way for NASA to one day launch teens to study the effects of space travel on young people. Way to go, Glenn!