What's the difference between i.e. and e.g.?
A program of rocket-powered flights undertaken by the United States with the goal of putting a man in orbit around the Earth. Each Mercury flight carried one astronaut. The program ran from 1961 to 1963 and was named after the Roman god Mercury, the messenger of the gods.
Note: The first United States suborbital flight was made by Alan Shepard in 1961.
Note: In 1962, John Glenn made the first orbital flight by an American astronaut.