The answer to the crossword for the term ONE OF THE MERCURY SEVEN is 'Glenn'. John Glenn was an American astronaut and United States Senator from Ohio. He was one of the original seven astronauts in Project Mercury, the first human spaceflight program of the United States. Glenn was the first American to orbit the Earth, circling it three times in 1962. He later became a U.S. Senator and in 1998, at age 77, he returned to space aboard the Discovery Space Shuttle.