The First Successful American Satellite on 31th January in 1958!

Launched less than two months after Vanguard 1A, the first American attempt to compete with Sputnik, blows up on the launchpad, Explorer 1 (officially called Satellite 1958 Alpha) achieves an orbit extending an astonishing 1,560 miles (2,500 kilometers) above the Earth. This leads to the first great scientific discovery of the space age, when instruments designed by Iowa physicist James Van Allen find the radiation belts now named in his honor. The 31-pound (14-kilogram) satellite transmits until May 23, when its batteries die, but it remains aloft for more than 12 years.

From: National Geographic