The first US probe sent into space was Explorer 1. It was launched on January 31, 1958, from Cape Canaveral, Florida. Explorer 1 was a satellite that weighed 30.8 pounds and it was about the size of a basketball. It was launched using a Juno I rocket. Explorer 1 orbited the Earth for nearly 12 years before its orbit decayed and it reentered the Earth's atmosphere on March 31, 1970.