Juno I launched Explorer 1, the United States’ first satellite, on 31 January 1958.
The four-stage Juno I was derived from the Jupiter-C research rocket. Its first stage used a modified Redstone missile, while clusters of solid-fuel upper stages supplied the additional velocity needed for orbit.
Explorer 1 carried instruments that discovered the Van Allen radiation belts, making the launch scientifically important as well as politically significant. The Soviet Union had already launched Sputnik 1, so the mission marked America’s entry into the space age.
Juno I is sometimes confused with Jupiter-C, the closely related vehicle used in earlier tests. The rocket was also called the AB-26, but Juno I is the standard name for its orbital-launch configuration.