The first US spacecraft was Explorer 1. The cylindrical 30 pound satellite was launched (above) as the fourth stage of a Jupiter-C rocket (a modified US Army Redstone ballistic missile) and achieved orbit on January 31, 1958.

This graceful arc traces a Delta rocket climbing through Thursday's early morning skies over Cape Canaveral Air Force Station in Florida, USA. Snug inside the rocket's Centaur upper stage were NASA's twin Radiation Belt Storm Probes (RBSP), now in separate orbits within planet Earth's Van Allen radiation belts.