Vanguard

Project Vanguard was a program managed by the United States Naval Research Laboratory (NRL), which intended to launch the first artificial satellite into Earth orbit using a Vanguard rocket as the launch vehicle.
In response to the surprise launch of Sputnik I on October 4, 1957, the U.S. restarted the Explorer program, which had been proposed earlier by the Army Ballistic Missile Agency (ABMA). Together with the Jet Propulsion Laboratory (JPL), ABMA built Explorer I in 84 days and launched it on January 31, 1958. Before work was completed, however, the Soviet Union launched a second satellite, Sputnik 2, on November 3, 1957. Meanwhile the spectacular televised failure of Vanguard TV3 on December 6, 1957 deepened American dismay over the country's position in the Space Race.
On March 17, 1958, Vanguard I became the second artificial satellite successfully placed in Earth orbit by the United States. It was the first solar-powered satellite. Just 152 mm (6 in) in diameter and weighing just 1.4 kg (3 lb), Vanguard I was described by then-Soviet Premier Nikita Khrushchev as, "The grapefruit satellite."
Vanguard I is the oldest artificial satellite still in space. Vanguard's predecessors, Sputnik 1, Sputnik 2 and Explorer I have fallen out of orbit.