Sputnik

Overview
On October 4, 1957, the Soviet Union surprised the world by launching Sputnik, the world's first artificial satellite; on November 3, 1957, the Soviets launched Sputnik-2. Despite the fact that the Soviets had announced it in advance, Sputnik's success greatly shocked the American people.

Sputnik evoked fast action on the part of the Eisenhower Administration. On November 7, 1957, the President announced the appointment of a Special Assistant who would chair the Presidential Science Advisory Committee (PSAC). The next day, as a backup to Project Vanguard, the Army was authorized to proceed with its proposed satellite program using the Redstone missile (thereby abandoning the U.S. attempt to maintain that its participation in the IGY was purely non-military and lowering ICBM development to second priority).

Source

 * U.S. Navy, ”From the Sea to the Stars: A Chronicle of the U.S. Navy’s Space and Space-related Activities, 1944-2009”," at 16 (2010) (full-text).