Sputnik 1 launched on October 4, 1957, opening the Space Age

Sputnik 1, the first artificial satellite, was launched by the Soviet Union on October 4, 1957, from a launch site in Kazakhstan. A pressurized aluminum-alloy sphere 58 centimeters (22.8 inches) across, it weighed 83.6 kg (184 lb) and circled Earth about every 98 minutes on an elliptical orbit.

The launch itself was not a bolt from the blue. Scientists had called for satellites during the International Geophysical Year (July 1957 to December 1958); the White House announced a U.S. satellite in July 1955, and the USSR answered with plans of its own that August. What stunned Americans was the scale. The U.S. Navy’s Vanguard was designed around a 3.5-pound payload; Sputnik was more than 50 times heavier, and the rocket that lifted it implied missiles able to reach the United States.

Sputnik is often remembered as a ball that merely beeped. The radio signal mattered, but the satellite was also an experiment. Its five objectives included testing radio and optical methods of tracking a satellite, studying how radio waves travel through the atmosphere, and gauging upper-atmosphere density from how quickly its orbit decayed.

What happened next

• November 3, 1957: Sputnik 2 carried the dog Laika into orbit.
• December 1957: the first U.S. Vanguard satellite launch exploded on the pad.
• January 4, 1958: Sputnik 1 fell back and burned up after 92 days in space.
• January 31, 1958: Explorer 1, America’s first satellite, revealed the Van Allen radiation belts.
• July 1958: Congress passed the Space Act, creating NASA.

The word sputnik originally meant “fellow traveler”; it has since become a synonym for “satellite.”