Sputnik

Sputnik (Russian: "Спутник-1" Russian pronunciation: [sputnik], "Satellite-1", ПС-1 (PS-1, i.e. "Простейший Спутник-1", or Elementary Satellite-1)) was the world's first Earth-orbiting artificial satellite. It circled the earth in 96.2 minutes. Launched into a low altitude elliptical orbit by the Soviet Union on October 4, 1957, it was the first in a series of satellites collectively known as the Sputnik program. The unanticipated announcement of Sputnik 1's success precipitated the Sputnik crisis in the United States and ignited the Space Race within the Cold War.

Sputnik helped to identify the upper atmospheric layer's density, through measuring the satellite's orbital changes. It also provided data on radio-signal distribution in the ionosphere. Pressurized nitrogen, in the satellite's body, provided the first opportunity for meteoroid detection. If a meteoroid penetrated the satellite's outer hull, it would be detected by the temperature data sent back to Earth.