Sputnik 1 (ˈspu̇t-nik, "Спутник-1", "Satellite-1", or literally "Co-pather-1" byname ПС-1 (PS-1, i.e. "Простейший Спутник-1", or Elementary Satellite-1)) was the first artificial satellite to be put into outer space. Launched into geocentric orbit by the Soviet Union on October 4, 1957, it was the first of a series of satellites collectively known as the Sputnik program.

The satellite helped to identify the density of high atmospheric layers through measurement of its orbital change and provided data on radio-signal distribution in the ionosphere. Because the satellite's body was filled with pressurized nitrogen, Sputnik 1 also provided the first opportunity for meteoroid detection, as a loss of internal pressure due to meteoroid penetration of the outer surface would have been evident in the temperature data sent back to Earth. The unanticipated announcement of Sputnik 1's success precipitated the Sputnik crisis in the United States and ignited the so-called Space Race within the Cold War.

Sputnik-1 was set in motion during the International Geophysical Year from Site No.1 at the 5th Tyuratam range in Kazakh SSR (now at the Baikonur Cosmodrome). The satellite traveled at 29,000 kilometers (18,000 mi) per hour and emitted radio signals at 20.005 and 40.002 MHz which were blank">monitored by amateur radio operators throughout the world. The signals continued for 22 days until the transmitter batteries ran out on October 26, 1957. Sputnik 1 burned up on January 4, 1958 as it fell from orbit upon reentering _Earth's atmosphere, after traveling about 60 million km (37 million miles) and spending 3 months in orbit.