Sputnik 1—in Russian Sputnik means “travelling companion”—was the world’s first man-made satellite, launched on 4 October 1957 by the Soviet Union.

Nicknamed the "simplest satellite", Sputnik 1 carried a radio transmitter emitting the famous beeping signals heard around the world, four antennas and temperature and pressure sensors to collect data about the upper atmosphere.

Although the use of satellites for science was still some way in the future, Sputnik was a strong symbol that kick-started the development of space applications. Back in 1955, the idea that satellites might serve a useful purpose was dismissed as fanciful. Now, their utility is undisputable.