Soviet rocketry commenced in 1921 with development of Solid-fuel rockets, which resulted in the development of the Katyusha rocket launcher. Rocket scientists and engineers, particularly Valentin Glushko and Sergei Korolev, contributed to the development of Liquid-fuel rockets, which were first used for fighter aircraft. Developments continued in the late 1940s and 1950s with a variety of ballistic missiles and ICBMs, and later for space exploration which resulted in the launch of Sputnik 1 in 1957, the first artificial Earth satellite ever launched.