Sputnik 1, the Soviet Union's first spacecraft, was launched on October 4, 1957, weighing 83.6 kg (184 pounds). Other unmanned Soviet and American spacecraft soon followed, followed four years later (April 12, 1961) by the first manned spacecraft, Vostok 1, which carried Soviet astronaut Yury Gagarin. Since then, a slew of human and unmanned vehicles have been launched to advance scientific understanding, strengthen national security, and offer critical services in fields like telecommunications and weather forecasting.

Most spacecraft are not self-propelled; they rely on a launch vehicle to give initial velocity, which then separates from the spacecraft once its mission is completed. Typically, the spacecraft is sent into an orbit around Earth or, if given enough velocity to escape Earth's gravity, proceeds toward another location in space.

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