Airplanes with internal combustion engines can fly in the atmosphere because they are able to take the necessary oxygen from the air.  Rockets that move according to the principle_of_jet_recoil fly above the atmosphere. They must carry along their entire requirement of fuel. 

The first calculations for rockets were made as early as in 1903 by the Russian K.E. Tsiolkovsky (1857-1935). He had recognized that instead of black gunpowder, liquid fuels were required for powering rockets and worked on models for reverse-thrust equipment. In 1926, the first rocket powered by liquid fuel was launched by Robert Goddard (1882-1945) from Massachusetts. Its engine ran for a little more than 2 seconds and launched the rocket 65 meters high. 

As early as in 1919, Goddard had claimed that it would at some stage be possible to fly to the moon. In 1942, Wernher von Braun (1912-1977) built the large A4 rocket in Peenemünde, and it was used to make the first trial flights at a height of 150 kilometers, i.e. in real space conditions. Based on the Peenemünde model, both the Americans and the Soviets built larger and larger rockets. They were essentially used for military purposes, but were also used for research tasks. 

The first human in space was Yuri Gagarin. In 1961, he orbited the earth in the space capsule Vostok at a height of between 180 and 300 kilometers. This was the practical proof, following successful experiment using animals, that humans could also fly in space. The years that followed saw competition between the USA and the Soviet Union for the fastest possible exploration of space and for landing on other planets.