In 1903 the Russian physicist Konstantin Tsiolkovsky was developing ideas for space rockets fuelled by liquefied gas and by 1926 Robert Goddard in the USA had successfully designed the first liquid-fuelled rocket. There followed considerable German research into rockets, culminating in the launch of the V-2 rocket in 1944. In 1957 the Soviet Union surprised the USA by putting the first artificial satellite, Sputnik I, in orbit; this was followed by the US Explorer I in 1958. Yuri Gagarin was the first man in space in 1961, followed by John Glenn in 1962. In 1961 President Kennedy proposed the Apollo programme to achieve a manned lunar landing by 1970, and in 1969 Neil Armstrong and Edwin (‘Buzz’) Aldrin landed on the Moon. The Soviet Union concentrated on unmanned flights, Luna IX achieving a soft landing on the Moon in 1966. In the early 1970s space stations were launched by both the USA and the Soviet Union, and in 1975 an Apollo capsule linked up with a Soviet Soyuz capsule. Unmanned flights have been made to Venus and Mars, while the US probe, Voyager 2, launched in 1977, reached Neptune in 1989. Its companion, Voyager 1, also launched in 1977, studied Jupiter (1979) and Saturn (1980); it was still functioning in 2013, when it became the first artificial object to leave the Solar System and enter interstellar space. In 1981 the USA launched a space shuttle, the first reusable spacecraft. The shuttle fleet remained in use until 2011, although its commercial and scientific programme was twice interrupted (1986–88; 2003–05) following the loss of, respectively, the shuttles Challenger on lift-off and Columbia while returning to Earth. In 1986 the giant Soviet modular space station, Mir, was launched, with astronauts being ferried to the station by Soyuz spacecraft; this was followed in 1987 by the placing in space of the powerful Energiya station. The Hubble space telescope, which can produce images of other solar systems, was launched from a US shuttle in 1990. Its faulty mirror limited observations until it was repaired by astronauts in the space shuttle Endeavour in 1993. Construction of an international space station, conceived by the USA in 1984, began in 1998 and it has been crewed continuously since 2000. Space technology has resulted in numerous applications: telecommunication satellites have greatly improved global communications, meteorological satellites provide advance weather information, positioning satellites allow precise navigation, and reconnaissance satellites register the Earth’s resources and military information.