Space exploration, investigation of planets, stars, and space through the use of satellites, spacecraft, and probes built by human beings. At 10:56 P.M. (E.D.T.) on July 20, 1969, Neil Armstrong stepped off Apollo 11 and became the first human to set foot on the moon. This was the climax of an intensive U.S. space program sparked by the successful launch of the Soviet artificial satellite Sputnik 1 in 1957 and accelerated by Yuri Gagarin's flight in Vostok 1, the first spacecraft flown by a human, in 1961. Later that year Alan Shepard piloted the first U.S. spacecraft, and President John F. Kennedy set the goal, to be realized within the decade, of landing astronauts on the moon and returning them safely to earth.
On Feb. 20, 1962, John Glenn orbited the earth 3 times in the first Mercury craft to be boosted by an Atlas rocket. The next Soviet mission, in June 1963, involved 2 craft. Piloting Vostok 5, Valery Bykovsky set the 1-person endurance record with a 5-day mission; and piloting Vostok 6, Valentina Tereshkova became the first woman cosmonaut. Aleksei Leonov completed the first space walk in Mar. 1965. But then it was the turn of the Gemini missions to break all records. Both countries lost men, on the ground and in space: among them Virgil Grissom, Edward White, and Roger Chaffee (in a fire on board Apollo during ground tests in 1967) and the crew of Soyuz 11, killed during reentry in 1971. Earlier Soyuz missions had docked successfully with the first space station and set new records.
Meanwhile unpiloted probes—such as Orbiter, Ranger, and Surveyor—were searching out Apollo moon-landing sites; teams preparing the Soviet Luna and Lunokhod craft were also studying the moon. In 1968 Apollo 7 carried out an 11-day earth-orbit flight, and at Christmas Apollo 8 made 10 lunar orbits. The lunar landing craft was tested on the Apollo 9 and Apollo 10 missions, opening the way for the triumphant success of Apollo 11.
Apollo 12 was equally victorious, landing only 600 yards from the lunar probe Surveyor 3, but Apollo 13's aborted mission in 1970 was a near disaster. An explosion damaged the craft on its way to the moon, and reentry was achieved only with great difficulty. Apollo 14 had no such problems in 1971, visiting the moon's Fra Mauro area and collecting a wide range of lunar samples. Apollo 16 brought back 213 lb (96.6 kg) of moon rock, and in Dec. 1972 Apollo 17 made the last lunar landing, remaining on the moon for a record 75 hours.
In 1973 the United States launched the Skylab space station, a kind of satellite designed so that astronauts can live and work in orbit for several weeks. The station serves as a laboratory and as a base for other spacecraft.
Exploration of the planets has been carried out by unmanned probes: the Mariner series to Mars, Venus, and Mercury, and the Pioneer missions to the outer planets. There have been a number of Soviet contributions, such as the Venera soft-landing missions to Venus, the Zond bypass probe, and the Mars soft-landing craft. Results from the 2 U.S. Viking probes that soft-landed in Mars in 1976 did not show conclusively existence of life there. Voyagers 1 and 2 (1977) revealed a wealth of new information about Jupiter and Saturn.The United States launched the first reusable manned space vehicle, the space shuttle Columbia, in 1981. In 1983 Sally K. Ride, one of five crew members aboard the space shuttle Challenger, became the first U.S. woman in space. In the 25th space shuttle mission (1986), the shuttle Challenger exploded immediately after its launch, killing all seven crew members. A commission appointed by President Ronald Reagan to investigate the accident criticized NASA's decision to launch the shuttle and made several recommendations regarding safety measures to be used in future missions.The United States' Magellan space probe (launched 1989) reached Venus in 1990 and relayed to the earth clear images of Venus's surface. The Ulysses probe, launched by the United States in 1990, reaced the sun's south pole in 1994 and the north pole in 1995.