Space exploration, the investigation, by means of manned and unmanned spacecraft, of the reaches of the universe beyond Earths atmosphere and the use of the information so gained to increase knowledge of the cosmos and benefit humanity. A complete list of all manned spaceflights, with details on each missions accomplishments and crew, is available in the section Chronology of manned spaceflights.

Humans have always looked at the heavens and wondered about the nature of the objects seen in the night sky. With the development of rockets and the advances in electronics and other technologies in the 20th century, it became possible to send machines and animals and then people above Earths atmosphere into outer space. Well before technology made these achievements possible, however, space exploration had already captured the minds of many people, not only aircraft pilots and scientists but also writers and artists. The strong hold that space travel has always had on the imagination may well explain why professional astronauts and laypeople alike consent at their great peril, in the words of Tom Wolfe in The Right Stuff (1979), to sit on top of an enormous Roman candle, such as a Redstone, Atlas, Titan or Saturn rocket, and wait for someone to light the fuse. It perhaps also explains why space exploration has been a common and enduring theme in literature and art. As centuries of speculative fiction in books and more recently in films make clear, one small step for [a] man, one giant leap for mankind was taken by the human spirit many times and in many ways before Neil Armstrong stamped humankinds first footprint on the Moon.

Achieving spaceflight enabled humans to begin to explore the solar system and the rest of the universe, to understand the many objects and phenomena that are better observed from a space perspective, and to use for human benefit the resources and attributes of the space environment. All of these activitiesdiscovery, scientific understanding, and the application of that understanding to serve human purposesare elements of space exploration. (For a general discussion of spacecraft, launch considerations, flight trajectories, and navigation, docking, and recovery procedures, see spaceflight.)

Although the possibility of exploring space has long excited people in many walks of life, for most of the latter 20th century, only national governments could afford the very high costs of launching people and machines into space. This reality meant that space exploration had to serve very broad interests, and it indeed has done so in a variety of ways. Government space programs have increased knowledge, served as indicators of national prestige and power, enhanced national security and military strength, and provided significant benefits to the general public. In areas where the private sector could profit from activities in space, most notably the use of satellites as telecommunication relays, commercial space activity has flourished without government funding. In the early 21st century, entrepreneurs believed that there were several other areas of commercial potential in space, most notably privately funded space travel.

In the years after World War II, governments assumed a leading role in the support of research that increased fundamental knowledge about nature, a role that earlier had been played by universities, private foundations, and other nongovernmental supporters. This change came for two reasons. First, the need for complex equipment to carry out many scientific experiments and for the large teams of researchers to use that equipment led to costs that only governments could afford. Second, governments were willing to take on this responsibility because of the belief that fundamental research would produce new knowledge essential to the health, the security, and the quality of life of their citizens. Thus, when scientists sought government support for early space experiments, it was forthcoming. Since the start of space efforts in the United States, the Soviet Union, and Europe, national governments have given high priority to the support of science done in and from space. From modest beginnings, space science has expanded under government support to include multibillion-dollar exploratory missions in the solar system. Examples of such efforts include the development of the Curiosity Mars rover, the Cassini-Huygens mission to Saturn and its moons, and the development of major space-based astronomical observatories such as the Hubble Space Telescope.

Soviet leader Nikita Khrushchev in 1957 used the fact that his country had been first to launch a satellite as evidence of the technological power of the Soviet Union and of the superiority of communism. He repeated these claims after Yury Gagarins orbital flight in 1961. Although U.S. Pres. Dwight D. Eisenhower had decided not to compete for prestige with the Soviet Union in a space race, his successor, John F. Kennedy, had a different view. On April 20, 1961, in the aftermath of the Gagarin flight, he asked his advisers to identify a space program which promises dramatic results in which we could win. The response came in a May 8, 1961, memorandum recommending that the United States commit to sending people to the Moon, because dramatic achievements in spacesymbolize the technological power and organizing capacity of a nation and because the ensuing prestige would be part of the battle along the fluid front of the cold war. From 1961 until the collapse of the Soviet Union in 1991, competition between the United States and the Soviet Union was a major influence on the pace and content of their space programs. Other countries also viewed having a successful space program as an important indicator of national strength.

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Even before the first satellite was launched, U.S. leaders recognized that the ability to observe military activities around the world from space would be an asset to national security. Following on the success of its photoreconnaissance satellites, which began operation in 1960, the United States built increasingly complex observation and electronic-intercept intelligence satellites. The Soviet Union also quickly developed an array of intelligence satellites, and later a few other countries instituted their own satellite observation programs. Intelligence-gathering satellites have been used to verify arms-control agreements, provide warnings of military threats, and identify targets during military operations, among other uses.

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In addition to providing security benefits, satellites offered military forces the potential for improved communications, weather observation, navigation, timing, and position location. This led to significant government funding for military space programs in the United States and the Soviet Union. Although the advantages and disadvantages of stationing force-delivery weapons in space have been debated, as of the early 21st century, such weapons had not been deployed, nor had space-based antisatellite systemsthat is, systems that can attack or interfere with orbiting satellites. The stationing of weapons of mass destruction in orbit or on celestial bodies is prohibited by international law.

Governments realized early on that the ability to observe Earth from space could provide significant benefits to the general public apart from security and military uses. The first application to be pursued was the development of satellites for assisting in weather forecasting. A second application involved remote observation of land and sea surfaces to gather imagery and other data of value in crop forecasting, resource management, environmental monitoring, and other applications. The U.S. and Soviet governments also developed their own satellite-based global positioning systems, originally for military purposes, that could pinpoint a users exact location, help in navigating from one point to another, and provide very precise time signals. These satellites quickly found numerous civilian uses in such areas as personal navigation, surveying and cartography, geology, air-traffic control, and the operation of information-transfer networks. They illustrate a reality that has remained constant for a half centuryas space capabilities are developed, they often can be used for both military and civilian purposes.

Another space application that began under government sponsorship but quickly moved into the private sector is the relay of voice, video, and data via orbiting satellites. Satellite telecommunications has developed into a multibillion-dollar business and is the one clearly successful area of commercial space activity. A related, but economically much smaller, commercial space business is the provision of launches for private and government satellites. In 2004 a privately financed venture sent a piloted spacecraft, SpaceShipOne, to the lower edge of space for three brief suborbital flights. Although it was technically a much less challenging achievement than carrying humans into orbit, its success was seen as an important step toward opening up space to commercial travel and eventually to tourism. Nearly a decade after SpaceShipOne reached space, several firms were poised to carry out such suborbital flights, with one, Virgin Galactic, projecting the beginning of service before the end of 2014. Suggestions have been made that in the future other areas of space activity, including remote sensing of Earth, utilization of resources found on the Moon and near-Earth asteroids, and the capture of solar energy to provide electric power on Earth, could become successful businesses.

Most space activities have been pursued because they serve some utilitarian purpose, whether increasing knowledge, adding to national power, or making a profit. Nevertheless, there remains a powerful underlying sense that it is important for humans to explore space for its own sake, to see what is there. Although the only voyages that humans have made away from the near vicinity of Earththe Apollo flights to the Moonwere motivated by Cold War competition, there have been recurrent calls for humans to return to the Moon, travel to Mars, and visit other locations in the solar system and beyond. Until humans resume such journeys of exploration, robotic spacecraft will continue to serve in their stead to explore the solar system and probe the mysteries of the universe.

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