Spaceflight, or simply space travel, is the application of astronautics to fly spacecrafts to or through outer space. It involves a change in speed, known as delta-v, to reach other planets in the Solar System. Despite the potential for life in space, the lack of private property and difficulty in establishing property rights has been an obstacle to developing space for human habitation. Humans have only ventured outside Earth's vicinity with Apollo flights to the Moon, but there have been calls for humans to return to the Moon, travel to Mars and visit other places in the solar system and beyond.
In 1986, Voyager 2's visit to Uranus revealed few visible atmospheric phenomena, but when it reached Neptune it discovered bands, clouds, auroras and a system of anticyclonic storms that rivaled Jupiter's Great Red Spot in size. In 2004, a privately funded company sent a piloted spacecraft, SpaceShipOne, to the lower edge of space for three short suborbital flights. It has been suggested that in the future other areas of space activity, such as the use of resources found on the Moon and near-Earth asteroids and the capture of solar energy to provide electrical energy to the Earth, could become successful businesses. The development of rockets and advances in electronics and other technologies in the 20th century made it possible to send machines and animals and then people above Earth's atmosphere into outer space.
Examples of these efforts include the development of the Curiosity Mars rover, the Cassini-Huygens mission to Saturn and its moons, and important space-based astronomical observatories such as the Hubble Space Telescope. Yuri Gagarin's 1957 flight was a breakthrough for space exploration as it showed that spaceflight was not lethal to living beings. In the 2000s, China began a successful manned spaceflight program while India launched Chandraayan 1; meanwhile, the European Union and Japan also planned future manned space missions. Numerous spaceships dedicated to observing the Sun have been launched since Apollo telescope mount.
Space exploration has been a common theme in literature and art due to its importance for humans to explore space for themselves “to see what's there”. Although there has been discussion about stationing force-delivery weapons in space at the beginning of the 21st century, such weapons had not been deployed nor had space-based anti-satellite systems.
