The exploration of space is among the most ambitious, complex, and expensive undertakings that humans have ever undertaken. It has captivated people of all walks of life, and it is an important part of the human imagination. It has also been a major source of literature and film.
Space exploration has provided valuable scientific data from the study of living things that have been placed in space or in special laboratory habitats. In addition, scientists have been able to conduct a wide variety of experiments that could not be done on Earth, because of the virtual absence of gravity.
In the mid-20th century, uncrewed spacecraft were sent to the Moon and to other planets within our Solar System. Some, like the Voyager 1 and 2 spacecraft, have even travelled far enough to leave the Solar System’s heliosphere, which is a bubble of particles surrounding our Sun.
Those who have been sent into space to fly or live in space are generally called astronauts or, depending on the nationality of the space agency in question, cosmonauts (for instance, “taikonaut” in China). Candidates for these programs must pass extensive training and medical examinations.
Until very recently, only governments could afford to send people and equipment into space, because of the high costs involved. Now, private companies are launching commercial satellites, and the technology to make rockets partially or fully reusable is rapidly evolving. This could lead to lower spacecraft costs, and allow us to explore beyond Earth orbit, to destinations such as the Moon or Mars.