Space exploration

Space exploration is the physical investigation of outer space by uncrewed robotic space probes and through human spaceflight.

While the observation of objects in space, known as astronomy, predates reliable recorded history, it was the development of large and relatively efficient rockets during the mid-twentieth century that allowed physical space exploration to become a reality. Common rationales for exploring space include advancing scientific research, national prestige, uniting different nations, ensuring the future survival of humanity, and developing military and strategic advantages against other countries.

The early era of space exploration was driven by a "Space Race" in which the Soviet Union and the United States vied to demonstrate their technological superiority. Landmarks of this era include the launch of the first human-made object to orbit Earth, the Soviet Union's Sputnik 1, on 4 October 1957, and the first Moon landing by the American Apollo 11 mission on 20 July 1969. The Soviet space program achieved many of the first milestones, including the first living being in orbit in 1957, the first human spaceflight (Yuri Gagarin aboard Vostok 1) in 1961, the first spacewalk (by Alexei Leonov) on 18 March 1965, the first automatic landing on another celestial body in 1966, and the launch of the first space station (Salyut 1) in 1971.

In the 1970s, focus shifted from one-off flights to renewable hardware, such as the Space Shuttle program, and from competition to cooperation, the foremost example being the International Space Station (ISS), built between 1998 and 2011.

The 2000s brought advancements in the national space-exploration programs of China, the European Union, Japan, and India. The 2010s saw the rise of the private space industry in earnest with the development of private launch vehicles, space capsules, and satellite manufacturing. In the 2020s, the two primary global programs gaining traction are Moon-focused: the Chinese-led International Lunar Research Station and the U.S.-led Artemis Program, with its plan to build the Lunar Gateway and the Artemis Base Camp, each with a set of international partners.

The first telescope is said to have been invented in 1608 in the Netherlands by an eyeglass maker named Hans Lippershey, but their first recorded use in astronomy was by Galileo Galilei in 1609. In 1668 Isaac Newton built his own reflecting telescope, the first fully functional telescope of this kind, and a landmark for future developments due to its superior features over the previous Galilean telescope.

A string of discoveries in the Solar System (and beyond) followed, then and in the next centuries: the mountains of the Moon, the phases of Venus, the main satellites of Jupiter and Saturn, the rings of Saturn, many comets, the asteroids, the new planets Uranus and Neptune, and many more satellites.

The Orbiting Astronomical Observatory 2 was the first space telescope launched 1968, but the launch of the Hubble Space Telescope in 1990 set a milestone. As of 1 December 2022, there were 5,284 confirmed exoplanets discovered. The Milky Way is estimated to contain 100–400 billion stars and more than 100 billion planets. There are at least 2 trillion galaxies in the observable universe. HD1 is the most distant known object from Earth, reported as 33.4 billion light-years away.