Space Exploration

For almost all of human history, the sky was out of reach. Then, in a single human lifetime, we learned to throw machines into orbit, to send people to the Moon and back, and to fly robots past every planet in the solar system. Space exploration is one of the great adventures of the modern age, and it has changed life on the ground as much as our view of the heavens.

How rockets work

A rocket works by pushing hot gas out of its back end very fast. As Isaac Newton described, every action has an equal and opposite reaction: as the gas rushes one way, the rocket is pushed the other. Unlike a jet engine, a rocket carries its own oxygen as well as its fuel, so it can work in the vacuum of space.

Getting into orbit is not mainly about going up; it is about going sideways fast enough. A spacecraft in low orbit is falling towards Earth all the time, but it moves sideways at about 28,000 kilometres per hour, so the ground curves away beneath it as fast as it falls. That speed takes huge amounts of fuel, which is why most of a rocket's weight at launch is propellant, and why rockets drop empty sections, called stages, as they climb.

The space race

The age of spaceflight began on 4 October 1957, when the Soviet Union launched Sputnik 1, a metal ball the size of a beach ball that beeped radio signals as it circled the Earth. In 1961 the Soviet cosmonaut Yuri Gagarin became the first human in space. The United States answered with the Apollo programme, and on 20 July 1969 Neil Armstrong and Buzz Aldrin landed on the Moon. Twelve people walked on the Moon between 1969 and 1972 and brought back 382 kilograms of rock.

Living in orbit

After the Moon landings, the focus shifted to staying in space for longer. Space stations such as the Soviet Mir showed that people could live in orbit for months. Since November 2000 the International Space Station, built by the United States, Russia, Europe, Japan and Canada, has always had people aboard. Astronauts there study how plants grow, how fluids and flames behave without gravity, and how the human body changes, losing bone and muscle unless they exercise for hours each day. China now operates its own station, Tiangong.

Robot explorers

Most of what we know about other worlds comes from robotic spacecraft. Probes have orbited or landed on the Moon, Mercury, Venus, Mars, Jupiter, Saturn, comets and asteroids. Rovers like Curiosity and Perseverance are driving across Mars, studying rocks for signs of ancient water and life. The two Voyager spacecraft, launched in 1977, flew past Jupiter, Saturn, Uranus and Neptune and are now travelling between the stars, still sending faint signals home. New Horizons gave us the first close-up pictures of Pluto in 2015.

Space telescopes have transformed astronomy too. Above the blurring atmosphere, Hubble and the James Webb Space Telescope see galaxies whose light set out more than 13 billion years ago.

Space in everyday life

Thousands of satellites now circle the Earth. They forecast the weather, beam television and internet, guide sat-nav through the GPS system, track storms, wildfires and melting ice, and help farmers, rescuers and scientists. Technologies developed for space have found their way into medical scanners, water filters, cordless tools and the cameras in phones.

What comes next

Reusable rockets that land themselves have made launches cheaper. Space agencies plan to return astronauts to the Moon and eventually to send people to Mars, a journey of many months each way. Big challenges remain: protecting crews from radiation, growing food far from Earth and keeping people healthy on long voyages. But every mission so far has taught us something new about our planet, our neighbours and our place in the universe.