Spaceflight and exploration

Spaceflight is the use of rockets and spacecraft to travel beyond the Earth's atmosphere. Reaching space requires overcoming the planet's gravity, which is done with rockets that work by expelling exhaust at high speed and gaining motion in the opposite direction. To stay in orbit rather than fall back, a craft must reach a high horizontal speed so that its path curves around the Earth as fast as gravity pulls it down. Different missions use different orbits, including the geostationary orbit in which a satellite circles the Earth once a day and so appears fixed over one spot.

Crewed exploration reached its best-known milestone with the Apollo programme, which carried astronauts to the Moon and landed the first humans on its surface in 1969. Later, reusable spacecraft such as the Space Shuttle carried crews and cargo to low Earth orbit over many missions, helping to build and service space stations and launch satellites and telescopes. Spaceflight also depends on careful navigation, using the known laws of orbital motion first described by Kepler to plan trajectories that can take a probe across the solar system.

Robotic spaceflight has extended human reach far beyond where astronauts have travelled. Probes have flown past or orbited the terrestrial planets, the giant outer planets and their moons, and some have crossed the heliosphere — the bubble of particles flowing from the Sun — toward interstellar space. Measuring the great distances involved, from the spacing of the planets to the scale of the wider solar system, is central to planning such missions. Together, crewed and robotic spaceflight have transformed knowledge of the solar system and the conditions beyond Earth.

Frequently asked questions

How does a rocket work?

A rocket expels exhaust gas at high speed from its engines and gains motion in the opposite direction, a reaction that works even in the vacuum of space.

What was the Apollo programme?

Apollo was the spaceflight programme that carried astronauts to the Moon, landing the first humans on its surface in 1969.

What is a geostationary orbit?

It is an orbit in which a satellite circles the Earth once per day above the equator, so that it appears to stay fixed over a single point on the surface.