In 1945 Arthur C. Clarke published his seminal paper on what we would now call communications satellites. He predicted that such ‘extra-terrestrial relay stations' would enable telephone calls to be beamed around the world. His vision came true in the 1960s when the first communications satellites were launched by rocket into very high Earth orbits.
Today there are constellations of satellites in a variety of orbits that carry our phone calls, e-mails and television signals. They form a vital part of the growing global information network. Other spacecraft tell us where we are on the planet – whether in the air, on land or at sea. There are also eyes in the sky – satellites that look down on the Earth, its continents, oceans and atmosphere. We depend on such space platforms to forecast the weather and, increasingly, to tell us how we are affecting the Earth's environments.