Satellites and How They Help Us

A satellite is any object that orbits another in space. The Moon is Earth's natural satellite. But since 1957 we have also sent thousands of artificial (human-made) satellites into orbit. Right now, thousands of these machines are circling our planet, quietly helping with all sorts of everyday tasks.

Why does a satellite stay up instead of falling back down? It is actually falling all the time — but it is also moving sideways so fast that it keeps missing the Earth. This perfect balance between falling and racing forward is what we call an orbit. Cut the speed and it would spiral down; speed it up too much and it would fly off into space.

Today satellites do an astonishing number of useful jobs. Communication satellites relay phone calls, television signals, and internet data across the globe. Weather satellites photograph clouds and storms, helping forecasters warn us of bad weather days in advance. Navigation satellites — the GPS system — let your phone tell you exactly where you are.

Satellites are launched by rockets and placed in orbit at different heights. Low Earth orbit satellites are just a few hundred kilometres up and complete one orbit in about 90 minutes. The International Space Station is one of these. Higher up, geostationary satellites sit about 36,000 km above the equator and appear to hover in the same spot, which makes them perfect for TV and communications.

How does GPS know where you are? Your device listens for signals from several navigation satellites at once. By measuring how long each signal took to arrive, it can work out its distance from each satellite, and then pinpoint your exact spot on the map. It usually needs signals from at least four satellites to be accurate.