Space elevator

Launching into space is a hazardous process. Wouldn’t it be simpler if we could take a lift?

A space elevator is the idea of building a lift connecting the ground to Earth orbit. The first person to consider it was Konstantin Tsiolkovsky, who was also the first to set out the equations that govern orbital rocket launches. In 1895 he was inspired by the new Eiffel Tower, pointing out that if such a tower could be built 35,800 kilometres (22,245 miles) tall, you could go to space just by taking the lift up the tower. To appreciate why – and why this distance – we must consider how orbits work.

When spacecraft launch into space, they don’t just pass out of the atmosphere and start floating. Getting past the atmosphere is fairly easy; the boundary of space is only 100 kilometres (62 miles) up. To be in orbit, a craft has to be travelling fast enough horizontally – about eight kilometres (five miles) per second – that the tendency to be flung away from Earth is balanced by the gravity trying to pull it back down, so that it continuously circles Earth. The higher the orbit, the faster the spacecraft must travel, and the longer it takes to orbit. 35,800 kilometres (22,245 miles) high is an orbit called ‘geostationary’ (GEO). In GEO it takes 24 hours to make one orbit, so spacecraft appear to hover over the same spot on Earth – this is used for satellite TV so you get continuous signal.