A space rocket plunges earthward, twitching its steering fins and firing gas jets to stabilise itself. It looks for all the world like it is doomed. But as it nears the surface, the motors burn stronger and the rocket slows considerably, landing legs spring from its sides and, as the billowing smoke disperses, it's clear it has touched down upright – and in one piece.

It's a feat that was inconceivable only a decade ago. But after many spectacular failed attempts the Californian rocket maker SpaceX has in the last four months landed an orbital rocket stage four times – once on land in December 2015 at Cape Canaveral, Florida, and in April for the first time on a remote-controlled barge in the mid-Atlantic. And these were not dummy rockets: both were the 40-metre-high first stages of Falcon 9 rockets that had just launched commercial spacecraft into orbit.

By returning rocket stages to Earth for reconditioning and reuse, SpaceX's founder, billionaire Elon Musk, hopes eventually to make spaceflight as economical as commercial aviation. His point: airlines don't throw away a Boeing 747 after every flight, so why do it with spaceships?

Sci-fi has predicted reusable spacecraft for a century or more, and space engineers have experimented with the idea since the mid-20th Century – the partially reusable Space Shuttle is arguably the closest we’ve got. So why has reusability taken so long to be seriously considered?