Mining in space is moving from science fiction to commercial reality but metals magnates on this planet need not fear a mountain of extraterrestrial supply - the aim is to fuel human voyages deeper into the galaxy.

Within three years, two firms plan prospecting missions to passing asteroids. When even a modest space rock might meet demand for metals like platinum or gold for centuries, it is little wonder storytellers have long fantasised that to harness cosmic riches could make, and break, fortunes on Earth.

But with no way to bring much ore or metal down from the heavens, new ventures that have backing from some serious - and seriously rich - business figures, as well as interest from NASA, will focus on using space minerals in interplanetary "gas stations" or to build, support and fuel colonies on Mars.

There may be gold up there, but the draw for now is water for investors willing to get the new industry off the ground.

Governments believe it has a future; NASA has a project that may put astronauts on an asteroid in under a decade and on Mars in the 2030s. And if the costs seem high, grumblers are told that one day the new skills might just save mankind from sharing the fate of the dinosaurs - if we can learn how to stop a massive asteroid smashing into Earth.

"We are dreamers," declares the web site of Deep Space Industries (DSI), next to an image of a wheel-like metal station hooked up to a giant floating rock. But what the U.S.-based start-up firm calls the first small steps in a "long play" to develop the resources of space are about to happen.

To read more, click here.