Deep Space Industries (DSI) intends to send a fleet of small prospecting spacecraft into the solar system in 2015.

In a decade or so, it hopes to be harvesting metals from the space rocks as well as sources of water and fuel for interplanetary missions.

The 55lb FireFly robots will undertake journeys of two to six months to search for candidate asteroids.

To cut costs, the aim is to hitch rides into orbit with larger communication satellites.

The FireFlies will pave the way for a flotilla of larger 70lb spacecraft equipped to collect samples and bring them back to Earth.

Starting in 2016, the DragonFly craft will be launched on round trips lasting two to four years, depending on the target.

The missions are part of a long-term project to harvest metals and other materials from asteroids passing near the Earth.

They will initially be used to build, equip and fuel satellites and space vehicles, including those being sent on long-distance missions to Mars and beyond.

''Using resources harvested in space is the only way to afford permanent space development,'' said DSI chief executive David Gump.

''More than 900 new asteroids that pass near Earth are discovered every year. They can be like the Iron Range of Minnesota was for the Detroit car industry last century - a key resource located near where it was needed.
''In this case, metals and fuel from asteroids can expand the in-space industries of this century. That is our strategy.''

Water makes up 20 per cent of the mass of some asteroids. Broken down into oxygen and hydrogen, asteroid water could provide a valuable source of propellant for future space missions, including manned trips to Mars, it is claimed.

In addition, the space rocks are enriched with precious metals, including gold and platinum. Some asteroid ores potentially yield more gold than any found on Earth.
DSI has longer term plans to mine platinum-group metals for uses on Earth, such as anti-pollution devices.

''Mining asteroids for rare metals alone isn't economical, but makes sense if you already are processing them for volatiles and bulk metals for in-space use,'' said Mark Sonter, a DSI director.