The companies vying to turn asteroids into filling stations

Private companies want to mine asteroids for fuel, and build filling stations in space. A bill now in front of the US Congress would help by allowing them to own what they discover - but it might, if passed, meet stiff international opposition.

Chris Lewicki is trying to get water from a stone. A really big stone thousands of miles from Earth.

The president of space mining firm Planetary Resources used to oversee robotic Mars missions at Nasa, but today he's betting big on asteroids.

The chunks of matter hurtling through the cosmos are rich in valuable minerals, he says, but finding water could be like striking liquid gold.

"We can tell from telescopes that look out from mountaintops here on Earth that certain types of asteroids can be relatively abundant in water and water-bearing minerals," he says.

But why is water, which covers much of our planet, so valuable in space?

According to Lewicki, it currently costs nearly $2bn (£1.2bn) per year to launch enough water - six tons per person - to sustain the six astronauts aboard the International Space Station.

But, in addition to providing drinking water, H20 can also be converted into breathable air, and into fuel - liquid hydrogen and oxygen form the most efficient rocket fuel known to man.

Currently, spacecraft must carry all the fuel they require, adding significant weight and driving up the cost of getting beyond Earth's gravity. Once in space, expensive equipment may be abandoned because it's too costly to take back to Earth.

But, says Lewicki, "Imagine being able to get into space and refuel your spaceship [there]."

Asteroids have little gravity, he adds, so landing on and taking off from them does not require too much energy. Their prevalence and proximity to Earth make them valuable potential way stations for refuelling on longer missions into space.

BBC