A human mission to Mars will be launched in the next 10 years, the chief executive of Tesla Motors has predicted.
Elon Musk, the founder of the private space transport company SpaceX designs, said he was "hopeful" of a manned mission to the red planet by 2024, even if Nasa is not.
In an interview with CNBC, Musk said he was currently bidding for a Nasa contract against other established firms including Boeing. The company's Dragon V2 will potentially be the next crew carrier headed to the International Space Station.
However, even if SpaceX does not get the contract, he plans to continue to work to put humans on Mars.
"It's possible that we may not win the commercial crew contract. ... We'll do our best to continue on our own, with our own money. We would not be where we are today without the help of NASA.
"I'm hopeful that the first people could be taken to Mars in 10 to 12 years, I think it's certainly possible for that to occur. But the thing that matters long-term is to have a self-sustaining city on Mars, to make life multiplanetary."
Earlier this year, Nasa's chief scientist Ellen Stofan outlined plans for a manned mission to Mars.
Speaking at the Natural History Museum, she said it was essential to send humans to the red planet: "To unambiguously settle the questions of whether there was life on Mars it will take scientists down on the surface."
However, she said the technology needed to send humans is just not ready yet: "We're working to reduce the risks so that people can arrive on Mars happy and healthy and ready to work."