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Billionaire Elon Musk is planning to send his Dragon spacecraft to Mars as early as 2018.

Mr Musk has long targeted a trip to Mars and has previously said he can get humans to the red planet by 2026.

His company, SpaceX, is planning "Red Dragon" missions to Mars to test technology for bigger missions.

In a tweet, Mr Musk said that its Dragon 2 spacecraft is "designed to be able to land anywhere in the solar system".

But Mr Musk "wouldn't recommend transporting astronauts beyond Earth-moon region" as the internal area of the spacecraft is only the size of a large car.

"Wouldn't be fun for longer journeys," he said in a tweet.

SpaceX has been developing rockets and has a $1.6bn (£1.08bn) contract with Nasa to supply the International Space Station.

On Wednesday it won an $83m contract from the US Air Force to launch a satellite for GPS navigation services.

It is a significant win for the company as, for the last decade, Lockheed Martin and Boeing have been supplying space launches for the military.

Last December SpaceX had another breakthrough, landing its Falcon-9 unmanned rocket upright.

That was an important development in its plan to cut the cost of space launches by re-using rockets.