Elon Musk to create rockets that will people from city to city immediately

Mr Elon Musk made the promise at the International Astronautical Congress (IAC) in Adelaide, Australia.

Mr Musk told the audience he aimed to start sending people to Mars in 2024. His SpaceX company would begin building the necessary ships to support the mission next year.

He says he is refocusing SpaceX to work on just one type of vehicle - known as the BFR - which could do all of the firm's current work and interplanetary travel.

Mr Musk first laid out his Mars travel ambitions at the IAC in 2016. Twelve months on, he returned with more detail.

His BFR, although still massive, is now a little smaller at 106m in height and 9m in width.

The major difference compared with the original version, however, was cost, the South African-born American said.

"I think we've figured out how to pay for it. This is very important."

The route to affordability, he explained, was in refocusing all of the company's efforts into the one system - and then using that to meet all its customers' needs.

This means the BFR would launch satellites and service the space station - as SpaceX's Falcon 9 and Dragon capsule do now - but also take people to the Moon and Mars, and do what is termed "point to point" travel on Earth.

"Most of what people consider to be long-distance trips could be completed in less than half-an-hour," he told the Adelaide audience.

"Some of our customers are conservative and they want to see the BFR fly several times before they're comfortable launching [on it]," Mr Musk said.

"So what we plan to do is to build ahead and have a stock of Falcon 9 and Dragon vehicles, so that customers can be comfortable if they want to use the old rocket, the old spacecraft - they can do that because we'll have a bunch in stock.

"But all of our resources will then turn to building BFR."