San Francisco, Aug 14 (IANS): SpaceX CEO Elon Musk has not stopped at lofty talks of colonising Mars. He has even estimated the cost of having a self-sustaining civilization on the Red Planet which is "between $100 billion and $10 trillion".

Musk tweeted his estimates of building a city on Mars in response to a question posed by the Twitter handle @marstronauts.

So according to the estimate by Musk, building a city on Mars could cost anywhere between 10 per cent of the US' 2019 military budget and three times the the country's 2018 tax revenue, Futurism.com reported on Tuesday.

Musk calculated the approximate future cost of sending a minimum payload to Mars "to nearest order of magnitude", at $100,000 per tonne.

So if building a self-sustaining city on Mars requires a million tonnes of cargo, the cost would be around $100 billion, he calculated.

Musk earlier advocated the need of a "backup" planet.

Speaking in an interview with Axios in November 2018, Musk said that that there is "70 per cent chance that he will go to Mars", despite a "good chance" of him not surviving either on the way or after landing.

SpaceX is building "Starship" (formerly known as the BFR), a fully reusable vehicle designed to take humans and supplies to Mars.