Elon Musk thinks it would take 1,000 rockets 20 years to set up a self-sustaining city on Mars

• SpaceX and Tesla CEO Elon Musk tweeted some maths for how long he thinks it would take SpaceX to transport the necessary materials to Mars to build a self-sustaining city.
• Musk said it would take 1,000 of SpaceX's Starship rockets 20 years to transport the cargo.
• Musk has a history of bombastic claims about his hopes to colonize Mars, once outlining a plan to nuke the planet's atmosphere
  
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Elon Musk has made another grand claim about his plans to colonize the red planet with his space exploration company SpaceX.

Speaking at the US Air Force Space Pitch Day on Tuesday, Musk estimated that Starship, SpaceX's 100-passenger reusable rocket design, will cost $2 million to launch.

In a series of follow up tweets, Musk threw out a few more figures about how many rockets will have to bring the necessary amount of cargo to properly set up base on Mars.

"A thousand ships will be needed to create a sustainable Mars city... As the planets align only once every two years," he said. This led him to conclude it would take 20 years to transport one million tons of cargo which would "hopefully" allow for building a self-sustaining Mars base.

By Musk's mathematics, that would mean a total $2 billion spent on launching the rockets - although over 20 years the cost could fluctuate.

Musk has a history of making alarming predictions about his plans to colonize Mars. Notably he has espoused the idea of targeting nuclear weapons to detonate just above the planet's ice caps, thereby causing the frozen water to evaporate releasing CO2 into the air and warming the planet's surface - rendering it more habitable for humans.

The theory has little scientific grounding however. A study published in Nature found there is unlikely to be enough CO2 in Mars' icecaps to engineer the desired greenhouse effect and, even if there were, Mars' atmosphere is constantly leaking into deep space so the gas would gradually disappear.