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 Nov. 5, 2019, 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 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.
This article originally appeared on Business Insider. Follow @BusinessInsider on Twitter.