The founder of SpaceX and Tesla, Elon Musk, said on a Twitter account that his space firm is launching a program to convert carbon dioxide from the atmosphere into rocket fuel.

Billionaire Elon Musk is set to use climate-contributing emissions to create rocket fuel. SpaceX will launch a program to remove carbon dioxide from the atmosphere and use it to power spacecraft. The chairman and CEO of Space Exploration Technologies Corp. announced the project on December 13, shortly after Time magazine named it as Person of the Year.

“SpaceX is launching a program to remove CO2 from the atmosphere and turn it into rocket fuel,” he tweeted. The use of carbon dioxide for space travel “will also be important for Mars,” he added.

Musk’s proposal was quickly criticized by some of his Twitter followers, who questioned the viability of the idea. The new propellant initiative will build on direct air capture (DAC) technology, which is still in its early stages of development.