Elon Musk: “Orbital Refilling Is Essential for Becoming Space-Faring — SpaceX Will Begin Next Year

Elon Musk: Orbital refilling is a key technology needed to become space-faring. SpaceX will start demonstrating it next year.

“A crucial technology that we hope to demonstrate next year is orbital refilling, much like aerial refueling. It's essential for being able to send significant payload to Mars.

You send a ship to orbit with a few hundred tons of payload, but once it gets to orbit, the tanks will be mostly empty. And then you send up additional tanker ships to refill the Mars ship's tank so it can thrust from Earth orbit to Mars and have enough propellant left for landing.

Orbital refilling is not something that's ever been demonstrated before. That would be a brand new technology. We obviously have, at SpaceX, figured out how to dock repeatedly with the space station. So in a lot of ways this is like docking. And in some ways it's easier in that SpaceX is docking with its own craft. But no one has ever demonstrated propellant transfer in orbit to the best of our knowledge. And so, this would be propellant transfer at very large scale.

Full reusability and propellant transfer, those are the key technologies needed for building a city on Mars.”

SpaceX Conversation with Elon Musk and Bill Riley, August 25, 2025