“A key technology for Mars is orbital propellant transfer, like aerial refueling for airplanes, but for rockets. It’s never been done but is technically feasible”

Elon: And one of the technologies that is key for Mars, is doing orbital propellant transfer. So you can think of this like, similar to aerial refueling for airplanes, but in this case it’s orbital refilling of rockets, which has never been done before, it is technically feasible. I always feel like these things are a little NSFW (laughter), sort of.

Listen, you’ve got to transfer fluid somehow, it’s just got to be done! So the two Starships would get together, and one Starship would transfer fuel and oxygen, and most of the mass is oxygen. It is almost 80% oxygen that gets transferred. A little over 20% fuel and so you send a Starship to orbit that is full of payload and then you send up a bunch of other Starships up and then you would refill the propellant on that Starship. And once the propellant tanks are mostly full then you can depart for Mars or the Moon.

This is important technology, which we should hopefully demonstrate next year.

Source: Video from Elon Musk’s 2026 Mars Company Talk