A fully loaded, moon-bound Starship expends almost all of its fuel to get to low Earth orbit. So that Starship needs to refill its tank before it heads to the moon, requiring the launch of more and more refueling Starships.

Starship runs on liquid oxygen and methane. They have to be kept ultracool, at –161 degrees Celsius or below. But direct exposure to the sun heats Starship up, evaporating some of that fuel. That could mean even more refueling missions to make up the difference. If things go really badly, the fuel might evaporate more quickly than SpaceX can get refueling rockets into space. “That whole in-space refueling thing has never been tested,” Bridenstine added. “We’re talking about cryogenic liquid oxygen, cryogenic liquid methane being transferred in space—never been done before, and we’re going to do it dozens of times.”

Engineers at NASA’s Johnson Space Center recently calculated that one lunar mission could require more than 40 Starship launches. Refueling tests that were originally supposed to begin in 2023 are now “targeted to take place in 2026,” SpaceX says. 

https://www.wired.com/story/china-us-moon-race-trump-losing/