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On-orbit refueling is neither very complex nor untried.

Really? We've loaded that much cryogenic fuel before on a manned mission?

Pretty sure it's untried. Theoretically easy, just like launching starship is theoretically easy.

Fuel transfer is mechanically the same whether there are people around or not, and whether you are talking 1 ton of propellant or 100 tons.

It does matter if people aboard, there are more rules and procedures. You need a vessel with safeties that can allow them to eject safely if there's an anomaly.

Of course it's more challenging.

And it does matter if there's more fuel, you have to have valves and pipes that won't freeze after lengthy contact with cryogenic fuel. And you need larger pressure vessels, which scale in volume differently from surface area. It's not at all the same whether you move one ton or a hundred.

The fueling is done without people onboard.

But you still have to build additional safeties into the craft if it's rated for humans. A refueling craft is more complex than a non refueling craft. A crewed craft is more complex than an uncrewed craft (even if no one is aboard). A crewed, refueling craft is more complex still.

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