Multiplier of Producing Fuel on Planets

Robert Zubrin describes the multiplier of producing fuel on the moon or Mars.

Producing oxygen on the moon and with hydrogen (that you brought) would be a 7X multiplier for what you brought. There is also water on the moon which can produce fuel directly. This means a 450 ISP engine with oxygen on the moon would be like a 3000 ISP vehicle.

Producing methane-oxygen fuel on Mars with hydrogen (that you brought) would be a 18X multiplier. A 350 ISP engine would be like a 7000 ISP engine. Mars again can have all of the fuel produced from in situ resources. The weight cost is the weight of the simple systems that would generate fuel.

Zubrin again argues for the mini-starship that would go on top of a SpaceX Falcon 9. A mini-starship could also be carried inside a larger starship.

Zubrin indicates that landing the first Starship on the moon will cause a crater and a lot of debris that could reach lunar and even earth orbit. We need a smaller lunar lander that will first make the landing pads.