In yesterday’s post on bypassing the moon, a commenter writes:

As long as you’re going somewhere where there are no in-situ resources to produce fuel with, you’ve got no, repeat NO advantage in terms of the amount of mass you have to put into space to get something somewhere.

Orbital refueling is the same whether it takes place next to a space-station or in the middle of nowhere. You still have to launch all your fuel from Earth. Constructing a fuel-factory base on the moon, on the other hand, means that you only have to get the payload in an agreeable orbit for the booster rockets/tanks to be launched to it from the moon.

This isn’t necessarily the case. Not all payloads are created equal. It’s conceivable that propellants could be launched more cheaply than other things (for instance, with catapults, or relatively unreliable but cheap boosters). So fueling in LEO would make sense under those conditions. In addition, you might be able to deliver propellants to GEO or EML1 much more cheaply than other payloads (e.g., by sending them on a slow tanker with a high Isp, with trip times that wouldn’t be tolerable to humans, particularly through the Van Allen belts). So there is potentially a lot of benefit to orbital fueling even in the absence of ISRU.

[Early afternoon update]

I should note that it’s also not true that “you’ve got no, repeat NO advantage in terms of the amount of mass you have to put into space to get something somewhere.”

If you can deliver propellant to a staging point (like EML1) for your return more cheaply than conventional means, you can in fact reduce the total amount of propellant required for the mission, and that must thus be delivered to space. That’s because it takes propellant to move propellant. If you deliver your return propellant as part of the total lunar insertion payload, it costs just as much, in terms of injection propellant requirements, as a pound of anything else. But if you can get it out there using low-thrust systems or (as Jon Goff suggests in comments) by Weak Stability Boundary trajectories, you can get the propellant there with a lot less propellant. There are really huge payoffs to the ability to store and transfer propellants on orbit, regardless of the cost of launch from earth.