Lots to parse there. (1) the interesting politics that Lunarians would be possessive of volatiles on the moon and not want to spend them on refueling rockets or other exports but rather keep them in a circular economy (2) a believable mass driver doesn’t like like Acela the way you’d picture from Heinlein or O’Neill but looks more like the Paris Gun and goes up in one Starship load ex. the power supply and cooling system and (3) O’Neill never came up with a plausible catcher but I can picture a rotating cone that is in a sort of halo orbit slightly displaced from the L1 or L2 point where cargo is coming in close to the separatrix and not moving that fast.