We have all sorts of spacecraft orbiting just above a huge reservoir of nitrogen and oxygen. Isn't there some way one could be designed to reach down and pump that air into canisters, and store them until a ship came, picked them up, and left a new supply of empty canister?
Perhaps some type of tether system could make that feasible - electrodynamic or momentum-exchange tethers. The tether could extend down from the main body of the spacecraft in LEO far enough for there to be enough air that it can be pumped into air cylinders. Cylinders and pumps could be lowered down the tether for filling and then drawn back up.
This comes up due to fretting about volatiles on the Moon, which is becoming sort of a pastime. Could some kind of setup like this work? If it could, what hurdles would be involved in making it? Could it be cheaper than shipping from the surface of Earth (or Mars)?