Flywheels / NEO Retrieval

Well, the H2 is really a waste product in this system, and could be vented into space as exhaust. There is
not really enough of it justify building in a
system to reclaim it, at least on the way there.

During the cruise TO the asteroid, relatively little propellant will be used, so the penalty for venting the hydrogen will be quite minimal.

But during the phase of actually towing the asteroid, the economics might be different.

Some NEO asteroids contain quite a lot of water, so rather than bring water or oxygen from Earth, we
could obtain it locally and electrolyze that to get oxygen propellant.

The higher SI of the Hall thruster means we would
consume much less of the asteroid as propellant than
with a mass driver.

The hydrogen produced could perhaps be stored as metal
hydride. I wonder if there might be oxides present on the NEO which could be reduced using the hydrogen.

CFR