He details how we can use quirks of lunar gravity to use a mass driver to send passive loads to lunar orbit, where they can then be picked up with active, high-efficiency systems and sent elsewhere in the solar system for processing.

Anomalies in the Moon’s gravitational field have been known for some time. Typically, mission planners view them as a nuisance to be avoided, as they can cause satellite orbits to degrade more quickly than expected by nice, simple models. However, according to Dr. Janhunen, they could also be a help rather than a hindrance.

This satellite mapped the Moon’s gravity in great detail and found several places on the lunar surface where a mass driver could potentially launch a passive payload into an orbit that would last up to nine days.

Huh, so I'm understanding it correctly, it might be possible for the lumpy lunar gravitational field to circularize an orbit in lieu of an upper stage. Seems pretty nifty.