I admittedly don't know too much about this topic specifically, however I'd presume that 'hollow'might be an oversimplification & might be referencing elaborate tunnel-systems (due to any or all like mining, natural caves, underground habitats, etc...) throughout the crust of the moon.
Large-scale mining of Helium-3 on the moon would be the most practical method of fueling interplanetary travel & powering orbital or extraplanetory settlements with fission reactors. Because despite the moon having miniscule amounts of H-3 it still has considerably more than can be found on Earth & would be the most viable source of H-3 until we developed facilities to extract it from the system's gas giants.
I admittedly don't know too much about this topic specifically, however I'd presume that 'hollow'might be an oversimplification & might be referencing elaborate tunnel-systems (due to any or all like mining, natural caves, underground habitats, etc...) throughout the crust of the moon.
Large-scale mining of Helium-3 on the moon would be the most practical method of fueling interplanetary travel & powering orbital or extraplanetory settlements with fission reactors. Because despite the moon having miniscule amounts of H-3 it still has considerably more than can be found on Earth & would be the most viable source of H-3 until we developed facilities to extract it from the system's gas giants.