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Shielded dumbbell L5 settlement

We present a two-sphere dumbbell configuration of a rotating settlement at Earth-Moon L5. The two-sphere configuration is chosen to minimize the radiation shielding mass which dominates the mass budget. The settlement has max 20 mSv/year radiation conditions and 1 g artificial gravity. If made for 200 people, it weighs 89000 tonnes and provides 60 m$^2$ of floorspace per person. The radiation shield is made of asteroid rock, augmented by a water layer with 2 % of the mass for neutron moderation, and a thin boron-10 layer for capturing the thermalized neutrons. We analyze the propulsion options for moving the material from asteroids to L5. The FFC Cambridge process can be used to extract oxygen from asteroid regolith. The oxygen is then used as Electric Propulsion propellant. One can also find a water-bearing asteroid and use water for the same purpose. If one wants to avoid propellant extraction, one can use a fleet of electric sails. The settlers fund their project by producing and selling new settlements by zero-delay teleoperation in the nearby robotic factory which they own. The economic case looks promising if LEO launch costs drop below $\sim$ \$300/kg.