Availability and delta-v requirements for delivering water extracted from near-Earth objects to cis-lunar space

We have calculated the number of water-bearing near-Earth objects as a function of return-trip delta-v (Δv_RT). First, we combined a model of the near-Earth object's (NEO) orbit and size-frequency distribution with other measurements of their provenance, and the taxonomic distribution of asteroids in the NEO's main belt sources, to calculate the taxonomic distribution of NEOs as a function of their orbital elements and size. Our calculations are in agreement with recent measurements of the ratio of C- and S-complex bodies within the population of small NEOs. Then we developed a simplified mission model to calculate an upper limit on Δv_RT for a mission from an NEO to distant retrograde lunar orbit (DRLO) in cis-lunar space. Combining the first two steps allowed us to develop a synthetic population of low Δv_RT NEOs that includes their taxonomic distribution. Finally, we used measurements of the water-bearing content of the taxonomic classes based on their assumed meteorite associations to calculate the number of water-bearing NEOs as a function of Δv_RT. We find that there are likely thousands of H₂O-rich NEOs larger than about 5 m diameter with Δv_RT≲3kms⁻¹ and the number of objects increases as Δv_RT ³. The rapid increase in the number of objects with Δv_RT suggests that in-situ resource utilization (ISRU) of asteroid-derived water can expand quickly throughout the solar system. NEOs with Δv_RT≲3kms⁻¹ tend to be on Earth-like orbits with semi-major axes a∼1au, eccentricities e≳0, and inclinations i≳0^∘. The small, dark, low Δv_RT NEOs are difficult or impossible to detect with Earth-based telescopes because many orbit the Sun interior to Earth's orbit and others have such long synodic periods that they are rarely visible.