Optimized continuous-thrust round-trip trajectories to ultra-low Δv ISRU targets

We present the results and implications of our optimized round-trip trajectories to thousands of synthetic but realistic ultra-low Δv (≲ 8 ​km ​s−1) asteroids for the purpose of in-space resource utilization (ISRU) of water extracted from the targets. We show that our carpe diem mission scenario works — ISRU missions utilizing ‘hibernating’ spacecraft on loosely-bound orbits in cis-lunar space can begin soon after targets are discovered if the asteroids are rapidly characterized with accurate and precise orbits. Our algorithm identified ultra-low Δv round-trip mission trajectories for 100% of the ISRU targets that approach to within 0.05 au of Earth. The median minimum distance between the targets and Earth during the rendezvous/mining phase is ∼ 0.23 au (∼ 115 light-seconds) while the maximum one-way communication time is ​≲ ​4 ​min. The return-trip missions have a median Δv ∼ 2.9 ​km ​s−1 so that the typical mission returns about 50% of the extracted H2O to cis-lunar space. We estimate a steady-state rate of about 2 water-mining missions per year returning about 100 tonne yr−1 to the Earth-Moon system. Converting the water to LOX/LH2 is ∼ 93% efficient, suggesting that asteroid H2O mining could provide ∼ 93 tonne of bipropellant to cis-lunar space on an annual basis. We applied our mission optimization algorithm to 168 known near-Earth objects (NEO) with orbital elements similar to our synthetic ultra-low Δv population and estimate that almost 95% of the population of ultra-low Δv NEOs remain to be discovered.