Shepherd: A Concept For Gentle Asteroid Retrieval With A Gas-Filled Enclosure

Sealing a small asteroid within an enclosure enables innovative approaches to the Asteroid Redirect Mission concept that pave the way for future in situ asteroid resource utilization. A sealed enclosure would make it possible to use an introduced atmosphere of xenon gas to detumble and despin the asteroid, and then to push the asteroid by using a steady xenon gas flow inside this enclosure to transfer the force of the spacecraft's exterior solar electric propulsion engine to the asteroid. The gas will affect the cohesion forces of the asteroid, but the differential pressures exerted on the asteroid and surface regolith will be much less than the expected combined cohesion forces of weakly consolidated rubble piles and fragile primitive asteroids, which are of prime scientific interest for planetary defense and origin-of-life studies. That makes it possible to bring such a weakly consolidated asteroid mostly intact to the Earth-Moon system. Once released into lunar orbit, a small intact asteroid can be a viable proving ground for manned missions to more distant and larger asteroids in solar orbit. The development of this technology will benefit future asteroid resource utilization operations, in which enclosures are essential for providing protection from loose regolith and dust, capturing volatiles from icy objects, and enabling the use of reactive gasses in processing the asteroid material.