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Spin gravity cities fabricated from Near Earth Asteroid rubble piles

A cylindrical, spin gravity space settlement constructed from asteroid rubble like that from the Near Earth Asteroid Bennu. The regolith provides radiation shielding contained by a rigid container beneath the solar panels. The structure is spun up to provide artificial gravity for people living on the inner surface. Credits: Peter Miklavčič et al.*

Scientists and engineers* at the University of Rochester have conceived of an innovative way to capture a Near Earth Asteroid (NEA) and construct a cylindrical space colony using it’s regolith as shielding. In a paper in Frontiers in Astronomy and Space Sciences they propose a spin gravity habitat called Bennu after the NEA of the same name. Readers will recall that NASA’s OSIRIS-REx spacecraft launched in September 2016, traveled to Bennu, collected a small sample in October 2018 and is currently in transit back to Earth where the sample return capsule will reenter the atmosphere and parachute down in Utah later this year.

Near Earth Asteroid Bennu imaged by the spacecraft OSIRIS-REx. Credit: NASA Goddard Space Flight Center

It would be ideal if an asteroid could be hollowed out for radiation shielding and spun up to create artificial gravity. However, it is shown in this paper that this would not work for larger solid rock asteroids because they don’t have the tensile strength to withstand the rotational forces and smaller rubble pile asteroids (like Bennu) would fly apart because they are too loosely conglomerated.

The problem is solved by containing the asteroid in a carbon fiber collapsible scaffolding that initially has the same radius of the asteroid. As the container is spun up, the centrifugal force will cause the disintegrating rubble to push open the expandable cylinder to its final diameter.

“…a thick layer of regolith is created along the interior surface of this structure which forms a shielded interior volume that can be developed for human occupation.”

The mechanism to initiate the rotation of the structure is interesting. Solar arrays on the outer surface would power mass driver cannons which eject rubble tangentially exerting torque to produce spin.

Detailed engineering analysis and simulations are performed to calculate the stresses on a Bennu sized asteroid to create a cylindrical space colony 3 kilometers in diameter. This structure would have a shielded livable space of 56 square kilometers, an area roughly equivalent to Manhattan.

The authors conclude that the physics of harvesting small asteroids and converting them into rotating space settlements is feasible. They note that this approach would cost less and be easier from an engineering standpoint then fabrication of classic O’Neill cylinders. Concepts for asteroid capture and utilization have already been covered on SSP such as TransAstra’s Queen Bee and SHEPHERD.

The University of Rochester News Center provided a good write up of the paper last December.

* Authors of cited paper: Miklavčič PM, Siu J, Wright E, Debrecht A, Askari H, Quillen AC and Frank A – (2022) Habitat Bennu: Design Concepts for Spinning Habitats Constructed From Rubble Pile NearEarth Asteroids. Front. Astron. Space Sci. 8:645363. doi: 0.3389/fspas.2021.645363

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Seeding asteroids with fungi for space habitat soil

Illustration of a process for making soil for space habitats by seeding asteroids with fungi. Credits: Jane Shevtsov

The asteroid belt will be a treasure trove of raw material for space settlers to use to build their habitats, especially the O’Neill-type rotating cylinder variety. To support plentiful green spaces and robust agricultural systems envisioned for these large scale settlements, an abundant source of fertile soil will be needed. But how could the enormous cost of bringing soil from Earth be avoided? An innovative in situ method under development by Jane Shevtsov of Trans Astronautica Corporation may provide the answer. In a just awarded NASA NIAC Phase 1 grant proposal, she explains that the envisaged soil-making process would be a “…natural fit for asteroid mining operations targeting volatiles, as they use carbonaceous asteroids and leave behind leftover regolith that should make a suitable parent material for soil production.”

The Phase 1 research will be broken down into two tasks. In Task 1 the leading fungal species will be identified for experimentation on asteroid material simulant followed by determination of soil production rates of the fungi along with the effects of environmental factors such as temperature, humidity and oxygen concentration. Task 2 will explore various methods of breaking down asteroid regolith by the chosen fungi in the space environment optimizing for productivity and costs, with the ultimate goal of determining the size of a payload to support a reference mission habitat within a feasible timeframe.

In the above diagram, there are hints that the concept may use an inflatable enclosure around the asteroid to retain volatiles, reminiscent of some of the applications of the SHEPHERD asteroid capture architecture previously covered by SSP, in which a gas atmosphere within the enclosure can keep water in a liquid phase so that the asteroid provides a substrate for introduced biological agents for the generation of foodstuffs and other consumables.

Trans Astronautica has been working on their own asteroid capture method which may come in handy when used in combination with the output of Ms. Shevtsov’s project.