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
Image credit: NASA/Goddard/Arizona State University
The Cislunar Science and Technology Subcommittee of the White House Office Science and Technology Policy Office (OSTP) recently issued a Request for Information to inform development of a national science and technology strategy on U.S. activities in cislunar space.
Dennis Wingo provided a response to question #1 of this RFI, namely what research and development should the U.S. government prioritize to help advance a robust, cooperative, and sustainable ecosystem in cislunar space in the next 10 to 50 years?
In a prolog to his response Wingo reminds us that historically, NASA’s mission has focused narrowly on science and technology. What is needed is a sense of purpose that will capture the imagination and support of the American people. In today’s world there seems to be more dystopian predictions of the future than positive visions for humanity. We seem to be dominated by fear of “…doom and gloom scenarios of the climate catastrophe, the degrowth movement, and many of the most negative aspects of our current societal trajectory.” This fear is manifested by what Wingo defines as a “geocentric” mindset focused primarily within the material limitations of the Earth and its environs.
“The question is, is there an alternative to change this narrative of gloom and doom?”
He recommends that policy makers foster a cognitive shift to a “solarcentric” worldview: the promise of an economic future of abundance through utilization of the virtually limitless resources of the Moon, Asteroids, and of the entire solar system. An example provided is to harvest the resources of the asteroid Psyche which holds a billion times the minable metal on Earth, and to which NASA had planned on launching an exploratory mission this year but had to delay it due to late delivery of the spacecraft’s flight software and testing equipment.
Artist rendering of NASA’s Psyche Mission spacecraft. Credits: NASA/JPL-Caltech/Arizona State Univ./Space Systems Loral/Peter Rubin
Back to the RFI, Wingo has four recommendations that will open up the solar system to economic development and address many of the problems that cause the geocentrists despair.
First, we should make the Artemis moon landings permanent outposts with year long stays as opposed to 6 day “camping trips”. This should be possible with resupply missions by SpaceX as they ramp up Starship launch rates (assuming the launch vehicle and lander are validated in the same timeframe, which seems reasonable). Next, we need power and lots of it – on the order of megawatts. This should be infrastructure put in place by the government to support commerce on the Moon. By leveraging existing electrical power standards and production techniques, large scale solar power facilities could be mass produced at low cost on Earth and shipped to the moon before the capability of in situ utilization of lunar resources is established. Some companies such as TransAstra already have preliminary designs for solar power facilities on the Moon.
Which brings us to ISRU. The next recommendation is to JUST DO IT. This technology is fairly straightforward and could be used to split oxygen from metal oxides abundant in lunar regolith to source air and steel. Pioneer Astronautics is already developing what they call Moon to Mars Oxygen and Steel Technology (MMOST) for just this application.
Conceptual illustration of the Lunar OXygen In-situ Experiment (LOXIE) Production Prototype. Credits: Mark Berggren / Pioneer Astronautics
And lets not forget the wealth of in situ resources that could be unlocked via synthetic geology made possible by Kevin Cannon’s Pinwheel Magma Reactor.
Conceptual depiction of the Pinwheel Magma Reactor on a planetary surface in the foreground and in free space on a tether as shown in the inset. Credits: Kevin Cannon
Of course there is water everywhere in the solar system just waiting to be harvested for fuel and life support in a water-based economy.
Illustration of an ice extraction concept for collection of water on the Moon. Credits: George Sowers / Colorado School of Mines
Wingo’s final recommendation is industrialization of the Moon in preparation for the settlement of Mars followed by the exploration of the vast resources of the Asteroid Belt. He makes it clear that this is more important than just a goal for NASA, which has historically focused on scientific objectives, and should therefore be a national initiative.
“…for the preservation and extension of our society and to preclude the global fight for our limited resources here.”
With the right vision afforded by this approach and strong leadership leading to its implementation, Wingo lays out a prediction of how the next fifty years could unfold. By 2030 over ten megawatts of power generation could be emplaced on the Moon which would enable propellant production from the pyrolysis of metal oxides and hydrogen production from lunar water. This capability allows refueling of Starship obviating the need to loft propellent from Earth and thereby lowering the costs of a human landing system to service lunar facilities. From there the cislunar economy would begin to skyrocket.
The 2040s see a sustainable 25% annual growth in the lunar economy with a burgeoning Aldrin Cycler business to support asteroid mining and over 1000 people living on the Moon.
By the 2050s, fusion reactors provide power and propulsion while the first Ceres settlement has been established providing minerals to support the Martian colonies.
“The sky is no longer the limit”
By sowing these first seeds of infrastructure a vibrant cislunar economy will enable sustainable settlement across the solar system. A solarcentric development mythology may be just what is needed to become a spacefaring civilization.
Artist’s concept of an O’Neill space colony. Credits: Rachel Silverman / Blue Origin
Conceptual rendering of TransAstra Honey Bee Optical Mining Vehicle designed to harvest water from near-Earth asteroids: Credits: TransAstra Corporation
Advocates for mining the Moon and asteroids for resources to support a space based economy are split on where to get started. Should we mine the Moon’s polar regions or would near-Earth asteroids (NEAs) be easier to access?
Joel Sercel, founder and CEO of TransAstra Corporation, is positioning his company to be the provider of gas stations for the coming cislunar economy. In a presentation on asteroid mining to the 2020 Free Market Forum he makes the case (about 10 minutes into the talk) that from an energy perspective in terms of delta V, NEAs located in roughly the same orbital plane as the Earth’s orbit may be easier to access for mining volatiles and rare Earth elements.
Scott Dorrington of the University of New South Wales discusses an architecture of a near-Earth asteroid mining industry in a paper from the proceedings of the 67th International Astronautical Congress. He models a transportation network of various orbits in cislunar space for an economy based on asteroid water-ice as the primary commodity. The network is composed of mining spacecraft, processing plants, and space tugs moving materials between these orbits to service customers in geostationary orbit.
Illustration depicting the layout of a transportation network in an asteroid mining industry in cislunar space. Credits: Scott Dorrington
On the other side of the argument, Kevin Cannon of the Colorado School of Mines in a post on his blog Planetary Intelligence lays out the case for the Moon being the best first choice. All of the useful elements available on asteroids are present on the Moon, and in some cases they are easier to access in terms of concentrated ore deposits. Although delta V requirements are higher to lift materials off the Moon, its much closer to where its needed in a cislunar economy. Trips out to a NEA would take a long time with current propulsion systems. In addition, he thinks mining NEAs would be an “operational nightmare” as most of these bodies are loose rubble piles of rocks and pebbles with irregular surfaces and very low gravity. This makes it hard to “land” on the asteroid, or difficult to capture and manipulate them. In an email I asked him if he was aware of SHEPHERD, a concept for gentle asteroid retrieval with a gas-filled enclosure which SSP covered in a previous post, but he had not heard of it. TransAstra’s Queen Bee asteroid mining spacecraft has a well thought out capture mechanism as well, although this concept like SHEPHERD are currently at very low technology readiness levels.
SHEPHERD-Fuel variant harvesting ice from a NEA and condensing it into liquid water in storage tanks, then subsequent separation into hydrogen and oxygen (top). These tanks become the fuel source for a self-propelling tanker block (bottom) which can be delivered to a refueling rendezvous point in cislunar space. Credits: Concept depicted by: Bruce Damer and Ryan Norkus with key design partnership from Peter Jenniskens and Julian Nott
Cannon also makes the point that there is very little mass in the accessible NEAs when compared to the abundance of elements on the Moon.
“There’s more than enough material for near-term needs on the Moon too, and it’s far closer and easier to operate on.”
Finally, he believes that the Moon would be a better stepping stone to mining the asteroids then NEAs would be. This is because most of the mass in the asteroid belt is located in the largest bodies Ceres and Vesta. Operations for mining on these worlds would be more akin to activities on the Moon then on near-Earth asteroids.
Image of Vesta taken from the NASA Dawn spacecraft. Credit: NASA/JPL
What about moving a NEA to cislunar space as proposed by NASA under the Obama Administration with the Asteroid Redirect Mission? Paul Sutter, an astrophysicist at SUNY Stony Brook and the Flatiron Institute, investigates this scenario and suggests that at least the argument for these asteroids being too far away might be mitigated by this approach, although it would take a long time to retrieve them using solar electric propulsion, as recommended in the article. The trip time might be reduced with advanced propulsion such as nuclear thermal rockets currently under investigation by NASA.
Conceptual illustration of TransAstra’s Sun Flower™ power towers collecting solar energy above a permanently shadowed region on the Moon to provide power for ice mining operations. Credits: TransAstra Corp.
Update 28 August 2021: Take a deep dive into TransAstra’s future plans with Joel Sercel interviewed by Peter Garretson, Senior Fellow in Defense Studies at the American Foreign Policy Council podcast Space Strategy.
Image of Biosphere 2, a research facility to support the development of computer models that simulate the biological, physical and chemical processes to predict ecosystem response to environmental change. Credits: Biosphere 2 / University of Arizona
Once cheap access to space is realized, probably the most important technological challenge for permanent space settlements behind radiation protection and artificial gravity is a robust environmental control and life support system (ECLSS). Such a system needs to be reliably stable over long duration space missions, and eventually will need to demonstrate closure for permanent outposts on the Moon, Mars or in free space. In his thesis for a Master of Science Degree in Space Studies, Curt Holmer defines the stability of the complex web of interactions between biological, physical and chemical processes in an ECLSS and examines the early warning signs of critical transitions between systems so that appropriate mitigations can be taken before catastrophic failure occurs.
Holmer mathematically modeled the stability of an ECLSS as it is linked to the degree of closure and the complexity of the ecosystem and then validated it against actual results as demonstrated by NASA’s Lunar-Mars Life Support Test Project (LMLSTP), the first autonomous ECLSS chamber study designed by NASA to evaluate regenerative life support systems with human crews. The research concluded that current computer simulations are now capable of modeling real world experiments while duplicating actual results, but refinement of the models is key for continuous iteration and innovation of designs of ECLSS toward safe and permanent space habitats.
This research will be critical for establishing space settlements especially with respect to how much consumables are needed as “buffers” in a closed, or semi-closed life support system, when the model’s metrics indicate they are needed to mitigate instabilities. Such instabilities were encountered during the first test runs of Biosphere 2 in the early 1990s.
As SpaceX races to build a colony on Mars, they will need this type of tool to help plan the life support system. Holmer believes that completely closed life support systems for relatively large long term settlements are at least 15 to 20 years away. That means that SpaceX will need to resupply materials and consumables due to losses in their initial outpost who’s life support system in all probability will not be completely closed during the early phases of the project over the next decade. Even SpaceX cannot reduce launch costs low enough to make long term resupply economically viable. They will eventually want to drive toward a fully self sustaining ECLSS. That said, depending on how the company funds its initiatives and sets up it’s supply chains, they may not need a completely closed system for quite some time.
Of course there are sources of many of the consumables on Mars that could support a colony but not all the elements critical for ecosystems, such as nitrogen, are abundant there. There are sources of some consumables outside the Earth’s gravity well which could lower transportation costs and extend the timeline needed for complete closure. SSP covered the SHEPHERD asteroid retrieval concept in which icy planetesimals, some containing nitrogen and other volatiles needed for life support, could be harvested from the asteroid belt and transported to Mars as a supply of consumables for surface operations. TransAstra Corporation is already working on their Asteroid Provided In-situ Supplies family of flight systems that could help build the infrastructure needed for this element of the ecosystem. It may be a race between development of the competing technologies of a self-sustaining ECLSS vs. practical asteroid mining. The bigger question is if humans can thrive long term on the surface of Mars under .38G gravity. In the next century, O’Neill type colonies, perhaps near a rich source of nitrogen such as Ceres, may be the answer to where safe, long term space settlements with robust ECLSS habitats under 1G will be located.
Curt Holmer appeared recently on the The Space Show discussing his research. I called the show and asked if he had used his modeling to analyze the stability of ecosystems sized for an O’Neill-type colony. He said he had only studied habitats up to the size of the International Space Station, but that it was theoretically possible to analyze this larger ecosystem. He said he would like to pursue further studies of this nature in the future.
