Posted on

The prospects for mining precious metals and structural materials from asteroids

Artist impression of an asteroid smelting operation. Credits: Bryan Versteeg / spacehabs.com

When humanity migrates out into the solar system we’ll need a variety of elements on the periodic table to build settlements and the infrastructure needed to support them such as solar power satellites. But before that future becomes a reality, there may be a near term market on Earth for precious metals sourced in space as transportation costs come down. There is also the added benefit of moving the mining industry off planet to preserve the environment. Could the asteroid belt provide these materials? Kevin Cannon, assistant professor at the Space Resources Program at the Colorado School of Mines describes the prospects for mining precious metals and building materials for space infrastructure asteroids in a recent paper in Planetary and Space Science. Coauthors on the paper Matt Gialich and Jose Acain, are CEO and CTO, respectively, at the asteroid mining company AstroForge which just came out of stealth mode last year.

The asteroids have accessible mining volume that exceeds that available on the Moon or Mars. This is because only the thin outer crust of these bodies is reachable by excavation, whereas the asteroids are small enough to be totally consumed resulting in higher accessible mining volume.

To-scale accessible mining volume of terrestrial bodies, calculated as the total volume for the asteroids (main belt mass of 2.39 x 1023 kg, mean bulk density of 2000 kg/m3), and as the volume for an outer shell 1.2 km in thickness for the Moon, Mercury, and Mars, equivalent to the deepest open pit mine on Earth. Note the combined volume of the near-Earth asteroids (~5 x 1012 m3) is too small to be visible at this scale. Figure 1 in paper. Credits K.M. Cannon et al.

The authors take a fresh look at available data from meteorite fragments of asteroids. Their analysis found that for Platinum Group Metals (PGMs), the accessible concentrations are higher in asteroids than ores here on Earth making them potentially profitable to transport back for use in commodity markets.

“Asteroids are a promising source of metals in space, and this promise will mostly be unlocked in the main belt where the Accessible Mining Volume of bodies greatly exceeds that of the terrestrial planets and
moons”

PGMs are indispensable in a wide range of industrial, medical, and electronic applications. Some examples of end-use applications include catalysts for the petroleum and auto industries (palladium and platinum), in pacemakers and other medical implants (iridium and platinum), as a stain for fingerprints and DNA (osmium), in the production of nitric acid (rhodium), and in chemicals, such as cleaning liquids, adhesives, and paints (ruthenium).

It has been pointed out by some analysts that flooding markets here on Earth with abundant supplies of PGMs from space will cause prices to plummet, but the advantage of reducing carbon emissions and environmental damage associated with mining activities may make it worth it. The authors also point out that there are probably various uses where PGMs offer advantages in material properties over other metals but are not being used because they are currently too expensive.

Asteroids are rich in other materials such as silicon and aluminum which would be economically more useful for in-space applications. As the authors point out, some companies are already planning for use of metals and manufacturing in space such as Redwire Corporation with their On-Orbit Servicing, Assembly and Manufacturing (OSAM) and Archinaut One, which will attempt to build structural beams in LEO. Another example mentioned in the paper has been covered by SSP: the DARPA NOM4D program with aspirations to develop technologies for manufacturing megawatt-class solar arrays and radio frequency antennas using space materials. Finally, another potential market for aluminum sourced in space is fuel for Neumann Thrusters (although spent upper stage orbital debris may provide nearer term supplies). And of course, silicon will be needed to fabricate photovoltaic cell arrays for space-based solar power.

AstroForge will test their asteroid mining technology on two missions this year. Brokkr-1, a 6U CubeSat just launched on the SpaceX Transporter 7 mission last April, will validate the company’s refinery technology for extracting metals by vaporizing simulated asteroid materials and separating out the constituent components. Brokkr-2 will launch a second spacecraft on a rideshare mission chartered by Intuitive Machines attempting their second Moon landing later this year. Brokkr-2 will hitch a ride and then fly on to a target asteroid located over 35 million km from Earth. The journey is expected to take about 11 months and will fly by the body and continue testing for two years to simulate a roundtrip mission.

Posted on

Lunar-derived propellant fueling a cislunar economy may be competitive with Earth

AI generated image depicting a propellant factory on the Moon. Credits: DALL-E

The economics of an in-space industry based on lunar-derived rocket propellant was examined by Florida Space Institute planetary physicist Philip Metzger in a prepublication paper submitted to arXiv on March 16 . The study will be published in the June issue of Acta Astronautica. Many skeptics of this approach believe that with launch costs plummeting, driven down primarily due to reusability pioneered by SpaceX, it will be cheaper to power the nascent cislunar economy with propellant launched from Earth rather then fuel derived from lunar ice mining.

In his analysis, Metzger examines a cislunar economy of companies that operate geostationary satellites which need to purchase boost services using orbital transfer vehicles fueled by cryogenic hydrogen and oxygen. The question is, would sourcing H2/O2 from ice mined on the Moon be competitive with launching propellant from Earth. He notes that previous studies that favored Earth to solve this problem were flawed because they compared the different technologies for mining water on the Moon (e.g. strip mining, borehole sublimation, tent sublimation, or excavation with beneficiation) rather than analyzing the economics of the cis-lunar economy as a sector.

With that approach in mind, Metzger develops an economic model with figures of merit to assess how various technologies for ice mining compare to Earth sourced propellant. One such parameter is the “gear ratio” G, which in the parlance of orbital dynamics, is the ratio of the mass of hardware and propellant before versus after moving between two locations in accordance with the rocket equation. The other key metric is the production mass ratio Ø, which is the mass of propellant delivered to a specific location divided by the mass of the capital equipment needed to produce the fuel.

The “tent sublimation technology” mentioned in the paper was invented by George Sowers and is featured in his 2019 NIAC Phase I Final Report on ice mining from cold bodies in the solar system covered by SSP previously.

Although G is constrained by the laws of physics, reasonable values are possible and a value of Ø ≥ 35 is the threshold above which lunar propellant wins out. The tent sublimation technology is estimated to have Ø over 400, an order of magnitude higher than the minimum to gain an advantage. Metzger’s new approach took into account that launch costs will eventually come down as far as possible but even then, found that lunar propellant can be produced at a competitive advantage. The only caveat is validation of the TRL and reliability of ice mining technologies.

“Lunar-derived rocket propellant can outcompete rocket propellant launched from Earth, no matter how low launch costs go.”

Although not included in Metzger’s study, a method for extraction of water from lunar regolith is heating by low power microwaves. A recent study found that this technology is effective for extracting water from simulated lunar soil laced with ice. It would be interesting to see if Ø for this technique exceeds the advantage threshold.

Developing the business case for lunar water is the first step in rapidly bootstrapping an off-Earth economy.  Metzger has written about this previously where he sees robotics, 3D printing and in situ resource utilization being leveraged to accelerate growth of a solar system civilization.

Posted on

The limits of space settlement – Pancosmorio Theory and its implications

Artist’s impression of the interior of an O’Neill Cylinder space settlement near the endcap. Credits: Don Davis courtesy of NASA

Its a given that space travel and settlement are difficult. The forces of nature conspire against humans outside their comfortable biosphere and normal gravity conditions. To ascertain just how difficult human expansion off Earth will be, a new quantitative method of human sustainability called the Panscosmorio Theory has been developed by Lee Irons and his daughter Morgan in a paper in Frontiers of Astronomy and Space Sciences. The pair use the laws of thermal dynamics and the effects of gravity upon ecosystems to analyze the evolution of human life in Earth’s biosphere and gravity well. Their theory sheds light on the challenges and conditions required for self restoring ecosystems to sustain a healthy growing human population in extraterrestrial environments.

“Stated simply, sustainable development of a human settlement requires a basal ecosystem to be present on location with self-restoring order, capacity, and organization equivalent to Earth.”

The theory describes the limits of space settlement ecosystems necessary to sustain life based on sufficient area and availability of resources (e.g. sources of energy) defining four levels of sustainability, each with increasing supply chain requirements.

Level 1 sustainability is essentially duplicating Earth’s basal ecosystem. Under these conditions a space settlement would be self-sustaining requiring no inputs of resources from outside. This is the holy grail – not easily achieved. Think terraforming Mars or finding an Earth-like planet around another star.

Level 2 is a bit less stable with insufficient vitality and capacity resulting in a brittle ecosystem that is subject to blight and loss of diversity when subjected to disturbances. Humans could adapt in a settlement under these conditions but would required augmentation by “…a minimal supply chain to replace depleted resources and specialized technology.”

Level 3 sustainability has insufficient area and power capacity to be resilient against cascade failure following disturbances. In this case the settlement would only be an early stage outpost working toward higher levels of sustainability, and would require robust supplemental supply chains to augment the ecosystem to support human life.

Level 4 sustainability is the least stable necessitating close proximity to Earth with limited stays by humans and would require an umbilical supply chain supplementing resources for human life support, and would essentially be under the umbrella of Earth’s basal ecosystem. The International Space Station and the planned Artemis Base Camp would fall into this category.

Understanding the complex web of interactions between biological, physical and chemical processes in an ecosystem and predicting early signs of instability before catastrophic failure occurs is key. Curt Holmer has modeled the stability of environmental control and life support systems for smaller space habitats. Scaling these up and making them robust against disturbances transitioning from Level 2 to 1 is the challenge.

How does gravity fit in? The role of gravity in the biochemical and physiological functions of humans and other lifeforms on Earth has been a key driver of evolution for billions of years. This cannot be easily changed, especially for human reproduction. But even if we were able to provide artificial gravity in a rotating space settlement, the authors point out that reproducing the atmospheric pressure gradients that exist on Earth as well as providing sufficient area, capacity and stability to achieve Level 1 ecosystem sustainability will be very difficult.

Peter Hague agrees that living outside the Earth’s gravity well will be a significant challenge in a recent post on Planetocracy. He has the view, held by many in the space settlement community, that O’Neill colonies are a long way off because they would require significant development on the Moon (or asteroids) and vast construction efforts to build the enormous structures as originally envisioned by O’Neill. Plus, we may not be able to easily replicate the complexity of Earth’s ecosystem within them, as intimated by the Panscosmorio Theory. In Hague’s view Mars settlement may be easier.

Should we determine the Gravity Rx? Some space advocates believe that knowledge of this important parameter, especially for mammalian reproduction, will inform the long term strategy for permanent space settlements. If we discover, through ethical clinical studies starting with rodents and progressing to higher mammalian animal models, that humans cannot reproduce in less than 1G, we would want to know this soon so that plans for the extensive infrastructure to produce O’Neill colonies providing Earth-normal artificial gravity can be integrated into our space development strategy.

Others believe why bother? We know that 1G works. Is there a shortcut to realizing these massive rotating settlements without the enormous efforts as originally envisioned by Gerard K. O’Neill? Tom Marotta and Al Globus believe there is an easier way by starting small and Kasper Kubica’s strategy may provide a funding mechanism for this approach. Given the limits of sustainability of the ecosystems in these smaller capacity rotating settlements, it definitely makes sense to initially locate them close to Earth with reliable supply chains anticipated to be available when Starship is fully developed over the next few years.

Companies like Gravitics, Vast and Above: Space Development Corporation (formally Orbital Assembly Corporation) are paving the way with businesses developing artificial gravity facilities in LEO. And last week, Airbus entered the fray with plans for Loop, their LEO multi-purpose orbital module with a centrifuge for “doses” of artificial gravity scheduled to begin operations in the early 2030s. Panscosmorio Theory not withstanding, we will definitely test the limits of space settlement sustainability and improve over time.

Listen to Lee and Morgan Irons discuss their theory with David Livingston on The Space Show.

Posted on

Making Martian regolith safe for agriculture

AI generated image of crops growing in sealed enclosure within a radiation protected lava tube on Mars. Credits: Microsoft DALL-E Image Creator

Agriculture on Mars is problematic. Even if radiation exposure could be solved (perhaps by locating greenhouses in lava tubes) and sufficient sources of water secured, there is that pesky perchlorate in the soil. Not to worry. The Interstellar Research Group has us covered. IRG, who’s mission is to assist in building a technological, philosophical, and economic infrastructure that advances the goal of establishing outposts throughout the Solar System and, finally, achieving a pathway to the stars, has initiated MaRMIE – the Martian Regolith Microbiome Inoculation Experiment. An informative summary of the project is provided by Alex Tolley over on Centauri Dreams.

SSP has addressed the biological remediation of perchlorates in Martian regolith previously. The research paper linked in that article examined phytoremediation which uses aquatic plants for perchlorate removal and microbial remediation processes utilizing microorganisms and extremophiles. IRG focused on the latter but noted that since the contaminants are water soluble, simply rinsing of the Martian regolith may be a potential solution for removal of the contaminants if sufficient sources of water can be found.

Perchlorates are only one piece of the puzzle to create fertile soil on Mars. So IRG expanded the scope of this initiative to design an experiment to simulate crop growth under the extreme conditions we can expect on Mars, taking into account the composition and pressure of the atmosphere, temperature extremes and high levels of ionizing radiation. The group envisioned a framework of research that would include five phases. The first phase would address the perchlorate issue experimenting with a variety of bacterial and microfungal agents applied to simulated Martian regolith mixed with perchlorates.

In the next phase, the simulated regolith would be conditioned by creating a microbiome to inoculate the regolith. This would include evaluation of pioneer plant species under Martian environmental conditions to transition the regolith into fertile soil.

The third phase would then attempt to grow crops in the mock soil under Martian lighting and atmospheric conditions with increasing ambient pressures until plant growth is satisfactory.

In the fourth phase, the experiment would be repeated with the same settings as in the third phase but decreasing the temperature to find when plant grow tapered off to unacceptable levels. This approach would home in on the optimum conditions for crop growth in the prepared Martian soil.

Finally, the infrastructure to create a farm implementing these conditions on the surface of Mars with appropriate protection from radiation would be defined.

It is not the intention of IRG to actually run these experiments. The output of the effort would be a published paper documenting the known issues and providing an outline of the required studies. Tolley explains that “IRG hopes that this framework will be seen and used as a structure for designing experiments and building on the results of previous experiments, by any researchers interested in the ultimate goal of viable large-scale agriculture on Mars.”

Others are undertaking similar studies. Researchers at the University of Naples Federico II are studying the use of lunar and Martian regolith simulates for plant growth in a paper published last year in Frontiers of Astronomy and Space Science.

Posted on

Solar cell manufacturing using lunar resources

Conceptual rendering of a Blue Alchemist solar cell fabrication facility on the Moon. Credits: Blue Origin

Jeff Bezos’ new initiative called Blue Alchemist made a splash last month boasting that the team had made photovoltaic cells, cover glass and aluminum wire from lunar regolith simulant. This is an impressive accomplishment if they have defined the end-to-end process which (with refinements for flight readiness) would essentially provide a turnkey system to fabricate solar arrays to generate power on the Moon. The announcement claimed that the approach “…can scale indefinitely, eliminating power as a constraint anywhere on the Moon.” Actually, this may not be possible at first for a single installation as surface based solar arrays can only collect sunlight during the lunar day and would have to charge batteries for use during the 14 day lunar night, unless they were located at the Peaks of Eternal Light near the Moon’s south pole. But if scaling up manufacturing is possible, coupled with production of transmission wire as described, a network of solar power stations in lower latitudes could be connected to distribute power where it is needed during the lunar night.

Very few details were revealed about the design outputs of the end products (not surprisingly) in Blue Origin’s announcement, particularly the “working prototype” solar cell. An image of the component was provided but it was unclear if the process fabricated the cells into a solar array or if the energy conversion efficiency was comparable to current state of the art (around 21%). Nor do we know how massive the manufacturing equipment would be, how much periodic maintenance is needed or if humans are required in the process. Still, if a turnkey manufacturing plant could be placed on the Moon and it’s output was solar arrays sourced from in situ materials, it would significantly reduce the costs of lunar settlements by not having to transport the power generation equipment from Earth. This particular process has the added benefit of producing oxygen as a byproduct, a valuable resource for life support and propulsion.

Research into production of solar cells on the Moon from in situ materials is not new. NASA was looking into it as recently as 2005 and there are studies even dating back to 1989. Blue’s process produces iron, silicon, and aluminum via electrolysis of melted regolith, using an electrical current to separate these useful elements from the oxygen to which they are chemically bound. Solar cells are produced by vapor deposition of the silicon. The older studies referenced above proposed similar processes.

It would be interesting to perform an economic analysis comparing the cost of a solar power system supplied from Earth by a company focusing on reducing launch costs (say, SpaceX) with that of a company like Blue Origin that fabricated the equipment from lunar materials. Peter Hague has done just that in a blog post on Planetocracy using his mass value metric.

Hague runs through the numbers comparing SpaceX’s predicted cost per kilogram delivered to the Moon by Starship with that of Blue Origin’s New Glenn. At current estimates the former is 5 times cheaper than the latter. Thus, to best Starship in mass value, Blue Alchemist would have to produce 5kg of solar panels for every 1kg of equipment delivered to the Moon, after which it would be the economic winner. Siting a recent analysis of lunar in situ resource utilization by Francisco J. Guerrero-Gonzalez and Paul Zabel (Technical University of Munich and German Aerospace Center (DLR), respectively) predicting comparable mass output rates, Hague believes this estimate is reasonable.

Perhaps we should not get ahead of ourselves as Blue Origin’s timeline for development of their New Glenn heavy-lift launch vehicle is moving a glacial pace and one wonders if they have the cart before the horse by siphoning off funds for Blue Alchemist. Jeff Bezos is free to spend his money any way he wishes and definitely seems to be in no hurry.

Conceptual illustration of New Glenn heavy-lift launch vehicle on ascent to orbit. Credits: Blue Origin

But SpaceX’s Starship has not made it to space yet either and after we see the first orbital flight, hopefully as early as next week, the company will have to demonstrate reliable reusability with hundreds of flights to achieve economies of scale commensurate with their predicted launch cost of $2M – $10M. As SpaceX has demonstrated with it’s launch vehicle development process it is not a question of if, it is one of when.

Image of full stack Starship at Starbase in Boco Chica, TX. Credits: SpaceX

As both companies refine their approach to space development, will it be the tortoise or the hare that wins the mass value price race for the cheapest approach to power on the Moon? Or will each company end up complementing each other with energy and transportation infrastructure in cislunar space? Either way, it will be exciting to watch.

Posted on

Autonomous conversion of asteroids into rotating space settlements

Artist impression of a rotating space settlement constructed from an asteroid. Credits: Bryan Versteeg, spacehabs.com

When Gerard K. O’Neill first proposed building enormous rotating space settlements at the Earth-Moon Lagrange points back in the 1970s he envisioned many space shuttle flights to launch the initial equipment and people into space. He thought that mass drivers placed on the Moon would be an efficient and cost effective mechanism for lofting copious amounts of lunar regolith needed for radiation shielding to protect colonists aboard the settlements. Alas, the economics of the shuttle did not work out back then, as reusability (among other things) was not ready for prime time, making launch costs a show stopper. Also, O’Neill thought that hundreds of people would be working under weightless conditions in space to fabricate the settlements. This was problematic because of the health hazards of exposure to radiation and microgravity.

All three problems can be solved according to David W. Jensen in an article posted on the ArXiv server. He envisions restructuring an asteroid into a spin gravity space settlement using self replicating robots to process asteroid materials in situ. High launch costs would be solved with a single modest-size probe containing a small number of seed robots that fashion more robots, tools and equipment. This approach bootstraps the colony fabrication through self replicating machines and in situ resource utilization.

“The restructuring process improves the productivity using self-replication parallelism and tool specialization.”

By removing humans from the initial asteroid processing activities, health risks from radiation and the deleterious effects of microgravity would be eliminated. Restructuring of the asteroid would take about a decade, after which colonists would have a rotating space settlement the size of a Stanford Torus providing Earth normal gravity and a safe living space shielded from radiation, ready for buildout and eventual occupation.

Cutaway view of a Stanford Torus space settlement. Credits: Rick Guidice / NASA

The key to this approach is self replication of robots delivered in the initial seed payload which significantly reduces costs by launching only one rocket to the target asteroid. The first machines sent are called replicators, or spiders for short. Four of these spiders with a minimum of supplies use the raw materials of the asteroid to make thousands of copies of themselves plus additional helper machines (tools and equipment). The spiders and helpers cooperate to produce end products of construction materials and the colony structures.

Jensen does not assume total self-replication, meaning that the robots do not need to make complete copies of themselves. A small percentage of more complex mechanisms such as microprocessors are provided in the initial payload as supplemental “vitamins” to finish out the machines. The intent is to minimize the need for humans in the initial construction phase. The objective is to fabricate a basic scaffolding for a rotating space settlement with access to an abundant storehouse of volatiles and metals. The final enclosed structure would then support migration of colonists who would complete construction and add more advanced manufacturing technologies such as solar cell production and microelectronics. As SSP has explained previously, complete closure of self-replicating machines is very challenging, but is not needed in this case.

The technology has wide applications and could be applied to Earth’s desserts, on the surface of the Moon or Mars, or even on the satellites of Jupiter and Saturn.

“We plan to apply and study these concepts for use in lunar, Titan, and Martian environments.”

Jensen’s restructuring process could complement or be combined with other asteroid mining architectures such as the University of Rochester’s approach which builds spin gravity cities starting with a carbon fiber collapsible scaffolding completely encapsulating the target asteroid. As the process matures it could be applied to even larger bodies such as the asteroid Ceres eventually combining settlements into a mega satellite community as envisioned by Pekka Janhunen.

“The equipment and process are scalable and … create a
space station structure that can support a population of nearly
one million people.”

Posted on

Lunar landing pad trade study

Artist’s impression of a lunar landing pad. Credits: SEArch+

When humanity returns to the Moon and begins to build infrastructure for permanent settlements, propulsive landings will present considerable risk because rocket plumes can accelerate lunar dust particles in the bare regolith to high velocities which could result in considerable damage to nearby structures. Obviously, nothing can be done about the first spacecraft that will return to the moon later this decade unless they use their own rocket plume to create a landing pad like the concept proposed in a NIAC Grant by Masten Space Systems (now part of Astrobotic).

Flight Alumina Spray Technique (FAST) instant landing pad deployment during lunar landing. Source: Matthew Kuhns, Masten Space Systems Inc (now Astrobotic)

Therefore, before significant operations can begin on the Moon that require lots of rockets, a high priority will be construction of landing pads to prevent sandblasting by rocket plume ejecta of planned structures such as habitats, science experiments and other equipment. Several methods are currently being studied. Some require high energy consumption. Others could take a long time to implement. Still others are technologically immature. Which technique makes the most economic sense? Phil Metzger and Greg Autry examine options for the best approach to this urgent need in a November 2022 paper in New Space.

A lunar landing pad should have an inner and outer zone. The inner zone will have to withstand the intense heat of a rocket plume during decent and ascent. The outer zone can be less robust as the expanding gases will cool rapidly and decrease in pressure but will still be expanding rapidly, so erosion will have to be mitigated over a wider area.

Landing pad layout showing inner and outer zone measurements proposed in this study (Figure 1 in paper). Credits: Philip Metzger and Greg Autry / New Space – Lunar surface image credit: NASA.

Several processes of fabricating landing pads were examined by the authors. Sintering of regolith is one such technique, where dust grains are heated and fused by a variety of methods including microwave heating or focused solar energy. SSP has reported on the latter previously, but in this study it was noted that that technology needs further development work. Fabricating pavers by baking in ovens in situ was also examined in a addition to infusion of a polymer into the regolith to promote particle adhesion.

An economic model was developed to support construction of landing pads for NASA’s Artemis Program based on experimental data and the physics for predicting critical features of construction methods. Factors such as the equipment energy consumption, the mass of microwave generators compared to the power output needed to sinter the soil to specified thickness, and the mass of polymer needed to infuse the regolith to fabricate the pads were included in the model. Other factors were considered including the costs associated with program delays, hardware development, transportation of equipment to the lunar surface, and reliability.

When varying these parameters and comparing different combinations of manufacturing techniques, the trade study optimized the mass of construction equipment to balance the costs of transportation with program delays. The authors found that from a cost perspective, microwave sintering makes the most sense for both the inner and outer regions of the landing pad, at least initially. When transportation costs come down to below a threshold of $110K/kg then a hybrid combination of microwave sintering in the inner zone and polymer infusion of regolith in the outer zone makes the most sense.

Once astronauts land safely and begin EVAs on the lunar surface, they can keep from tracking dust into their habitat by taking an electron beam shower.

Other lunar dust problems and their risks can be mitigated with solutions covered previously on SSP.

Posted on

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

Posted on

Space development on the Moon, Mars and beyond featured in 2023 NIAC Phase I Grants

Conceptual illustration of an oxygen pipeline located at the lunar south pole. Credits: Peter Curreri

This year’s list of NASA Innovative Advanced Concepts (NIAC) Phase I selections include a few awards that look promising for space development. For wildcatters (or their robotic avatars) drilling for water ice in the permanently shadowed craters at the lunar south pole and cracking it into hydrogen and oxygen, Peter Curreri of Houston, Texas based Lunar Resources, Inc. describes a concept for a pipeline to transport oxygen to where it is needed. Clearly oxygen will be a valuable resource to settlers for breathable air and oxidizer for rocket fuel if it can be sourced on the Moon. The company, whos objective is to develop and commercialize space manufacturing and resources extraction technologies to catalyze the space economy, believes that a lunar oxygen pipeline will “…revolutionize lunar surface operations for the Artemis program and reduce cost and risk!”.

Out at Mars, Congrui Jin from the University of Nebraska, Lincoln wants to augment inflatable habitats with building materials sourced in situ utilizing synthetic biology. Cyanobacteria and fungi will be used as building agents “…to produce abundant biominerals (calcium carbonate) and biopolymers, which will glue Martian regolith into consolidated building blocks. These self-growing building blocks can later be assembled into various structures, such as floors, walls, partitions, and furniture.” Building materials fabricated on site would significantly reduce costs by not having to transport them from Earth.

A couple of innovations are highlighted in this NIAC grant. First, Jin has studied the use of filamentous fungi as a producer of calcium carbonate instead of bacteria, finding that they are superior because they can precipitate large amounts of minerals quickly. Second, the process will be self-growing creating a synthetic lichen system that has the potential to be fully automated.

In addition to building habitats on Mars, Jin envisions duel use of the concept on Earth. In military logistics or post-disaster scenarios where construction is needed in remote, high-risk areas, the “… self-growing technology can be used to bond local waste materials to build shelters.” The process has the added benefit of sequestration of carbon, removing CO2 from the atmosphere helping to mitigate climate change as part of the process of producing biopolymers.

Graphical depiction of biomineralization-enabled self-growing building blocks for habitats on Mars. Credits: Congrui Jin

To reduce transit times to Mars a novel combination of Nuclear Thermal Propulsion (NTP) with Nuclear Electric Propulsion (NEP) is explored by Ryan Gosse of the University of Florida, Gainesville.

Conceptual illustration of a bimodal NTP/NEP rocket with a wave rotor enhancement. Credits: Ryan Gosse

NTP technology is relatively mature as developed under the NERVA program over 50 years ago and covered by SSP previously. NTP, typically used to heat hydrogen fuel as propellant, can deliver higher specific impulse then chemical rockets with attractive thrust levels. NEP can produce even higher specific impulse but has lower thrust. If the two propulsion types could be combined in a bimodal system, high thrust and specific impulse could improve efficiency and transit times. Gosse’s innovation couples the NTP with a wave rotor, a kind of nuclear supercharger that would use the reactor’s heat to compress the reaction mass further, boosting performance. When paired with NEP the efficiency is further enhanced resulting in travel times to Mars on the order of 45 days helping to mitigate the deleterious effects of radiation and microgravity on humans making the trip. This technology could make an attractive follow-on to the NTP rocket partnership just announced between NASA and DARPA.

Finally, an innovative propulsion technology for hurling heavy payloads rapidly to the outer solar system and even into interstellar space is proposed by Artur Davoyan at the University of California, Los Angeles. He will be developing a concept that accelerates a beam of microscopic hypervelocity pellets to 120 kilometers/s with a laser ablation system. The study will investigate a mission architecture that could propel 1 ton payloads to 500 AU in less than 20 years.

Artist depiction of pellet-beam propulsion for fast transit missions to the outer solar system and beyond. Credits: Artur Davoyan

Posted on

Engineering analysis of pressurized lunar lava tubes for human habitation

Conceptual illustration of a lunar base in Mare Tranquilitatis Hole, believed to be an entrance to a lava tube about 100 meters below the lunar surface. Credits: Dipl.-Ing. Werner Grandl

In a new paper in Acta Astronautica Raymond P. Martin, a propulsion test engineer at Blue Origin and Haym Benaroya, a professor of mechanical and aerospace engineering at Rutgers describe the former’s research he carried out as a graduate student under the latter analyzing the structural integrity of lunar lava tubes after pressurization with breathable air. As reported previously on SSP, subterranean lava tubes on the Moon and Mars hold much promise as naturally occurring enclosures that are believed to be structurally sound, thermally stable and would provide natural protection from micrometeoroids as well as radiation. If they could be sealed off for habitation and filled with breathable air, life could be simplified for colonists as they would not have to don space suits for routine activities.

“This paper makes the argument that … lunar lava tubes present the most readily available route to long-term human habitation of the Moon”

Two views of a lunar skylight revealing a potential subsurface lava tube in Mare Ingenii. Credit: NASA/Goddard Space Flight Center/Arizona State University

Martin opens the paper with a history of the discovery and physical characteristics of lunar lava tubes tapping geological data dating back to the Apollo program. The existence of a lava tube is sometimes revealed by the presence of a “skylight”, a location where the roof of the tube has collapsed, leaving a hole that can be observed from space. Using an engineering simulation software called ANSYS, he developed a computer model to assess the structural integrity of these formations when subjected to internal atmospheric pressure.

Martin creates a model for his simulation based on the morphology of a relatively small lava tube known to exist from imagery taken by the Chandrayaan-1 spacecraft, the first lunar probe launched by the Indian Space Research Organisation . This structure averages 120 meters in diameter and was chosen because it has a rille-type opening level to the surface and could be sealed off at two locations. This approach makes sense as a starting point because the cavern would be easy to access and less energy would be be required to pressurize a smaller enclosure. Thus, the amount of infrastructure needed to establish early settlements would be minimized.

The goal of the simulation was to assess the integrity of the enclosed space under varying roof thicknesses and pressurization levels. Failure conditions were defined using commonly employed methods of assessing stability of tunnels in civil engineering and based on lunar basaltic rock general material properties known from testing of samples brought back from the Moon in the Apollo program and lunar meteorites. Finally, a formula was derived for safety factors associated with the failure conditions to ensure robustness of the design.

When running the simulation over various roof thicknesses and internal pressures, an optimum solution was found indicating that it is possible to pressurize a lava tube with a roof thickness of 10 meters with breathable air at nearly a fully atmosphere while maintaining its structural integrity. This would would feel like sea level conditions to people living there.

Being able to pressurize a lava tube for habitation could significantly simplify operations on the Moon as the infrastructure needed to make surface dwellings safe from radiation, micrometeorite bombardment and thermal extremes would be extensive adding costs to the settlement.

“A habitat within a pressurized tube would offer large reductions in
weight, complexity, and shielding, as compared to surface habitats.”

Once a permanent settlement has been established and engineering knowledge advances to enable expansion into larger lava tubes, we can imagine how cities could be built within these spacious caverns, and what it would be like to live and work there. SSP explored just this scenario with Brian P. Dunn, who painted a scientifically accurate picture of such a future in Tube Town – Frontier, a hard science fiction book visualizing life beneath the surface of the Moon. Dunn envisions a thriving cislunar economy with factories producing spacecraft for Mars exploration.

Conceptual illustration of a spacecraft manufacturer inside a lava tube. Credit: Riley Dunn

Martin and Benaroya dedicated their paper to the memory of Brad Blair, a mining engineer who was a widely recognized authority on space resources.

The authors both appeared on The Space Show last December to share insights on this groundbreaking research. Benaroya has been featured previously on SSP with another of his graduate student’s (Rohith Dronadula) thesis on hybrid lunar inflatable structures.

Update March 16, 2023: Martin and Benaroya were featured in The Economist, via a recent licensed post in Yahoo Finance.