Conceptual illustration of lunar regolith extraction and beneficiation operations creating feedstock for an oxygen production factory on the Moon. Credits: Grok 2
The European Space Agency (ESA) on October 24 initiated their Second Space Resources Challenge. The Space Resources Challenge is an initiative aimed at stimulating innovation in the field of in-situ resource utilization (ISRU) for lunar and potentially other planetary bodies’ development. Launched in partnership with the Luxembourg Space Agency and their joint European Space Resources Innovation Centre (ESRIC), the competition encourages participants from various backgrounds—including students, startups, and established companies—to develop technologies that can collect, process, and utilize resources on the Moon. The challenge focuses on extracting valuable resources like oxygen for human life support and rocket fuel, as well as metals for construction, from lunar regolith. By fostering a competitive environment, ESA seeks to advance technologies that could reduce the dependency on Earth-supplied materials, thereby making long-term lunar missions more economically viable. The competition not only aims to develop new ISRU technologies but also to build a community of innovators interested in the value of space resources, potentially leading to commercial opportunities in the burgeoning space economy.
Launched on October 24, the second Challenge will focus on extraction and beneficiation of lunar regolith, critical steps in establishing a sustainable human presence on the lunar surface. Teams have until February 20th 2025 to submit proposals. Competition winners can claim €500K for the best performing team and will be awarded a development contract for a feasibility study. A second place prize worth €250K will be awarded to the best team in the category of beneficiation.
The first Challenge, which targeted resource prospecting, took place in 2021 and featured a competition between robotic protypes in ESA’s Lunar Utilisation and Navigation Assembly (LUNA) facility, an advanced research and simulation center designed to support Europe’s efforts in lunar exploration. Located within ESA’s European Space Research and Technology Centre (ESTEC) in the Netherlands, LUNA serves as a testing ground for technologies and systems intended for lunar missions. The facility includes a moon-like environment where various aspects of lunar landing, operations, and human habitation can be simulated.
The Second Resource Challenge will focus on:
Extraction: The collection, hauling and handling of lunar regolith. In LUNA this will be modeled using lunar simulant, which mimics the Moon’s soil. The problem to be solved in this area of the challenge involves designing robotic systems that can collect and transport material efficiently in the harsh lunar environment.
Beneficiation: a term adapted from the terrestrial mining industry, is the process whereby the economic value of an ore is improved by removing the gangue minerals, resulting in a higher-grade product. In the context of ISRU on the Moon, beneficiation will convert regolith into a suitable feedstock through particle sizing and mineral enrichment, preparing it for the next step in the value chain. On the Moon the next process could be extracting valuable resources like oxygen for life support and rocket fuel, and metals for construction or manufacturing, which will be essential for sustaining a long-term human presence on the Moon.
The technology development program will award the teams with the most innovative robotic systems that exhibit autonomy, durability, efficient handling and processing of regolith in the extreme conditions of vacuum, temperature extremes and dust expected in the lunar environment.
Alignment with Strategic Roadmap:
The Second Space Resources Challenge is a pivotal part of ESA’s Space Resources Challenge strategic roadmap to build out the ISRU Value Chain. The next phase of the program will focus on “Watts on the Moon”, i.e. reliable surface power sources for lunar operations. Subsequent phases will develop ISRU applications including extraction of oxygen and water for life support and rocket fuel, with the goal of sustainable in situ factories in the 2030s providing resource supply chains for settlements and the cislunar economy. Integrated systems downstream in the Value Chain, such as Pioneer Astronautics’ (now part of Voyager Space) Moon to Mars Oxygen and Steel Technology (MMOST) application to produce oxygen and metallic iron/steel from lunar regolith, are already under development.
Space Resources Challenge strategic roadmap depicting gradual progression of ISRU development activities. Challenges are planned to be solicited every three years. Credits: ESA
The Second Space Resources Challenge competition is a critical forward-thinking step in ESA’s plans for space development. By concentrating on the extraction and beneficiation of lunar regolith, ESA is not only preparing for the logistics of long-term lunar habitation but also setting a precedent for how future space missions might operate autonomously and sustainably. This challenge underscores ESA’s commitment to innovation, sustainability, and the strategic use of space resources, paving the way for humanity’s next steps in the settlement of the Moon and other worlds in the Solar System.
Conceptual illustration of a SpaceX Starship on a lunar landing pad made from in situ materials by Ethos Space, which plans to use lunar resources for space development. Credits: Starship image: SpaceX; Lunar landing pad and landscape: Grok 2
Kevin Cannon, one of our favorite researchers on ISRU here on SSP, recently appeared on The Space Show to discuss his new position as Senior Lunar Geologist for Ethos Space, a Los Angeles based lunar infrastructure startup that just emerged from stealth last June. Near term (by 2028), the company plans to support the Artemis program by attempting to robotically building landing pads for Starship using lunar regolith, an application SSP covered last year in a ground breaking trade study. Ethos also hopes to extract oxygen from lunar regolith which makes up 80% of rocket propellant and could be a major market segment in a cislunar economy. Incidentally, a few years ago Cannon looked into where on the Moon is the best place to source oxygen.
Long term (20 – 30 years from now) Ethos hopes to use lunar materials to manufacture a sunshade commissioned by world governments that would be placed at the L1 Sun-Earth Lagrange point to combat global warming by blocking 2% of sunlight that reaches our planet. Ethos Space CEO, Ross Centers, is founder of the nonprofit Planetary Sunshade Foundation which issued a report on the state of space based radiation modification about a year ago.
Conceptual illustration of planetary sunshade fabricated from materials sourced on the Moon. Credits: Ethos SpaceDiagram depicting the proposed location for a sunshade located at the L1 Sun-Earth Lagrange point (not to scale). Credits: Planetary Sunshade FoundationRay trace showing that the more acute umbra shadow of a sunshade would not reach Earth while the diffuse penumbra is what would cover our planet (not to scale). Credits: Planetary Sunshade Foundation
Cannon believes that a sunshade is a better geoengineering solution to cool the climate then cloud seeding with sulfur dioxide aerosols as at least one startup company, Make Sunsets, is proposing. Cannon believes this approach, which he says amounts to “using pollution to fight pollution”, will not be very popular with the general public. Make Sunsets counters this argument with an analysis available on their website showing that sulfur dioxide released high in the stratosphere is highly effective in counteracting the warming effect of carbon dioxide while dispersing to negligible levels globally reducing the chance of producing acid rain, the primary concern of sulfur releases in the lower atmosphere. In fact, a paper in Geophysical Research Letters published last August documents evidence that recent regulations on cargo ship emissions limiting sulfur pollutants may have actually contributed to global warming. In 2020 the International Maritime Organization (IMO) instituted new regulations reducing the maximum allowed sulfur emission per kg of fuel in ships by 80%. As a result, artificial clouds created by ship emissions decreased causing northern hemisphere surface temperatures to rise. This example reinforces the need to study geoengineering projects carefully to prevent unforeseen consequences. With respect to the sunshade, Cannon anticipates that international coordination will definitely be required as some countries may have farm land that would actually benefit from anticipated warming so may not want these regions shaded.
Back to the Moon: On The Space Show podcast Cannon mentioned that Ethos will be partnering with Astrolab, a Hawthorne, California based company which has already been awarded a NASA contract to develop a Lunar Terrain Vehicle for the Artemis program. Astrolab’s current concept, dubbed FLEX, is designed to carry two suited astronauts, has a robotic arm for science excavations, and can survive the extreme temperatures at the Lunar South Pole. The rover can be teleoperated remotely from Earth or driven by suited astronauts. The Ethos robotic system for fabricating lunar landing pads would be towed behind this rover while melting the regolith in place forming molten stripes over multiple passes that cool into igneous rock that would be very robust. The mechanism for how the regolith will be melted was not disclosed but if they are guided by the trade study mentioned above, microwave sintering makes the most sense.
Image of Astrolab’s FLEX rover which may tow the Ethos Space robotic system for melting lunar regolith to fabricate landing pads on the Moon. Credits: Astolab
In a post a few years ago on his blog Planetary Intelligence, Cannon makes the case that mining Luna for platinum group metals (PGM) would be more economically feasible than from near-Earth objects (NEO) because of transit times and operational difficulties due the typical NEO being an “…irregular shaped rubble pile–or basically a space sandcastle of loose dust and boulders–held weakly together by cohesion and microgravity, and spinning rapidly.” In addition, terrestrial ore grades are higher than in NEOs potentially making the economics challenging to compete with mines on Earth. The CEO of asteroid mining company Astroforge, Matt Gialich, begs to differ. He thinks there is a business case for mining NEOs and has venture capital backers that agree. Cannon actually collaborated with Gialich on a paper making the case for mining PGMs from main belt asteroids which SSP covered last year. However, the distances involved make near term profits difficult, and Astroforge is now focusing on NEO’s relatively close to Earth. Gailich also appeared on The Space Show this year and addressed the terrestrial ore grade question when I posed it to him, essentially saying that extraction of PGMs from NEOs could be economically competitive with terrestrial mines because they are so deep and have slim profit margins.
Both Ethos and Astroforge will have mission results in the next decade, although they are targeting completely different markets. Hopefully, both will succeed.
Artist’s depiction of a space farm in a 56m radius rotating space settlement. Credits: Bryan Versteeg / Spacehabs.com
Editors Note: This post is a summary of a presentation by Marshall Martin that was accepted by the Mars Society for their conference that took place August 8 – 11th in Seattle, Washington. Marshall was not able to attend but he gave me permission to publish this distillation of his talk. There are minor edits made to the original text with his permission. Marshall is an accomplished Software Engineer with decades of experience managing multiple high tech projects. He has Bachelor’s Degree in Mathematics and Physics from Northwestern Oklahoma State University and an MBA in Management of Information Systems from Oklahoma City University. He is currently retired and farms with his in-laws in Renfrow, Oklahoma. The views expressed by Marshall in this post are his own.
The Earth is a Biosphere supporting life which has evolved and thrived on sunlight as an energy source for more than 3.4 billion years.
Therefore!
You would think a few smart humans could reverse engineer a small biosphere that would allow life to exist in deep space on only sunlight.
Furthermore, eventually the sun will run short of hydrogen and transition into a red giant making the Earth uninhabitable in a few hundred mission years. Long before that time, we need to have moved into biospheres in space growing crops for food. But for now….
The cost of food in space (when launched from Earth) is too high. My Estimates: [1,2]
Launch Vehicle/Mission
Cost/pound (USD)
Cost/Person/Day* (USD)
Space Shuttle to ISS
$10,000
$50,000
Falcon 9 to ISS
$1134
$5670
Atlas V[3] to Mars (Perseverance[4] Mars Rover)
>$100,000
$500,000
2 year mission to Mars based on Atlas V costs
>$100,000
$365,000,000
* Assuming average consumption rate of 5 pounds/day
If we assume that the SpaceX Starship will reduce launch costs to Mars by at least two orders of magnitude, the cost/person/day for a two year mission would still exceed $3 million dollars.
Solution: farming in space
Starting with a rough estimate, i.e. a SWAG (Scientific wild-ass guestimate): – A space station farm sized at 1 acre producing 120 bushels per acre of wheat, 60 pounds per bushel, 4 crops per year, yields 28,000 pounds of wheat per year. Using Falcon 9 launch costs, this produces a crop valued at $31.7M per year. If your space farm is good for 50 years, the crops would be worth $1.585B when compared to an equivalent amount of food boosted from Earth at current launch costs.
SWAG #2 – I believe a space farm of this size can be built using the von Braun “Wet Workshop” approach applied to a spin gravity space station composed of several Starship upper stages at a projected cost of $513M. More on that later.
Do we know how to build a space farm? NO!
So how do we get there?
Biosphere X would be the next generation of ground-based Biospheres. You may consider the original Biosphere 2[5] as the first prototype. As an initial SWAG, it was marginally successful. As the design basis of a working space farm, it is nowhere close.
Image of the iconic Biosphere 2 experiment that attempted two missions, between 1991 and 1994, sealing a team of nine and seven Biospherians, respectively, inside the glass enclosure. The facility is now used for basic research to support the development of computer models that simulate the biological, physical and chemical processes to predict ecosystem stability. Credits: Biosphere 2 / University of Arizona
Biosphere Y will be placed in Equatorial Low Earth Orbit (ELEO) and will be based on the best iteration of Biosphere X.
Biosphere Z will be a radiation hardened version of Biosphere Y for deep space operations.
Key Metrics:
People per acre is an important metric. Knowing how many people are going to be on a space station or spaceship will imply the size of the farming operations required. [6]
Labor per acre is important. It determines how many farm workers are needed to feed the space population (assuming there will be no automation of farm operations). Note: every American farmer feeds about 100 people. Obviously, if it takes 11 farmers to support 10 people in the biosphere, that is a failure. If it takes 2 farmers to support 10 people that implies that 8 workers are available to work on important space projects. Like building the next biosphere that is bigger and better.
Cost per acre will be the major cost of supporting a person in space. There will be a huge effort to reduce the cost of space farmland.
Water per acre required to grow the crops. Since there is a metric for people per acre, the water per acre would include the water in the sewage system. I would think the water for fish farming would be separate or an option.
Soil per acre is literally the amount of dirt needed in tons. This gets fun. Will Biosphere X use hydroponics, aeroponics, light weight dirt, or high quality top-soil? It could be just standard sandy loam. The quality of the soil will have a big impact on what crops can be grown, which in turn, has a big impact on People per acre.
Watts per acre is the power required to operate a farm. Another major cost of food grown in space. Direct sunlight should be very cheap via windows, at least for biospheres in ELEO. In deep space far removed from the protection of Earth’s magnetic field, radiation would pose a problem for windows unless some sort of angled mirror configuration could be used to reflect sunlight adjacently. Electricity from solar panels has been proven by ISS. Power from a small modular nuclear reactors might be a great backup power for the first orbiting biosphere. Note, diesel fuel would be extremely expensive and emissions would cause pollution to the biosphere in space; that implies, farming would be done using electrical equipment.
Improvements based on the Biosphere 2 experience to make a successful Biosphere X:
Updated computers for: better design, data collection, environmental control systems, subsystem module metrics, communication.
Humans: I suggest 2 men & 2 women and work up from there.
Remote ground support: start big and reduce as fast as possible, goal = zero.
Testing Biosphere X:
Can a team live in the biosphere for two years? (See Biosphere 2 test which was 2 years, i.e. a round trip to Mars and back) How much food was produced? Debug the biosphere. Make upgrades and repeat the tests. Calculate Mean Time to Failure (MTTF), Mean Time to Repair (MTTR), system flexibility, cost of operations, farming metrics (see above). etc.
With enough debugging, Biosphere X will become a comfortable habitat for humans of all ages. This will include old people, children, and perhaps babies. I think a few babies should be born in a Biosphere X (e.g. a few dozen?) before proceeding to Biosphere Y. Obviously, it may be challenging to find motivated families willing to make the generational commitment for long term testing required to realize this noble goal of space settlement. Alternatively, testing of Biosphere X could be simplified and shortened by skipping having babies, deferring this step to the next stage.
Biosphere Y potential configuration:
Once a reasonably well designed Biosphere X has been tested it will be time to build a Biosphere Y. This will require figuring out how to launch and build the first one – not easily done! Let’s posit a reasonably feasible design using orbital spacecraft on the near-term horizon namely, the SpaceX Starship. Using nine upper stages with some modifications to provide spin gravity, sufficient volume could be placed in ELEO for a one acre space farm. Here’s one idea on what it would look like:
A central hub which we will call the 0G module will be composed of three Starship upper stages. Since they would not be returning to Earth, they would not need heat shield tiles, the aerodynamic steerage flaps, nor the three landing rockets. Also, there would not be a need for reserve fuel for landing. These weight reductions would allow the engineers to expand Starship and/or make more built-in structure and/or carry more startup supplies.
We will assume the current length of 165 feet with a 30 foot diameter. Three units placed nose-to-tail make 495 feet. But internally there would be 3 workspaces per unit: Oxygen tank, methane tank, and crew cabin. Times three units makes 9 chambers for zero gravity research.
The three units are connected forward and aft by docking hatches. Since the return to Earth engines have been deleted, the header tanks in the nose of Starship (the purpose of which is to offset the weight of the engines) would be eliminated allowing a docking port to be installed in front. In addition, with the 3 landing engines eliminated, there should be room for a tail end docking port. This will allow crew to move between the three Starship units in the 0G hub.
An aside: I am assuming that the nose of the station is always pointing towards the sun. The header tanks in the nose of the first unit could be retained and filled with water to provide radiation shielding to block solar particle events for the trailing units.
The 0G-units will need access ports on each of their sides to allow a pressurized access and structural support tube extending out to the 1G-units located at 100 meters on either side of the hub. This distance is calculated using Theodore W. Hall’s SpinCalc artificial gravity calculator with a spin rate of 3 rpm. There would be three access tubes extending out to connect to each of the 3 Starship 1G units. I assume the standard Starship has an access door which can be modified to connect to the tube.
Conceptual illustration of a possible configuration of an initial Biosphere Y in LEO using modified SpaceX Starship upper stages docked nose to tail. The station spins at 3 rpm around the central 0G hub with the outer modules providing 1G artificial gravity and enough volume for an acre of space farm. Credits – Starship images: SpaceX. Earth image: NASA
One or more standard Starships would deliver supplies and construction materials. They would also collect the three Raptor engines from each modified unit (36 in total) for return to Earth.
I note that the engineering modifications, methods and funding for operations in space to construct Biosphere Y have yet to be determined. However, applying a SWAG for launching the primary hardware to LEO:
This would require 18 starship missions. Using Brian Wang’s estimates of $37M per Starship[21] we get the following cost:
9 Starships times $37M per starship = $333M
18 Starship launches times $10M per launch = $180M
Total SWAG cost: $513M
What’s on the inside?
As mentioned previously, the interior of Biosphere Y will be a Wet Workshop utilizing the empty oxygen and methane tanks in addition to the payload bay volume (roughly 60ft + 39ft + 56ft long, respectively, based on estimates from Wikipedia), for a total length of 155 feet by 30 feet wide for each individual Starship unit. With six 1G Starship units this amounts to about 657, 000 cubic feet of usable volume for our space farm experiencing normal gravity and its associated support equipment (half that for the 0G hub).
Note: Biosphere Y is designed to be placed in Equatorial Low Earth Orbit (ELEO). This orbit is below the Van Allen belts where solar particle events and galactic cosmic ray radiation are reasonably low due to Earth’s protective magnetic field.
Since the first Biosphere Y will spin to produce 1G, eventually experiments will need to be performed to determine the complete Gravity Prescription[12, 13]: 1/2g, 1/3g, 1/6g and maybe lower. You would think this would be required before trying to establish a permanent colony on the Moon and/or Mars in which children will be born. This will probably require several iterations of Biosphere Y space stations to fine tune the optimum mix of plants, animals, and bio-systems.
What other things can be done with a Biosphere Y?
Replace International Space Station
Astronomy
Space Force bases in orbit
Repair satellites
Fueling station
De-orbit space junk
Assemble much larger satellites from kits (cuts cost)
Lunar material processing station
Families including children and babies[13] in space
Biosphere Z:
Once Biosphere Y is proven, it is ready to be radiation hardened to make a Biosphere Z. I assume the radiation hardening material would come from lunar regolith. It is much cheaper than launching a lot of radiation shielding off Earth.
Biosphere Z will be able to do everything that Biosphere Y can do – just further away from Earth.
After an appropriate shake-down cruise (2 years orbiting the Moon, Lagrange 1, and/or Lagrange 2), a Biosphere Z design should be ready to go to Mars. Note several problems will have been solved to ensure positive outcomes for such a journey: • What does the crew do while going to Mars — farming. • Building Mars modules to land on Mars • The crew has been trained and tested for long endurance flights • Other typical Biosphere Y, Z activities
Biosphere S — Major Milestone:
Eventually a biosphere will be manufactured using only space material, thus the designation Biosphere S. Regolith can be processed into dirt. Most metals will come from the Moon and/or Mars surface material. Oxygen is a byproduct of smelting the metals. Carbon and Oxygen can come from the Martian atmosphere. Water can be obtained from ice in permanently shadowed regions at the Moon’s poles or from water bearing asteroids. The first Biosphere S units will probably get Nitrogen from Mars. Later units could get nitrogen, water, and carbon-dioxide from Venus[14]. From the Moon we get KREEP[15]. (potassium, Rare Earth Elements, and Phosphorus) found by the Lunar Prospector mission.
People, plants, livestock, microbes, etc. will come from other Biospheres.
Electronics will probably still come from Earth, at least initially, until technology and infrastructure matures to enable manufacturing of integrated circuits in space.
Artist’s depiction of an agricultural section of Biosphere S, which could be of the Stanford Torus design built mostly from space resources. Credits: Bryan Versteeg / Spacehabs.com
At this point, humans will have become “A space faring species”
In a century, the number of Biospheres created will go from zero to one hundred per year.
Marshall’s Conjecture:
“400 years after the first baby is born in space, there will be more people living in space than on Earth.” After all, from the time of the signing of The Mayflower Compact to present day is about 400 years and we have 300+ million US citizens vs. the United Kingdom’x 68 million.
The explosion of life:
On Earth there are relationships between the number of humans, the number of support animals and plants. There are currently 8 billion people on Earth and about 1 billion head of cattle. I estimate that there are 100 billion chickens, a half billion pigs, etc.
As the number of Biospheres increases in number, so will the number of people, and the number of support plants and animals. To state it succinctly, there will be an explosion of life in space.
So how many Biosphere S colonies can we build?
Let us assume that they will be spread out evenly in the solar “Goldilocks Zone” (GZ). Creating a spreadsheet with Inputs: inside radius (IR), outside radius (OR) and minimum spacing; Output: Biosphere slot count.
Using: IR of 80,000,000 miles, OR of 120,000,000 miles, (120% to 33% Earth light intensity[16], respectively) and spacing of 1000 miles between Biospheres (both on an orbit and between orbits) you get: 40,000 orbits with the inner orbit having 502,655 slots and the outer orbit having 753,982 slots. This works out to over 25 billion slots for Biospheres to fill this region. Assuming 40 people per Biosphere S implies a space population of over a trillion people. And that is only within the GZ. With ever advancing technology like nuclear power enabling settlement further from the sun, there is no reason that humans can’t expand their reach and numbers throughout the solar system, implying many trillions more.
Can we build that many Biospheres?
Let us assume each Biosphere S has a mass of one million tons (10 times larger than a nuclear powered aircraft carrier[17]) That implies 25.1×1015 tons of metal for all of them. 16 Psche’s mass is estimated at 2.29×1016 tons[18]. There are the larger asteroids, e.g. Ceres (9.4×1017tons), Pallas, Juno, Vesta (2.5×1017 tons) and several others. Assuming the Moon (7.342×1019 tons) is reserved for near Earth use. If the asteroids are not enough, there are the moons of Mars and Jupiter. The other needed elements are readily available throughout the solar system, e.g. nitrogen from Venus, water from Europa, dirt from everywhere, so…
YES! My guess is that it will take 100,000 years to fill the GZ assuming a construction rate of about 250,000 Biospheres per year. That implies an expansion of the population by about 2 million people a year ( I acknowledge these estimates don’t take into account technological advances which will undoubtedly occur over such long stretches of time that may lead to drastically different outcomes. Remember! Its a SWAG!)
Is this Space Manifest Destiny? Is it similar to the Manifest Destiny[19] in America from 1840 to 1900? In my opinion, yes! But this is a very high-tech version of Manifest Destiny. The bottom line assumption is that the Goldilocks Zone is empty — therefore — we must go fill it! Just like the frontiersman of the 1800s.
The First Commandment:
This gives a new interpretation of the phrase from the Book of Genesis,
“Go forth, be fruitful and multiply“[20].
Not only are we people required to have children; but we are required to expand life in many forms wherever we go. For secular readers, this may be interpreted as the natural evolution of life to thrive in new ecosystems beyond Earth. Therefore, the big expansion of life will be in space.
It all starts with Biospheres X, Y, and Z optimized for farming in space
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When considering humanity’s expansion out into the solar system, look at the concepts put forward above and ask: “Is this proposal missing a key step or two in the development of biospheres in space?”
Editor’s Note: Marshall appeared on The Space Show on August 27 to talk about his space farming vision. You can listen to the archived episode here.
G.K. O’Neill, The High Frontier, 1976, p. 71 – based on Earth-base agriculture – 25 People/Acre; p72 – Optimized for space settlement (i.e. predictable, controlled climate) – 53 People/Acre.
Conceptual illustration of the ice-mining lunar rover showing its main components including a Radioisotope Power System (RPS) employing Americium-241. Credits: Mazzotti et al. (2024)
Lunar space settlements will need supplies of water for life support and rocket fuel in the coming water economy in cislunar space. Given how expensive it is to launch water out of Earth’s gravity well, mining the liquid gold in situ on the Moon makes the most economic sense. Until recently, it was thought that most of the water on the Moon was trapped in the permanently shadowed regions (PSRs) in craters near the poles. Although recent data from the Indian Space Research Organization’s Chandrayaan-1 mission has found evidence that water and hydroxyl is more wide spread across all latitudes, the icy deposits in the PSRs may be more concentrated and readily accessible then that bound up in regolith away from the poles.
A team of researchers* in the UK and Italy have developed a lunar rover capable of mining for ice in PSRs. In a paper in Acta Astronautica they describe their approach using an innovative power source, a Radioisotope Power System (RPS) using Americium-241 (241Am). One of the problems for ice mining in a PSR is that by definition, the crater floors never see sunlight and they are as cold as 40o K. Solar powered mining equipment would be severely challenged in this environment as its batteries would have to be frequently recharged at the crater rim and the extreme cryogenic temperatures would affect performance. Rovers utilizing an onboard RPS could operate autonomously and continually in a PSR. 241Am has a half life of 432 years enabling decades of power output without the need to refuel. It is the preferred isotope in Europe because it can be economically separated from spent nuclear fuel produced in civil reactors.
The current state of the art for ice mining methods are either mechanical or thermal. Mechanical processes require beneficiation of excavated regolith by either pneumatic, magnetic or electrostatic separation. SSP has covered one such mechanical extraction technique called Aqua Factorem proposed by Philip Metzger at the University of Central Florida. These techniques require prior assessment of the regolith so that the appropriate type of separation method can be tailored to the specific ice content.
Thermal mining employs various ways of heating the regolith to induce sublimation of the icy deposits directly to water vapor which is then refrozen in cold traps for collection. One method is direct solar heating perfected by George Sowers at the Colorado School of Mines. Heating can also be induced by electricity, microwaves or, as proposed by the authors, radioisotope decay heating. Such methods can skip the step of characterizing the regolith for ice content prior to mining operations.
The rover described in the paper is innovative in that the RPS, which would generate a total of 400W, not only provides electrical power, its waste heat could be utilized for ice mining. The electrical power would be generated by thermal input to a Stirling convertor with an efficiency of ∼20% to produce ∼80W of electric power leaving ∼320W for the mining operations. A related program in Europe is developing such a Stirling convertor using 241Am for deep space applications.
Here’s how it works: waste heat from the RPS is directed to a plate in a sealed enclosure lowered beneath the rover to sublimate icy deposits in the lunar regolith. The extracted water is directed to the cold trap via a pressure differential in the sealed environment. A PSR ice mining campaign would be divided into four Phases. Phase I (Roving to Ice Deposit) starts with the rover operating on battery power to traverse the PSR surface to the target area. Once an ice deposit has been located Phase II (Isolating ICE Deposit) would situate the rover over the deposit and lower a sealing enclosure over the deposit beneath the rover. Phase III (Volitile Extraction) directs waste heat from the RPS to the plate initiating sublimation of the ice in the regolith for collection in the cold trap. This phase lasts about 2 days. Finally, Phase IV (Separation from Deposit) raises the sealing walls after full extraction of the ice deposit. The rover is then ready to move on to the next target area and repeat the process.
Validation of the heat transfer and thermal management was caried out using 3D Finite Element Methods on the rover design and anticipated environment conditions, i.e. the temperatures of the primary rover elements including the sublimation plate, cold trap, and volatiles tube. Four simulations of ice mining were conducted under varying conditions of icy regolith volumetric content ( 1.0, 5.0, and 10.0%, respectively). The experiment showed that most element temperatures were stable for each ice content scenario.
From the results of the study, the researchers conclude that “…it is feasible to extract ice in a PSR crater of the lunar poles using the waste heat from a RPS radiated downwards to the icy Lunar regolith by a sublimation plate. Ice deposits within the regolith can be successfully sublimated, volatiles can be collected in a pressure-controlled environment, directed to a cold trap, and captured.”
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* Authors of the paper Ice-Mining Lunar Rover using Americium-241 Radioisotope Power Systems : Marzio Mazzotti 1 2, Hannah M. Sargeant 1, Alessandra Barco 1, Ramy Mesalam 1, Emily Jane Watkinson 1, Richard Ambrosi 1, Michèle Lavagna 2
1 University of Leicester, Space Park Leicester, 92 Corporation Road, LE4 5SP Leicester, UK 2 Politecnico di Milano, Piazza Leonardo da Vinci, 32, 20133 Milano MI, Italy
Concept illustration of Offworld’s Prospector 1 Mobile Excavator. Credits: Dallas Bienhoff / Offworld, Inc.
At the intersection of AI, swarm robotics and mining technology lies the key to sustainable, affordable space development. Offworld, Inc. is on the cutting edge of this frontier with their suite of diverse robot species that when coordinated with collective intelligence, will enable sustainable in situ resource utilization (ISRU) thereby lowering the cost of establishing settlements on the Moon and beyond, while kickstarting a thriving off Earth economy. In a presentation to the Future In-Space Operations (FISO) Telecon on July 24, Space Systems Architect Dallas Bienhoff described Offworld’s plans for an ambitious demonstration mission called Prospector 1.
In April 2023, OffWorld Europe entered into an agreement with the Luxembourg Space Agency to collaborate on a Lunar ISRU exploration program commissioned by the European Space Agency. The multi-year initiative will develop a processing system focused on harvesting and utilizing lunar ice resources. The program will develop a Lunar Processing Module (LPM) to be integrated into a mobile excavator that will be launched to Moon’s south pole on the Prospector 1 mission currently scheduled for late 2027. The goal of Prospector 1 is to demonstrate the capability of processing icy lunar regolith to produce oxygen and hydrogen. The LPM when loaded with icy regolith will process the lunar soil to extract water, then via electrolysis produce oxygen and hydrogen. The module’s hopper is designed to receive up to 50 kg of regolith and batch process 2.5kg/hour. The unit will be housed on a mobile excavator massed at 2500 kg. Offworld has already completed TRL4 testing on the LPM in their Luxembourg office.
The company is exploring a variety of options for generation of power for the mission. Of course landers provide some minimal power but not nearly enough for processing lunar regolith. One promising system under consideration is the Vertical Solar Array Technology (VSAT) under development by Astorbotic which will provide 10kw of power (only in sunlight). But wait, there’s more! Astrobotic announced this month that they were just awarded a Small Business Innovation Research (SBIR) award by NASA to develop a larger version of the array called VSAT-XL capable of delivering 50kw. Designed to track the sun, VSAT is ideal for location at the lunar south pole where the sun’s rays are at very low elevation and provide semi-permanent illumination on the rims of permanently shadowed craters.
Comparison of relative sizes of the two VSAT solar arrays. Credit: Astrobotic
Another innovative alternative is a power source called the Nuclear Thermionic Avalanche Cell (NTAC ) under development by Tamer Space, a company providing a range of power and construction resources for settlements on the Moon, the Cislunar economy and sustainable pioneering of Mars. The device is an electrical generator that converts nuclear gamma-ray photons directly to electric power in a compact, reliable package with high power density capable of long-life operation without refueling. NTAC can provide higher power levels (e.g. starting at 100kw) and is not dependent on the sun to enable operations through the lunar night should Offworld elect to locate their facility far from the Moon’s poles or in permanently shadowed regions. Tamer described their technology at the 2023 Space Resources Roundtable
Image of a research prototype of the Nuclear Thermionic Avalanche Cell: Credit: Tamer Space
After Propector 1, Offworld’s follow on plans envision a second Prospector 2 to be launched in the 2029 timeframe. This mission will ramp up capability to include multiple robot species such as an excavator, hauler, and processor. In addition, liquefaction will be added to the process stream (not just gaseous products) and pilot plant capabilities will be demonstrated to reduce risk for the next mission. In 2031, a formal pilot plant will be established with multiple excavators and haulers. The facility will have a fixed processing plant and storage facilities capable of producing tons of water, oxygen, and hydrogen. By the end of 2034, OffWorld plans to launch an industrial scale ISRU plant with output of 100s of tons of volatiles, elements and bulk regolith per year.
Bienhoff said at the conclusion of his presentation that Offworld’s long term vision for lunar operations include: “Industrial scale ISRU, 10s – 100s of tons of product per year – by product [I mean] that’s processed regolith, that’s oxygen, that’s hydrogen, that’s water, that’s perhaps metals. We plan to monetize or use every gram we excavate. That’s a tall order, but in order to have a thriving lunar community, we need to produce as much as we can on the Moon, for the Moon, before we think about exporting from the Moon.”
Conceptual illustration of a Lunar Power Station beaming power to facilities on the Moon for energy intensive in situ resource processing . Credit: Astrostrom GMBH
Settlements on the Moon will eventually need to “live off the land” via in situ resource utilization (ISRU). This approach is essential to make settlements economically feasible and self sustaining, obviating the need to expensively import materials up out of Earth’s gravity well. Before we can utilize resources in situ on the Moon we need to understand how to process them there. Researchers at the University of Waterloo in Toronto, Canada are developing technologies for in situ resource processing (ISRP) of lunar soil to produce useful materials, but they will need power. Lots of it.
In a paper presented last October at the 74th International Astronautical Congress in Baku, Azerbaijan, Waterloo Department of Mechanical and Mechatronics Engineering Master of Science Candidate Connor MacRobbie and Team describe how a space-based solar power (SBSP) satellite in lunar orbit could provide the juice for several energy hungry processes that could generate consumables and building materials from lunar regolith.
The study includes a survey of the scientific literature on lunar regolith processing techniques under development, some with experimental results, that would benefit future lunar settlements. Using electrolysis, chemical reduction, pyrolysis and other reactions these methods can be used to extract metals, oxygen, water and other useful commodities from lunar regolith. The techniques have well established pedigrees on Earth, but will need further development for efficient operations on the Moon and will require very elevated temperatures. Thus, the need for an abundant power source like SBSP.
One such promising process is Molten Regolith Electrolysis (MRE). In this method, lunar soil is heated to the melting point in an electrolytic cell. When voltage is applied across the cathode and anode in the cell, the molten regolith decomposes into metal at the cathode and oxygen at the anode, both of which can be collected and stored for use by settlers. No inputs or materials are needed from Earth, only a local power source to melt the untreated regolith.
One of MacRobbie’s supervisors is Dr. John Wen, director of the Laboratory for Emerging Energy Research (LEER) at Waterloo. With the help of Wen and LEER, the Team developed a novel material processing method for MRE. In molten regolith solutions, the constituents and their oxides can be separated by an applied voltage enabling extraction from the solution. Because each individual oxide decomposes at different values, stepping the voltage will facilitate sequential removal and collection of the lunar soil constituents, e.g. iron, titanium, aluminum, silicon, and others; which can be utilized for building and manufacturing. The new method could reduce the cost of processing and provide purer end products. The Team will continue working with LEER on the design of the equipment toward proof of concept with small batches aiming for accurate and repeatable successive extractions of materials using MRE. The only remaining step would be to qualify flight-ready hardware for experiments on the Moon.
In another project LEER is investigating lunar regolith as an input to a power source in space for heating or manufacturing. The embedded metal oxides in lunar soil, when combined with a metal like aluminum, produce thermal energy via a thermite reaction. The aluminum could be sourced from defunct satellites in Earth orbit which has the added benefit of helping to address the orbital debris problem.
Other groups like Swiss-based Astrostom GMBH with their Greater Earth Lunar Power Station are already working on SBSP solutions to provide ample power for lunar surface settlements which could provide sufficient electricity for Waterloo’s ISRP technology. The Astrostom approach would place the power satellite at the L1 Earth-Moon Lagrange point, a location between the Earth and Moon at a distance of 60,000 km above lunar surface. Although not a gravitationally stable location, the station would could maintain a fixed point above a lunar ground station on the Moon’s nearside with minimal station keeping propulsion systems.
AI generated image of a rotating space station in Earth orbit providing 1g of artificial gravity in the outer ring, with partial gravity in the inner ring and microgravity at the central hub. Credits: Microsoft Designer
SSP has been covering research on artificial gravity (AG) and its impact on space settlement for years. Many of these posts have focused on the Gravity Prescription for human physiology with particular interest in reproduction as humanity will want to ensure that our space settlements are biologically self sustaining (meaning we will want to have children and raise them there). Should we discover that gravity levels on the Moon or Mars are not conducive to couples raising healthy offspring, rotating space settlements with AG may be our only long term option. But there are many other benefits that spin gravity cities can provide for settlers. In a position paper published online last May in Acta Astronautica, gravity researcher Jack J.W.A. van Loon leads a team of European scientists in an exploration of the possibilities and advantages of rotating space stations providing AG. Van Loon founded and manages the Dutch Experiment Support Center (DESC), which provides user support for gravity related research. This study posits a toroidal orbital station large enough and rotating at a sufficient rate to provide 1g of AG in an outer ring, with an intermediate location for partial gravity laboratories and a nonrotating microgravity research facility in a central module.
From an engineering and human factors perspective, pre-flight training would be simplified because practice operations and procedure planning can be performed on the ground in Earth’s normal gravity. Microgravity environments present challenges for physical phenomena like fluid flow, condensation, and heat convection. Provision of a gravity vector eliminates many of these problems simplifying design and use of equipment. This would also reduce development time.
Life support systems utilizing plants to provide breathable air and nutritional sustenance function more naturally and would be less complex in a biosphere with AG. Since plants evolved on Earth to develop gravitropism with roots growing down relative to a gravity vector and shoots sprouting upward, there is no need to develop complex systems to function in microgravity for proper water and nutrient supply as was necessary for NASA’s Passive Nutrient Delivery System aboard the ISS. There would be easier application of hydroponics systems and vertical farming could be leveraged in habitats with AG while harvested fruits and vegetables can be easily rinsed prior to consumption.
With respect to operations, tasks are similar to normal ground based activities so again, less training would be required. Clutter would be reduced and tie downs for tools that tend to float away in microgravity are not necessary. Schedule management would be improved because there would be less time spent on the extra exercise necessary to counteract health problems induced by exposure to microgravity. Activities like showering and sleeping can be challenging in the absence of gravity, so AG would improve the quality of life in regard to these and other routines we take for granted on Earth.
As readers of SSP are aware, the well documented deleterious effects of exposure to microgravity would be mitigated for crews in an AG environment. Such exposure could preserve crew health by preventing losses in bone and muscle mass, cardiovascular deconditioning, weakening of the immune system, vision changes, cognitive degradation and many other spaceflight induced pathologies as documented in the paper’s references. For tourists or visiting researchers, disorientation and days-long adjustment to microgravity due to Space Adaption Syndrome would be prevented.
Safety would be enhanced as well. For instance, combustion processes and flames behave very differently in microgravity making fire suppression less well understood when compared to normal gravity, necessitating development of new safety procedures. Free floating liquids and tools tend to move around unrestricted causing hazards that could potentially short out electrical equipment. Microorganisms and mold could present a health hazard as humidity control is problematic without a gravity vector. Surgery and medical procedures have not been developed for weightless conditions, requiring specially designed equipment and processes. Liquids drawn from vials containing drugs behave differently in microgravity because of surface tension effects. As mentioned above, training for all activities and equipment designed for use in Earth-normal gravity can be performed ahead of time on the ground. Testing of flight hardware would be simplified as it would not need to be redesigned for use in microgravity. Finally, decades of health studies on astronauts in space under microgravity conditions have found that pathological microorganisms are less responsive to antibiotics while at the same time, become more virulent. AG could make these microbes respond as expected on Earth.
The space station proposed in this paper would include an inner ring housing hypogravity facilities where AG equivalent to levels of the Moon and Mars could be provided for investigators to study and tourists to experience. Mammalian reproduction could be studied in ethical clinical experiments to determine if conception, gestation, birth and maturation to adulthood is possible in lower gravity over multiple generations, starting with rodents and progressing to higher primates. The central module would provide a microgravity science center for zero-g basic research or manufacturing where scientists could perform experiments then return to the outer ring’s healthy 1g conditions.
The author’s budgetary analysis found that the cost of such a facility would be about 5% higher than a microgravity habitat due to increased mass for propulsion and supplementary structures, but the benefits outlined above would be an acceptable trade off enabling a better quality of life for tourists and permanent inhabitants. This concept could be the first step in validating health studies and living conditions in artificial gravity informing the design of larger free space settlements.
Conceptual illustration depicting the design features of a Korean Space Solar Power Satellite (K-SSPS) Credits: Joon-Min Choi, Su-Jin Choi, Sang-Hwa Yi via Creative Commons License CC by 4.0
Researchers from the Korea Aerospace Research Institute (KARI) and the Korea Electrotechnology Research Institute (KERI) describe a concept for a Korean Space Solar Power Satellite in a new publication called the Journal of Space Solar Power and Wireless Transmission. Dubbed K-SSPS, its components would be launched with reusable rockets, robotically assembled and tested in LEO, then boosted to geostationary orbit (GEO) using solar electric thrusters powered by its own solar cell array.
The baseline conceptual design for K-SSPS provides 2GW of delivered power to the ground collected by a 4km diameter rectenna located in the Demilitarized Zone. There is sufficient space in this region for 60 rectennas of this size for a total collected power of 120 GW. In terms of electricity generation, such a system would provide a terawatt-hour of electricity per year which exceeds South Korea’s electricity consumption in 2021.
This study also addresses disposal of the system after its useful life estimated to be about three decades, Since such massive systems spanning an area measuring several square kilometers would present a rather large cross section increasing the risk of collision with other decommissioned satellites in the usual graveyard orbit located 235 km above GEO, the authors propose a novel but controversial approach: controlled crash landing the spent satellite in a safe zone on the far side of the Moon. This would enable future colonies on the Moon to harvest these valuable Earth-sourced materials from the impact zone, recycling them into useful commodities to help sustain lunar operations. Care would have to be taken to ensure that the structure is guided to a designated area far from established infrastructure, most of which (if not all) would be located on the near side facing Earth. Not considered in the study was recycling and/or repurposing the K-SSPS materials in space using material processing technology like Cislunar Industries’ Modular Space Foundry (previously Microspace Foundry).
South Korea’s space agency, the Korea Aerospace Research Institute (KARI), has set a goal of a test system deployment in LEO by 2040, with a full scale system in GEO by 2050. Since this effort will take considerable development time and significant financial investment, KARI plans a small-scale two-satellite pilot system demonstration in LEO within the next decade to validate the wireless power transmission technology and the deployment mechanisms. The pilot system, which was described in a paper presented at the 73rd International Astronautical Congress in September 2022, will be placed in a sun synchronous orbit and features a solar panel equipped antenna array beaming power to a receiver satellite 100m away, in a sun synchronous orbit.
Diagram depicting the operational concepts planned over the mission life of the KARI pilot space solar power demonstration. Credits: Joon-Min Choi, Su-Jin Choi, Sang-Hwa Yi via Creative Commons License CC by 4.0
KARI and KIRI have described their case studies on a space solar power program as a renewable energy option for Korea to help address global efforts to achieve net zero greenhouse gas emissions by 2050. This paper summarizes their concept design for a 2GW space solar satellite highlighting gaps in the economic and technological knowledge needed for success, proposed a responsible and sustainable disposal method, and outlined an achievable architecture for a near term pilot demonstration within a decade. Korea joins other global development efforts that SSP has been following with their own unique approach to space-based solar power (SBSP).
However, doubters have been surfacing recently highlighting the significant engineering and economic challenges that need to be addressed for SBSP to be competitive with ground-based renewable energy sources and backup storage systems, the technology of which are rapidly developing and improving. One skeptic, former European Space Agency engineer Henri Barde, published an article in IEEE Spectrum arguing that among other things, designers will have a significant challenge shaping and aiming the microwave beam of a kilometer-scale phased array antennae. In his opinion, this and other engineering obstacles will not be solved until fusion energy will be commercially available. In a rebuttal on LinkedIn, CEO of SBSP startup Virtus Solis John Bucknell responded that his company has proprietary software that can simulate greater than 2km transmission apertures and that SBSP is in the engineering phase while fusion is still in R&D, the complexity of which makes capital and operating costs a big unknown for commercialization.
NASA has yet again kicked the can down the road, claiming in their most recent study that expected greenhouse gas emissions and the cost of space hardware for current design options will be on a par with existing renewable electricity technologies and therefore recommends further study to close several technology gaps for SBSP to make economic sense. The next few years will be critical for engineering testing, not only for Korea’s pilot satellite, but Virtus Solis‘s in-space plans and Northrup Grumman’s end-to-end test in 2025 of their Space Solar Power Incremental Demonstrations and Research prototype system. Once in-space prototype testing demonstrates sufficient feasibility to retire technical risks, venture capital investors may feel comfortable funding subsequent operational phases toward profitable commercialization.
Artist’s depiction of the NASA Volatiles Investigating Polar Exploration Rover (VIPER) locating and assessing the concentration of ice and other resources near the Moon’s South Pole. Credits: NASA / Daniel Rutter
NASA and space settlement advocates are justifiably excited about resources on the Moon, especially water ice known to be present in permanently shadowed regions (PSR) at the lunar poles, because of it’s potential as a source of oxygen and fuel that could be sourced in situ saving the costs of transporting these valuable commodities from Earth. But how much ice is actually available, accessible and can be processed into useable commodities? In other words, in terms defined by the U.S. Geological survey, what are the proven reserves? A reserve is a subset of a resource that can be economically and legally extracted.
By way of background, under NASA’s Moon to Mars (M2M) Architecture where the agency is defining a roadmap for return to the Moon and then on to the Red Planet, an Architecture Definition Document (ADD) with the aim of creating an interoperable global lunar utilization infrastructure was released last year. The goals articulated in the document are to enable the U.S. industry and international partners to maintain continuous robotic and human presence on the lunar surface for a robust lunar economy without NASA as the sole user, while accomplishing science objectives and testing technology that will be needed for operations on Mars.
Of the nine Lunar Infrastructure (LI) goals in the ADD, LI-7 addresses the need to demonstrate in situ resource utilization (ISRU) through delivery of an experiment to the lunar South Pole, the objective of which would be demonstrating industrial scale ISRU capabilities in support of a continuous human lunar presence and a robust lunar economy. LI-8 aims to demonstrate a) the capability to transfer propellant from one spacecraft to another in space; b) the capability to store propellant for extended durations in space and c) the capability to store propellant on the lunar surface for extended durations – defining the objective to validate technologies supporting cislunar orbital/surface depots, construction and manufacturing maximizing the use of in-situ resources, and support systems needed for continuous human/robotic presence.
To accomplish these goals NASA initiated a series of Lunar Surface Science Workshops starting in 2020. The results of workshops 17 and 18 held in 2022 were summarized last January in a paper by Neal et al. in Acta Astronautica and discussed recently at a Future In-Space Operations (FISO) Telecon on 2/14/2024 in a presentation by Lunar Surface Innovation Consortium (LSIC) members Karl Hibbitts, Michael Nord, Jodi Berdis and Michael Miller. These efforts identified a conundrum: there is not enough data to establish how much proven reserves of lunar water ice are available to inform economically viable plans for ISRU on the Moon. Thus, a resource prospecting campaign is needed to address this problem. International cooperation on such an initiative, perhaps in the context of the Artemis Accords, makes sense to share costs while enabling the signatories of the Accords (39 as of this post) to realize economic benefits from commerce in a developing cislunar economy.
The campaign concept proposes a 3-tiered approach. First, confirming ice is present in the PSRs near potential Artemis landing sites – this could be done by low altitude orbital reconnaissance using neutron spectroscopy, radar and other techniques. Next, surface rovers already on the drawing board such as the Volatiles Investigating Polar Exploration Rover (VIPER), would be deployed to locate specific reserves.
Finally, detailed characterization of the reserve using rovers leveraging capabilities learned from VIPER and optimized for reconnaissance in the PSRs. Some technological improvements would be needed in this final phase to address power and long duration roving under the expected extreme conditions. Nuclear power sources and wireless power beaming from solar arrays on the crater rims, both requiring further development, could solve these challenges. This technology will be directly transferrable to equipment needed for excavation, which will face the same power and reliability hurdles in the ultra cold darkness of the PSRs.
As mentioned in the FISO presentation and pointed out by Kevin Cannon in a previous post by SSP, how water ice is distributed in lunar regolith “endmembers” is a big unknown and could be quite varied. Characterization during this last phase is paramount before equipment can be designed and optimized for economic extraction.
Artist’s impression of different types of lunar water ice / regolith endmembers, characterization of which will be required before extraction methods and equipment can be validated. Credits: Lena Jakaite / strike-dip.com / Colorado School of Mines
The authors of the paper acknowledge that coordinating an international effort will be difficult but involving all stakeholders will foster cooperation and shape positive legal policy within the framework of the Artemis Accords to comply with the Outer Space Treaty.
From the conclusion of the paper:
“If the reserve potential is proven, the benefits to society on Earth would be immense, initially realized through job growth in new space industries, but new technologies developed for sending humans offworld and commodities made from lunar resources could have untold important benefits for society back here.”
George Sowers, whose research was referenced in the paper and covered by SSP, believes that “Water truly is the oil of space” that will kickstart a cislunar economy. Once reserves of lunar water ice are proven to exist through a prospecting campaign and infrastructure is placed to enable economically feasible mining and processing for use as rocket fuel and oxygen for life support systems, technology improvements and automation will reduce costs. If it can be made competitive with supply chains from Earth lunar water will be the liquid gold that opens the high frontier.
Artist rendering of a family living in a rotating free-space settlement based on the Kalpana Two design, with a length of 110m and diameter of 125m. Credits: Bryan Versteeg / Spacehabs.com
This post summarizes my upcoming talk for the Living in Space Track at ISDC 2024 taking place in Los Angeles May 23 – 26. The presentation is a distillation of several posts on the Gravity Prescription about which I’ve written over the years.
Lets start with a couple of basic definitions. First, what exactly is a space settlement? The National Space Society defined the term with much detail in an explainer by Dale L. Skran back in 2019. I’ve extracted this excerpt with bolded emphasis added:
Space Settlement is defined as:
“… a habitation in space or on a celestial body where families live on a permanent basis, and that engages in commercial activity which enables the settlement to grow over time, with the goal of becoming economically and biologically self-sustaining …”
The point here is that people will want to have children wherever their families put down roots in space communities. Yes, a “settlement” could be permanent and perhaps inhabited by adults that live out the rest of there lives there, such as in a retirement community. But these are not biologically self-sustaining in the sense that settlers have offspring that are conceived, born and raised there living out healthy lives over multiple generations.
Next we should explain what is meant by the Gravity Prescription (GRx). First coined by Dr. Jim Logan, the term refers to the minimum “dosing” of gravity (level and duration of exposure) to enable healthy conception, gestation, birth and normal, viable development to adulthood as a human being…over multiple generations. It should be noted that the GRx can be broken down into at least three components: the levels needed for pregnancy (conception through birth), early child development, and adulthood. The focus of this discussion is primarily on the GRx for reproduction.
We should also posit some basic assumptions. First, with the exception of the GRx, all challenges expected for establishment of deep space settlements can be solved with engineering solutions (e.g. radiation protection, life support, power generation, etc…). The one factor that cannot be easily changed impacting human physiology after millions of year of evolution on Earth is gravity. We may find it difficult or even impossible to stay “healthy enough” under hypogravity conditions on the Moon or Mars, assuming all other human factors are dealt with in habitat design.
Lets dive into what we know and don’t know about the GRx. Several decades of human spaceflight have produced an abundance of data on the deleterious effects of microgravity on human physiology, not the least of which are serious reduction in bone and muscle mass, ocular changes, and weakening of the immune system – there are many more. So we know microgravity is not good for human health after long stays. Clearly, having babies under these conditions would not be ethical or conducive for long term settlement.
The first studies carried out on mammalian reproduction in microgravity took place in the early 1990s aboard the Space Shuttle in a couple of experiments on STS-66 and STS-70. 10 pregnant rats were launched at midpregnancy (9 days and 11 days, respectively) on each flight and landed close to the (22 day) term. The rat pups were born 2 days after landing and histology of their brain tissue found spaceflight induced abnormalities in brain development in 70% of the offspring.
It was not until 2017 that the first mammalian study of rodents with artificial gravity was performed on the ISS. Although not focused on reproduction, the Japan Aerospace Exploration Agency (JAXA) performed a mouse experiment in their Multiple Artificial-gravity Research System (MARS) centrifuge comparing the impact of microgravity to 1g of spin gravity. The results provided the first experimental evidence that mice exposed to 1g of artificial gravity maintained the same bone density and muscle weight as mice in a ground control group while those in microgravity had significant reductions.
Diagram depicting an overview of the first JAXA Mouse Project in the MARS centrifuge with photos of the experiment on the ISS. Credits: Dai Shiba et al. / Nature. http://creativecommons.org/licenses/by/4.0/
In 2019 JAXA carried out a similar study in the MARS centrifuge adding lunar gravity levels to the mix. This study found that there were some benefits to the mice exposed to 1/6g in that Moon gravity helped mitigate muscle atrophy, but it did not prevent changes in muscle fiber or gene expression.
Just last year, a team led by Dr. Mary Bouxsein at Harvard Medical School conducted another adult mouse study on the MARS centrifuge comparing microgravity, .33g, .67g and 1g. They found that hind quarter muscle strength increased commensurate with the level artificial gravity concluding, not surprisingly, that spaceflight induced atrophy can be mitigated with centrifucation. The results were reported at the American Society for Gravitational and Space Research last November.
Returning to mammalian reproduction in space, an interesting result was reported last year in the journal Cell from an experiment by Japanese scientists at the University of Yamanashi carried out on the ISS in 2019. The team, headed up by Teruhiko Wakayama, devised a way to freeze mouse embryos post conception and launch them into space where they were thawed by astronauts and allowed to develop in microgravity. Control samples were cultured in 1g artificial gravity on the ISS and Earth normal gravity on the ground. The mouse embryos developed into blastocysts and showed evidence of cell differentiation/gene expression in microgravity after 4 days. The researchers claimed that the results indicated that “Mammals can thrive in space”. This conclusion really can’t be substantiated without further research.
Which brings us to several unknowns about reproduction in space. SSP has explored this topic in depth through an interview with Alex Layendecker, Director of the Astrosexological Research Institute. Yet to be studied in depth is (a) conception, including proper transport of a zygote through the fallopian tube to implantation in the uterus. Less gravity may increase the likelihood of ectopic pregnancy which is fatal for the fetus and could endanger the life of the mother; (b) full gestation through all stages of embryo development to birth; and (c) early child development and maturation to adulthood in hypogravity. All these stages of mammalian reproduction need to be validated through ethical clinical studies on rodents progressing to higher primate animal models before humans can know if having children in lower gravity conditions on the Moon or Mars will be healthy and sustainable over multiple generations.
AI generated image of an expectant mother with her developing fetus in Earth orbit after mammalian reproduction has been validated via higher animal models through all stages of pregnancy for a safe level of gravity. An appropriate level of radiation shielding would also be required and is not shown in this illustration. Credit: DALL-E-3
Some space advocates for communities on the Moon or Mars have downplayed the importance of determining the GRx for reproduction with the logic that a fetus in a woman’s uterus on Earth is in neutral buoyancy and thus is essentially weightless. Therefore, why does gravity matter? I discussed this question with Dr. Layendecker and he had the following observations paraphrased here: True, gravity may have less of an impact in the first trimester. But on the cellular level, cytoskeletal development and proper formation/organization of cells may be impacted from conception to birth. Gravity helps orient the baby for delivery in the last trimester and keeps the mother’s uterine muscles strong for contractions/movement of the baby through the birth canal. There are many unknowns on what level of gravity is sufficient for normal development from conception to adulthood.
Why does all this matter? Ethically determining the right level of gravity for healthy reproduction and child development will inform where families can safely settle space. The available surface gravities of bodies where we can establish communities in space cluster near Earth, Mars and Moon levels. These are our only GRx options on solar system bodies.
Gravity level clustering of solar system bodies available for space settlement. Credit: Joe Carroll
The problem is that we don’t yet know whether we can remain healthy enough on bodies with gravity equivalent to that on the Moon or Mars, so we can’t select realistic human destinations or formulate detailed plans until we acquire this knowledge. Of course we can always build rotating settlements in free space with artificial gravity equivalent to that on Earth. Understanding the importance of the GRx and determining its value could change the strategy of space development in terms of both engineering and policy decisions. The longer we delay, the higher the opportunity costs in terms of lost time from failure to act.
What are these opportunity cost lost opportunities? Clearly, at the top of Elon Musk’s list is “Plan B” for humanity, i.e. a second home in case of cataclysmic disaster such as climate change, nuclear war, etc. This drives his sense of urgency. From Gerard K. O’Neill’s vision in The High Frontier, virtually unlimited resources in space could end hunger and poverty, provide high quality living space for rapidly growing populations, achieve population control without war, famine, or dictatorships. And finally, increase freedom and the range of options for all people.
If humans can’t have babies in less than Earth’s gravity then the Moon and Mars may be a bust for long term (biologically sustainable) space settlement. There will be no biologically sustainable cities with millions of people on other worlds unless they can raise families there.
Spin gravity rotating space settlements providing 1g artificial gravity may be the only alternative. If Elon Musk knew that the people he wants to send to Mars can’t have children there, would he change his plans for a self-sustaining colony on that planet? Having and raising children is obviously important to him. As Walter Isaacson wrote in his recent biography of Musk, “He feared that declining birthrates were a threat to the long-term survival of human consciousness.”
So how could he determine the GRx quickly? One solution would be to fund a partial gravity facility in low Earth orbit to run ethical experiments on mammalian reproduction in hypogravity. Joe Carroll has been refining a proposal for such a facility, a dual dumbbell Moon/Mars low gravity laboratory which SSP has covered, that could also be marketed as a tourist destination. Spinning at 1.5 rpm, the station would be constructed from a combination of Starship payload-sized habitats tethered by airbeams allowing shirt sleeve access to different gravity levels. Visitors would be ferried to the facility in Dragon capsules and could experience 3 gravity levels with various tourist attractions. The concept would be faster, cheaper, safer and better than establishing equivalent bases on the Moon or Mars to quickly learn about the GRx. The facility would be tended by crews at both ends that live & collect health data for up to a year or more. And of course, ethical experiments on the GRx for mammalian reproduction would be carried out, first on rodents and then progressing to higher primates if successful.
Left: Conceptual illustration depicting a LEO Moon-Mars dumbbell partial gravity facility constructed from Starship payload-sized habitats tethered by airbeams and serviced by Dragon capsules. Rectangular solar arrays deploy by hanging at either end as spin is initiated via thrusters at Mars module. Center: Image of an inflated airbeam demonstration. Right: diagram of an airbeam stowed for transport and after deployment. Credit: Joe Carroll
What if these experiments determine that having children in lower gravity is not possible and our only path forward are free-space rotating settlements? Physics and human physiology require that they be large enough for settlers to tolerate a 1g spin rate to prevent disorientation. As originally envisioned by O’Neill, the diameter of his Island One space settlement would be about 500 meters.
Conceptual illustration of an Island One space settlement. The living space sphere is sized at about 500m in diameter. Credits: Rick Guidice / NASA
As originally proposed, these settlements would be located outside the Earth’s magnetic field at the L5 Earth-Moon Lagrange Point necessitating that they be shielded with enormous amounts of lunar regolith to protect occupants from radiation. Their construction requires significant technology development and infrastructure (e.g. mass drivers on the Moon, automated assembly in space, advances in robotics, power sources, etc…). Much of this will eventually be done anyway as space development progresses…however, knowing the GRx (if it is equal to 1g) may foster a sense of urgency.
Some may take the alternative viewpoint that if we know that Earth’s gravity works just fine we could proceed directly to free-space settlements if we could overcome the mass problem. This is the approach Al Globus and Tom Marotta took in their book The High Frontier: An Easier Way with Kalpana One, a 450m diameter cylindrical rotating free-space settlement located in equatorial low Earth orbit (ELEO) protected by our planet’s magnetic field, thereby reducing the mass significantly because there would be far less need for heavy radiation shielding.
Artist impression of Kalpana One rotating free-space settlement located in equatorial low Earth orbit. Credits: Bryan Versteeg / Spacehabs.com
Artist rendering of the inside of a rotating free-space settlement based on the Kalpana Two design, with a length of 110m and diameter of 125m. Credits: Bryan Versteeg / Spacehabs.com
Even though these communities would be lower mass, they will still require significant increases in launch rates to place the needed materials in LEO, especially near the equator. Offshore spaceports, like those under development by The Spaceport Company, could play a significant role in this infrastructure. Legislation providing financial incentives to municipalities to build spaceports would be helpful, such as The Secure U.S. Leadership in Space Act of 2024 introduced in Congress last month. The new law (not yet taken up in the Senate) would amend the IRS Code to allow spaceports to issue tax-exempt Muni bonds for infrastructure improvements.
Wouldn’t orbital debris present a hazard for settlements in ELEO? Definitely yes, and the National Space Society is shaping policy in this area. The best approach is to emphasize “light touch” regulatory reform on salvage rights, with protection and indemnity of the space industry to encourage recycling and debris removal. Joe Carroll has suggested a market-based approach that would impose parking fees for high value orbits, which would fund a bounty system for debris removal. This system would incentivize companies like CisLunar Industries, Neumann Space and Benchmark Space Systems, firms that are developing space-based processes to recycle orbital debris into useful commodities such as fuel and structural components.
Further down the road in technology development and deeper into space, advances in artificial intelligence and robotics will enable autonomous conversion of asteroids into rotating space settlements, as described by David Jensen in a paper uploaded to arXiv last year. This approach significantly reduces launch costs by leveraging in situ resource utilization. Initially, small numbers of “seed” tool maker robots are launched to a target asteroid along with supplemental “vitamins” of components like microprocessors that cannot be easily fabricated until technology progresses, to complete the machines. These robotic replicators use asteroid materials to make copies of themselves and other structural materials eventually building out a rotating space settlement. As the technology improves, the machines eventually become fully self-replicating, no longer requiring supplemental shipments from Earth.
Artist impression of a rotating space settlement constructed from asteroid materials. Credits: Bryan Versteeg, spacehabs.com
Leveraging AI to enable robots to build space settlements removes humans from the loop initially, eliminating risk to their health from exposure to radiation and microgravity. Send it the robot home builders – families then safely move in later. There are virtually unlimited supplies in the asteroid belt to provide feedstock to construct thousands of such communities.
Artist impression of the interior of Stanford Torus free-space settlement. Advances in artificial intelligence and robotics will enable autonomous self replicating machines that could build thousands of such communities from asteroid material. Credits: Don Davis / NASA
If rotating space settlements with Earth-normal gravity become the preferred choice for off-Earth communities, where would be the best location, the prime real estate of the solar system? Jim Logan has identified the perfect place with his Essential Seven Settlement Criteria.
Low Delta-V – enabling easy access with a minimum of energy
Lots of RESOURCES … obviously!
Little or No GRAVITY WELL – half way to anywhere in the solar system
At or Near Earth Normal GRAVITY for People, Plants and Animals - like what evolved on Earth
Natural Passive 24/7 RADIATION Protection – for healthy living
Permit Large Redundant Ecosystem(s) – for sustenance and life support
Staging Area for Exploration and Expansion (including frequent, recurrent launch windows)
Using this criteria, Logan identified Deimos, the outermost moon of Mars, as the ideal location. As discussed above, AI and robotic mining technology improvements will enable autonomous boring machines to drill a 15km long core through this body with a diameter around 500 meters – sized for an Island One space settlement to fit perfectly.
Conceptual illustration of a 500 meter wide by 15km long core bored through Deimos. Credit: Jim Logan
In fact, 11 Island One space colonies (minus the mirrors) strung end to end through this tunnel would provide sea level radiation protection and Earth normal artificial gravity for thousands of healthy settlers.
Left: Artist impression of an Island One space settlement. Credits: Rick Guidice / NASA. Right: To scale depiction of 11 Island One space settlements strung end-to-end in a cored out tunnel through Deimos providing sea level radiation protection and Earth normal artificial gravity. Credit: Jim Logan
In conclusion, the GRx for reproduction will inform where biologically self-sustaining healthy communities can be established in space. If we find that the GRx is equal to Earth’s normal level, free-space settlements with artificial gravity will be the safest and healthiness solution for humans to live and thrive throughout the solar system. The sooner we determined the GRx the better, for current plans for settling the Moon or Mars may need to be altered to consider rotating space colonies, which will require significant infrastructure development and regulatory reform. Alternatively, since we know Earth’s gravity works just fine, we may choose to skip determination of the GRx and start small with Kalpana in low Earth orbit. Eventually, artificial intelligence will enable safe, autonomous self-assembly of space settlements from asteroids. The interior of Deimos would be the perfect place to build safe, healthy, biologically self-sustaining space settlements for thousands of families to raise their children, establishing a beachhead from which to explore the rest of the solar system and preserve the light of human consciousness.
Update June 3, 2024: Here is a recording of my presentation on this topic at ISDC 2024.
