Illustration of a cylindrical rotating space settlement in Low Earth Orbit. Credits: Grok 3
A paper by German astrophysicist Rainer Rolffs titled Rotation of Space Habitats published last October has been uploaded to the National Space Society (NSS) Space Settlement Journal. The study aims to quantify how much structural mass is required to support both the artificial gravity and the internal pressures in various designs of a rotating habitat. It expands on previous work the author completed on energy flow in such habitats, integrating considerations of cooling, energy collection (via mirrors and photovoltaics), and the distribution of interior mass.
Habitat Geometry and Design Options Rolffs analyzes several geometric configurations, including: – Cylinder: A habitat rotating about its central axis, with design trade-offs between compactness and rotational stability. – Tube: A cylindrical structure rotating perpendicular to its length, featuring rounded endcaps to ensure uniform gravity. – Oblate Spheroid: A sphere that is flattened along the rotation axis, offering a different balance between structural mass and interior volume. – Torus: A ring-like structure where the habitat’s thickness is a fraction of the overall rotational radius. – Dumbbell and Dumbbell with Tube: Two-sphere configurations connected either by cables or a tube; these shapes offer flexibility in managing rotational radius and gravity distribution, especially at smaller scales.
Scaling and Habitat Sizing The analysis scales the design by considering a constant interior volume per person, leading to a range of populations from very small (few individuals) to billions. Lower limits on habitat size are determined by constraints such as acceptable rotation rates (to maintain human comfort) and the mass needed for shielding against radiation. Upper limits are set by the challenges of maintaining co-rotation of critical components like mirrors for sunlight collection and the growing demands on structural integrity and cooling systems as size increases.
Gravity Distribution and Structural Considerations The paper provides detailed methods to compute the gravity distribution inside the habitat by dividing the interior into floors with heights that vary inversely with gravity. Rolffs examines how the structural mass must not only counteract the centrifugal forces (to create artificial gravity) but also support the self-weight of the structure, with different methods for vertical (hanging) versus horizontal (standing) support. A “critical co-rotational radius” is introduced, beyond which certain components (like non-rotating mirrors or photovoltaics) can no longer be kept in co-rotation with the habitat without incurring prohibitive mass penalties.
Trade-Offs in Mass Budget and Optimization Not surprisingly, shielding against radiation is identified as a dominant mass component for small habitats, while for larger habitats, the structural and cooling masses become more significant. The study shows that there exists an optimum size range—between tens of thousands and tens of millions of cubic meters of interior volume—where the payload (interior mass per person) dominates the overall mass budget, and the design can be optimized for cost and functionality. Rolffs finds that different shapes yield different trade-offs; for example, the dumbbell shape is preferable at smaller sizes due to its flexible rotational radius, whereas spheroidal shapes may offer lower structural mass for very large habitats.
Detailed Derivations and Appendices The work includes extensive mathematical derivations provided in three appendices: – Appendix A: Details the geometric parameters and derivations for determining the rotational radius and interior volume for each habitat shape. – Appendix B: Focuses on the gravity distribution within the habitat, explaining how the artificial gravity varies across different floors and regions. – Appendix C: Deals with structural integrity, deriving the requirements for supporting both the artificial gravity forces and the habitat’s own self-weight, including considerations for both vertical and horizontal support systems.
Rolffs’ analysis provides design guidelines that are critical for planning future space settlements, especially in the context of reducing launch costs and using in-situ resources (e.g., processed asteroid matter) for construction. He concludes that while very large habitats are theoretically possible (even accommodating populations in the billions), practical constraints related to cooling, light distribution, and structural integrity likely favor habitats in the medium-size range with optimized shapes such as the dumbbell or oblate spheroid.
Overall, Rolffs provides an in-depth exploration of the physical and engineering challenges associated with rotating space habitats, providing both theoretical foundations and practical design criteria that could inform future developments in space settlement engineering, earning the top spot on SSP’s Artificial Gravity Section as of this post.
Conceptual illustration of the Variable-Pitch Screw Launch system showing a launch vehicle (white) being accelerated by an adaptive nut (orange) that magnetically couples to variable pitch screws in an evacuated tube. Credits: Phil Swan and Alastair Swan.
The Variable-Pitch Screw Launch (VPSL) system, is a revolutionary ground-based electromagnetic launch technology that leverages magnetic coupling and variable-pitch leadscrews to accelerate payloads to very high exit velocities (e.g., >11,000 m/s) at a fraction of the cost of traditional chemical rockets. In a paper authored by Phil Swan and Alastair Swan of the Atlantis Project, details are presented on how VPSL overcomes limitations of existing mass drivers, such as the switching constraints of linear motors and rail wear in railguns. Phil Swan appeared on The Space Show last January to discuss the concept with Dr. David Livingston.
The capital cost of a VPSL system scales with the square of exit velocity (ΔV2), a significant improvement over the exponential cost growth of chemical propulsion (exp(ΔV/ΔVe )) and the cubic scaling (ΔV3 ) of some linear motor components in mass drivers. The authors present results from a parametric model that estimates a $33 billion USD capital cost (2024 dollars) for a human-rated system capable of accelerating vehicles to escape velocity for Mars missions, positioning VPSL as a game-changer for cost-effective space exploration.
As humans begin to explore and develop space beyond low Earth orbit (LEO), missions to the Moon, Mars, asteroids and beyond will demand significantly higher delta-v than those needed for LEO operations, especially for human round-trips, which nearly double the velocity requirements. High delta-v missions also reduce crew exposure to cosmic radiation and optimize provisions, but the rocket equation—where fuel mass grows exponentially with delta-v—makes traditional rockets increasingly expensive. VPSL is presented as a scalable, infrastructure-based solution that mitigates these costs, offering both economic and environmental benefits. By reducing reliance on chemical propellants, it aligns with global climate goals, marking a pivotal shift toward sustainable spaceflight.
As a starting point for economic considerations the Swans provided a historical context for exploration costs (in 2020 USD) of the Apollo Program ($257 billion), Space Shuttle ($197 billion) and the International Space Station annual costs ($500 million per-person-year; total of $150B to date); with an estimate that the Artemis Program will cost $93 billion through the end of FY2025 (likely over $100 billion by the time Artemis III returns to the Moon according to ChatGPT). Since the dawn of human spaceflight these programs demonstrate the immense financial burden associated with traditional (chemical rocket) spaceflight, yet their broader benefits—economic stimulus, technological innovation, and geopolitical prestige—justify the investment. The aim of VPSL is to reduce these costs dramatically.
The analysis then moves to a cost comparison of all rocket systems using empirical data that show an exponential relationship between launch cost and delta-v reflecting the “tyranny of the rocket equation” where higher velocities require exponentially more fuel, driving up costs for missions beyond LEO, which will become increasingly important as global space agencies push out into the solar system toward high delta-v destinations.
The paper contrasts the economics of rockets with mass drivers where the latter scale as the cube of the velocity (ΔV3) due to increased power demands at higher velocities. VPSL avoids this by converting electrical energy into rotational energy in screws, then transferring it magnetically to the payload, minimizing expensive pulsed-power electronics. For example, scaling a traditional mass driver from 100 m/s to 10,000 m/s increases costs by a million-fold as ΔV3 dominates, but a well designed VPSL mitigates this issue.
Cost curve generated from a digital twin computer model for the Variable Pitch Screw Launcher (dark blue) versus empirical curve fit for all-rocket systems (light blue) showing significant cost savings. Credits: Phil Swan and Alastair Swan
The specific implementation of a VPSL system is presented with an architecture targeting a 22-year Mars outpost program, with launches during Mars transfer windows. The payload is human-rated, assuming fit crews and acceleration couches, and is designed with sufficient capacity for life support, power generation systems, and rocket propulsion for in-space maneuvering as well as decent to the Martian surface.
This VPSL system includes a 774 km submerged floating underwater section, an 83 km underground ramp curving upward, and a 122 km aeronautically supported elevated tube with the exit aperture at an altitude of 15 km. The entire 979 km launching conduit would be evacuated to minimize drag with air locks at both ends, and face East to take advantage of the Earth’s rotation. For a Mars transfer orbit the exit velocity was calculated to be 11,129 m/s taking into account the Earth’s rotation.
VPSL system scale compared to the Hawaiian Islands, the site under consideration for implementation. Credits: Phil Swan and Alastair Swan
VPSL outperforms rockets for high delta-v missions, leveraging fixed infrastructure costs and low marginal launch costs. It’s quadratic cost scaling and sustainable design make it a transformative option when compared to rockets for high delta-v missions.
I reached out to Phil Swan after his appearance on The Space Show to discuss VPSL and he graciously agreed to participate in an interview with me via email to dive deeper into some of the challenges for implementation of the architecture of the Mars mission. His outstanding responses below are backed up with rigorous engineering reasoning and I thank him for his time collaborating with me on this post.
Many of my interview questions arose from public feedback he received from over 125,000 YouTube views of his presentation on VPSL at the International Space Development Conference last May (Section F of the paper). This approach will hopefully help ascertain what actions are needed to realize the system as well as further engineering development needed to advance it’s technical readiness level. The first two questions involve funding mechanisms for implementation.
SSP: There didn’t appear to be a funding mechanism proposed for the VPSL system although there were a few references to features that would provide incentives for investors. Do you envision the project to be funded by private venture capital, governmental sources or a combination through public/private partnerships?
PS: Our funding strategy is designed to attract private investment through a phased development approach, where some liquidity and financial flexibility is offered by allowing employees and early-stage investors to sell shares to later-stage investors as key technical and engineering milestones are met, similar to staged investment rounds in deep-tech ventures. It would be like many other tech startups where for many years the company’s primary focus is growth as opposed to profits. While we anticipate private venture capital to play a significant role, we are also exploring potential government grants or public-private partnerships to support critical advancements. Revenue generation from early-stage prototypes and other technologies we develop along the way may provide additional funding streams, but the most significant returns will come when we enable affordable interplanetary spaceflight.
SSP: The $33.3B price tag included capital and operations costs but I did not see research and development included. While your calculations show that VPSL costs are very competitive and environmentally beneficial when compared to rockets, this system will require significant development costs to reach TRL 9. Do you have an estimate of the R&D budget?
PS: We anticipate the R&D budget to be 10% of the total estimated capital and operational costs. Our research and development efforts thus far have led to substantial reductions in the estimated costs, so strategic investment in R&D can drive down capital expenditures and improve overall system profitability. For example, a while ago our R&D work led to an improvement where we placed grapplers on both sides of the screws instead of just on one side. This innovation dramatically reduces the forces transmitted to the brackets that support the screws. In this sense, R&D serves as a cost-reduction mechanism. If we do the right amount of R&D and focus it on the most important problems, it could end up paying for itself.
SSP: The remainder of interview questions probe deeper into issues identified through public feedback in Section F of your paper. With respect to constructing a 979 km long vacuum tube and designing fast-acting doors to maintain vacuum while allowing high-speed exit of the vehicle, what are the specific engineering requirements and cost estimates for designing and maintaining fast-acting airlock doors capable of sealing a vacuum tube after a vehicle exits at 11,129 m/s, and how do these compare to existing vacuum systems like LIGO (Laser Interferometer Gravitational-Wave Observatory)?
PS: To exit the tube, the vehicle will pass through an already open fast-acting door first, and that door will start closing immediately. The other end of the airlock is covered with a burst disk. The ambient air pressure at the airlock’s altitude (15km) is around 12000 Pa and the pressure inside the tube is 5 Pa. When the vehicle breaks through the burst disk, the rarified outside air will start travelling into the tube at the speed of sound. The fast-acting door needs to finish closing before the ambient air rushing into the tube reaches it. The math in the model estimates that to meet these requirements the airlock needs to be at least 288 m long if the fast-acting door is engineered to close in 1 second. I should add that the fast-acting door can be backed by a second slower door that is designed to achieve a better vacuum seal.
After the vehicle exits, a new membrane needs to be stretched over the end of the tube to from a new burst disk, and then the airlock needs to be pumped down again from 12000 Pa to 5 Pa. Our current model estimates that it will take 10 minutes and cost 312 dollars to pump the air out of the airlock each time we cycle it.
For LIGO, the exterior pressure is roughly 100,000 Pa and its interior pressure is 1.33 × 10⁻⁷ Pa to 2.67 × 10⁻⁷ Pa – which is a vacuum that it has maintained for 25 years. That’s a ratio of ~7e11 to 1. For VPSL, the exterior pressure is 12000 Pa and it has an interior pressure of 5 Pa for a ratio of only ~2.4e3. So, in one sense, LIGO’s vacuum engineering problem is eight orders of magnitude harder than the problem for VPSL. So, what we’re proposing here falls comfortably within established engineering capabilities. But, VPSL introduces operational dynamics that LIGO does not face – such as repeated venting and sealing at the airlocks and high-speed vehicle interaction. So, in another sense, we will be facing some new challenges that LIGO doesn’t have to deal with.
SSP: To address skepticism about sourcing materials robust enough to endure the high speeds, heat, and magnetic forces cost-effectively, you asserted that the choice of steel and aero-grade aluminum would have sufficient engineering margins when compared to rockets. What are the maximum stresses, thermal loads, and electromagnetic forces experienced by steel screws and aluminum tubes at peak speeds, and can existing manufacturing processes scale these materials to a 979 km system without cost escalation?
PS: This question assumes that extreme forces or heat are unavoidable, but that’s not how we approached the problem. From both an engineering and architectural perspective, we began with the constraints of existing materials and designed a system that stays within those limits.
For example, let’s start with the mechanical stresses. If we want a launcher for sending missions to Mars, this creates a requirement – we will need to launch vehicles at a speed of ~11,129 m/s relative to the surface of the spinning Earth. This is the speed at which the maximum mechanical stresses will occur.
The idea is that the spinning screws drive the adaptive nut. It’s basically a leadscrew and nut with a certain gear ratio. To figure out what that ratio needs to be, we first need to figure out how fast we can turn the screws without exceeding the stress limits of existing affordable materials. To ballpark that, we know that the yield strength for M2 High-Speed Steel can reach 1,300 to 2,200 MPa. But let’s assume we use a cheaper steel with a yield strength of 700 MPa and a density, ρ, of 7850 kg/m3. If we apply an engineering factor of 1.5, then we can set the maximum stress, σ, that we want to see in the steel to a value of 467 MPa. The rate that you can spin a spinning pipe without exceeding this level of stress is
[ref] where ω is in radians-per-sec, and ri and ro are the inner and outer radii in meters. Multiplying ω by ro gives the max rim speed of 404 m/s. This is a value similar to what the tips of airliner fans blades reach during takeoff.
From this value we can calculate the maximum slope of the screw flights, which is 11129/404=27. This means that the total force of the screw flights needs to be ~27 times higher than the force you need to accelerate the spacecraft, sled, and adaptive nut.
Since the coupling is magnetic, you can work out the coupling force across the “airgap” per square meter (see math in above linked paper). This works out to be 795775 N/m2, or less than 1 MPa (about 1/500th the internal tensile stress due to the centrifugal forces).
While you didn’t ask about this in the question, I feel that it’s important to mention that for this to work the screws and rails need to be very straight. To achieve that we will need automatic alignment actuators and something akin to an ultra-high-precision GPS system to achieve the required straightness.
You also asked about heating. This is a good question to use to validate the practicality of a launch architecture. For example, if a launcher was 1000 km long and it was made up of 1 million 1-meter segments, and each of those segments heated up by, say, 5 degrees each launch, then you could estimate how much energy was being dissipated as heat rather than being converted into kinetic energy—and it could be a lot. If each segment weighed one ton, heated up by 5°C, and had the heat capacity of water (about 4,200 J/kg·°C), then the total energy lost to heat would be:
1,000,000 segments × 1,000 kg × 5°C × 4,200 J/kg·°C = 21,000,000,000,000 J. That’s 2.1 × 10¹³ joules, or about 5.8 gigawatt-hours of energy lost to heating per launch.
By comparison, the kinetic energy of a 10-ton spacecraft (10,000 kg) in low Earth orbit at 7.8 km/s is:
So, the energy lost to heating in this example would be about 70 times greater than the kinetic energy delivered to the payload. In other words, such a launcher would not be very energy efficient.
In other architectures, this heat is generated because the segments rapidly convert energy from one form to another in the process of accelerating the vehicle, and such high-power conversions invariably generate heat. But the VPSL doesn’t rapidly convert energy from one form to another. The kinetic energy in spinning screws is directly channeled into the kinetic energy of the vehicle through what is essentially a magnetic worm gear. So, the screws and guideway will not heat up significantly during a launch because they are not heated up by the process of rapid high-power energy conversion.
Now there is still some friction that generates heat. Even a train on rails will generate some heat due to friction between its wheels and the rails, but the friction and heat generation associated with magnetic levitation systems is low enough that most people think of them as being “frictionless” – even though that’s not entirely true – maglev tracks and magnetic bearings are really just “very low” friction technologies.
SSP: Concerns were raised about potential eddy currents from the spinning screws and electromagnetic interactions causing energy losses and heat buildup which could reduce efficiency. In view of your acknowledgement that more engineering work is needed to quantify these interactions, have you calculated the magnitude of eddy current losses in a VPSL system at peak velocity, and have you designed experiments or computer code to run simulations or small-scale tests to determine how effective uniform magnetic fields and laminated components would be in reducing these losses?
PS: There are devices that are designed to use Eddy currents for braking, and there are technologies, such as magnetic bearings and maglev trains, that are designed to generate far less friction and wear than their mechanical counterparts. We’ve certainly designed devices to explore the limits of the low-friction high-speed magnetic levitation, but given the high speeds involved, we’ve chosen to implement these designs later on our prototyping roadmap. For one of them, we worked with a well-credentialed Ph.D. and an ASME Fellow in the field of rotordynamics and magnetic bearings. We shared our concerns with him about venturing into uncertain or poorly understood engineering territory. He reassured us that he was not aware of any engineering or physics reasons why our proposed technology would not work, and wrote us a letter of support where he stated, “I am confident in the merits of the proposed research.” That said, pushing beyond the speeds already achieved with maglev trains, the world-record-holding magnetic levitation rocket sled track at Holloman Airforce Base, energy storage flywheels, etc. certainly will involve doing more research and experimentation.
In addition to building physical prototypes, we plan to license advanced engineering software and bring on specialized talent to develop a multi-physics simulation using finite element analysis (FEA) techniques. These simulations will be validated through data collected from instrumented small-scale prototypes. They will give us more visibility on a wide variety of performance metrics.
SSP: Regarding fast-acting components, to ensure operational reliability and test real-world applicability of existing technology to VPSL’s extreme speeds, how reliably can electromagnetic grappler pads and actuators maintain synchronization and stability at speeds up to 11,129 m/s, and what are the failure rates of similar systems (e.g., magnetic bearings) under comparable conditions?
PS: It becomes easier to maintain synchronization as the vehicle approaches the muzzle of the launcher because the screw geometry changes more slowly at the muzzle end. Near the beginning, the geometry changes quickly and the grapplers need to reposition more rapidly, but the forces that they need to manage are also much smaller. If you haven’t yet seen Isaac Arthur’s video, “Mass Drivers Versus Rockets”, you should check it out. It has some good clips that show how the screw geometry changes and how the grapplers reposition during a launch.
Compared to ball and roller bearings, magnetic bearings exhibit extremely low failure rates in industrial use due to the lack of mechanical contact. Although, I suppose there must be some failures due to, for example, defective solid-state electronics in the controllers, power surges, corrosion of wires, fouling of sensors, etc.
Getting the failure rate to the level we need it to be at is a well-understood engineering exercise – like perfecting jet engines or building fault tolerance into hard drives. You need to test, iterate, and apply good engineering practices—refinement, redundancy, early fault detection, and so on. We will be building upon a substantial amount of experience that already exists within other industries – we’re not starting from scratch here.
SSP: You mentioned that to maintain investor confidence, you had a roadmap for developing the technology using a combination of physical prototypes and simulated “digital twin” prototypes. To address scalability physics and ensure the system can handle larger payloads effectively, how does magnetic field strength and consistency vary across a 979 km screw system compared to a small prototype, and what payload mass thresholds trigger performance degradation in digital twin simulations?
PS: Magnetic fields are not generated by the launcher’s guideway or screws’ flights (there are fields inside the magnetic bearings and electric motors that support and spin the screws though). Magnetic fields are generated by the adaptive nut and the sled. The strength of the fields between the grappler pads and the screw flights does peak as the vehicle approaches the muzzle end of the launcher. The strength of the fields between the sled and the guideway’s rail is constant during forward acceleration, and then it jumps up to its peak when the vehicle is on the ramp. Some of the small-scale prototypes will explore the same peak field strengths so that we can avoid surprises later as we scale up.
The system’s cost is expected to scale linearly with payload mass and payload mass will not trigger performance degradation. But if we were to go in the other direction, and scale down too far, that may introduce challenges – particularly with respect to vehicle stability and thermal protection during reverse reentry.
In the paper we said that cost scales with the square of delta-v – which is a lot better than the way that chemical rocket cost scales with the exponent of delta-v. However, we haven’t really explored how cost will scale at speeds much beyond 11,129 m/s. If we try to go much faster than that we’ll probably start running into material limits. Switching to more exotic materials will likely alter the cost-versus-delta-v relationship. We certainly do not want to suggest that the technology can scale up to the speeds needed for interstellar travel or anything like that.
SSP: To validate the economic and efficiency claims of VPSL when compared to existing rockets using energy data, have you done a detailed breakdown of the system’s $33.3 billion capital cost compared to the lifecycle cost of a chemical rocket program delivering 9.6 million kg to Mars, showing how much energy is saved by regenerative braking in real-world conditions?
PS: Yes, the capital and operating costs are computed by code within the digital twin and this includes the power savings from regenerative braking. While there has been some analysis of chemical rocket costs, much of our discussion in the public sphere revolves around addressing and correcting overly optimistic claims—particularly those made by Elon Musk—which are often repeated uncritically by some space enthusiasts. For example, this paper attempts to demonstrate that based on empirical evidence there is clearly an exponential relationship between cost and delta-v. As a widely circulated quote attributed to Peter Diamandis says, “Our brains are wired for linear thinking in an exponential world, and its causing us a great deal of strife.”
Personally, I haven’t felt it was in our best interests to publish a study that emphasizes how prohibitively expensive a permanently manned outpost—or a city—on Mars would be using chemical rockets. While some people argue that attempting to settle Mars is fundamentally misguided, I personally don’t share that view since I believe in the potential of launch infrastructure.
But if you think that rockets are the only option available to us, then right now the cost-per-kg to Mars is on the order of 1.2 million USD. While many are excited about Starship and the potential of full reusability, we’re far more cautious about its ability to fundamentally change the cost of spaceflight for the delta-v’s and mission durations required for one-way and round trips to Mars. We’ve shared some of our reasoning and the available data on this – see: https://youtu.be/Apu6nDahjB4 and https://youtu.be/GvqAM9p4hss. In the absence of a game-changing development, sending a million tons to Mars with chemical rockets will cost on the order of ($1.2 x 106 /kg )(1 x 109 kg) = $1.2 x 1015, or 1200 trillion dollars. This isn’t the kind of problem that will “fix itself” anytime soon through experience curve effects.
SSP: Related to your preferred site of Hawaii’s Big Island, the ongoing legal, cultural, and logistical hurdles encountered by Caltech and the University of California in getting approval to build the Thirty Meter Telescope (TMT) seem insurmountable. Native Hawaiian groups and environmentalists who consider Mauna Kea a sacred site have caused a decade of delays. The telescope’s future is still uncertain so a project of the scale of a VPSL system seems very challenging. While your plan to engage with the community in a respectful and productive manner by clearly communicating benefits to the indigenous people like economic opportunity and cultural legacy make sense, it has likely already been tried by the TMT team. Have you identified specific alternate coastal sites with high elevation, low latitude, and access to large bodies of water that may not present such difficult environmental and cultural challenges?
PS: The summit of Mauna Kea is a culturally sensitive area. For many Native Hawaiians, the numerous telescopes located there are seen as an incursion on sacred land. Additionally, the U.S. military has used portions of the mountain’s slopes for training exercises, causing ecological damage. As a result, the local population is particularly sensitive to further disruption and, in many cases, would prefer the mountain be restored to its original, undisturbed state.
The VPSL system’s acceleration segment would be located offshore and underwater, while the ramp portion would be on the island but almost entirely contained within a tunnel. The tunnel would exit well below the summit—away from the existing observatories—through a small opening situated to avoid culturally significant sites. The elevated, evacuated launch tube would be a temporary structure, deployed every two years for a few weeks during Mars transfer windows.
A potential path forward could involve a three-way agreement: the launcher could be used to deploy multiple space telescopes. These offer a path to eventually phase out the existing summit observatories without impacting the scientific community that relies on them. In return, the Hawaiian community would agree to permit the construction and limited use of the launcher, for example during Mars transfer windows and on a few other occasions.
Over time, the Hawaiian people may come to see the launcher not only as a less intrusive alternative but as a source of enduring pride—an opportunity to contribute to humanity’s next great era of exploration. Rather than diminishing their culture, it could elevate it, building upon the proud legacy of the Polynesian navigators who first discovered and settled the islands. This vision, however, must be informed by dialogue with Native Hawaiian leaders and cultural practitioners – not just outreach – to ensure the project is shaped in a way that reflects and respects their values. In this way, Hawai‘i’s role in space exploration could be seen as a modern extension of their deep tradition of voyaging and discovery.
But, if Hawaii choses to pass on the opportunity, there are many alternative sites around the world that would suffice. Developing and characterizing alternative sites simply hasn’t received priority yet.
SSP: What are the projected environmental impacts (e.g., land use, wildlife disruption) and cultural consultation costs for siting a VPSL system on Hawaii, and how do these compare to alternative sites like desert-mountain regions in terms of construction feasibility and community acceptance?
PS: We don’t expect there to be a significant amount of environmental disruption but with an ecology that’s very sensitive, we will need to be careful. The launcher is underwater and should not impede marine life. The ramp is within a shallow tunnel, so it shouldn’t affect ecologies on the surface, but we’d need to come up with a good plan for dealing with the excavated material generated during tunneling. I expect that birds would tend to avoid the elevated evacuated tube. Vehicles will exit the system far offshore and at an altitude of 15 km, so they shouldn’t generate a lot of noise. Rockets, on the other hand, generate a lot of noise and a lot of pollution from their exhaust. By eliminating the need for rocket launches, VPSL’s net benefit to the environment would be enormously positive.
To close out, we view VPSL not just as an engineering challenge, but as a test case for a new kind of sustainable, infrastructure-led approach to spaceflight – one grounded in realism, openness to critique, and collaborative development.
Left: Artist impression of the inside of Kalpana One, a free space settlement providing artificial gravity. Credits: Bryan Veerseeg / Spacehabs.com; Right: Conceptual illustration of a colony on the surface of Mars. Credits: SpaceX.
Until recently, space settlement advocates have typically split into two camps: those who favor building colonies on the surfaces of the Moon or Mars, and those who prefer constructing O’Neill cylinders in free space, spinning to provide artificial gravity outside of planetary gravity wells. Readers of this blog know I lean toward the latter, mainly because colonies on worlds with gravity lower than Earth’s could pose problems for human physiology, particularly reproduction. Truthfully, we won’t know if humans can reproduce in less than 1g until we conduct long-term mammalian reproduction experiments under those conditions. It would be far cheaper and quicker to perform these experiments in Low Earth Orbit (LEO) rather than waiting for sufficient infrastructure to be established on the Moon or Mars for biological research.
Another approach involves not sending humans into space at all, instead entrusting space colonization to human-level artificial general intelligence (HL-AGI) and conscious machines—a non-biological strategy. With recent advancements in AGI and automation, conscious HL-AGI robots may become feasible in the near future (though the exact timeline—whether decades or longer—remains a matter of debate). This prospect might disappoint many space advocates who view migration beyond Earth as the next phase of natural biological evolution hopefully starting within our lifetimes. Deploying sentient machines would effectively remove humanity from the equation altogether.
If you’ve been following space colonization in the press you’ve most likely heard of the book A City on Mars by Kelly and Matt Weinersmith. I have not purchased the book but I’ve read several reviews and heard the authors interviewed by Dr. David Livingston on The Space Show to get an understanding of the Wienersmith’s overall viewpoint, which is at the very least skeptical, and to some space advocates downright anti-settlement. The book is very pessimistic taking the position that the science and engineering of space settlements for large populations of people is too challenging to be realized in the near future.
Peter Hague, an astrophysicist in the UK, wrote an excellent three part review setting the record straight correcting some of the critical facts that the Wienersmith’s get wrong. But in my opinion the best critique by far was written by Dale Skran, Chief Operating Officer & Senior Vice President of the National Space Society (NSS). In a recent post on the NSS blog, he links to a 90 page Critique of “A City on Mars” and Other Writings Opposing Space Settlement in the Space Settlement Journal where he provides a chapter-by-chapter, section-by-section response to the entire book as well as rebuttals to a few other naysayer publications [“Dark Skies” (2021) by Daniel Deudney; “Why We’ll Never Live in Space” (2023) in Scientific American by Sarah Scholes; “The Case against Space” (1997) by Gary Westfahl].
However, Skran credits the Weinersmiths with an innovative idea he hadn’t encountered before, one that addresses the challenge of human reproduction in low gravity. They suggest establishing orbital spin-gravity birthing centers above surface colonies on the Moon or Mars, where children would be born and raised in an artificial gravity environment—essentially a cosmic crèche. Skran builds on this concept, proposing that the life cycle of Moon or Mars colonists could be divided into phases. The first phase would take place in space, aboard rotating settlements with Earth-normal gravity, where couples would conceive, bear children, and raise them to a level of physical maturity—likely early adulthood—determined by prior research. Afterward, some individuals might opt to relocate to the low-gravity surfaces of these worlds. There, surface settlements would focus on various activities, including operations to extract and process resources for building additional settlements.
Skran elaborated on this split life cycle concept and outlined a roadmap for implementing it to settle low-gravity worlds across the solar system during a presentation at the 2024 International Space Development Conference. He granted me permission to share his vision from that presentation and emphasized that the opinions expressed in his talk were his own and did not reflect an official position or statement from the NSS.
Taking a step back, the presentation summarized research that has been performed to date on mammalian physiology in lower gravity, e.g. studies SSP covered previously on mice by JAXA aboard the ISS in microgravity and in the Kibo centrifuge at 1/6g Moon levels. The bottom line is that studies show some level of gravity less then 1g (artificial or otherwise) may be beneficial to a certain degree but microgravity is a horrible show stopper and much more research is needed in lower gravity on the entire reproduction process, from conception through gestation, birth and early organism development to adulthood. The question of reproduction in less then 1g is the elephant in the space station living room. In my presentation at ISDC last year, I took the position that the artificial gravity prescription for reproduction could impact the long term strategy for where to establish biologically self-sustaining space settlements leading to a fork in the road: a choice between O’Neill’s vision of free space rotating settlements vs. lower gravity surface colonies (because outside of the Earth all other solar system worlds where it is practical to establish surface settlements have less then 1g – e.g. the Moon, Mars, Asteroids and the moons of the outer planets – I exclude cloud settlements in Venus’s atmosphere as not realistic). I’ve been swayed by Skran’s proposal and have come to the realization that we don’t need to be faced with a choice between surface settlements or free space artificial gravity habitats – we can and should do both with this split life cycle approach.
How would Skran’s plan for settling the solar system work? He suggests we start small with rotating space settlements in LEO like Kalpana Two, an approach first conceived by Al Globus and popularized in his book coauthored by Tom Marotta The High Frontier: an Easier Way. Locating the habitats in LEO leverages the Earth’s protective magnetic field, shielding the occupants from radiation caused by solar particle events. This significantly reduces their mass and therefore costs because heavy radiation shielding does not need to be launched into orbit. In addition, the smaller size simplifies construction and enables an incremental approach. Kasper Kubica came up with a real estate marketing plan for Kalpana in his Spacelife Direct scenario.
Skran promoted a different design which won the Grand Prize of the NSS O’Neill Space Settlement Contest, Project Nova 2. The novel space station, conceived by a team of high school students at Tudor Vianu National High School of Computer Science, Bucharest Romania, slightly resembles Space Station V from the film 2001: A Space Odyssey. Many other designs are possible.
Project Nova 2 rotating space settlement, one possible design of a rotating space settlement initially built in LEO then moved out to the Moon and beyond. Credit: Tudor Vianu National High School Research Centre Team / NSS O’Neill Space Settlement Contest 2024 Grand Prize Winner
But to get there from here, we have to start even smaller and begin to understand the physics of spin gravity in space. To get things rolling Kasper Kupica has priced out Platform 0, a $16M minimum viable product artificial gravity facility that could be an early starting point for basic research.
These designs for space habitats will evolve from efforts already underway by private space station companies like Vast, Above, Axiom Space, Blue Origin (with partner Sierra Space) and others. Vast, which has for years had AG space stations on its product roadmap, recently revealed plans to use its orbital space station Haven-1 to be launched in 2026 to study 1/6g Moon level AG in a few years, albeit without crew. And of course let’s not forget last month’s post which featured near term tests proposed by Joe Carroll that could be carried out now using a SpaceX Falcon 9 as an orbital laboratory where researchers could study human adaptation to AG.
Illustration depicting a SpaceX Crew Dragon spacecraft tethered to a Falcon 9 second stage which could be spun up (in direction of down arrow) to test centrifugal force artificial gravity. Credit: Joe Carroll
Back the plan – once the rotating space habitat technology has been proven in LEO, a second and third settlement would be built near the Moon where lunar materials can be utilized to add radiation shielding needed for deep space. The first of these facilities becomes a factory to build more settlements. The second one becomes a cycler, the brilliant idea invented by Buzz Aldrin, initially cycling back and forth in the Earth Moon system providing transportation in the burgeoning cislunar economy just around the corner. The next step would be to fabricate three more copies of the final design. Two would be designated as cyclers between the Earth and Mars. Building at least two makes sense to establish an interplanetary railroad that provides transportation back and forth on a more frequent basis then just building one unit.
Here’s the crown jewel: the third settlement will remain in orbit around Mars as an Earth normal gravity crèche, providing birthing centers and early child development for families settling in the region. Colonists can choose to split their lives between rearing their young in healthy 1g habitats until their offspring are young adults then moving down to live out their lives in settlements on the surface of Mars – or they may choose to live permanently in free space.
This approach enhances the likelihood that settlements on the Moon or Mars will succeed. The presence of an orbiting crèche significantly reduces the risks associated with establishing surface communities by providing an orbital station that can support ground settlements and offer a 1g safe haven to where colonists can retreat if something goes wrong. This alleviates the pressure on initial small crews on the surface, meaning they wouldn’t have to rely solely on themselves to ensure their survival. Finally, an incremental strategy, involving a series of gradual steps with technology readiness proven at each stage through increasingly larger iterations of orbital settlements, offers a greater chance of success.
The final step in this vision for humanity to become a truly spacefaring civilization is to rinse and repeat, i.e. cookie cutter duplication and dispersal of these space stations far and wide to the many worlds beyond Mars with abundant resources and settlement potential. There’s no need to choose between strategies focused solely on surface communities versus spin-gravity colonies in free space. We can pursue both, as they will complement each other, providing families with split life cycle settlement options to have and raise healthy children while tapping the vast resources of the solar system.
Images of resource rich lower gravity worlds beyond Mars with potential for split life cycle settlement (not to scale). Top: the asteroid Ceres. Middle: Jupiter’s Moons, from left to right, Io, Europa, Ganymede, and Callisto. Bottom left: Saturn’s moon Titan. Bottom right: Neptune’s moon Triton. Credits: NASA.
Conceptual illustration of three stages in the construction of an Artificial Gravity Orbital Station (AGOS), envisioned to be a potential replacement for the International Space Station. Credits: Werner Grandl and Clemens Böck
In this month’s post we explore a few concepts and challenges related to artificial gravity (AG) that when explored and understood will enable human’s to live healthy lives and thrive in space. First up, Austria-based architect and civil engineer Werner Grandl, a researcher of space stations and space colonies, and mechanical engineer Clemens Böck describe their concept for the evolving construction of a spinning Artificial Gravity Orbital Station (AGOS) in this Research Gate working paper. AGOS is envisioned as a potential successor to the International Space Station (ISS).
The primary aim of AGOS is to mitigate the adverse health effects of microgravity on humans by providing AG. This includes preventing bone density loss, muscle atrophy, and other physiological issues associated with long-duration spaceflight (more on this later). The station would also serve as a platform for scientific research under varying gravity conditions, potentially including zero-gravity, Mars-like gravity (0.38 g), and Earth-like gravity.
AGOS is proposed as a modular, rotating space station with an initial stage composed of four living modules for a crew of 24 and four zero-gravity central modules. The station is designed to be 78 meters in length, span 102 meters, have a rotation radius of 40 meters and rotate at 4.2 rpm to provide approximately 0.9 g of AG for comfortable living conditions. A non-rotating central hub would carry solar panels providing power as well as docking modules, connecting tubes, and a structural framework to maintain stability. The next stage would double the living quarter modules to eight for 48 occupants. The final configuration would finish out the station with 32 modules for 180 inhabitants.
While the ISS operates in microgravity, which is ideal for certain types of research, AGOS would provide a dual environment where both microgravity and AG conditions can be studied. This dual capability could enhance research in life sciences, materials research, and space technology development.
There are difficulties associated with the concept though, which will have to be resolved. The paper acknowledges that the engineering complexities of maintaining a rotating structure in space, ensuring stability, and dealing with the dynamics of spin gravity on the human body, especially disorientation caused by Coriolis forces, will be quite challenging to overcome.
Still, the future benefits made possible by AGOS will make overcoming these challenges worth the effort. When realized, AGOS would help enable more ambitious space exploration goals, including using the facility for human missions to Mars, where AG may be necessary and beneficial for long-term crew health during transit. It also could open avenues for commercial space ventures in Low Earth Orbit (LEO), including tourism and manufacturing under partial gravity conditions. Ultimately, AGOS could be a significant leap in space station design, enhancing both the scientific output and the prospects for human health in space for extended periods.
In a recent update on their concept penned by Grandl in ResearchOutreach, along with collaborator Adriano V. Autino, CEO of Space Renaissance International, they extend the possibility of constructing self-sustaining colonies in space via utilization of lunar and asteroid materials. Asteroids, in particular, could be hollowed out to serve as natural shields against cosmic radiation and micrometeoroids while mining for resources like metals and water.
Grandl describes a feasible design where a mined-out asteroid provides radiation shielding for a rotating toroidal habitat built inside the body for a population of 2000 people. Rotationally driven by magnetic levitation and natural lighting provided by reflected sunlight, the facility would mimic Earth gravity and environmental conditions for healthy living. This colony could sustainably support human life with integrated systems for air, water, food, and waste management.
Artistic rendition and cross sectional layout of an asteroid habitat for 2,000 colonists with a rotating torus driven by magnetic levitation while sunlight is reflected into the enclosure along the central axis illuminating the living space via a mirror cone. Credits: Werner Grandl
This approach would only work for larger solid body asteroids which are fewer in abundance and tend to be further away from Earth in the main asteroid belt. Smaller “rubble pile” bodies that are loose conglomerations of material like the Near Earth Object (NEO) Bennu recently sampled by the spacecraft OSIRIS-REx, could be utilized in an innovative concept covered a couple of years ago by SSP. The asteroid material is “bagged” with an ultralight carbon nanofiber mesh enclosure creating a cylindrical structure spun to create AG on the inner surface. Physicist and coauthor on this work Adam Frank, mentioned this approach when he recently appeared on the Lex Friedman podcast (timestamp 1:01:57) discussing (among many other space related topics) the search for life in the universe and alien civilizations that may have established space settlements throughout the galaxy and beyond (highly recommended).
A cylindrical, spin gravity space settlement constructed from asteroid rubble like that from the NEO Bennu. The regolith provides radiation shielding contained by a flexible mesh bag made of ultralight and high-strength carbon nanofibers beneath the solar panels. The structure is spun up to provide artificial gravity for people living on the inner surface. Credits: Michael Osadciw / University of Rochester
SSP has covered a scenario conceived by Dr. Jim Logan similar to Grandl’s but going big using several O’Neill Island One rotating colonies strung end-to-end in a tunnel drilled through the Martian moon Deimos.
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
The authors see the creation of these permanent spin gravity settlements in space as the next step in human evolution. This vision, once considered science fiction, is grounded in realistic engineering and scientific principals.
Back to the near future, Joe Carroll addresses two topics pertinent to how AG might help mitigate deterioration of human health in space in a couple of articles in the December 9, 2024 issue of the Space Review. In the first piece, Carroll poses the provocative question “What do we need astronauts for?”, and argues that robotic spacecraft have surpassed human astronauts in space exploration due to their ability to travel farther, endure harsher conditions, and deliver more data over longer periods at lower costs. This advantage will become even greater as robotic technology and AI progress in the near future.
As an aside, for the foreseeable future there will be a debate over humans vs. machines in space. Regardless of concerns related to risks to safety, costs, and physical limitations, humans will still have the edge over robots for a while when it comes to adaptability/problem solving, complex task execution, spontaneous scientific decisions and public inspiration. A collaborative approach, leveraging the strengths of both humans and robots to achieve more efficient and effective outcomes may be better for space development in the near term.
That being said, Carroll suggests that human spaceflight activities should be focused on assessing the viability of settlements off Earth, particularly by studying human health in lunar and Martian gravity. He emphasizes the lack of data on long-term health effects in low-gravity environments and proposes the use of AG systems in LEO to simulate lunar and Martian gravity for research purposes. Carroll concludes that understanding human health in low-gravity environments is crucial for future space settlements and that humans will play a vital role in this research.
This leads into his second article which provides suggestions on how to quickly test AG in LEO. He suggests launching and deploying a long, duel dumbbell variable gravity station composed of a Crew Dragon capsule tethered to a Falcon 9 second stage that rotates to produce AG. Providing lunar gravity at one end and Martian gravity at the other, the facility would provide an on orbital laboratory where researchers could study human adaptation to these conditions. Such tests would be more cost-effective and less risky than conducting experiments directly on the Moon or Mars.
Illustration depicting a SpaceX Crew Dragon spacecraft tethered to a Falcon 9 second stage which could be spun up (in direction of down arrow) to test centrifugal force artificial gravity. Credit: Joe Carroll
But there are challenges associated with determining appropriate spin rates. This is vital as they influence the station’s radius and cost. Previous studies using vertical-axis rotating rooms on Earth have shown that higher spin rates can cause discomfort, including nausea and headaches. However, these ground-based tests may not accurately represent the sensory effects experienced in space-based AG facilities, where the spin axis is perpendicular to the direction of gravity.
And in case you missed it, Kasper Kupica shared with SSP his Spacelife Direct approach to quickly getting started by selling AG real estate in LEO.
Implementing AG in space habitats could enhance human health and improve various aspects of space station operations (e.g. fluid flow, heat conduction, fire safety) while enabling studies of human physiology under low gravity conditions. Conducting AG tests in LEO is a prudent step toward understanding human health, determining biology related requirements for future lunar or Martian colonies and may ultimately determine the long term strategy for space settlement.
Illustration of a Lunar ISRU Energy Storage and Electrical Generation concept (not to scale). The system utilizes three heat transfer fluid circuits. The collection loop in the receiver tube is heated by sunlight from a field of mirrors during the lunar day and circulates to the thermal mass raising its temperature. Upon lunar nightfall, a discharge loop transfers heat from the thermal reservoir to the Stirling engine for electricity production. While the engine is running a thermal regulation loop dissipates heat through the radiator. Credits: system layout by Mario F. Palos and Ricard González-Cinca, modified to add component labels; lunar landscape by Grok 2
One of the difficulties of designing solar power systems for use on the Moon is the challenge of energy storage during the 14 day lunar night at lower latitudes far from the peaks of eternal light at the poles. Such systems would benefit from technology that leverages in situ resource utilization (ISRU) for this critical function rather then expensively transporting batteries from Earth. It would be ideal to model these systems prior to use via computer simulations to optimize the design before bending metal. In the journal Advances in Space Research, Spanish physicists Mario F. Palos and Ricard González-Cinca explore this approach in a paper that examines an ISRU-based system for energy storage and electricity generation.
The architecture of the proposed system, dubbed Lunar ISRU Energy Storage and Electrical Generation (LIESEG), collects solar energy during the lunar day via a mirror field to concentrate sunlight on a receiving pipe containing a heat transfer fluid (e.g. molten sodium). The heated fluid flows to a thermal mass raising the temperature of the energy reservoir. The resultant stored thermal energy from the reservoir is discharged through a second fluid loop used to drive a Stirling engine for electricity production during both day and night. A third heat rejection loop thermally regulates the system by transferring heat from the cold side of the heat engine to the radiator. This modular design balances efficiency and durability under extreme lunar conditions.
The ISRU implementation angle of the study emphasizes the use of lunar regolith and other local materials to minimize reliance on Earth-based supplies. This not only reduces launch costs but also aligns with long-term sustainability goals for lunar habitats.
To analyze the LIESEG system performance, simulations were carried out using EcosimPro software, a tool used by the European Space Agency in multiple aerospace applications, to assess power output, efficiency, and scalability. A comprehensive theoretical model based on the thermodynamics of the subsystems under lunar conditions was developed to analyze the energy flow and efficiency of the system. The study evaluated the specific power performance (power output divided by launch mass) of the system, highlighting its potential to be superior to other conventional methods like photovoltaic systems or nuclear reactors in terms of mass efficiency and sustainability. It also discusses the influence of key factors like the thermal conductivity of lunar regolith, the size and orientation of solar collectors, and the efficiency of the Stirling engine.
The authors conducted a detailed trade-off analysis of technologies, considering criteria like transportability, installation complexity, operational reliability, scalability, and lifespan. Solar collection and thermal conversion technologies were highlighted as critical components for achieving operational stability.
The proposed LIESEG system offers a promising approach for sustainable energy production on the Moon, potentially reducing reliance on Earth-launched resources and enabling longer, more autonomous missions. The system’s feasibility was demonstrated through computer modeling whose results show LIESEG to be practical for initial lunar missions with lower energy needs, as well as for later advanced bases requiring higher power outputs (up to 100 kWe and beyond). This research shows that a LIESEG system has merit for planning future development of energy infrastructure supporting initial lunar outposts and eventually, permanent settlements on the Moon.
Artist rendering of the Lunar Outpost Eagle Lunar Terrain Vehicle. Credit: Lunar Outpost
Space News recently reported that Colorado-based Lunar Outpost has signed an agreement with SpaceX to use Starship to deliver their lunar rover, known as the Lunar Outpost Eagle, to the Moon. Announced November 21, the contract supports the Artemis program with surface mobility and infrastructure services. The agreement positions Starship as the delivery vehicle for Lunar Outpost’s Lunar Terrain Vehicle (LTV), which is a contender for NASA’s Lunar Terrain Vehicle Services (LTVS) program. The exact terms of the contract, including the launch schedule, were not disclosed in the announcements. Lunar Outpost has assembled a contractor team under the banner “Lunar Dawn” to execute the company’s LTV solution. The collaborative development program includes in industry leaders Leidos, MDA Space, Goodyear, and General Motors.
Rover Design Features
Mobility and Functionality: The Lunar Outpost Eagle is designed to support both crewed and autonomous navigation on the lunar surface. It’s built to operate even during the harsh lunar night, exhibiting resilience against the Moon’s extreme temperature changes.
Collaborative Development: The Lunar Dawn team brings expertise in spacecraft design, robotics, automotive technology, and tire manufacturing, ensuring a robust and versatile design.
Size and Capacity: Described as truck-sized, the Eagle LTV is intended to be a valuable vehicle for lunar operations, capable of transporting heavy cargo to support NASA’s Artemis astronauts and commercial activities.
Testing and Refinement: The design has undergone human factors testing at NASA’s Johnson Space Center, with feedback from astronauts being used to refine the vehicle’s usability and functionality.
Future Plans
NASA’s LTV Program: Lunar Outpost is one of three companies selected by NASA for the LTV program to develop rovers to support future Artemis missions. The other two companies are Intuitive Machines and Venturi Astrolab. After a preliminary design review (PDR), NASA will select at least one company for further development and demonstration, with the goal of having a rover operational in time for Artemis 5, currently scheduled for 2030.
Commercial Operations: Beyond NASA’s usage, the rovers will be available for commercial operations when not in use by the agency, aiming to support a sustainable lunar economy. This includes plans for infrastructure development and scientific exploration.
Series A Funding: Lunar Outpost has recently secured a Series A funding round to accelerate the development of the Lunar Outpost Eagle, ensuring that the rover project moves forward regardless of the outcome of NASA’s selection process.
Long-Term Vision: The company’s vision extends to enabling a sustainable human presence in space, with plans to leverage robotics and planetary mobility for development of infrastructure to harness space resources.
This partnership with SpaceX and the development of Eagle under the Lunar Dawn program are pivotal steps in advancing both NASA’s lunar exploration goals and commercial activities on the Moon.
Once delivered to the Moon by Starship, the Eagle rover will drive over harsh regolith terrain which, as discovered by Apollo astronauts when driving the Lunar Roving Vehicle, presents several unique challenges due to the Moon’s distinct environmental conditions. First, lunar dust is highly abrasive and can become electrostatically charged sticking to surfaces and mechanisms resulting in wear and degradation of wheels, bearings, and sensors potentially leading to equipment failure. The Moon’s low gravity can make traction difficult. Rovers might slip or skid becoming less stable when accelerating, braking or turning. Terrain variability and nonuniformity on loose powdery dust or sharp, rocky outcrops could cause stability issues.
These problems can be solved by creating roads with robust, smooth surfaces for safe and reliable mobility on the Moon. Initially, the regolith could be leveled by robots with rollers to compact the regolith to make it less likely to be kicked up by rover wheels. Eventually, technology being developed by companies like Ethos Space for infrastructure on the Moon using their robotic system for melting regolith in place for fabricating lunar landing pads, could be used to build smooth, stable roads.
A network of roads could be constructed to transport water and other resources harvested at the poles to where it would be needed in settlements around the Moon extending from high latitudes down to the equatorial regions. As envisioned by the Space Development Network, this system of roads could be created to provide access to a variety of areas to mine valuable resources as well as thoroughfares to popular exploration and tourism sites. The development of the highway system could start at the poles with telerobots, then eventually be expanded to include equatorial areas and would be fabricated autonomously prior to the arrival of large numbers of settlers.
Longer term, a more efficient method of transportation on the Moon could be magnetic levitation (maglev) trains. Research into this technology has already been proposed by NASA which is actively developing a project named “Flexible Levitation on a Track” (FLOAT), which aims to create a maglev railway system on the lunar surface. This system would use magnetic robots levitating over a flexible film track to transport materials, with the potential to move up to 100 tons of material per day. The FLOAT project has advanced to phase two of NASA’s Innovative Advanced Concepts (NIAC) program.
Artist’s rendering of the Flexible Levitation on a Track (FLOAT) maglev lunar railway system to transport materials on the Moon. Credit: Ethan Schaler / Jet Propulsion Laboratory
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
