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Wohrad: The first serious design of an artificial gravity space station

The Habitat Wheel (Wohrad). Redrawing of Fig. 84 from The Problem of Space Travel (Noordung, 1929). Color codes identify various categories of human activities – Blue: Sleep; Yellow: Hygiene; Green: Food; Red: Work and leisure, Grey: Circulation and ancillary spaces. Image and minor edits to text based on Figure 16 of the author’s paper. Credits: Fig. 16, from paper by Sandra Häuplik-Meusburger / Used under CC by 4.0

Before O’Neill’s Stanford Torus. Before Stanley Kubrick’s Space Station V in 2001: A Space Odyssey. Before Von Braun’s Space Wheel. There was Hermann Potočnik’s “Wohnrad”, or Habitat Wheel. Writing under the pseudonym Herman Noordung, his 1929 book Das Problem der Befahrung des Weltraums (The Problem of Space Travel) lays out the first serious architectural design of a rotating space station intended to incorporate artificial gravity for human habitation. In the forthcoming issue of Acta Astronautica coming out in April, space architect Sandra Haeuplik-Meusburger examines the early space station architecture via a digital and physical reconstruction. Noordung’s design is considered a milestone in space habitat concepts predating practical spaceflight by many decades.

Noordung’s Wohnrad provided one of the earliest fully developed technical designs for a rotating space station. Unlike speculative ideas before it, his design included three components with specific functions — a rotating Habitat Wheel spinning to create artificial gravity for living spaces at the rim. A free flying lab called the Observatory for scientific discovery. And a much larger sun facing solar power plant (Machine Room), also free flying, which would provide power and life support for the Observatory. Earlier scientists (e.g., Konstantin Tsiolkovsky, Hermann Oberth) suggested early ideas for space stations, but Noordung was the first to produce comprehensive architectural and mechanical drawings of one.

Noordung’s rotating wheel was the first space station intended to provide centrifugal force artificial gravity — a hugely influential idea that foreshadowed decades of later space habitat concepts including Von Braun’s Space Wheel in the 1950s, space station depictions in seminal science fiction movies such as Kubrick’s 2001: A Space Odyssey and of course, O’Neill’s Stanford Torus which didn’t come along until 1975. His design not only addressed physiological needs (countering weightlessness) but architecturally integrated human life support, observation, and workspaces into one cohesive structure — a novel systems-level vision at the time.

Artist impression of the interior of a Stanford Torus. Credits: Don Davis / NASA

Haeuplik-Meusburger’s paper underscores how Noordung’s concept was architecturally rich — detailing spatial organization, functional modules, interior arrangements, including the logic for transitions between rotating and non-rotating sections. Her reconstruction work though modern digital modeling and 3D printed archetypes reveals architectural relationships between modules in more detail than prior historical treatments. Digital reconstruction of the original design provides new insights into proportional relationships, functional layout, and how Noordung envisioned human interactions in space. 3D printing prototypes helped the author reinterpret design logic in ways not possible from 2D archival drawings.

Lets dive in to the details. The author uses a mixed-method architectural and design research approach combining historical analysis with digital and physical reconstruction of Noordung’s original space station concept. She starts by collecting and studying the original material from Noordung’s 1929 book Das Problem der Befahrung des Weltraums — including diagrams, plans, textual descriptions, and images of the Wohnrad (Habitat Wheel) and associated modules (Observatory and Machine Room). The historical review also places the design in the context of other early spaceflight concepts and later influences (e.g., von Braun’s work and science-fiction imagery). This established a baseline understanding of the original design intent and the architectural logic behind the space station.

Next, Haeuplik-Meusburger created a virtual reconstruction taking historical, two-dimensional drawings and texts and translating the original figures into a detailed 3D digital model, probably using CAD or architectural modeling tools (the paper did not specify the software explicitly). This digital reconstruction allowed her to visualize and analyze the spatial layout, proportions, and structural relationships that aren’t obvious in the original flat plans.

After the digital model was created, the author 3D printed a physical prototype enabling tangible exploration of how spaces and modules relate — a method often used in architecture to test and critique design concepts. Moving between digital and physical forms helped identify aspects of the design that might be missed solely through drawing interpretation. Throughout the reconstruction, she provided an architectural interpretation of the design informed by human factors to understand how people would live, move, and interact with spaces under rotational artificial gravity — a layer of analysis beyond mere geometric reconstruction.

The author’s 3D modeling revealed the relationships between modules more clearly than the original drawings. Her findings included unexpected details about occupant circulation in the Habitat Wheel (e.g., access paths, stairs/elevator placement) and how spaces might feel or operate under rotation. This is significant because Noordung’s original descriptive text and flat plans alone could not convey the experience of inhabiting these spaces — a key gap filled by the reconstruction method.

The Habitat Wheel interior is partitioned into activity spaces and individual rooms in the outer rim structure accessed via a central corridor. This is where the crew would spend most of their time close to Earth-like conditions. In the illustration provided above by the author, the layout of the functional areas is shown color coded by the activities envisioned by Noordung.

His original design pegged the radius of the Habitat Wheel at 15 meters with a spin rate of 7.5 rpm resulting in level of artificial gravity of 0.94g. What we know now from many decades of research on human physiology under spin gravity conditions, this arrangement was impractical. The rate of rotation and relatively short radius of the station would likely result in significant Coriolis effects causing vestibule discomfort and disorientation in the occupants. Still, Haeuplik-Meusburger’s analysis places Noordung’s work on firm architectural and design grounds including the practicality of the Habitat Wheel as a concept with enduring lessons for how we might design rotating habitats in the future.

Realizing the issue with the Habitat Wheel’s short radius and high rotation rate, Haeuplik-Meusburger makes use of a Comfort Chart developed by Theodore Hall, a space architect and recognized expert on artificial gravity. The tool is a graph with habitat radius plotted against angular velocity with comfort zones where disorientation is minimized mapped on the plane of the chart. Armed with this information, the author proposes increasing the radius and reducing the rotation rate to a tolerable level, or even considering partial gravity levels of 0.2 to 0.5 g. Incidentally, Hall coauthored a paper on a Mars Cycler with artificial gravity covered by SSP last November.

Exploded axonometric view of the Habitat Wheel components with dimentions according to The Problem of Space Travel (Noordung, 1929). Credit: Fig 14 from paper (with minor caption text edits) by Sandra Häuplik-Meusburger / Used under CC by 4.0

Haeuplik-Meusburger’s use of physical and virtual models helps us better interpret how Noordung imagined habitability and use. For example, spatial organization suggests how living quarters, laboratories, and circulation were meant to function under artificial gravity conditions. In addition, her research clarified how functional logic (like the location of service spaces versus leisure or observation spaces) reflected deliberate design choices, not just schematic ideas.

The Observatory was intended primarily for scientific observation and microgravity research. It was designed to be free flying tethered to the Machine Room which provided power and breathable air via cables and flexible tubes, respectively. The weightless environment would minimize motion enabling equipment to operate more effectively in the absence of vibration. The facility would be equipped with instruments for astronomical observations, Earth monitoring, and telecommunications. The low-gravity environment made precise pointing of telescopes easier and instrument mounting simpler. In addition, there was a laboratory for performing experiments in microgravity. Noordung envisioned the station not just as a place to live but as a scientific platform in orbit, decades before orbital observatories and research facilities became reality.

One notable aspect of the Observatory was that the facility was intended to be placed in geostationary orbit 35,900 km above the Earth’s surface completing one orbit per day fixing it in the sky above the same location. Noordung suggested it could be used as a telecommunications relay station seventeen years before Arthur C. Clark introduced the concept of a communications satellite in a 1945 article in Wireless World.

The Machine Room was the station’s primary power plant, the earliest know example of a solar thermal-engine for use in space. The system featured a 120 meter concave mirror permanently facing the sun and focusing sunlight on heat pipes, whose working fluid would drive a turbine to generate electricity. The condenser and radiator in the thermal-engine circuit would be located at the back of the facility shielded from sunlight. Noordung chose nitrogen as the working fluid for the system over water as it results in significantly lower condenser temperature, leveraging the extreme cooling of the vacuum of space. The Machine Room was the largest facility of the space station containing the main solar power plant with storage batteries, a large transmission station, and a ventilation system serving the Observatory. Noordung’s design was remarkably forward-thinking, addressing real thermodynamic and space-environment challenges in a way that holds up conceptually even now.

One of the most innovative aspects of the space station was the design of the airlock located at the hub of the Habitat Wheel. In addition to addressing the core functions of maintaining internal atmospheric pressure during ingress/egress, allowing safe transition to vacuum and conserving breathable air, Noordung had a novel solution for resolution of the rotating-to-inertial frame problem created by a spinning space station – a rotating airlock chamber capable of counter-rotation.

Since the station’s rim would be rotating to generate artificial gravity and is mechanically connected to the hub, obviously the airlock would be rigidly attached to this rotating structure and have the same angular momentum as the station. Docking spacecraft or individuals on EVAs would have to synchronize their rotational motion to match the door of the airlock, which complicates entry or exit. Noordung’s solution was a system in which the astronaut would enter the airlock (e.g. when exiting the station) while it is rotating with the the habitat wheel. The chamber would be then mechanically driven to de-spin in the opposite direction of the station’s spin. When its angular velocity cancels out the station’s rotation, the airlock would become inertially stationary relative to space outside of the ship, upon which the outer hatch could be safely opened. Noordung’s design included ball-bearing systems, rotational drive mechanisms and sealed rotational interfaces implying that there would be a structural ring allowing relative motion between rotating and non-rotating sections, a mechanical transmission capable of controlled deceleration and a pressure sealing mechanism across a rotating joint. The latter requirement is mechanically demanding and remains challenging even in modern engineering – but he anticipated the mechanical need even though he did not mathematically model these issues in modern terms.

As an aside, the airlock concept was not the first ever conceived (airlocks were already used in mining, tunneling, and civil engineering projects on Earth in those times), but it is one of the earliest detailed proposals of an airlock in spaceflight literature of that period, specifically designed for a space station and EVA-type operations.

Since the station’s life support system was not intended to be ecologically closed and the facility was not intended to be crewed permanently, Noordung understood that supplies needed to be conserved as resupply from Earth would be expensive, especially prior to the advent of reusable rockets. Thus, his design pumped precious air in the airlock back into the station rather then vent it to space upon exit.

Original illustration of Noordung’s airlock concept (Figure 76 in The Problem of Space Travel, Noordung, 1929) Top view of the exterior door and section through the rotating airlock of the Habitat Wheel.  Credit: text by Sandra Häuplik-Meusburger with minor modification / Used under CC by 4.0

Haeuplik-Meusburger’s modeling and 3D printed physical reproductions reveal clearer spatial and operational insights about how the airlock access points functioned within the overall station layout showing relationships to the hub, circulation paths, and machinery areas. These aspects were not apparent in Noordung’s original 2D drawings as they compressed depth and circulation in ways that are hard to interpret from flat figures. For example, the air lock’s position in the axial hub is not incidental. It sits in a circulation node, not an isolated compartment. Her reconstruction reinforces that the airlock was not an accessory to the station but was embedded in a carefully organized hub as part of a systems cluster including machinery, life-support infrastructure, low-gravity workspace and external access. Seeing that integration clearly in 3-D strengthens the argument that Noordung was thinking in systems-architectural terms, one of the main conclusions of the paper. This systems integration is easier to recognize when viewing the station as a volumetric structure rather than separate diagrams.

Haeuplik-Meusburger’s analysis is innovative in how it reconstructs Noordung’s foundational ideas that deeply influenced both the technical lineage of space habitat design, and the cultural imagery of space stations in science and fiction. Her methods demonstrate how digital/physical reconstruction can deepen understanding of design concepts that were never constructed. Finally, the work reveals architectural details and ergonomic considerations that had previously been obscured in the original diagrams. By re-evaluating Noordung’s work with new modeling techniques, the paper provides both historical clarity and design insight that enriches our understanding of Noordung’s prescient visions for living in space, many of which were ahead of his time.

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TESSARAE for orbital biolabs and more

Conceptual illustration of an orbital biolab constructed using TESSERAE architecture. Credit: Aurelia Institute

At last year’s International Conference on Environmental Systems (ICES), Aurelia Institute Vice President of Engineering Annika Rollock presented a paper on development of an orbital TESSERAE habitat to conduct biotechnology research. TESSERAE (Tessellated Electromagnetic Space Structures for the Exploration of Reconfigurable, Adaptive Environments) covered previously on SSP, was conceived and developed by Ariel Ekblaw, cofounder and CEO of Aurelia as part of her doctoral thesis at MIT. A TED Talk by Ekblaw from last April provides more detail on the concept with footage of prototypes demonstrated in space on the International Space Station (ISS).

The paper “Development of a Flight-Scale TESSERAE Habitat Concept for Biotechnology Research Outpost Applications” by Rollock, Max Pommier, William J. O’Hara, and Ekblaw, presents preliminary findings from a case study on the TESSERAE habitat which aims to bridge traditional space station architectures with future-oriented, adaptive designs. Legacy space habitats, such as the ISS, rely on monolithic hulls or cylindrical modules constrained by launch vehicle fairings, limiting scalability and geometric flexibility. TESSERAE offers a departure from these norms by using flat-packed, tile-based modules that self-assemble in orbit to form a truncated icosahedron. This structure, commonly known as a “buckyball” sharing the same shape as the carbon molecule buckminsterfullerene (C60) named after architect and inventor R. Buckminster Fuller due to its resemblance to his geodesic dome designs, will enable larger volumes and novel configurations when connected together.

The authors provide more detail on the concept referencing a trade study presented at ICES 2023 by the Aurelia Institute, which reviewed historical and contemporary space architecture to identify gaps and opportunities. They underscore the need for habitats that are both innovative and grounded in proven engineering principles. The paper serves as a “dynamic snapshot” of the ongoing TESSERAE case study as of spring 2024, inviting collaboration rather than presenting a finalized design. It envisions a platform based on TESSERAE as a commercial biotechnology research outpost in Low Earth Orbit (LEO), aligning with NASA’s Commercial LEO Destinations (CLD) goals and the burgeoning market for microgravity-enabled research. The paper highlights subsystem analyses for environmental control, thermal management, and power, alongside novel interior layouts informed by user research and terrestrial architecture best practices.

The authors make the case that self-assembling structures like TESSERAE could revolutionize human spaceflight by enabling adaptive environments that support diverse crews, including non-professional astronauts. This is particularly timely as the ISS nears decommissioning in 2031, necessitating new orbital platforms for critical research with increasing involvement by private industry..

The mission overview lays out one possible operational vision for the 2030s: a TESSERAE microgravity platform sustaining human life, scientific inquiry with a biotechnology focus, and ancillary activities in LEO. Designed for a crew of four—two biotechnologists and two career astronauts—it features biotechnology applications, capitalizing on microgravity’s unique properties for protein crystallization and biologic medicines production.

Protein crystal growth in space yields superior quality due to reduced sedimentation and convection, facilitating precise structural data for drug discovery. The paper references applications in treating among other maladies, muscular dystrophy, breast cancer, and periodontal disease, citing decades of ISS-based experiments by pharmaceutical firms. Similarly, biologic medicines—proteins, enzymes, nucleic acids, and antibodies derived from natural sources—benefit from low-gravity acceleration in discovery and preclinical testing. The global biologics market is projected to reach over $700 billion by 2030, underscoring the potential economic upside. Innovations like Redwire’s seed-based crystal manufacturing and Varda’s in-orbit ritonavir production (an HIV antiviral) have demonstrated feasibility, with microgravity enabling bulk-free returns via seeds or small samples.

The concept of operations (ConOps) details a 32-tile assembly (20 hexagons, 12 pentagons, each 2.26 m edge length, 0.46 m thick), launched in a dispenser stacked aboard a SpaceX Falcon 9 launch vehicle. After dispensing out of the payload bay, orbital self-assembly employs electro-permanent magnets for bonding at the tile edges, forming a 493 m³ pressurized volume post-clamping and gasketing. Outfitting prioritizes autonomy: critical systems integrate into the tiles, with secondary elements (e.g., storage, mobility aids) added via robotics or minimal EVAs. After full systems checkout post-assembly, operations include 1–6 month crewed expeditions, cargo resupplies, and uncrewed intervals.

Comparative occupancy analysis positions TESSERAE favorably: at 123 m³ per person, it rivals the ISS (168 m³ for six) and Tiangong (113 m³ for three) emphasizing permanent quarters and lab space for its four-person upper limit, ensuring psychological and functional adequacy. This aligns with NASA’s CLD objectives, fostering commercial viability while accommodating “visiting scientists” alongside professionals.

With respect to interior concepts and design principles, TESSERAE’s non-cylindrical, open-central geometry introduces unique interior challenges and opportunities, diverging from conventional axial modules. The paper explores layouts tailored for diverse crews, drawing on user interviews (astronauts, analogue astronauts, scientists) and literature like Sharma et al.’s Astronaut Ethnography Project and Häuplik-Meusburger’s activity-based approach. Five core design principles and “desirements” guide this strategy: a human-centered approach accounting for bodily navigation and psychosocial needs; contextual affordances leveraging microgravity (e.g., multi-axis movement in open volumes); sensory mediation via lighting, acoustics, and airflow for zoned activities; accessibility with ample, clutter-free stowage; and a balance of permanence (fixed volumes) with flexibility (reconfigurable elements like folding partitions).

These principles inform environmental mediations for biotechnology: labs require vibration isolation and containment for experiments, while communal spaces mitigate isolation via views and biophilic design elements. The paper discusses layouts prioritizing flow, orientation, and adaptability. One configuration features a central “node” for socialization and exercise, ringed by radial spokes: private quarters, labs, hygiene nodes, and utility closets embedded in the shell. This exploits the buckyball’s symmetry for efficient use of space, with tethers and handrails guiding microgravity transit. Labs allocate ~100 m³ total, segmented for crystallization (vibration-dampened gloveboxes) and biologics (flow benches, incubators), in accordance with preliminary user needs.

Diagram (Figure 5 from paper) depicting four internal layout options, with key space dividers and elevation maps depicting the arrangement of functional areas on each external tile. Credits: Annika E. Rollock et al. / Aurelia Institute
Exploded view (Figure 6 from paper) of the Lofted layout option for the TESSERAE habitat. Credits: Annika E. Rollock et al. / Aurelia Institute

Sensory design mitigates monotony: variable LED lighting simulates diurnal cycles, acoustic panels dampen noise, and materiality ( e.g., fabric panels) enhances tactility. Stowage integrates nets and modular racks, addressing chronic ISS issues. Flexibility allows crew reconfiguration via magnetic mounts, supporting mission evolution. Hygiene and galley zones emphasize efficiency, with water-efficient fixtures tied to the Environmental Control and Life Support System (ECLSS). Overall, interiors blend spacecraft rigor with architectural humanism, fostering well-being for non-experts.

The authors provide a subsystem analysis discussing trades for ECLSS, thermal control, and power. ECLSS recommendations draw from ISS heritage leveraging NASA’s Carbon Dioxide Removal and Oxygen Generation Assemblies but adapt to TESSERAE’s modularity: distributed nodes per each individual tile reduce single-point failures, with regenerative loops for water and air.

Thermal management addresses the buckyball’s high surface-area-to-volume ratio, prone to radiative losses. Multi-layer insulation and variable-emittance coatings are proposed, integrated into tiles for passive control, supplemented by active radiators and heat exchangers. Finite element modeling was used to inform stress distribution across the tile seams.

Power generation leverages roll-out solar arrays deployed post-assembly, sized for 20–30 kW demands for the needs of the labs, ECLSS and other power systems. Trades evaluate photovoltaics vs. emerging tech, prioritizing launch mass. Batteries buffer eclipse periods, with guidance navigation integrated with attitude control via control gyroscopes, minimizing propellant use.

These analyses emphasize scalability: TESSERAE’s tiles enable redundant, upgradable subsystems, contrasting with legacy monolithic designs.

The paper identifies a few challenges. For instance, assembly reliability (magnet actuation in vacuum), pressurization integrity at seams, and outfitting logistics. But opportunities abound in biotech such as enabling “fly-your-own-experiment” for scientists, accelerating drug pipelines, and demonstrating adaptive habitats for lunar/Mars precursors. User research highlights psychosocial needs—privacy amid openness, sensory variety against confinement—which will inform iterative designs.

Future work matures hardware testing in microgravity (e.g., parabolic flights), refines trades via modeling, and pursues partnerships for CLD certification. The authors invite input, positioning TESSERAE as a collaborative pivot toward reconfigurable space living.

This case study encapsulates one of TESSERAE’s promises: a self-assembling, biotech-focused habitat merging innovation with pragmatism. By the 2030s, it could sustain crews in 493 m³ of adaptive volume in LEO, tapping into a $700B+ market while advancing human-centered space architecture. Preliminary insights from this work — from ConOps to design of interiors— lay the groundwork for transformative outposts that not only return benefits to human lives on Earth, but are preparing humanity to become a spacefaring species.

While the Aurelia Institute is a nonprofit organization, Ariel Ekblaw cofounded a startup called Rendezvous Robotics which aims to generate revenue building large-scale structures like antenna apertures, space solar power arrays and orbital data centers, all autonomously fabricated in space using TESSARAE. Rendezvous Robotics recently partnered with another startup called Starcloud which plans to fabricate gigawatt-scale orbital AI data centers using Ekblaw’s invention, a potentially huge new market forecasted to be just over the horizon by several tech leaders in the news recently. Blue Origin CEO Jeff Bezos just announced he’ll be leading a new AI company called Project Prometheus and says AI orbital data centers are coming in the next decade or two. Last May former Google chief executive Eric Schmidt acquired Relativity Space to put data centers in orbit. Earlier this month Elon Musk says in not more than 5 years, the lowest cost way to do AI compute, will be in space. And Mach33 Research, an investment research firm focused on the industrialization of space, predicts that orbital compute energy will be cheaper than on Earth by 2030. TESSARAE could be leveraged to assemble these space-based hyperscalers autonomously and quickly while proving out this reconfigurable technology which can be used to build large-scale adaptable habitats and other infrastructure in space for a multitude of applications. As stated on the their website,

“Aurelia is working toward geodesic dome habitats, microgravity concert halls, space cathedrals—the next generation of space architecture that will delight, inspire, and protect humanity for our future in the near, and far, reaches of space.”

Artist illustration of a habitat constructed from TESSARAE modules in Earth orbit. Credit: Aurelia Institute

Finally, in celebration of the 50th anniversary of the 1975 NASA Space Settlements: A Design Study, the Institute announced today they are sponsoring The Aurelia Institute Prize in Design for Space Urbanism. An award of up to $20,000 will granted for concepts of a functioning space station in one of three categories: A space station in LEO or at a Lagrange point; a space habitat in lunar orbit or on the surface of the Moon; or an automated industrial facility (e.g. focused on space mining, energy, biotech, etc.) in one of those locations.

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Novel design of a Mars Cycler

Above – Mars Cycler exploded section. Below – Cruise ship-sized Mars Cycler booster (left) and docking configuration (right). Credits: Offworld Industries Corp.

At the 54th International Conference on Environmental Systems held in Prague, Czechia, this past July, a paper was presented describing an innovative design of a large-scale Mars Cycler. The authors, A. Scott Howe, John Blincow, Theodore W. Hall, and Colin Leonard, make the assumption that a significant planetary migration to Mars will happen in the near future, citing Elon Musk’s often stated goal of establishing a one-million person colony on the Red Planet by 2050. The authors argue that Starship will not be a suitable transportation method for a large, non-professional clientele on what has historically been a six-month journey due to the physiological and psychological health risks of a long-duration mission (not withstanding a recent paper penned by University of Santa Barbara physics undergrad Jack Kingdon proposing two trajectories that reduce transit times to between 90 to 104 days each way).

Instead, they envision a “cruise ship” approach using a large, robotically constructed Mars Cycler that would continuously travel between Earth and Mars. The concept for a Mars Cycler was first conceived by Buzz Aldrin in a 1985 paper, and in recognition of his invention, is often referred to as an Aldrin cycler. This particular cycler design is advantageous because it would use minimal propellant to maintain its trajectory. The concept features a dual-torus structure, with a non-rotating outer torus for docking and a rotating inner torus to provide artificial gravity. The paper lays out in detail the specifications for a minimal-sized version with crew capacity of 52-61 people, and calculates the mass and equipment required for the vessel. The authors estimate that it would take 63 Starship launches (version 3) to deliver the construction materials and propellant to low Earth orbit (LEO). A scaled up larger cruise ship-sized version with a capacity of 1000 occupants would take 428 Starship version 3 launches, which is within the range of engineering possibility and certainly within the launch rate of thousands of Starships Elon Musk envisions as part of his Mars colonization plans.

The Mars Cycler would be assembled using Offworld Industries Corporation’s Sargon System, a family of new construction machines the company claims could build an entire space station in half a year (Blincow is CEO of Offworld Industries Corp). The novel construction technology autonomously assembles preformed hull panels loaded in a magazine, robotically dispensed, formed and welded into large toroidal (or other shaped) space stations ready to be pressurized.

The paper advocates for the cycler to provide artificial gravity to mitigate the deleterious health impacts of microgravity allowing occupants to maintain healthy muscle and bone density throughout the journey. The proposed design decouples an inner artificial gravity centrifuge from an outer non-rotating torus, which offers several operational benefits:

  • Distributed docking ports: The non-rotating outer torus can accommodate multiple visiting vehicles docking at various points around its perimeter.
  • Fixed systems: Solar panels and radiators can be mounted without the need for gimbals or motorized mounts, simplifying the design.
  • Seamless transfer: Crew and cargo can be transferred between visiting vehicles and the cycler without the need for spin-up or spin-down procedures.

The paper identifies several challenges to overcome in order to realize an operational Mars Cycler. The top five include:

  1. Large-scale space construction: The project requires the construction of very large orbital structures. A key challenge is maintaining tolerance control during assembly, ensuring panels fit together precisely and the torus closes properly.
  2. Attitude control and maneuvering: The paper assumes, but does not detail, that maneuvering large quarter-toroids in proximity to each other will be possible without “exotic solutions’. This is a significant challenge because each section would have its own center of mass and orbit, creating strain on connected elements.
  3. Artificial gravity implementation: A number of difficulties are discussed, including economic spin-up/spin-down, docking procedures while the structure is spinning, and performing extra-vehicular activities (EVAs) under rotation. The paper also notes that transferring power, control, information, and liquids between the rotating and non-rotating segments would be challenging.
  4. Mars surface infrastructure: The paper acknowledges that a major challenge is the “big elephant in the room of Mars surface infrastructure”. The entire concept is based on the assumption that the necessary infrastructure, such as propellant production facilities, will be in place on Mars by the time the cycler is ready.
  5. Life Support Systems: Sustaining human crews on a cycler for extended periods (e.g., months-long transits) requires robust life support systems for air, water, food, and waste management. The paper underscores the challenge of maintaining these systems with minimal resupply over multiple cycles.

Assuming these challenges could be solved, this interplanetary cruise ship design of a Mars Cycler is a new approach to deep-space travel, elegant in its simplicity. It offers a potential solution to the challenges of long-duration missions by providing artificial gravity via a rotating inner torus to ensure the health and well-being of future Mars colonists.

In addition to these cyclers providing a mode of safe space transportation, such large artificial gravity space stations could be permanently located in orbit around planets or moons that have surface communities in split life cycle space settlements which SSP covered recently. Such a facility could have duel use as an Earth-normal gravity crèche, providing birthing centers and early child development for families settling in the region. Colonists could choose to split their lives between rearing their young in healthy normal gravity settings until their offspring are young adults, then moving down to live out their lives in lower gravity surface settlements – or they may choose to live permanently in free space.

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AI networks for space settlements

Artist rendering of a robotic space farm on Mars controlled by a computer network utilizing artificial intelligence. Credits: Bryan Versteeg / Spacehabs.com

In an article in the National Space Society Space Settlement Journal, Bryce Meyer examines the integration of Artificial Intelligence (AI) into computer networks for space settlements. Meyer, an aerospace engineer, computer scientist and biologist is the founder and CEO of Cyan React, LLC, a startup that designs compact photobioreactors and provides expertise in space agriculture and life support for space habitats.

The paper describes the critical role of AI networks will play in enabling sustainable space settlements whether they be on the Moon, Mars, or in free space. These colonies, envisioned to minimize Earth resupply and achieve self-sustaining commercial operations, will face challenges due to limited human occupants (often under 100) and the absence of specialized expertise. AI systems can provide a solution that will bridge knowledge gaps, manage complex operations, and ensure rapid responses to critical issues, such as life support failures, where human reaction times may be insufficient.

The article categorizes AI into distinct families suited for space applications. Neural networks, good at pattern recognition, could help identify equipment anomalies. Generative AI (GAI), excellent at diagnostics and creative problem-solving, could propose solutions for crop failures in space farms or other equipment failures. Regression models would be leveraged for predictive analytics like forecasting resource needs.

These AI systems require robust integration with settlement infrastructure, using standard protocols like TCP/IP for communication. Training of AI agents involves learning from a pre-settlement knowledge base, periodic updates from Earth, and real-time inputs from sensors monitoring environmental conditions, equipment, and biological systems. Error management will be managed with AI outputs cross-checked by other AIs, rule-based systems, or human oversight to prevent cascading failures in critical systems.

Network architectures are key, with Local Area Networks (LANs) enabling low-latency, high-speed communication for real-time tasks like alarms and life support, while Wide Area Networks (WANs) connect settlements to external systems, such as orbital infrastructure or Earth-based servers . AI placement is strategic, positioned near action points within habitats (e.g., farms, life support systems) to minimize latency and ensure reliability in harsh extraterrestrial environments. Power constraints and radiation hardening are critical considerations for AI hardware.

The article presents a detailed scenario illustrating AI coordination in a mass flow system, as would be required in space farm. For example, crop wilting is detected by sensors, triggering a cascade of AI-driven actions: neural networks diagnose the issue, GAI suggests solutions (e.g., adjusting nutrient levels), and regression models predict outcomes. Human settlers, guided by augmented reality interfaces, validate and implement solutions, ensuring effective collaboration. The scenario underscores the need for AI to operate at multiple scales—individual plants, farm systems, and settlement-wide networks.

Bryce agreed to be interviewed via email on this enabling technology for space settlement. I am very grateful for him taking the time to dive deeper into the topic and for his detailed responses to my questions. Here is our discussion:

SSP: You mentioned that many of these AI systems are already in use in indoor farms and factories. Can you provide some examples of these instances?

BM…Not trying to pump a particular company but here are common examples:
Siemens is one of many companies that make networks of these AI enabled control systems, with control center software now: Siemens Industrial Copilot and SmartTron as well as AIRLOCK(InterLock) Systems.

Water Control: Evonik

There are also many new entry startups in this area, such as AGEYE (see below), and others, many have already tried and failed as businesses. Emerson Process is similar, with many offerings and architectures in Chemical Process Automation and Response. BASF is another with it’s xarvio® Digital Farming Solutions. Monnit makes Internet of Things (IoT) plant sensors and sensor reporting software.

It is a very active business area bridging strict rules based to AI enabled rules based and GAI systems with IoT.

SSP: In your example of an AI farm agent detecting a wilting problem with a tomato plant and coming up with a solution, you acknowledged that there are many ways in which ecosystem failures could a occur in a space farm and these scenarios would have to be anticipated to train the AI systems. Has work already been started on an AI controlled farm fault tree analysis, perhaps by the entities running the indoor farms you mentioned in Item 1?

BM…Absolutely! IoT and AI are used in combination in many indoor farms now, just not all the way to the point as shown in the paper, including the ‘recreational plant’ market and for food plants.  This is in active work now by many companies, AGEYE is one company that does have integrated solutions like the farm part of the paper (or very close to it). With a little development, automated control will combine the systems in #1, with the farm systems, with more advanced and trained systems, IoT sensors and controllers, to get to the settlement level.  It will take a merger of these to get there, but we are very close. Have parts, just need to integrate to get to the vision in the paper.

SSP: Prior to implementation for safe use in a space colony, AI systems would have to be trained on a variety of settlement functions in ground-based analogs. Perdue University’s Resilient ExtraTerrestrial Habitats Institute is doing work in this area as well as the Space Analog for the Moon and Mars at the Biosphere 2 facility in Arizona, and of course MELISSA in the EU. Are you aware of any other teams in academia or government working on this now?

BM…Really miss Ray Wheeler’s et al. NASA Biomass Production Chamber, which was the right size and type, would just need updates.

South Pole research station would work well for testing these systems…in a harsh place, limited human presence.

I know Space Development Network is proposing an inflatable farm to develop this technology too, though it needs funding.

AI control for factories and indoor farming is an active corporate area and they have their own extensive facilities, including near my home in St. Louis with Bayer (formerly Monsanto), though they aren’t focused on the particulars of space, per se, yet.

China also has extensive analog labs, since they do seek to beat the USA to long term Moon and Mars settlement. They occasionally publish.

Many colleges have funded work on vertical and indoor farming, several in my home state including at [University of Missouri-St. Louis] UMSL’s planned Yield Lab.  Technical Schools like Ranken also teach and develop methods for indoor farming that could help development of these AIs. All of these facilities can be used to shake out AI systems too.

SSP: In private industry, a few companies are actively involved in developing space-based agriculture. I’ve covered one such company, Orbital Farms, which leverages Earth’s “Dark Ecosystem”, the food chain based on bacteria that are chemotrophic, i.e. deriving their energy from chemical reactions rather than photosynthesis. An example of these type of organisms are bacteria that live near volcanic sulfur vents at the bottom of the ocean. The energy inputs and material flows of these ecosystems are 100 times more efficient in water and energy use per unit volume when compared to conventional photosynthetic food production. The very same organisms can be engineered to make pharmaceuticals, plastics, and a variety of other useful complex organic compounds. Have you considered this approach to optimize mass flows and utility in space farm ecosystems?

BM…Of course. I have considered bioreactors, both photobioreactors and non-light based systems, for a decade. They are the Swiss Army Knife of mass balancing, though I don’t see them as primary food source except in emergencies unless 3d printing and other methods become far better in the culinary sense. Food is critical for psychology too. As is the need to see green and feel and smell plants and crops. Bioreactors have many profiles and uses on Earth now, and the dark cycle chemosynthetic systems are among these. I don’t see a lack of electrical power a problem, just my 2 cents, due to nuclear reactors or space solar power in long term settlements, so I see gardens and farms. Carbon is the problem in a mass cycle. However, the dark cycle systems would be essential for making biochemicals that are either lacking from farms and algae or needed to control the mass cycling in systems. Since we are minus the huge soil ecosystem on Earth for a long while, and may need time sensitive production, the dark cycle systems would be a must just to control the overall system. I do see those on spacecraft that have limited volume, that provide bulk calorie cycling, along with smaller plant systems.

SSP: In your example in Figure 12 of a small settlement of 10 people where the mass flows are 22kg per day to and from the farm, how big is the farm in cubic meters and what would be grown there to provide enough sustenance and oxygen for the occupants?

BM…Around 1400 square meters, 2400 cubic meters (very pessimistically) assuming a VERY diverse crop mix including a few shrimp, multiple veggies and crops like potatoes or peanuts/soy, and bioreactor array with tanks, and walking areas, with continuous crop production ad infinitem. Sounds big, but that is about the size of two three-story healthy midwestern suburban houses, very roughly. Less diverse crop sets can shrink the farm drastically, to around 25% of the size, but with less dietary diversity.

SSP: With respect to training AI systems to be “space rated”, the first iterations to be implemented off Earth will not be entirely autonomous (as you have shown in your examples) and will have humans in the loop until error rates can be reduced to some tolerable level. With the speed at which AI and robotics are progressing today, while at the same time, settlement of the Moon and Mars seems to be advancing at a snail’s pace, do you see the two technologies converging in the near future so that when permanent colonies are finally established, AI networks will be able to autonomously control most critical functions without human intervention?

BM…I never will fully trust AI for everything, and I don’t think the settlers will either, at a minimum due to cybersecurity. That said, the advances in both systems and software will continue to allow more complex settlements monitored by fewer people. Automation will really will be a core technology in expanding settlements, and starting them. Farms could be growing and operating steady state before the first long term residents arrive, and as a settlement expands, it could add modules and let AI get it started and growing before bolting it onto a smaller settlement. Some things will see robotics as repair agents. The AI technology expansion will allow for more long term optimization as well, and continue to add resiliency to the settlement.

You could see a retirement home or factory on the moon with only a few human workers to keep the settlement running, a few medical technicians that are AI assisted, and robots that fix many things without bothering the staff.

SSP: You have suggested in a previous post on SSP that space farms on Mars could be the bread basket for the outer solar system. Another space farm advocate, retired software engineer Marshall Martin, has proposed a roadmap for their implementation starting with ground based analogs, but progressing mainly to rotating free space settlements, eventually resulting in millions of farms feeding billions of people throughout the solar system. When do you think we’ll see the first prototype closed loop farm implemented in space?

BM…I want farms everywhere, grounded and floating [in free space], because I want to see Trillions of Happy, Smiling Babies everywhere.

I would bet either Artemis, a company, or China fields one in the next 35 years for sure, likely sooner, just to prove the concept. Orbital factories could drive the need as much as a lunar base, just to limit resupply, but a Mars base or space station that is beyond cis lunar space will have to have such a close[d] cycle farm as a must due to limited resupply. So, when depends on if the cost to orbit gets very cheap, and cost to [the] Moon gets cheap. Cheap lift in cislunar space would limit the need to fully recycle, but beyond that distance the case gets much stronger. If it stays expensive to [get to] the Moon, the Moon would drive the need, and the farm gets built sooner.

In his conclusion to the article Meyer holds that AI complexity must align with settlement needs, balancing sophistication with reliability. Interdisciplinary collaboration is essential to refine these systems through scenario-based testing and practical implementation. By empowering minimally trained settlers, AI networks enhance sustainability, safety, and mission success, laying a foundation for long-term human presence in space.

Meyer has his own website where he collates his research and links about closed cycle farming and other space ecology topics. He is also a NSS Space Ambassador.

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Design considerations for rotating space settlements

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.

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Split life cycle approach to settling the solar system

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.

Conceptual illustration of Platform 0, a habitable artificial gravity minimum viable product. Credits: Platform 0 – Kasper Kubica / Earth image – Inspiration4

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.
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A potpourri of artificial gravity topics

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.

This approach, on which Joe graced the pages of SSP previously, could help determine whether human settlements on the Moon or Mars are feasible and sustainable, especially when it comes to human reproduction and agriculture in lower gravity levels. Incidentally, he contributed to my piece on the impact of the human Gravity Prescription on space settlement presented last May at the International Space Development Conference 2024.

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.

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Biosphere X, Y and Z: The future of farming in space – guest post by Marshall Martin

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/MissionCost/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.
  • Oxygen production:  Greenfluidics[7] (algae farm subsystem)
  • Improved windows:  2DPA-1 polycarbonate[8]  vs. ISS windows[9]
  • Robots vs. manual labor.  (and better tools)
  • Soil vs. regolith vs. aeroponics vs. hydroponics vs. ??
  • Improved animal and plant selections

Cost of a Biosphere X compared with other ground-based facilities:

FacilityArea
(Acres)		Cost
(USD)
Biosphere 23.14$150M[12]
Regional Mall5.7$75M [13]
Walmart0.22$2.5M
Biosphere X1.0$10M 
Special building issues – SWAG: $20M

Biosphere X design options:

  • Crops: Wheat, Oats, Barley, Rye, Corn, Rice, Milo, Buckwheat, Potato, …
  • Animals: Fish, Goats, Chickens, Sheep, “Beyond Meat”, cultured meat …
  • Insects: Honeybees, edible Insects, Meal worms, Butterflies, …
  • 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

========

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.

References:

  1. B. Venditti, The Cost of Space Flight Before and After SpaceX, The Visual Capitalist, January 27, 2022
  2. M. Williams, How to make the food and water Mars-bound astronauts will need for their mission, , Phys.org, June 1, 2020, Paragraph 4
  3. Perseverance (Rover)/Cost, Wikipedia
  4. Perseverance (Rover) – Dry Mass, Wikipedia
  5. Biosphere 2, Wikipedia
  6. 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.
  7. L. Blain, Algae Biopanel Windows Make Power, Oxygen and Biomass, and Suck Up CO2, New Atlas, July 11, 2022
  8. A. Trafton, New Lightweight Material is Stronger than Steel, MIT News, February 2, 2022
  9. Cupola (ISS module) -Specifications, Wikipedia
  10. Biosphere 2 (Planning and Construction), Wikipedia
  11. How much does it cost to develop a shopping mall?, Fixr, October 13, 2022
  12. J. Jossy, The Space Show with Dr. David Livingston, Broadcast 4061, July 25, 2023
  13. J. Jossy, The Impact of the Gravity Prescription on the Future of Space Settlement, Space Settlement Progress, March 29, 2024; J. Jossy and T. Marotta, The Space Show with Dr. David Livingston, Broadcast 3852, April 5, 2022
  14. Atmosphere of Venus (Structure and Composition), Wikipedia, “…total nitrogen content is roughly four times higher than Earth’s…”
  15. KREEP, Wikipedia
  16. Habitable zone (i.e. “Goldilocks Zone”), Wikipedia, Picture/graph, Top-right.
  17. Gerald R. Ford-class aircraft carrier (Design features, displacement), Wikipedia
  18. 16 Psyche (Mass and bulk density), Wikipedia – Note: the mass of all main asteroids are available on Wikipedia
  19. D. M. Scott, The Religious Origins of Manifest Destiny, Divining America, TeacherServe©. National Humanities Center, 2024
  20. Bible: Genesis 1:28 (Adam & Eve), Genesis 9:1 (Noah), Genesis 35:11 (Jacob), and generally repeated elsewhere in the book.
  21. B. Wang, Mass Production Rate of SpaceX Starship Costs, May 28, 2020

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The benefits of artificial gravity for space settlements

AI generated image of a rotating space station in Earth orbit providing 1g of artificial gravity in the outer ring, with partial gravity in the inner ring and microgravity at the central hub. Credits: Microsoft Designer

SSP has been covering research on artificial gravity (AG) and its impact on space settlement for years. Many of these posts have focused on the Gravity Prescription for human physiology with particular interest in reproduction as humanity will want to ensure that our space settlements are biologically self sustaining (meaning we will want to have children and raise them there). Should we discover that gravity levels on the Moon or Mars are not conducive to couples raising healthy offspring, rotating space settlements with AG may be our only long term option. But there are many other benefits that spin gravity cities can provide for settlers. In a position paper published online last May in Acta Astronautica, gravity researcher Jack J.W.A. van Loon leads a team of European scientists in an exploration of the possibilities and advantages of rotating space stations providing AG. Van Loon founded and manages the Dutch Experiment Support Center (DESC), which provides user support for gravity related research. This study posits a toroidal orbital station large enough and rotating at a sufficient rate to provide 1g of AG in an outer ring, with an intermediate location for partial gravity laboratories and a nonrotating microgravity research facility in a central module.

From an engineering and human factors perspective, pre-flight training would be simplified because practice operations and procedure planning can be performed on the ground in Earth’s normal gravity. Microgravity environments present challenges for physical phenomena like fluid flow, condensation, and heat convection. Provision of a gravity vector eliminates many of these problems simplifying design and use of equipment. This would also reduce development time.

Life support systems utilizing plants to provide breathable air and nutritional sustenance function more naturally and would be less complex in a biosphere with AG. Since plants evolved on Earth to develop gravitropism with roots growing down relative to a gravity vector and shoots sprouting upward, there is no need to develop complex systems to function in microgravity for proper water and nutrient supply as was necessary for NASA’s Passive Nutrient Delivery System aboard the ISS. There would be easier application of hydroponics systems and vertical farming could be leveraged in habitats with AG while harvested fruits and vegetables can be easily rinsed prior to consumption.

With respect to operations, tasks are similar to normal ground based activities so again, less training would be required. Clutter would be reduced and tie downs for tools that tend to float away in microgravity are not necessary. Schedule management would be improved because there would be less time spent on the extra exercise necessary to counteract health problems induced by exposure to microgravity. Activities like showering and sleeping can be challenging in the absence of gravity, so AG would improve the quality of life in regard to these and other routines we take for granted on Earth.

As readers of SSP are aware, the well documented deleterious effects of exposure to microgravity would be mitigated for crews in an AG environment. Such exposure could preserve crew health by preventing losses in bone and muscle mass, cardiovascular deconditioning, weakening of the immune system, vision changes, cognitive degradation and many other spaceflight induced pathologies as documented in the paper’s references. For tourists or visiting researchers, disorientation and days-long adjustment to microgravity due to Space Adaption Syndrome would be prevented.

Safety would be enhanced as well. For instance, combustion processes and flames behave very differently in microgravity making fire suppression less well understood when compared to normal gravity, necessitating development of new safety procedures. Free floating liquids and tools tend to move around unrestricted causing hazards that could potentially short out electrical equipment. Microorganisms and mold could present a health hazard as humidity control is problematic without a gravity vector. Surgery and medical procedures have not been developed for weightless conditions, requiring specially designed equipment and processes. Liquids drawn from vials containing drugs behave differently in microgravity because of surface tension effects. As mentioned above, training for all activities and equipment designed for use in Earth-normal gravity can be performed ahead of time on the ground. Testing of flight hardware would be simplified as it would not need to be redesigned for use in microgravity. Finally, decades of health studies on astronauts in space under microgravity conditions have found that pathological microorganisms are less responsive to antibiotics while at the same time, become more virulent. AG could make these microbes respond as expected on Earth.

The space station proposed in this paper would include an inner ring housing hypogravity facilities where AG equivalent to levels of the Moon and Mars could be provided for investigators to study and tourists to experience. Mammalian reproduction could be studied in ethical clinical experiments to determine if conception, gestation, birth and maturation to adulthood is possible in lower gravity over multiple generations, starting with rodents and progressing to higher primates. The central module would provide a microgravity science center for zero-g basic research or manufacturing where scientists could perform experiments then return to the outer ring’s healthy 1g conditions.

The author’s budgetary analysis found that the cost of such a facility would be about 5% higher than a microgravity habitat due to increased mass for propulsion and supplementary structures, but the benefits outlined above would be an acceptable trade off enabling a better quality of life for tourists and permanent inhabitants. This concept could be the first step in validating health studies and living conditions in artificial gravity informing the design of larger free space settlements.

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The impact of the Gravity Prescription on the future of space settlement

Artist rendering of a family living in a rotating free-space settlement based on the Kalpana Two design, with a length of 110m and diameter of 125m. Credits: Bryan Versteeg / Spacehabs.com

This post summarizes my upcoming talk for the Living in Space Track at ISDC 2024 taking place in Los Angeles May 23 – 26. The presentation is a distillation of several posts on the Gravity Prescription about which I’ve written over the years.

Lets start with a couple of basic definitions. First, what exactly is a space settlement? The National Space Society defined the term with much detail in an explainer by Dale L. Skran back in 2019. I’ve extracted this excerpt with bolded emphasis added:

Space Settlement is defined as: ​

​“… a habitation in space or on a celestial body where families live on a permanent basis, and that engages in commercial activity which enables the settlement to grow over time, with the goal of becoming economically and biologically self-sustaining …”

​The point here is that people will want to have children wherever their families put down roots in space communities. Yes, a “settlement” could be permanent and perhaps inhabited by adults that live out the rest of there lives there, such as in a retirement community. But these are not biologically self-sustaining in the sense that settlers have offspring that are conceived, born and raised there living out healthy lives over multiple generations.

Next we should explain what is meant by the Gravity Prescription (GRx). First coined by Dr. Jim Logan, the term refers to the minimum “dosing” of gravity (level and duration of exposure) to enable healthy conception, gestation, birth and normal, viable development to adulthood as a human being…over multiple generations. It should be noted that the GRx can be broken down into at least three components: the levels needed for pregnancy (conception through birth), early child development, and adulthood. The focus of this discussion is primarily on the GRx for reproduction.

We should also posit some basic assumptions. First, with the exception of the GRx, all challenges expected for establishment of deep space settlements can be solved with engineering solutions (e.g. radiation protection, life support, power generation, etc…)​. The one factor that cannot be easily changed impacting human physiology after millions of year of evolution on Earth is gravity. We may find it difficult or even impossible to stay “healthy enough” under hypogravity conditions on the Moon or Mars, assuming all other human factors are dealt with in habitat design.

Lets dive into what we know and don’t know about the GRx. Several decades of human spaceflight have produced an abundance of data on the deleterious effects of microgravity on human physiology, not the least of which are serious reduction in bone and muscle mass, ocular changes, and weakening of the immune system – there are many more. So we know microgravity is not good for human health after long stays. Clearly, having babies under these conditions would not be ethical or conducive for long term settlement.

The first studies carried out on mammalian reproduction in microgravity took place in the early 1990s aboard the Space Shuttle in a couple of experiments on STS-66 and STS-70. 10 pregnant rats were launched at midpregnancy (9 days and 11 days, respectively) on each flight and landed close to the (22 day) term. The rat pups were born 2 days after landing and histology of their brain tissue found spaceflight induced abnormalities in brain development in 70% of the offspring.

It was not until 2017 that the first mammalian study of rodents with artificial gravity was performed on the ISS. Although not focused on reproduction, the Japan Aerospace Exploration Agency (JAXA) performed a mouse experiment in their Multiple Artificial-gravity Research System (MARS) centrifuge comparing the impact of microgravity to 1g of spin gravity. ​The results provided the first experimental evidence that mice exposed to 1g of artificial gravity maintained the same bone density and muscle weight as mice in a ground control group while those in microgravity had significant reductions.

Diagram depicting an overview of the first JAXA Mouse Project in the MARS centrifuge with photos of the experiment on the ISS. Credits: Dai Shiba et al. / Nature. http://creativecommons.org/licenses/by/4.0/

In 2019 JAXA carried out a similar study in the MARS centrifuge adding lunar gravity levels to the mix. This study found that there were some benefits to the mice exposed to 1/6g in that Moon gravity helped mitigate muscle atrophy, but it did not prevent changes in muscle fiber or gene expression​.

Just last year, a team led by Dr. Mary Bouxsein at Harvard Medical School conducted another adult mouse study on the MARS centrifuge comparing microgravity, .33g, .67g and 1g. They found that hind quarter muscle strength increased commensurate with the level artificial gravity concluding, not surprisingly, that spaceflight induced atrophy can be mitigated with centrifucation. The results were reported at the American Society for Gravitational and Space Research last November.​

Returning to mammalian reproduction in space, an interesting result was reported last year in the journal Cell from an experiment by Japanese scientists at the University of Yamanashi carried out on the ISS in 2019. The team, headed up by Teruhiko Wakayama, devised a way to freeze mouse embryos post conception and launch them into space where they were thawed by astronauts and allowed to develop in microgravity. Control samples were cultured in 1g artificial gravity on the ISS and Earth normal gravity on the ground. The mouse embryos developed into blastocysts and showed evidence of cell differentiation/gene expression in microgravity after 4 days​. The researchers claimed that the results indicated that “Mammals can thrive in space”. This conclusion really can’t be substantiated without further research.

Which brings us to several unknowns about reproduction in space. SSP has explored this topic in depth through an interview with Alex Layendecker, Director of the Astrosexological Research Institute. Yet to be studied in depth is (a) conception, including proper transport of a zygote through the fallopian tube to implantation in the uterus. Less gravity may increase the likelihood of ectopic pregnancy which is fatal for the fetus and could endanger the life of the mother; (b) full gestation through all stages of embryo development to birth​; and (c) early child development and maturation to adulthood in hypogravity​. All these stages of mammalian reproduction need to be validated through ethical clinical studies on rodents progressing to higher primate animal models before humans can know if having children in lower gravity conditions on the Moon or Mars will be healthy and sustainable over multiple generations.

AI generated image of an expectant mother with her developing fetus in Earth orbit after mammalian reproduction has been validated via higher animal models through all stages of pregnancy for a safe level of gravity. An appropriate level of radiation shielding would also be required and is not shown in this illustration. Credit: DALL-E-3

Some space advocates for communities on the Moon or Mars have downplayed the importance of determining the GRx for reproduction with the logic that a fetus in a woman’s uterus on Earth is in neutral buoyancy and thus is essentially weightless. Therefore, why does gravity matter? ​ I discussed this question with Dr. Layendecker and he had the following observations paraphrased here: True, gravity may have less of an impact in the first trimester. But on the cellular level, cytoskeletal development and proper formation/organization of cells may be impacted from conception to birth​. Gravity helps orient the baby for delivery in the last trimester​ and keeps the mother’s uterine muscles strong for contractions/movement of the baby through the birth canal​. There are many unknowns on what level of gravity is sufficient for normal development from conception to adulthood.

Why does all this matter? Ethically determining the right level of gravity for healthy reproduction and child development will inform where families can safely settle space​. The available surface gravities of bodies where we can establish communities in space cluster near Earth, Mars and Moon levels​. These are our only GRx options ​on solar system bodies.

Gravity level clustering of solar system bodies available for space settlement. Credit: Joe Carroll

The problem is that we don’t yet know whether we can remain healthy enough on bodies with gravity equivalent to that on the Moon or Mars, so we can’t select realistic human destinations or formulate detailed plans until we acquire this knowledge​. Of course we can always build rotating settlements in free space with artificial gravity equivalent to that on Earth. Understanding the importance of the GRx and determining its value could change the strategy of space development in terms of both engineering and policy decisions. The longer we delay, the higher the opportunity costs in terms of lost time from failure to act​.

What are these opportunity cost lost opportunities​? Clearly, at the top of Elon Musk’s list is “Plan B” for humanity, i.e. a second home in case of cataclysmic disaster such as climate change, nuclear war, etc. This drives his sense of urgency. From Gerard K. O’Neill’s vision in The High Frontier, virtually unlimited resources in space could end hunger and poverty, provide high quality living space for rapidly growing populations​, achieve population control without war, famine, or dictatorships​. And finally, increase freedom and the range of options for all people​.

If humans can’t have babies in less than Earth’s gravity then the Moon and Mars may be a bust for long term (biologically sustainable) space settlement.​ There will be no biologically sustainable cities with millions of people on other worlds unless they can raise families there​.

Spin gravity rotating space settlements providing 1g artificial gravity may be the only alternative​. If Elon Musk knew that the people he wants to send to Mars can’t have children there, would he change his plans for a self-sustaining colony on that planet?​ Having and raising children is obviously important to him. As Walter Isaacson wrote in his recent biography of Musk, “He feared that declining birthrates were a threat to the long-term survival of human consciousness.”

So how could he determine the GRx quickly? One solution would be to fund a partial gravity facility in low Earth orbit to run ethical experiments on mammalian reproduction in hypogravity. Joe Carroll has been refining a proposal for such a facility, a dual dumbbell Moon/Mars low gravity laboratory which SSP has covered, that could also be marketed as a tourist destination. Spinning at 1.5 rpm, the station would be constructed from a combination of Starship payload-sized habitats tethered by airbeams allowing shirt sleeve access to different gravity levels​. Visitors would be ferried to the facility in Dragon capsules and could experience 3 gravity levels with various tourist attractions​. The concept would be faster, cheaper, safer and better than establishing equivalent bases on the Moon or Mars to quickly learn about the GRx​. The facility would be tended by crews at both ends that live & collect health data for up to a year or more​. And of course, ethical experiments on the GRx for mammalian reproduction would be carried out, first on rodents and then progressing to higher primates if successful.

Left: Conceptual illustration depicting a LEO Moon-Mars dumbbell partial gravity facility constructed from Starship payload-sized habitats tethered by airbeams and serviced by Dragon capsules. Rectangular solar arrays deploy by hanging at either end as spin is initiated via thrusters at Mars module. Center: Image of an inflated airbeam demonstration. Right: diagram of an airbeam stowed for transport and after deployment. Credit: Joe Carroll

What if these experiments determine that having children in lower gravity is not possible and our only path forward are free-space rotating settlements? Physics and human physiology require that they be large enough for settlers to tolerate a 1g spin rate to prevent disorientation. As originally envisioned by O’Neill, the diameter of his Island One space settlement would be about 500 meters.

Conceptual illustration of an Island One space settlement. The living space sphere is sized at about 500m in diameter. Credits: Rick Guidice / NASA

As originally proposed, these settlements would be located outside the Earth’s magnetic field at the L5 Earth-Moon Lagrange Point necessitating that they be shielded with enormous amounts of lunar regolith to protect occupants from radiation. Their construction requires significant technology development and infrastructure (e.g. mass drivers on the Moon, automated assembly in space, advances in robotics, power sources, etc…)​. Much of this will eventually be done anyway as space development progresses…however, knowing the GRx (if it is equal to 1g) may foster a sense of urgency​.

Some may take the alternative viewpoint that if we know that Earth’s gravity works just fine we could proceed directly to free-space settlements if we could overcome the mass problem. This is the approach Al Globus and Tom Marotta took in their book The High Frontier: An Easier Way with Kalpana One​, a 450m diameter cylindrical rotating free-space settlement located in equatorial low Earth orbit (ELEO) protected by our planet’s magnetic field, thereby reducing the mass significantly because there would be far less need for heavy radiation shielding.

Artist impression of Kalpana One rotating free-space settlement located in equatorial low Earth orbit. Credits: Bryan Versteeg / Spacehabs.com

But there may be an even easier way. Kasper Kubica has proposed a 10 year roadmap to the $10M condo in ELEO based on Kalpana Two, a scaled down version of the orbital settlement described by Al Globus in a 2017 Space Review article.

Artist rendering of the inside of a rotating free-space settlement based on the Kalpana Two design, with a length of 110m and diameter of 125m. Credits: Bryan Versteeg / Spacehabs.com

Even though these communities would be lower mass, they will still require significant increases in launch rates to place the needed materials in LEO, especially near the equator​. Offshore spaceports, like those under development by The Spaceport Company, could play a significant role​ in this infrastructure. Legislation providing financial incentives to municipalities to build spaceports would be helpful, such as The Secure U.S. Leadership in Space Act of 2024 introduced in Congress last month. The new law (not yet taken up in the Senate) would amend the IRS Code to allow spaceports to issue tax-exempt Muni bonds for infrastructure improvements.

Wouldn’t orbital debris present a hazard for settlements in ELEO?​ Definitely yes, and the National Space Society is shaping policy in this area. The best approach is to emphasize “light touch” regulatory reform on salvage rights, with protection and indemnity of the space industry to encourage recycling and debris removal.​ Joe Carroll has suggested a market-based approach that would impose parking fees for high value orbits, which would fund a bounty system for debris removal. This system would incentivize companies like CisLunar Industries, Neumann Space and Benchmark Space Systems, firms that are developing space-based processes to recycle orbital debris into useful commodities such as fuel and structural components.

Further down the road in technology development and deeper into space, advances in artificial intelligence and robotics will enable autonomous conversion of asteroids into rotating space settlements, as described by David Jensen in a paper uploaded to arXiv last year.​ This approach significantly reduces launch costs by leveraging in situ resource utilization. Initially, small numbers of “seed” tool maker robots are launched to a target asteroid​ along with supplemental “vitamins” of components like microprocessors that cannot be easily fabricated until technology progresses, to complete the machines. These robotic replicators use asteroid materials to make copies of themselves and other structural materials eventually building out a rotating space settlement. As the technology improves, the machines eventually become fully self-replicating, no longer requiring supplemental shipments from Earth.

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

Leveraging AI to enable robots to build space settlements removes humans from the loop initially, eliminating risk to their health from exposure to radiation and microgravity​. Send it the robot home builders – families then safely move in later. There are virtually unlimited supplies in the asteroid belt to provide feedstock to construct thousands of such communities.

Artist impression of the interior of Stanford Torus free-space settlement. Advances in artificial intelligence and robotics will enable autonomous self replicating machines that could build thousands of such communities from asteroid material. Credits: Don Davis / NASA

If rotating space settlements with Earth-normal gravity become the preferred choice for off-Earth communities, where would be the best location, the prime real estate of the solar system? Jim Logan has identified the perfect place with his Essential Seven Settlement Criteria.

  • Low Delta-V​ – enabling easy access with a minimum of energy
  • Lots of RESOURCES​ … obviously!
  • Little or No GRAVITY WELL​ – half way to anywhere in the solar system
  • At or Near Earth Normal GRAVITY for​
    People, Plants and Animals ​- like what evolved on Earth
  • Natural Passive 24/7 RADIATION Protection​ – for healthy living
  • Permit Large Redundant Ecosystem(s)​ – for sustenance and life support
  • Staging Area for Exploration and Expansion​
    (including frequent, recurrent launch windows)​

Using this criteria, Logan identified Deimos, the outermost moon of Mars, as the ideal location. As discussed above, AI and robotic mining technology improvements will enable autonomous boring machines to drill a 15km long core through this body with a diameter around 500 meters – sized for an Island One space settlement to fit perfectly.

Conceptual illustration of a 500 meter wide by 15km long core bored through Deimos. Credit: Jim Logan

In fact, 11 Island One space colonies (minus the mirrors) strung end to end through this tunnel would provide sea level radiation protection and Earth normal artificial gravity for thousands of healthy settlers.

Left: Artist impression of an Island One space settlement. Credits: Rick Guidice / NASA. Right: To scale depiction of 11 Island One space settlements strung end-to-end in a cored out tunnel through Deimos providing sea level radiation protection and Earth normal artificial gravity. Credit: Jim Logan

In conclusion, the GRx for reproduction will inform where biologically self-sustaining healthy communities can be established in space. If we find that the GRx is equal to Earth’s normal level, free-space settlements with artificial gravity will be the safest and healthiness solution for humans to live and thrive throughout the solar system. The sooner we determined the GRx the better, for current plans for settling the Moon or Mars may need to be altered to consider rotating space colonies, which will require significant infrastructure development and regulatory reform​. Alternatively, since we know Earth’s gravity works just fine, we may choose to skip determination of the GRx and start small with Kalpana in low Earth orbit. Eventually, artificial intelligence will enable safe, autonomous self-assembly of space settlements from asteroids. The interior of Deimos would be the perfect place to build safe, healthy, biologically self-sustaining space settlements for thousands of families to raise their children, establishing a beachhead from which to explore the rest of the solar system and preserve the light of human consciousness.

Update June 3, 2024: Here is a recording of my presentation on this topic at ISDC 2024.