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National Space Society announces Orbital Space Settlement Design Project

Artist’s impression of the interior of a 500m diameter cylindrical spin-gravity space settlement, whose detailed engineering design is one possible output of the NSS Orbital Space Settlement Design Project. Credits: Bryan Versteeg / Spacehabs.com

In a presentation at this year’s International Space Development Conference, which took place in McLean, Virginia, June 4th through June 7th, National Space Society (NSS) COO/SVP Dale Skran announced the kickoff of an open-source Orbital Space Settlement Design (OSSD) Project. The initiative has been under active development for over a year within the NSS Space Settlement Advocacy Committee (SSAC) and the NSS Board of Scientific and Technical Advisors (BSTA). Full disclosure: Yours truly is a member of the SSAC. It was officially approved as an NSS Project last March. The content of this post is based on Skran’s presentation, supplemented with subsequent material presented to the SSAC, with permission.

The current OSSD project Study Group core team consists of Dale Skran, Frederick (Rick) Jenet, PhD, and Bryce Meyer, with all BSTA and SSAC members actively involved in review and discussion. Work is currently focused on establishing a foundational set of design inputs in the form of “Questions” (see below). A dedicated workshop to refine these questions will be held at the NSS Space Settlement Summit taking place at the University of Central Florida, October 25th and 26th. This will be followed by a public announcement and formal request for comment from the broader community. In addition, the “OSSD Terms of Reference” (TOR) and the design input Questions will be located on a dedicated NSS website. The final recommendations will be published in the NSS Space Settlement Journal.

What are Terms of Reference?
The TOR is a formal document that defines the mandate, scope, responsibilities, boundaries, and working methods of the OSSD project. TORs are recursive — a large project such as this one can be subdivided, with each subdivision having its own TOR. This powerful technique is derived from the International Telecommunications Union (ITU) standards development process.

What is the Objective of the OSSD Project?

The core goal is to produce the first complete buildable engineering design for a rotating space settlement. The project is primarily an engineering and systems-design effort, not a policy activity, although legal and economic aspects are necessarily included because they affect feasibility.

Why Pursue This Project?

Rotating space settlements as envisioned by Gerard K. O’Neill will remain an empty dream until they become buildable realities. To many observers, it has not yet been fully established that such settlements are feasible. A fully realized engineering design will be a huge leap forward in making the case that settlements in free space lie in humanity’s future. The research and development required could also address many important issues back on Earth (e.g., closed-loop systems, resource efficiency, energy production, materials science, and robotics).

Why Should the NSS Lead This Effort?

The NSS is uniquely positioned because it is:

  • Non-partisan.
  • Not aligned with any particular company or region.
  • Interested in broadening access to space for all of humanity.
  • Possesses the necessary contacts to convene such a project.
  • Has the longevity and reputation to be taken seriously.
  • Can serve as a respected “honest broker” between different companies, products, technologies, and design approaches.
  • Operates as a non-profit.

Why Now?

Several converging factors make 2026 the right moment:

  • It is over 50 years since the landmark 1975 NASA-Ames space settlement summer study and since the founding of the L5 Society, which later merged with the National Space Institute in 1987 to form the NSS.
  • The NSS laid critical groundwork with the invitation-only Space Settlement 2021 Workshop (SSW), resulting in the book “A Dream Renewed: O’Neill’s Vision in the 21st Century,” a paperback/magazine provided to NSS members, ISDC attendees, and coming out in hardcover on August 25, 2026, available for pre-order.
  • Sufficient knowledge has accumulated, and technology has improved over five decades, such that O’Neill’s original concepts can be updated to a buildable design.
  • Low-cost, fully reusable launch vehicles — which existed only on paper in 1975 — are now a reality on the launch pad.
  • The open-source movement has demonstrated a path to the democratization of technology that was not envisioned in O’Neill’s era.
  • Increasingly powerful artificial intelligence tools now enable a relatively small science and engineering team to address large, complex design questions at a level impossible during O’Neill’s time.

Scope and Boundaries of the OSSD Project

Scope of the Engineering Design:

  • A place where people, including families, can safely live on a permanent, economically self-sustaining basis.
  • Nominal population target: 1,000, with analysis covering populations from 100 to 10,000 for comparison.
  • Designed for direct comparison to the 10,000-person NASA Ames summer study and the British Interplanetary Society (BIS) Avalon project.
  • Positioned as a component in a cislunar economic network (not required to be autarkic or totally biologically self-sufficient).
  • Assumes the baseline human species; human modification or enhancement is explicitly out of scope.
  • Design target: 1 gravity or a high fraction of 1g (since humans have evolved over millions of years on Earth, and the minimum gravity level for long-term human thriving in space has not been firmly established).

What’s included:

  • Engineering design for a rotating space settlement.
  • Examination and development of assumptions related to available construction materials and their costs.
  • Exploration of the legal, treaty, and economic prerequisites needed for the engineering design to be feasible.
  • Investigation of resilience to both natural and artificial assaults, with particular attention to electromagnetic hazards, biological threats, and meteor/space debris strikes.

What’s excluded (The idea being “Don’t boil the ocean”; i.e., focus only on the space settlement design, not all the other ancillary infrastructure and supply chains):

  • Lunar mass drivers
  • Lunar mining technology
  • Construction shacks
  • Asteroid mining technology
  • Launch vehicles
  • In-space transport vehicles
  • Detailed design of robotic construction equipment
  • Weapons systems for settlement defense that are not necessary to protect against natural phenomena
  • Military plans relating to settlement defense

What Happens Next? The Five-Year Roadmap

The project will proceed through disciplined, question-driven workshops rather than attempting to design everything at once:

  • NSS, led by the BSTA, will organize high level workshops to define specific design input questions, to be drafted at this fall’s Space Settlement Summit and subsequently flowed down to subordinate working groups.
  • The questions will be categorized into a few topic areas to help assign subject matter experts, such as High-level Requirements, Agriculture/Biological, and Physical/Construction.
  • The BSTA will assign Rapporteurs to lead these working groups in each question area.

NOTE: Each Rapporteur is expected to organize their work as they see fit and report at least annually to the BSTA with a readout of their progress, including draft recommendations. The normal working method will be workshops, but other means can be used. Unlike the ITU-T, which rotates its meetings across continents, workshops will typically be held in the USA, although this is not strictly required. Rapporteurs are unpaid volunteers, typically with jobs in the space industry

  • In a workshop, carefully framed draft questions will be presented and tagged with a dependency (i.e., TOR, Economic Model, Location, etc.) The questions form the intellectual backbone driving the entire OSSD project.
  • The workshop groups will do the hard work to define good questions with the core philosophy that “Good questions drive good answers.”
  • Workshops will cover a focused set of questions and continue until a Recommendation is produced to define a design output.
  • Target: After five years, the accumulated Recommendations will add up to a complete, buildable engineering design.

The Questions:

The following list is an evolving work in progress as of the date of this post, of potential questions to be finalized by the BSTA and then flowed down to the working groups to flesh out the details. It is by no means complete.

  1. What is the target reliability/safety standard? (Depends on TOR)
    Options range from aviation-like to nuclear-plant-like, to “ISS-like”. Telecom, chip, or automotive standards? This decision drives redundancy, inspection cadence, acceptable risk to children, and the critical safety-vs-uptime trade-off (space habitats cannot have downtime). It also requires choosing a reliability level target (e.g., 5-sigma vs. 6-sigma) and deciding which parts of the habitat are held to which standards.
  2. What are the core services provided to residents? (Depends on TOR – for discussion)
    Includes housing space per person, privacy, recreation, food variety, internet latency, and governance/rights baseline. The question invites comparison to services provided by a small town on Earth and asks how to avoid the tragedy of the commons for “free goods,” while also defining the proper limits of what planners/designers should dictate.
  3. What is the Economic Model? (Depends on Q4)
    This involves answering fundamental questions like: How will settlers add economic value? How will the settlement be economically sustainable?
  4. Where exactly in cislunar space will the settlement be located? (Depends on TOR)
    Candidate locations: Near-Rectilinear Halo Orbit (NRHO), distant retrograde orbit, Earth-Moon Lagrange (EML)1/EML2 halo, high lunar orbit, or EML4/EML5. Location dramatically affects eclipses, station-keeping, communications, debris environment, thermal design, and the economic model itself.
  5. What is the logistics doctrine with Earth? (Depends on Q3, Q4)
    Covers cadence for spares and consumables, allowed lead times, acceptable downtime, and precisely which items must be “topped off” and how often. Items such as trace elements, pharmaceuticals, replacement electronics, specialty foods, nitrogen/argon, etc. need to be defined. Spares/consumables strategy may itself be an outcome of the economic model rather than a question per se.
  6. What population size and target demographics are required for social stability? (No dependency)
    Includes sex ratio, age distribution, and other demographic factors. Questions about non-cisgender humans are out of scope. This is not to exclude them explicitly, but the intent of the question is to focus on critical biological issues.
  7. What population size is required for operational stability? (No dependency)
    Focuses on skill sets, trades, and degree of automation needed for settlers to maintain safe operations. May depend on downstream recommendations about agriculture and other operations.
  8. What population size is required for economic viability? (Depends on Economic Model)
    Considers export/service revenue versus internal labor needs, degree of specialization, downtime tolerance, training pipeline, and explicitly excludes a small population of the very rich as a viable model.
  9. What population size, including pets, is required for mental health? (No dependency)
    Studies have found that 1 in 20 people who overwinter in Antarctica develop serious mental health issues. This suggests that a population of ~200 (typical Antarctic winter-over size) may be too small, or that aspects of the Antarctic station model need correction for space application.
  10. Therefore, what is the minimum viable steady-state population? (Depends on the Q6, Q7, Q8, Q9)
    A synthesizing question that derives a minimum that satisfies the criteria from the related questions, with a suggested floor of 100 occupants.
  11. What governance model applies? (Depends on TOR)
    The TOR states that the settlement is assumed to be under the legal jurisdiction of the launching state. The question explores issues arising from applying the laws of the launching state to the settlement and how those issues can be resolved.
  12. What Ownership Model Applies? (Depends on Economic Model)
    This question is strongly linked to the economic purpose of the settlement, and should cover corporate ownership/company townships, co-ops, condominiums, employee-owned corporations, and other models.
  13. What international legal regime is required to allow the first settlement to be funded? (Depends on TOR)
    Focuses on what legal interpretation of the Outer Space Treaty is necessary to permit construction of a settlement in orbital space.
  14. What maximum rotation rate (rpm) is acceptable for a multi-generation population? (Depends on TOR)
    Because artificial gravity is fixed at approximately 1g, the rotation rate directly sets the required radius, which in turn drives structural mass and construction approach. Why 1g? The TOR states: “Since the minimum gravity level for human thriving has yet to be firmly established, the design target will be either 1 gravity or a high fraction of 1 gravity…” I’ve posted on the topic previously.
  15. What radius/geometry follows from the g level and rpm? (Depends on Radius, also TBD)
    Explores torus vs. cylinder vs. multi-ring vs. hammerhead configurations, habitable deck layout, and zoning.
  16. What is the docking/visiting vehicle strategy relative to rotation? (Depends on Q15)
    Will there be total spin-down? Will there be a non-rotating hub, and if so, how will the transfer from rotating-to-nonrotating spaces be accomplished?
  17. What radiation standard do we design to for families/children? (Depends on Q1)
    Annual dose targets, pregnancy limits, and Solar Particle Event shelter requirements need to be specified. Note that Medevac doesn’t help for chronic exposure to Galactic Cosmic Radiation.
  18. What shielding approach meets Q17 at minimum mass/cost? (Depends on Q17, Q4)
    Decisions on how bulk shielding (e.g. water and/or regolith) will be distributed, need to be made, accounting for storm shelters. Shielding-as-storage, active shields, and layered shields should be considered.
  19. Where does shielding mass come from? (Depends on Q4, Q18)
    Weigh the options of Earth-launched vs lunar-derived vs extracted from an asteroid, keeping in mind that sourcing material for initial habitats may change for future growth.
  20. What closure level is required to be “permanent” with imports allowed? (Depends on Q2, Q3, Q4, Q5)
    Define which consumables must be recycled (e.g., water, oxygen, nitrogen) vs what can be imported.
  21. What food system meets nutrition, variety, and psychological considerations at minimum mass/power? (Depends on Q10, Q20, Q25)
    The hydroponics/vertical farming mix, lighting strategy, protein plan, and storage buffers all need to be determined, fully considering the recycling system and ecological balance of the biosphere.
  22. What will be the atmosphere model and fire safety regime? (Depends on Q1, TOR)
    The total pressure, O₂ fraction, diluents (N₂/Ar), toxic pollutants control, and fire suppression doctrine all need to be determined.
  23. What water/waste architecture achieves Q20 with acceptable failure modes? (Depends on Q1, Q2, Q20)
    Water recovery, sanitation, pathogen control, waste processing, and a plan for “what if” contingencies need to be defined.
  24. How can an overly clean habitat environment be avoided? (TBD)
    Children who grow on farms have very low allergy rates; we want to make sure kids in the settlement are exposed to diseases to develop their immune systems.
  25. What total power level is required (steady state and peak)? (Depends on Q1, Q3, Q21, Q23)
    This will be a cumulative summing the contributions from the habitat, agriculture, industry, propulsion, and reserves.
  26. What power source architecture is optimal in cislunar space?(Depends on Q4, Q25)
    Solar vs nuclear vs hybrid, taking into account storage needs, safety considerations, and maintenance.
  27. What thermal rejection system is required? (Depends on Q25, TBD)
    This will drive radiator design, cooling system loops, heat reuse, zoning, and orientation constraints.
  28. What minimum local manufacturing/repair capability is required? (Depends on Q5, Q9)
    Operations to consider include, but are not limited to, planning for spare parts, maintenance of seals/filters, facilities for machining, electronics repair, additive manufacturing, and QA.
  29. What structural concept meets loading requirements, while taking into account micrometeoroids, internal pressure, and rotation rate, and minimizing mass? (Depends on Q4, Q15, Q18, Q22)
    At a minimum, requires consideration of materials, compartmentalization approach, Whipple shielding design, and pressure hull segmentation.
  30. What is the assembly and spin-up strategy? (Depends on Q4, Q15, Q18, Q29)
    Requires decisions on which modules are preassembled vs built on-orbit. Will the construction be carried out robotically or by crew? What is the optimal timing of when shielding is added, taking into account how balance will be maintained when rotation is initiated?
  31. What is the fault-tolerant operations concept? (Depends on Q1, Q10, Q28)
    This will help determine the staffing requirements, levels of training, emergency response procedures, maintenance cycles, inspection needs, spares policy, and cross-training.
  32. What are the top “design basis accidents” and how are they handled? (Depends on Q1, Q22, Q23, Q29, Q31)
    Scenarios include, but are not limited to, fire, depressurization, toxic release, collision, loss of rotation control, and loss of power.
  33. What is the growth path from the minimum viable system to a larger one? (Depends on Q15, Q18, Q29, Q30)
    This question will help to decide when to add rings/modules, how governance and economy scale, and how to avoid redesign.

O’Neill’s Vision of Free Space Settlements is Closer Than Ever

The OSSD project is a major strategic step for the NSS. After completing and publishing the foundational 2021 workshop proceedings in both accessible paperback and soon-to-be-released premium hardback formats, the organization is now moving from vision and discussion to disciplined, engineering-driven action. By framing the project around a rigorous, design input question methodology with clear scope boundaries, plans to assign rapporteurs, workshop processes, and a five-year horizon for producing buildable recommendations, the NSS is taking the lead as the honest broker and convening authority capable of coordinating the complex, multi-disciplinary work required to turn O’Neill’s dream of rotating space settlements into engineering reality.

The interactive workshop approach using carefully crafted design questions demonstrates a commitment to grassroots community input and iterative refinement rather than a top-down prescription. The careful separation of in-scope engineering/systems issues from excluded topics (launch vehicles, mining technology, mass drivers, etc.) shows a mature project management philosophy designed to keep the effort focused and achievable.

In summary, the OSSD Project will bridge the inspirational legacy of Gerard K. O’Neill and the 1975 NASA-Ames study with the practical realities of 2026: reduced launch costs via reusable rockets, open-source methodology, powerful leverage of AI, accumulated knowledge, and an organized NSS ready to lead the next phase of space settlement engineering. This initiative is positioned as the logical next step after the SSW book — turning the “long list of areas for future research” identified in that publication into concrete, actionable engineering questions whose answers will collectively constitute the first credible, buildable design for a rotating space settlement. Visit the NSS OSSD project website for updates. Let’s make it happen!

Artist’s rendering of what the interior of a 125m diameter rotating space settlement might look like; another possible outcome from the NSS OSSD project. Credits: Bryan Versteeg / Spacehabs.com
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Homing in on the Gravity Prescription

Image of the JAXA Kibo module on the International Space Station which houses the MARS short arm centrifuge for artificial gravity studies. Credit: NASA/JAXA

The Gravity Prescription (GRx), a term first coined by Dr. Jim Logan, refers to the minimum “dosing” of gravity (level and duration of exposure) to enable healthy conception, gestation, birth and normal, viable development to and throughout 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 healthy pregnancy (conception through birth), early child development, and adulthood.

The Japan Aerospace Exploration Agency (JAXA) has been studying the adult gravity prescription for mitigation of mammalian physiological issues that arise in space due to microgravity using mice for about a decade. To conduct this research, they’ve been using the Multiple Artificial-gravity Research System (MARS) short arm centrifuge in the Kibo module on the International Space Station (ISS). This will help us understand what dosing level of gravity is required to prevent the myriad of health issues (e.g., serious reduction in bone and muscle mass, ocular changes, weakening of the immune system – there are many more) that arise in mature adults when exposed for long periods to microgravity, to inform countermeasures for long-duration spaceflight and settlement.

By way of background, I reported back in 2021 on JAXA’s first long-term mouse study comparing mice reared under microgravity conditions to a cohort raised under 1g artificial gravity in the MARS centrifuge, which found that Earth-normal artificial gravity appears to prevent the negative health effects of microgravity. In the same post, I provided an update upon publication of the results of a second experiment executed a couple of years later, which tested mice in Moon gravity and found that 1/6g prevents muscle atrophy in mice, with the downside that this level of artificial gravity cannot prevent changes in muscle fiber (myofiber) and gene modification induced by microgravity. There appeared to be a threshold between 1/6g and Earth-normal gravity, yet to be determined, for skeletal muscle adaptation. Then in 2023 we got a few more data points helping us zero in on the right dose, at least for the adult GRx, between Moon and Earth levels of gravity.

I mentioned this new preliminary data in my presentation at ISDC 2024 on how the GRx may impact the future of space settlement. The results came from a NASA-funded experiment in cooperation with JAXA, headed by Dr. Mary Bouxsein and collaborators, that studied adult mice launched to the ISS on SpaceX CRS-27. The mice were split into four groups and dosed in the MARS centrifuge at four levels of gravity (microgravity, 0.33g, 0.67g, and 1g). The results were presented at the American Society for Gravitational and Space Research (November 2023). Still, no formal paper had been published at that time, only an abstract from the conference talk. Preliminary results showed that hindquarter muscle strength increased commensurate with the level of artificial gravity, indicating that spaceflight-induced atrophy can be mitigated with artificial gravity – more is better. Now the full study has finally been published in Scientific Advances with further details.

After each of the cohorts were individually treated to the four gravity levels in the MARS centrifuge and returned to Earth, the mice were euthanized and the researchers examined their soleus muscle (the calf muscle which is very sensitive to gravity levels), along with strength tests and blood biomarkers.

Key findings included:

  • Muscle shrinkage (atrophy): In microgravity, the soleus muscle fibers shrank noticeably. At 0.33g, the muscle cross-sectional area was largely preserved—meaning it didn’t lose much mass. Higher gravity (0.67g and 1g) also protected muscle size.
  • Muscle fiber type: Muscles have different fiber types—slow-twitch (good for endurance) and fast-twitch. Microgravity causes slow fibers to switch to fast ones. 0.33g partially prevented this switch, but 0.67g fully stopped it, keeping the muscle composition closer to normal.
  • Muscle function: Strength tests (like grip strength) and electrical measurements showed that 0.67g was enough to maintain overall muscle performance. Lower gravity levels did not fully protect function.

The study also found 11 blood metabolites (small molecules that are intermediate or end products of metabolism) that changed depending on gravity level. These could serve as future biomarkers to monitor astronauts’ health without invasive tests.

Why does this matter? This is the first experiment to identify the adult GRx thresholds for muscle health. It suggests that 0.33g (close to Mars-level) helps prevent muscle weakening, but titrating to 0.67g is needed to fully maintain strength and normal muscle condition. For future space stations or vehicles with rotating sections to create artificial gravity, this information is valuable: partial gravity helps, but at least 0.67g is better for long-term missions. Crucially, these results could inform the spin-rate specifications for a Mars Cycler to generate artificial gravity to maintain muscular function for travelers to and from Mars.

In short, the paper shows that even moderate artificial gravity could mitigate the musculoskeletal problems astronauts face in space, helping keep crews healthier on deep-space journeys. The research used careful controls, multiple measurement methods, and advanced analysis to reach these clear conclusions.

The bigger question is what is the GRx for reproduction? If permanent settlements are to be established in space, they should be (in the long run) at destinations that enable biological self-sustainability, meaning we will want to have healthy children and raise families there as we expand out into the solar system.

One study conducted by Japanese researchers in 2019 aboard the ISS suggested that mouse embryonic growth may be possible in microgravity. But this experiment was only 4 days of embryo development, which took place after conception. Another study of pregnant mice from the shuttle era found serious issues with brain development after exposure to microgravity. These are just snapshots of embryo and later fetus development, and only in microgravity. There still have not been rigorous scientific experiments covering the full mammalian reproductive cycle through all its phases under variable gravity conditions mimicking the Moon, Mars, or higher levels below that of our home planet.

Conceptual AI generated image of an expectant mother in Earth orbit under appropriate GRx dosing conditions after mammalian reproduction has been validated via higher animal models through all stages of pregnancy for a safe level of artificial gravity. An appropriate level of radiation shielding would also be required and is not shown in this illustration. Credit: MS Designer

It is vitally important as the private space stations begin to replace the ISS and space tourism takes off (including maybe even hotels on the Moon), that we understand the risks and implications for having babies off Earth in lower gravity environments. Alex Layendecker, the founder of the nonprofit Advanced SpaceLife Research Institute (ASRI), told me the following in an interview about his Green Paper on Sex in Space: Consideration of uncontrolled human conception in emerging space tourism:

“With mass access to space, we’ll soon have groups of individuals going up solely for vacation/leisure purposes, and you can be assured some of them will be engaging in sexual activity.  While it would be absurd to try to implement or enforce laws preventing sexual activity in those environments, the dangers associated with potential conception still exist.  What is critically needed at this point is a better collective understanding of those dangers, their mitigation, and for space companies to be able to provide those paying customers with enough information that informed consent can be established – space is inherently dangerous already, and people launching into space are briefed on that.”

Besides JAXA and some limited research by NASA, there are just a couple of organizations dedicated to studying the GRx for reproduction. ASRI based at Cape Canaveral and a Dutch company called SpaceBorn United. SpaceBorn has space missions planned in the next few years using their ARTIS (Assisted Reproductive Technology in Space) platform, focused on mammalian conception and early embryo development, with a prototype “space-embryo-incubator” capable of treating samples with adjustable artificial gravity. Initial missions will send this device to space with male and female mouse gametes, where in vitro conception and 5-6 day embryo development will proceed under artificial gravity conditions. The embryos will then be cryogenically frozen and returned to Earth where, if approved, they will be implanted in natural wombs, where the pregnancy will progress on Earth. If successful, subsequent phases over the next couple of decades will focus on increasing stages of pregnancy in space and early embryo development on the Moon.

But SpaceBorn’s platform is a small, automated self-contained centrifugal device operated in microgravity. To really study the GRx for mammalian reproduction, a fully equipped (preferably crewed) variable gravity biolab large enough to rear lower organisms from conception through pregnancy to birth, maturing into adulthood – over multiple generations and progressing successively in higher mammals – would be required. A very tall order! But there are reasonable and well-thought-out concepts for such facilities I’ve explored here previously.

Currently, there are only a couple of companies with rotating space stations in their strategic plans to provide larger-scale artificial gravity laboratories that could be used for reproductive studies. Vast Inc., a well funded, privately held startup, explicitly lists an Artificial Gravity Station targeted for around 2035 in its official product roadmap, a long cylindrical design that will rotate end-over-end at ~3.5 RPM to create artificial gravity for long-term habitation. It would build on their modular (non-rotating) Haven-1 module currently planned for launch in 2027 and the follow-on Haven-2 station which would gradually add units, eventually leading to a 9-module configuration slated for 2032.

Conceptual illustration of Vast Space Haven-2 nine module configuration space station that could be placed in Earth orbit as soon as 2032. Credit: Vast Space

Above Space, with aspirations for rotating wheel type space stations in the 2030s, has significant engineering and funding hurdles, but is the only other player that has plans for variable gravity facilities in space.

In my presentation at ISDC2024 linked earlier in this post, I advocated for determining the GRx for reproduction sooner rather than later, especially given Elon Musk’s timelines for colonizing Mars. As Musk has made clear for years and with his recently revealed SpaceX compensation package tied to it, his vision for the company is to make humanity multiplanetary and build a city on Mars with a million people. Up until recently, he was projecting mid-century to achieve that milestone. His shifting focus from Mars to the Moon aside, does he expect the population of his Martian colony to be composed of just adults? Musk, who has warned of population collapse and low fertility rates here on Earth as one of humanity’s biggest challenges, has been quoted as saying, “People are going to have to revive the idea of having children as a kind of social duty. If you can, and are so inclined, you should. Otherwise civilization will just die.”

Image of Elon Musk holding his son X AE X-II after Grimes gave birth to him in May 2020. Credit: Elon Musk

I’m pretty sure he envisions that the people occupying his city on Mars will want to have children there. And he’d probably want to know the GRx for reproduction well before significant numbers of people began migrating there to stay. A variable gravity research facility in low Earth orbit dedicated to studying mammalian physiology, including reproduction in less than 1g, could be built using SpaceX hardware and would not cost much more than Musk’s pocket change, but I’ve seen no indication that this is a priority for him.

Of course, there are others, affectionately called O’Neillians, who say we know 1g works, so let’s not waste time and just get started building rotating space settlements like Kalpana One, a 500m diameter starter unit located in equatorial low Earth orbit. Shielded by Earth’s magnetic field and therefore requiring less mass for radiation shielding, it would be much easier to accomplish than the enormous miles-long settlements O’Neill envisioned to be placed out at Earth-Moon Lagrange Point L5. The attractiveness of this approach (in LEO) may be waning with the rise of AI and what will likely be a proliferation of orbital data centers in the next few years. Cowboy Space has just filed with the FCC for a literal Stampede of 20,000 satellites adding to the queue of companies seeking regulatory approval for their megaconstellations, including Blue Origin’s Project Sunrise (51,600), Starcloud (88,000), and SpaceX’s 1 million satellites, all in sun-synchronous orbits ranging from 500 to 2000 kilometers. It may be getting pretty crowded up there soon, increasing the risk of collision with large cross-section space stations that are not easily maneuvered out of the way.

Personally, my view has evolved on the urgency for determining the GRx for reproduction on the Moon or Mars. I still hold that healthy human reproduction in lower-gravity environments is highly uncertain, given millions of years of evolution in Earth’s gravity, and carries a substantial risk of complications at every stage of reproduction. Being inspired by O’Neill, I was admittedly biased toward his approach to mitigate these risks and had a preference for spacious artificial gravity worlds. This led me to believe that if we confirmed through studies of the GRx for reproduction that having children in less than 1g could lead to dangerous complications and, therefore, be morally wrong, the information might bend the arc of space development toward free space settlements. Knowing we could not have children on the Moon or Mars might start to change the mindset of many space settlement advocates, whom the great science fiction author Isaac Asimov called planetary chauvinists, leading to diversion of resources toward building the infrastructure needed to construct rotating space settlements like Kalpana. I’m old enough to remember that O’Neill invented one of the key technologies for building these huge structures: a mass driver intended to be placed on the Moon to launch massive amounts of lunar regolith into space so that it could be processed into radiation shielding for these colonies. Advances in robotics, in situ resource utilization (ISRU), in-space assembly, life support systems, and many other technologies are needed to enable O’Neill colonies. Many of them are proceeding at pace anyway, but I thought that if we found the GRx for reproduction was not less than 1g, it would put a sense of urgency around these efforts.

However, it looks like market forces may be changing all this. I did not anticipate Elon Musk advocating for mass drivers on the Moon. Though he says they would be used for launching SpaceX’s AI satellites, the infrastructure for ISRU and electromagnetic launchers looks like it may be coming to Luna sooner than we expected and can certainly be retooled to fling regolith into space for shielding rotating space settlements, even larger ones, if the drive (and markets) are there.

But rather than the GRx for reproduction being the determining factor for where we settle space – planetary surfaces or free space colonies – a split life cycle may be the solution. This approach, credited to Kelly and Matt Weinersmith in their book A City on Mars, suggests using both destinations! As clarified in a presentation at ISDC2024 by Dale Skran, Chief Operating Officer & Senior Vice President of the National Space Society, this new way of thinking (not an official position of NSS) acknowledges that we probably need Earth normal gravity for having children and suggests that a rotating space station birthing center be placed in orbit above surface colonies on the Moon or Mars. Couples would conceive, bear children, and raise them in a healthy artificial gravity crèche, allowing them to mature to early adulthood, after which families or individuals may choose to remain in space or relocate to the low-gravity surface communities below.

So research by Dr. Bouxsein et al. may be homing in on the adult GRx, with the results from their study paving the way for practical countermeasures against health issues adult astronauts will face in microgravity on long-duration missions in space. But the artificial gravity dose level for reproduction needs much further study before we can safely say biologically self-sustaining space settlements in less than 1g will be possible. Until then (and after, if the answer is no), split life cycle communities may be the strategy for an expanding population migrating out into the solar system and beyond.

Artist’s impression of the interior of Kalpana One, a cylindrical rotating colony providing Earth normal artificial gravity for healthy living in space. With the coming proliferation of AI orbital data centers later this decade, this approach may lose favor in LEO, but could be one possible in-space component of a split life cycle solution for settlement of the Moon or Mars. Credits: Bryan Versteeg / spacehabs.com

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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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Resilient ExtraTerrestrial Habitats Institute at Purdue University releases its Impact Report

Artist impression of a lunar habitat designed for resiliency and autonomy. Credit: Resilient ExtraTerrestrial Habitats Institute

The Resilient ExtraTerrestrial Habitats Institute (RETHi) is at the forefront of developing autonomous and resilient habitats essential for space settlement. The NASA-funded organization just released its Impact Report summarizing work completed to date. SSP reported on RETHi back in 2020.

A key driver for RETHi’s imperative of autonomy in these habitats is the increasing communication delays and limited bandwidth that will severely restrict interaction with controllers on Earth as habitats are established further from home. These limitations necessitate new approaches for managing space habitats autonomously, fundamentally shifting the operational philosophy for future missions. Unlike near-Earth operations where Mission Control provides real-time oversight and intervention, the remote and harsh environment of deep space demands that habitats become self-sufficient entities. This means that intelligence, diagnostic capabilities, and decision-making must reside on-board, transforming the paradigm from remote control to local autonomy. This is a critical design constraint that permeates all of RETHi’s research, influencing everything from structural design to life support systems and robotics.

RETHi’s research is organized into three interrelated thrusts, each addressing a critical aspect of a comprehensive framework for self-managing systems:

  • Resilience (Architecture): This thrust focuses on the fundamental design of habitats. It involves choosing design features and tools to maximize resilience, assessing safety controls, and developing a resilience-based design procedure aligned with NASA’s processes. This ensures that resilience is embedded into the very fabric of the habitat from its inception, making it inherently robust.
  • Awareness (Detection + Diagnosis + Decisions): Addressing the need for autonomy in operations, this thrust aims to detect damage and disruptions, diagnose issues, and support decision-making autonomously. This represents a significant departure from traditional human space flight operations, which rely heavily on large Mission Control teams. The goal is to enable the habitat to “understand” its own state and the nature of any anomalies.
  • Robotics (Enable Action): This thrust is dedicated to expanding the capabilities of autonomous systems by increasing the scope of interventions that can be carried out automatically by robots. This is crucial for construction, maintenance, and repair in hazardous environments where human presence might be limited or too risky.

RETHi’s research is supported by three complementary testbeds, each serving a distinct but integrated purpose, forming an efficient iterative design and validation pipeline:

  • HabSim: This is a computational model of core space habitat subsystems. It incorporates damageable and repairable properties, sensors, and agents for anomaly detection and repair. HabSim can simulate various disruption scenarios, including micrometeorite impacts, fires, Moonquakes, and nuclear leakage. It primarily helps users learn to create and maintain resilient habitats by assessing decision strategies and resilience through simulation-based design, which can reduce mission costs and increase crew safety.
  • CDCM (Control-oriented Dynamic Computational Model): This capability provides a specialized language for rapid prototyping of machine-readable models that capture causal relationships in complex systems. This enables automatic diagnostic reasoners and uncertainty quantification, which are crucial for developing intelligent, self-diagnosing systems.
  • HARSH (Human-Centered Autonomous Resilient Space Habitats): This testbed is a cornerstone of RETHi’s research, providing a unique cyber-physical platform for validating the complex interplay of hardware and software in autonomous space habitat systems. As the physical validation layer, HARSH takes the insights, algorithms, and models developed and refined in HabSim and CDCM, and tests them in a hardware-in-the-loop environment to confirm their real-world efficacy.

These three complementary testbeds provide a sophisticated, multi-stage approach to research and development. HabSim allows for broad, rapid computational exploration of scenarios and design strategies, providing initial insights. CDCM provides the formal language and tools for precise diagnostic reasoning and model building. HARSH then serves as the high-fidelity, cyber-physical validation platform, where the most promising concepts from the computational realm are rigorously tested against physical realities. This iterative process—from broad simulation to precise modeling to hardware validation—minimizes risk, optimizes design, and accelerates the development cycle for a mature engineering pipeline of complex, safety-critical systems.

The RETHi Impact Report summarized the status of many of the Institute’s research initiatives. Although all are important, this post will highlight progress in two key areas of interest: The HARSH testbed and the design of a habitat’s Environmental Control and Life Support System (ECLSS).

Purpose and Unique Capabilities of HARSH

HARSH is a cyber-physical testbed designed to investigate advanced systems health management capabilities for complex systems with deep informational dependencies. The facility bridges the gap between digital simulation and physical reality, allowing for a more comprehensive understanding of system behavior.

The platform’s unique strength lies in its ability to trigger realistic disruption scenarios using hardware and test autonomous recovery. This capability distinguishes HARSH from purely computational models by enabling real-world interaction, sensor feedback, and the validation of autonomous responses against actual physical system behavior. While computational models like HabSim and CDCM are invaluable for initial design and rapid prototyping, HARSH serves as the crucial validation bridge from simulation to reality. It is where theoretical models and algorithms are put to the ultimate test against physical realities, including hardware limitations, sensor noise, latency, and real-world environmental interactions. This is an indispensable step for ensuring reliability and eventual flight certification of autonomous systems.

Facilitating Investigation of Advanced Systems Health Management

HARSH’s cyber-physical nature allows for the investigation of advanced systems health management capabilities, which are crucial for maintaining complex space habitats, especially those with deep informational dependencies. This entails a focus on integrated diagnostics, prognostics, and self-healing mechanisms across multiple interconnected subsystems. In a deep space habitat, a failure in one system, such as a power supply, can quickly cascade to others, like the ECLSS or communication networks.

The ability to test autonomous recovery under realistic hardware-induced disruptions is central to HARSH’s role in validating the Awareness (detection, diagnosis, decision) and Robotics (enable action) thrusts in a practical, integrated setting. To attain advanced systems health management capability, a focus that transcends simple fault detection is required. It implies a sophisticated ability to continuously monitor, diagnose, and predict the health of complex, interconnected systems. HARSH’s ability to test deep informational dependencies and autonomous recovery provides a proactive approach to resilience, where the system not only identifies a problem but also takes corrective action to prevent cascading failures and restore functionality, thereby minimizing the need for human intervention and ensuring mission continuity.

Advancing Life Support Systems for Deep Space: RETHi’s ECLSS Research

As we all know, the ECLSS is critical for sustaining human life in the hostile, closed environment of deep space settlements. The life support system provides essential functions such as breathable air revitalization, water recovery, waste management, and thermal control, directly impacting crew health and performance. The extended durations of deep space missions (and eventual evolution to permanent communities) necessitate a highly reliable and resilient ECLSS, capable of operating autonomously and recovering from disruptions without immediate help from Earth, given the significant communication delays and the unlikelihood of the success of rescue operations due to long transit times.

While a habitat’s structural integrity and autonomous systems are vital, the ECLSS provides the breathable air, potable water, and stable thermal environment necessary for human survival. Any significant failure in these systems directly jeopardizes the safety of the habitat’s occupants, making them the ultimate determinant of mission duration and crew survivability. Therefore, the resilience of an ECLSS will directly dictate how long a mission can last and whether the crew can survive unforeseen events, particularly when autonomous recovery is the only option.

Development of High-Fidelity, Physics-Based Simulation Models

RETHi has developed a high-fidelity, physics-based simulation model for an ECLSS, a sophisticated approach that accounts for the underlying physical principles governing the system’s behavior, allowing for a deep and accurate understanding of its performance.

This advanced model is specifically designed to predict interior conditions under nominal and disruptive scenarios. This capability is vital for understanding how the habitat’s internal environment responds to various stresses, from equipment failures to external impacts, and for evaluating the effectiveness of mitigation strategies. This method of modeling can predict interior conditions under nominal and disruptive scenarios, enabling a proactive, rather than reactive, approach to resilience. Instead of waiting for failures to occur and then responding, RETHi is developing tools to anticipate how the ECLSS will behave under various forms of stress. This predictive capability allows designers to identify vulnerabilities, optimize system responses, and develop robust contingency plans before a space habitat is established, significantly enhancing safety, reliability, and the potential for autonomous recovery. It moves beyond simple performance modeling to detailed stress-testing and failure mode analysis in a virtual environment.

Evaluation of ECLSS Resilience Under Nominal and Disruptive Scenarios

The ECLSS simulation model allows for the evaluation of system resilience. This means the model can assess the system’s ability to withstand disturbances, adapt to changing conditions, and recover from various challenges, ensuring continuous life support. By simulating disruptive scenarios, researchers can understand the precise impact of failures, optimize control strategies, and develop autonomous recovery protocols for critical life support functions, minimizing the need for human intervention during emergencies.

Evaluating system resilience under disruptive scenarios goes beyond merely ensuring individual ECLSS components are reliable. It validates that the system has the ability to maintain its critical functions even when components fail or external disturbances occur. This shifts the focus from preventing individual failures to ensuring the overall system can adapt and recover, which is a hallmark of true resilience in complex, high-stakes environments where human intervention may be limited. This holistic view is essential for long-duration deep space missions, where adaptability is paramount.

SSP covered similar research by Curt Holmer in his master degree thesis modelling the stability of an ECLSS back in 2021. That work attempted to capture the complex web of interactions between biological, physical and chemical processes and detecting early warning signs of critical transitions between systems so that appropriate mitigations can be taken before catastrophic failure occurs. RETHi’s approach takes stability modelling to a deeper level, enabling ECLSS designers to understand the complex interdependencies and vulnerabilities of the system to determine proactive countermeasures.

Conclusion: Paving the Way for Future Space Habitats

The Resilient ExtraTerrestrial Habitats Institute at Purdue University is playing an indispensable role in driving the design and development of resilient and autonomous habitats, which are critical for the future of space colonization. The institute’s integrated, multi-faceted approach to autonomous resilience, exemplified by the HARSH cyber-physical testbed and its pioneering ECLSS research, is foundational for achieving long-duration human presence off Earth.

RETHi’s strategic organization into resilience, awareness, and robotics initiatives address the complex challenges of human survival in deep space, where communication delays necessitate on-board intelligence and self-sufficiency. HARSH serves as the crucial validation bridge, transforming theoretical models and algorithms into tested, real-world solutions for autonomous recovery and systems health management. Concurrently, the high-fidelity ECLSS models ensure that the fundamental life support functions remain robust and adaptable under stress, directly impacting crew safety and settlement longevity.

The comprehensive nature of RETHi’s work positions it as a leader in future large-scale, interdisciplinary research initiatives for resilient space habitats. The Institute’s holistic understanding of the complex challenges of space colonization fosters integrated solutions across multiple scientific and engineering domains, supported by robust testing infrastructure. The Institute’s current research findings are a blueprint for effective advanced research and development needed for the next frontier of human expansion into the solar system, emphasizing a paradigm shift towards self-sufficient extraterrestrial settlements.

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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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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 Advanced SpaceLife 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.

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Progress on mammalian reproduction in microgravity

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. Credits:DALL∙E 3

We are one step closer to determining the gravity prescription for human reproduction in space. Okay, so we still don’t have the green light for having children at destinations in space with less than normal Earth gravity or higher radiation environments….yet. But a team of Japanese scientists report positive results after running an experiment aboard the International Space Station in 2019 that examined mouse embryos cultured in both microgravity and artificial gravity in space, then compared them to controls on Earth after a few days of development. The researchers published their results in a paper in iScience.

The researchers developed equipment and a protocol for freezing two-cell embryos after fertilization on the ground and launching them to the ISS where they were thawed then split into two groups, one allocated to growth in microgravity, the other treated with spin gravity to artificially simulate 1g. A control group remained on Earth. The procedure was designed to be executed by untrained astronauts. Cultured growth continued for 4 days after which the samples were preserved and refridgerated until they could be returned to Earth for analysis.

The samples were also monitored for radiation with a dosimeter and as expected aboard the ISS, were exposed to radiation levels higher then developing fetuses experience on the ground but far lower than those known to exist in deep space outside the Earth’s atmosphere and protective magnetic field. Still, this can be a “worst case” data point for radiation exposure to developing embryos as it is unlikely that pregnancy would be ethically sanctioned at higher levels.

Upon thawing by astronauts, the embryos were cultured through initial mitosis to eventual cell differentiation and blastocyst formation. A blastocyst is the multicellular structure of early embryonic development consisting of an an outer layer of cells called the trophectoderm surrounding a fluid-filled cavity in which an inner cell mass (ICM) called the embryoblast eventually develops into the embryo.

The study was concerned with how gravity may influence cell differentiation, the placement of the ICM within the blastocyst and if radiation effects gene expression in the these cells which will later develop into the fetus. Gene expression within the trophectoderm is also critical for proper development of the placenta.

The results were very promising as the data showed that there were no significant effects on early cell differentiation during embryo development and that proper gene expression manifested in microgravity when compared to 1g artificial and normal Earth gravity.

A human blastocyst with the inner cell mass at upper right. Credits: Wikipedia

A highlight of the paper implied that the results indicate that “Mammals can thrive in space.” It is too early to make such a bold statement with only this one study. It should be noted that this experiment only focuses on one early stage of embryo development. Conception in microgravity is not addressed and as pointed out by Alex Layendecker of the Advanced SpaceLife Research Institute, may have a whole other set of problems that raise ethical concerns as may the effects of lower gravity on later stages of gestation, in actual live birth and in early child development.

No matter how positive these recent results appear to be for early embryo development, as was determined by a landmark experiment on pregnant mice during the Shuttle era, we already have a data point on mammalian fetal development in later stages of gestation in microgravity: serious brain developmental issues were discovered in mice offspring born after exposure to these conditions. So mammalian reproduction in microgravity may start out relatively normally (assuming conception is successful) but appears to have problems in later stages, at least according to the limited data we have so far. On the bright side, the recent study found that 1g artificial gravity had no significant effects on embryo development.

Clearly more data is needed to determine which level of gravity will be sufficient for all stages of mammalian reproduction in space. Fortunately, SpaceBorn United is working on this very problem. They have plans for research into all stages of human reproduction in space to enable independent human settlements off Earth. SpaceBorn CEO Egbert Edelbroek in a recent appearance on The Space Show described upcoming missions later this decade that will study mammalian conception and embryo development using the company’s assisted reproductive technology in space (ARTIS). They have developed a space-embryo-incubator that will contain male and female mouse gametes, which upon launch into orbit, will initiate conception to create embryos for development in variable gravity levels. After 5-6 days the embryos would be cryogenically frozen for return to Earth where they would be inspected and if acceptable, placed in a natural womb for the rest of pregnancy and subsequent birth. If successful with mice the the company plans experiments with human stem cell embryos and eventually human gametes.

The gravity prescription for human reproduction in less than normal Earth gravity is still not known. But at least researchers are starting to gather data on this critical factor for long term biologically sustainable space settlement.

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Sex in space and its implications for space tourism and settlement

AI generated image of an amorous couple embracing in a space tourist destination. Credits: DALL-E

Last April, an international team of researchers published a green paper to solicit public consultation on the urgent need for dialogue concerning uncontrolled human conception which will be problematic for space tourism when it takes off in the near future.   A coauthor on the paper, Alex Layendecker of the Florida based Advanced SpaceLife Research Institute (ASRI) studied the subject for his PhD thesis. Layendecker gave a talk at ISDC 2023 entitled Sex in Space in the Era of Space Tourism in which he emphasized the huge knowledge gap we have on mammalian conception, gestation and birth in the high radiation and lower gravity environments of outer space.  Since humans evolved for millions of years in Earth’s gravity protected from radiation by our planet’s magnetic field and atmosphere, there is a significant risk of developmental abnormalities in offspring which could result in legal liability and potential impacts on commerce if conception occurs in space without consideration of the potential hazards.  After his talk, I discussed these matters and the implications for space settlement with Alex who agreed to continue our discussion in an interview by email for this post.

SSP: Alex, it was a pleasure meeting you at ISDC and thank you for taking the time to answer my questions on this important topic.  The green paper is attempting to foster discussion from relevant stakeholders on addressing “uncontrolled human conception”.  Uncontrolled is defined in the paper as “…without societal approval for human conception – i.e. without regulatory approval from relevant bodies representing a broad societal consensus.” I am not aware of any regulatory authority on these matters at this time and there will likely be considerable challenges to obtain consensus across the space community before tourism becomes mainstream. The intent of the paper appears to be to help develop a framework for regulations (or guidelines) before space tourism takes off. Given how long it takes for regulations to be implemented and the challenges of international consensus, will there be enough time to implement sufficient controls before conception happens in space?

AL:  Great question – short answer up front, no, I don’t believe any “controls” will be implemented before the first incidence of human conception in space, given the timelines we’re currently looking at.  As you mentioned, regulations can take a long time to come into effect and you need to have a basis for establishing regulations/law – space law itself is still being developed.  Our knowledge of reproduction in space is minimal at this stage, certainly not at the level it needs to be at this point of history.  We’re also in virtually unexplored territory when it comes to mass space tourism – there have been space tourists in the past, Dennis Tito being the first “official” space tourist in history over 20 years ago – but all previous individuals that went into space for tourism purposes have done so while integrated into the crew, typically with very little privacy and a considerable amount of training.  With mass access to space, we’ll soon have groups of individuals going up solely for vacation/leisure purposes, and you can be assured some of them will be engaging in sexual activity.  While it would be absurd to try to implement or enforce laws preventing sexual activity in those environments, the dangers associated with potential conception still exist.  What is critically needed at this point is a better collective understanding of those dangers, their mitigation, and for space companies to be able to provide those paying customers with enough information that informed consent can be established – space is inherently dangerous already, and people launching into space are briefed on that.  They will need to be briefed on the dangers associated with conception in space as well, which could not only potentially threaten the life of the baby but also that of the mother, depending on the times and distances involved.

SSP: Will this be a government effort (since a green paper typically implies government sponsorship) or a self-imposed industry-wide trade association consensus approach like CONFERS? Or a combination?

AL: I think in the immediate sense, there will need to be a self-imposed industry consensus on establishing informed consent among space tourism customers. Sex and potential conception in space is currently a blind spot for would-be space tourism companies, because up to this point many of them haven’t considered the dangers it could pose to their customers, and corporate liability here is also an issue. It’s their responsibility to keep their passengers safe, and to inform them of any dangers to the max extent possible. I don’t necessarily see governments being able to implement or enforce any regulations in this regard, because regulating people doing what they want with their own bodies in the privacy of their own bedrooms typically doesn’t fare well over the long term. Where governments may get involved is if any medical situation develops to the point of needing rapid rescue, but Space Rescue capabilities is another topic.

SSP: Space tourism is likely to attract thrill seekers and risk-takers who are likely to have rebellious personalities with a reluctance to follow rules and regulations, let alone respect for societal norms. If this is the case, will pre-flight consultations on the risks of uncontrolled conception and legal waivers be sufficient to prevent risky behavior? Can the effectiveness of this approach be tested prior to implementation?

AL: Prevent risky behavior? Absolutely not. As you point out, these are folks who are intentionally undertaking an enormously risky endeavor in flying to space already, and at least in the early years, will be primarily comprised of your limits-pushing, boundary-breaking types. So they’re already about risk as individuals. However, legal waivers will of course be part of the whole operation, likely to include waivers around the risks of conception. Waivers or not, people are still going to engage in sex in space, and relatively soon, and if the individuals in question are capable of conception, the act itself brings that risk. Not to mention that there are individuals out there who will be vying for the title of “first couple to officially have sex in space,” despite speculation over the years that it could have occurred in the past. To be part of the first publicly declared coupling in outer space will land their names in history books. Now, there will be individuals who decide that they don’t want to deal with those risks after a thorough briefing on the potential dangers, but not everyone – probably not even a majority, knowing humans – will be deterred.

SSP: The paper highlights concerns about pregnancy in higher radiation and microgravity environments. From a space settlement perspective, radiation is less of a problem as there are engineering solutions (i.e. provision for adequate shielding) to address that issue. The bigger challenge will be pregnancies in microgravity, or in lower gravity on the Moon and Mars. The physiology of human fetus development in less than 1g is a big unknown. Some space advocates such as Robert Zubrin brush this off with the logic that a fetus in vivo on Earth is developing in essentially neutral buoyancy, and is therefore weightless anyway, so gestation in less than 1g probably won’t matter. Setting aside the issues associated with conception in lower gravity, if a woman can become pregnant in space, do you think this logic may be true for gestation or are there scientific studies and/or physiological arguments on the importance of Earth’s gravity in fetal development that refute this position?

AL: I’ve heard the neutral buoyancy argument before but it doesn’t address all the issues by a long shot. There is more neutral buoyancy during the first trimester of gestation but in the second and third gravity is very important, even just logistically speaking. Gravity helps the baby orient properly for delivery, and helps keep the mother’s uterine muscles strong enough to provide the necessary level of contractions to safely move the baby through the birth canal. On a more cellular level, cytoskeletal development is impacted by gravity, so even proper formation and organization of cells can be affected by microgravity throughout the span of gestation, from conception to birth. Gravity has a huge impact on postnatal development as well – in the small handful of NASA experiments we’ve conducted using mammalian young (baby rat and mouse pups), there were significant fatality rates among younger/less developed pups against ground control groups when exposed to microgravity during key postnatal phases. The youngest pups (5 days old) suffered a 90% mortality rate, and any of the survivors had significant developmental issues. So gravity is crucial not just to fetal development but to newborns and children as well, that much is evident from the data we do have.

SSP: Following up on your response, the Moon/Mars settlement advocates will say partial gravity levels on these worlds may be sufficiently higher than in microgravity to address the issues you mentioned – baby orientation, cytoskeletal development, cellular formation/organization, postnatal development – and a full 1g may not be needed for healthy reproduction.  The mammalian studies you mentioned with detrimental postnatal development were in microgravity.   We now have a data point at the lunar gravity level from JAXA with their long awaited results of a 2019 study on postnatal mice subjected to 1/6g partial gravity in a paper in Nature that was published last April. The good news is that 1/6g partial gravity prevents muscle atrophy in mice. The downside is that this level of artificial gravity cannot prevent changes in muscle fiber (myofiber) and gene modification induced by microgravity. There appears to be a threshold between 1/6g and Earth-normal gravity, yet to be determined, for skeletal muscle adaptation.  Have you seen these results, can you comment on them and do you think they may rule out mammalian postnatal development in lunar gravity?  

AL: With regard to the JAXA study, I think I’ve seen a short summary of preliminary results but haven’t gotten to read the full study yet. What I will comment for now is that there’s at least some promise in those results from a thousand foot view. While we still need to determine/set parameters for what we as a society/species consider medically/ethically acceptable for level of impact (obviously there was gene modification in the JAXA mice), there are clearly still some benefits to even lower levels of gravity.

SSP: With respect to risk mitigation and the paper’s recommended area of research: “Consolidation of existing knowledge about the early stages of human (and mammalian) reproduction in space environments and consideration of the ensuing risks to human progeny”, SSP has covered off-Earth reproduction and highlighted the need for ethical clinical studies in LEO to determine the gravity prescription (GRx) for mammalian (and eventually human) procreation.  During our personal discussions at ISDC, you mentioned ASRI’s plans for such studies in space.  Can you elaborate on your vision for mammalian reproduction studies in variable gravity?  What would be your experimental design and proposed timeline?

AL:  Well, with regard to timelines, humanity as a whole is already behind, so we’ll need to move as quickly as we possibly can while still upholding safe medical and ethical standards.  We’re approaching an inflection point where human conception in space is more probable to occur, and we still have vast data gaps that need to be filled on biological reproduction.  I’d advocate that the best way to go about filling those gaps would be a systematic approach using mammalian test subjects to determine safe and ethically acceptable gravity parameters for reproduction.  We already know a decent amount about the impacts of higher radiation levels on reproduction from data gathered on Earth, but with microgravity we’ve still got a long way to go, and we don’t know what the synergistic effects of microgravity and radiation are together either.  With regard to experiments, NASA researchers have actually already designed extensive mammalian reproduction experiments with university partners, but those experiments haven’t been funded by the agency.  There was a comprehensive experiment platform called MICEHAB (Multigenerational Independent Colony for Extraterrestrial Habitation, Autonomy and Behavior) that was proposed back in 2015, around the time I was completing my PhD dissertation.  It would effectively be a robot-maintained mini space station that would study the microgravity and radiation effects on rodents in spaceflight over multiple generations, which of course requires sexual reproduction.  That experiment alone would prove enormously beneficial to data collection efforts.  It would be important to study said generations and physiological impacts at variable gravity levels as you mentioned – think the Moon, Mars, 0.5g, 0.75g and so on, so we could fine tune what level of impact we as a species are medically and ethically willing to accept in order to settle new worlds.  With regard to ASRI’s experiment roadmap, our intent is to start with smaller, simpler experiments that will garner us more data on individual stages of reproduction first using live mice and rats, with the hope of eventually moving on to complex and comprehensive experiments like MICEHAB.  Once we have a good plot of data over the course of many experiments, we can hopefully move on to primate relative studies to establish safe parameters for human trials.  I anticipate the small mammal experiments alone will take at least five years were we to launch our first mission at this very moment – though speed is often dependent on level of funding, as happens with most science.

SSP: If contraceptives are recommended to prevent conception during space tourism voyages, the paper calls for validation of the efficacy of these methods in off-world environments.  Do your plans for variable gravity experiments include such studies and how would you design the protocol?

AL: Well, the first important thing to remember is that contraceptives are known to fail occasionally on Earth – condoms can break (especially if used incorrectly), and even orally-taken birth control pills aren’t considered 100% effective. Currently ASRI doesn’t have plans for contraception studies because that’s further forward than we can reasonably forecast at this point. Frankly we need to establish medical parameters first regarding conception in space and know where the risk lines are before we implement birth control studies using humans. We have to take many small steps before we get there. Once we do have established limits for safe reproduction in space environments, we would look to operate any birth control studies within those parameters to determine efficacy. That way if the contraceptives do fail, we at least know the resulting pregnancy has a reasonable chance of success.

SSP: Should experiments on mammalian reproduction in variable gravity determine that fetal developmental or health issues arise after conception and gestation in less than 1g, do you think this may lead to a significant shift in the long-term strategy for space settlement (e.g. toward O’Neill type artificial gravity space settlements) if children are to be born and raised in space?

AL:  I certainly think so.  There’s a lot at stake here.  If we can’t safely birth and grow new generations of humans at a Martian gravity level (0.38 Earth G), then we’ve largely lost Mars as a destination for permanent multigenerational settlement. Fully grown adults can live and work down on the planet itself, but we’d need to come up with an alternate nearby solution for pregnant mothers and children growing up to certain age.  From an engineering perspective, artificial gravity space settlements like an O’Neill cylinder make the most sense to me personally, so long as there’s Earth-level radiation shielding and gravity, and you can recreate Earth-like environments within those structures.  During our conversation at ISDC I referred to it as an “Orbital Incubator” concept, though I’m of course not the first person to ever discuss something like that.

SSP: I appreciate you sharing your PhD Thesis with me. In that work you developed the Reproduction and Development in Off-Earth Environments (RADIO-EE) Scale to provide a metric that could help future researchers identify potential issues/threats to human reproduction in space environments, i.e. microgravity and radiation. Respecting your request that the images of the metric not be published at this time, qualitatively, the scale plots the different phases of reproduction, fetal development, live birth and beyond against levels of gravity or radiation in outer space environments encompassing the range from microgravity all the way up to 1g (and even higher). The scale displays green, amber, and red areas mapping safe, cautionary, and forbidden zones, respectively, dependent on location (e.g. Moon, Mars, free space, etc.). When I originally read your thesis I thought you included both gravity and radiation on the same chart but after our discussions I understand that they would have to be separated out. I also acknowledge that we have no data at this time and the metric is a work in process to be filled in as experiments are performed in space. Have you considered using three dimensions (gravity on x-axis, radiation on the y-axis, viability on the z-axis) and create a surface function for viability. Does that make sense?

AL: I’m totally with you on the 3D model scale (I’ve always thought of it like navigating a “tunnel” made up of green data points to reach the end of the reproductive cycle safely).  The scale was originally envisioned as separate graphs for Microgravity/Hypergravity and Radiation, but obviously we couldn’t combine those in 2D because those two different factors can vary wildly depending on where you’re physically located in the solar system/outer space in general.  So the best answer is to effectively plot green, amber, and red “zones” on each chart (again based on location), then make sure that wherever we’re trying to grow/raise offspring (of any Earth species) we’re keeping our expectant mothers and children in double-green zones (for both gravity, and radiation).  Now the third axis would actually be time (i.e. what point are you at in the reproductive cycle), with viability being determined by where all three axes meet in a green/amber/red zone.

I’d like to thank Alex for this informative discussion and look forward to further updates as his research progresses. We urgently need his insights to inform ethical policies and practices regarding reproduction for the space tourism industry in the short term, and eventually for having and raising healthy children wherever we decide to establish space settlements. Readers can listen to Alex describe his research live and talk to him in person when he appears on The Space Show currently scheduled for August 27.