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

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

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

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

Space Settlement is defined as: ​

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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Economic benefits from space mining

A fictional depiction of an ore ship servicing mining operations on an asteroid. Credits: DALL∙E 3

The clean energy transition away from fossil fuels promoted by the Biden Administration and other world governments will require significant increases in mining of critical materials for clean energy technology. To support the huge projected growth in solar, wind, and battery technologies over the next few decades, demand for key minerals such as lithium, graphite, nickel and rare-earth metals will balloon significantly according a 2021 report by the International Energy Agency: The Role of Critical Minerals in Clean Energy Transitions. When compared to current supply levels, sourcing of these materials will need to grow by several hundred percent, with lithium in particular predicted to explode by 4,200% to keep pace with the needed battery production for EVs and other energy storage systems. There is insufficient mining capability in the world today to meet this demand, and if capacity were ramped up to these levels, there would be serious environmental and economic consequences. If we ignore other promising alternatives (which SSP does not advocate) such as ramping up licensing of new nuclear fission power plants and funding development of fusion energy or space solar power, what can be done?

In the journal PNAS, a research article makes the case for why mining in space may be a viable solution and help lay the foundation for sustainable growth on Earth. The author’s* objective for the paper was to perform a trade study on the economic outcomes associated with the environmental and social impacts of terrestrial mining compared to the costs of sourcing from asteroids, focusing primarily on metals required for the clean energy technologies such as copper, nickel cobalt and lithium. The methodology of the paper used a neoclassical Ramsey economic model to predict economic growth under those two scenarios. The study quantifies the economic benefits and projected timelines of mining in space for increasing metal use in clean technologies on Earth for the rest of this century and concludes that the reduction in costs due to environmental damage to our planet’s biosphere may be worth the investment in asteroid mining.

Along similar lines another economic analysis by Matthew Weinzierl makes the potential case for an expanding space economy as a solution to secular stagnation, that condition that some economists fear is happening in the US: a chronic lack of demand as if the economy is operating below capacity even when it appears to be booming. Weinzierl says “In simple terms, secular stagnation is the idea that a sluggish outlook for the economy causes people to save more and firms to invest less, and if interest rates cannot fall enough to spur investment (perhaps because of the sluggish outlook), the lack of investment makes the low-growth prospects all the more likely to be fulfilled, initiating a vicious cycle.” How could space development help prevent this problem? Space settlement, i.e. world building, would unlock abundant resources in the solar system to sustain not only capital investment in expanding economic activity, but robust population growth without limits.

An interesting perspective on off-Earth mining as a commercial engine driving a space economy, with a focus on a thriving Martian colony, was proposed a few years ago in a paper by Robert Shishko and others. The study examined the role of space mining in an economy based on mineral extraction, ice/water, and other resources obtained in situ on the Red Planet. The analysis provided a better understanding of the market conditions and technology requirements for that economy to grow and prosper. This approach would definitely benefit from the recent discovery of massive amounts of subsurface water ice under the Medusae Fossae Formation near the equator of Mars.

Mars Express radar image of subsurface water ice beneath the Medusae Fossae Formation near the equator of Mars. Credits: ESA

If an economic case can be made for space mining and funding secured, it will be dependent on the location of the most profitable and accessible space resources in terms of energy and abundance of useful material. Where will this motherlode for space mining be? SSP has covered this debate.

One of the companies on this frontier is UK based Asteroid Mining Corporation which has the goal of becoming the first profitable space resources business. The startup is working on an autonomous robotic platform call Space Capable Asteroid Robot Explorer with a roadmap that plans for revenue payout at each milestone with eventual return of asteroid resources in the mid-2030s.

Asteroid Mining Corporation’s Space Capable Asteroid Robotic Explorer. Credits: Asteroid Mining Corporation.

And of course readers of SSP are familiar with AstroForge, the company focusing on returning precious metals to Earth from asteroids.

Upon full maturation of AI and space-based robotics technology, it will be possible to autonomously restructure an asteroid to construct spin gravity space settlements using materials in situ.

Artist impression of a rotating space settlement under construction using material from an asteroid. Credits: Bryan Versteeg, spacehabs.com

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* Authors of research article in PMAS Mining in Space Could Spur Sustainable Growth: Maxwell Fleming, Ian Lange, and Sayeh Shojaeinia of the Colorado School of Mines; Martin Stuermer of the International Monetary Fund.

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Curriculum for Astrochemical Engineering

An engineer pondering chemical processes for use in space learned in an advanced postgraduate course in Astrochemical Engineering. Credits: DALL∙E 3

In a paper in the journal Sustainability a global team of researchers has created a two year curriculum to train the next generation of engineers who will design the chemical processes for the new industrial revolution expected to unfold on the high frontier in the next few decades.

Current chemical engineering (ChE) training is not adequate to prepare the next generation of leaders who will guide humanity through the utilization of material resources in space as we expand out into the solar system.

Astrochemical Engineering is a potential new field of study that will adapt ChE to extraterrestrial environments for in situ resource utilization (ISRU) on the Moon, Mars and in the Asteroid Belt, as well as for in-space operations. The body of knowledge suggested in this paper, culminating in Master of Science degree, will provide training to inform the design ISRU equipment, life support systems, the recycling of wastes, and chemical processes adapted for the unique environments of microgravity and space radiation, all under extreme mass and power constraints.

The first year of the program focuses on theory and fundamentals with a core module teaching the physical science of celestial bodies of the solar system, low gravity processes, cryochemistry (extremely low temperature chemistry), and of particular interest, circular systems as applied to environmental control and life support systems (ECLSS) to recycle materials as much as possible. Students have the option to specialize in either process engineering or a more general concentration in space science.

For the process engineering option in year one, students will learn how materials and fluids behave in the extreme cold of space. This will include the types of equipment needed for processes in a vacuum environment including microreactors and heat exchangers, as well as methods for separation and mixing of raw materials.

In the space science specialization, year one will include production of energy and its utilization in space. Applications include solar energy capture and conversion to electricity, nuclear fission/fusion energy, artificial photosynthesis, and the role of energy in life support systems.

In the second year, students learn basic chemical processes for ISRU on other worlds. Processes such as electrolysis for cracking hydrogen and oxygen from water; and the reactions Sabatier, Fischer-Tropsch and Haber-Bosche for production of useful materials.

The second year process engineering specialization focuses on ISRU on the Moon with ice mining, processing regolith and fluid transport under vacuum conditions. Propulsion systems are also covered including methane/oxygen engines, hydrogen logistics, cryogenic propellent handling in space and both nuclear thermal and electric propulsion. Space science specialization in year two covers life support systems and space agriculture.

A design project is required at the end of each year to demonstrate comprehension of the concepts learned in the curriculum, and is split between an individual report and a group project.

Coupled with synthetic geology for unlocking a treasure trove of space materials in the Periodic Table, innovative equipment for ISRU on the drawing board and research on ECLSS, Astrochemical Engineering will be a valuable skill set for the next generation of pioneers at the dawn of the age of space resource utilization.

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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 Astrosexological 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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Why settle space?

Artist depiction of the interior of a cylindrical space colony during an eclipse of the sun. Credits: Don Davis / NASA Ames Research Center

This question has come up a lot lately in the press, usually in the context of how public funds should be spent in space.  On the affirmative side, the answer has been addressed well by many space advocates over the years. Elon Musk wants to make the human race a multi-planetary species in case of a catastrophe on Earth and to expand consciousness out into the cosmos starting with Mars. Jeff Besos wants to move industrial activity off world and eventually fulfill Gerard K. O’Neill’s vision of trillions of people living in free space colonies. When asked the question last year by American Enterprize Institute’s James Pethokoukis, Robert Zubrin said: “In order to have a bigger future. In order to have an open future. In order to open the possibility to create new branches of human civilization that will add their creative talents to the human story. ” He thinks Intellectual Property will be the main export of a Mars colony and he’s already kickstarting that process with the Mars Technology Institute. And of course, The National Space Society (NSS) provides clear rationale in the introduction to their Roadmap to Space Settlement.

On the negative side, there are many naysayers. Some even say humans will never live in space. NSS Board Member Al Globus does a great job of refuting these viewpoints.

In an effort to gain deeper insights and clarify the vision of space settlement, SSP reached out to several space advocates, academicians and entrepreneurs to gather as many viewpoints as possible. They were asked if they agreed with the viewpoints above or if they had a different take.  Regardless of if we are asking for public support for government efforts through space agencies, if the efforts will be funded by private individuals or through a combination of public/private partnerships, why should humanity settle space? Here are their answers:

Doug Plata MD MPH, President & Founder of the Space Development Network, makes the case that there is no need to convince the public of the value of space:

“Many space advocates argue that the general public needs to be convinced of the value of space if we are ever going to see space development occur. So, these advocates come up with a wide variety of arguments including: the necessity of securing large amounts of public funding, the value of satellites in our everyday lives, the potential for a huge “space economy”, inspiring the next generation, and even for the survival of the human species.

“But is convincing the general public actually necessary? Put another way, will off-Earth settlement be impossible unless polls show a large percentage of the public supports space settlement?

“Secondly, it is not the general public who will be deciding whether they will settle on the Moon and Mars. Specifically, the uninterested, the cynical, nor the leftist opponent will need to be convinced over their objections. The ones who will decide will be countries choosing to send their hero astronauts to represent their own people and also private citizens who have saved up enough money. If countries have national pride (practically all) and if there are any “early adopters” with enough savings to pay for their ticket and stay, then it will be those who will decide to go. From Elon’s first BFR presentation (Guadalajara), this has been his business case and I find it to be sufficient. We don’t have to imagine some sort of unobtanium to trade with Earth to figure out where the funding will come from.

“For starters, much of the recent progress in space has not been the result of a groundswell of support from the public. Both Elon Musk and Jeff Bezos started their path to radically reducing the cost of launch independent of any groundswell of support for space by the public. And it is significant to note that they obtained their considerable wealth thanks to their Internet companies that had little, if anything, to do with space. It is their vast wealth that now gives them the ability to develop the reusable rockets which will make space development and settlement affordable and, as a result, inevitable. Even if NASA’s budget is cut to zero, Bezos will still have 20 X the wealth of NASA’s annual human spaceflight budget with Musk’s wealth at 30 X. And both are making progress with their heavy lift vehicles in a significantly more cost-effective manner than NASA.

“In conclusion, the cynic cannot be convinced, and it is probably a waste of time to try. But for those who have their own reasons for wanting to go, so long as the price has been brought down low enough…it is they who will inherit the stars. To each his own.”

Image of the Space Development Network’s full-scale mockup of an inflatable permanent habitat for the Moon or Mars at ISDC 2023. The concept is intended to demonstrate how a 100 tonne SpaceX Starship payload could be delivered and deployed to create a habitat with a 1 acre footprint. Credits: Doug Plata / Space Development Network

Dr. Daniel Tompkins, an agricultural scientist and founder of GrowMars weighs in:

“To address the term settlement from a biological view, for me it means to settle on a process or methodology to sustain and expand water/food/housing. There is settling the land to provide these things (where and how to get clean water, grow/harvest food, get building material). there is settling on practices that are reproducible with multi generational intent. Building schools, planning for expanding population. Different than an oil platform or remote research center which aren’t considered sea steading or settling Antarctica for the multigenerational intent reason.

“To answer directly on various views, mixed on positions:

“Musk- agree Mars is “easy” and most scaleable [sic]. Disagree that sustainable cites or a million people is a magically successful benchmark. Showing ability to support expanding population regardless of scale is important. How do you go from the resources to support 2 people, to 4 people.

“Zubrin- practical and pragmatic about challenges for human missions to Mars and how they can potentially accelerate the science and search for life beyond Earth. Agree IP is best export to support Mars economy lb for lb., particularly genetic engineering and synthetic biomanufacturing. Also agree on term resource creation vs term ISRU.

“Bezos- Moon is more difficult then Mars to “settle” lacking useful carbon and nitrogen than Mars, but opens a bigger range of options for where we can, the trillion people in the solar system model. The thermodynamics of habitats and greenhouses in these places isn’t well established or realized and there are misconceptions to this point of Mars being too cold.

“NSS- disagree with undertone of unlimited power needed to solve for space and earth to bring post scarcity. Unlimited biology vs unlimited power argument.

“O’Neill mostly addressed in above views, specifically cylinders are inspiring, but the process to make them not shown to make people think reproducible. Also, micrometer impacts.

“My short response to the space community and wider is that regardless of where in space (orbit, lunar, Mars etc.), space settlement is about learning to thrive independent of Earth’s natural resources in extreme environments. Whether we go to space or not, we are going to have to solve the same problem sets, i.e. clean air, water, food, materials on Earth in 50-100 years, if not sooner. It means you don’t have to fight with [your] neighbor or chop down the rainforest for more resources, you can do resource creation anywhere on Earth and meet basic needs.

“Space settlement level hardware should not be an eventually, it can be smaller than traditional mission payloads and de-risk certain mission architectures. Which is less mass/volume. Food for 3 years, greenhouses, or a machine to make greenhouses? Some of all three would be good, especially in certain scenarios.

“With sustainable independent settlement as a benchmark, practices and processes need to be inherently reproducible and serviceable. Similar and inspired methods could be used on Earth with limited resources in extreme environments to bootstrap resource creation to meet basic needs.”

Conceptual illustration of a habitat on Mars constructed from self-replicating greenhouses. Credits: GrowMars / Daniel Tompkins

Dr. Tiffany Vora, VP of Innovation Partnerships at Explore Mars and Vice Chair of Digital Biology and Medicine at Singularity University, had the following take:

“In my mind, there are three big arguments in favor of humans moving off-planet for extended, if not permanent, habitation.

“First, we more or less have the technologies that we need in order to do so, as well as a burgeoning space economy. I view crewed space habitation and settlement as further spurs to technological and economic development that will drive deeper understanding of the world around us while creating jobs and, hopefully, prosperity beyond a privileged few. That technology development has the added benefit of improving life on Earth, for example by contributing to solutions to the UN SDGs—on the way to setting the stage for sustainable human habitation off Earth.

“Second, as a biologist, I simply cannot believe that we are alone in the universe. I can’t even bring myself to believe that we’re alone in the Solar System! I view exploration and long-term settlement as key components of finding life off Earth, learning how it works, and learning from how it works. Serving as stewards of non-Terran life would be a momentous responsibility for humanity; although we have a dismal record of that here at home, I believe that life anywhere in the universe is a precious thing that would be worth a deep sense of obligation on the part of humans. Alternatively, failing to locate life elsewhere in the Solar System could provide strong messaging about the fundamental science of life—and hammer home the precarity and beauty of life on Earth.

“Third, I still believe in the capacity of space to inspire people, across generations and boundaries and even ideologies. The goal of settling space isn’t only about setting boots on exotic landscapes: it’s about staring at unbelievably complicated and dangerous challenges and saying, “Let’s do this—and here’s how I’m going to help.” I grew up in Florida, standing in my backyard watching shuttle launches. I have never lost the feeling that I had as a kid, witnessing that. I want every child on Earth to feel that sense of inspiration, of desperate excitement about the future—as well as a compelling urge to be part of it. Sure, I’d love for that to inspire STEMM careers, but there are so many other ways to contribute!

“Obviously, every word that I’ve written here comes with its own caveats. But just as I believe in these words, I also believe in our ability to make choices that open up an abundance of possible futures to bring prosperity and peace, not just to as many people around the world as possible, but to our own planet. The key is choices, and those choices have to be made starting today.”

Science journalist and historian Robert Zimmerman in his book Genesis, The Story of Apollo 8, wrote this:

“The new century will see a renaissance of space exploration as exciting and as challenging as the space race in the 1960s. And this rebirth will happen under the banner of freedom and private property, the very principles for which the United States fought the Cold War.”

Zimmerman continues:

“In a larger more philosophical perspective, we settle space because that’s what humans must do. It is the noblest thing we can do. To quote myself again, this time from my 2003 history, Leaving Earth:

‘Our hopes and dreams are a definition of our lives. If we choose shallow and petty dreams, easy to accomplish but accomplishing little, we make ourselves small. But if we dream big, we make ourselves great, taking actions that raise us up from mere animals.’ “

“Earthrise” image taken by astronaut Bill Anders from Apollo 8 on Christmas Eve 1968. Note that this is the original orientation of the image. As pointed out by Zimmerman, it was rotated 90o by the press for dramatic effect. Credits: William Anders/NASA

Entrepreneur and inventor Ryan Reynolds had a refreshingly unique perspective:

“So, why should humanity settle space (remotely and in-person)?:

  • To be confronted with a new set of challenging environments.
  • Feel the struggle to understand and adapt to them. 
  • Benefit from the effort through shared insights and tangible gains for all. 
  • To observe ourselves outside of the cradle, and know better what we are. 
  • To gain a broader view of our kinship with all that exists. 
  • To be surprised and appalled at our behavior out there. 
  • To ensure that the story does not end here. 
  • To extend biology’s reach.”

Dr. Peter Hague, an astrophysicist in the UK who blogs on Planetocracy had this to say:

“The solar system can and will, eventually, support civilisation on a more larger scale than exists on Earth. There is 2 billion times as much energy available from the Sun in the wider solar system as falls on the Earth alone, and huge reserves of raw materials. The composition of this civilisation will be determined by which nations make investments now – they will get to populate the new society, set the rules and inspire the culture. So it’s in the interests of nations to have a stake in the future, or be irrelevant in a few centuries.”

Haym Benaroya, Distinguished Professor of Mechanical and Aerospace Engineering at Rutgers University and author of Building Habitats on the Moon provided these views:

“I often have to defend the efforts and resources that have been used, and will continue to be allocated, for the space program, and especially the manned space program. While one can rightly say that the funds expended is miniscule as compared to other things that governments and people spend vast sums on, this argument rings hollow. I prefer to point to space, its exploration and its settlement, as an open-ended human adventure and imperative that provides young generations a positive vision of their future, one that gives hope to them and their decedents. Simultaneously, it offers the likely significant technical developments that would not occur otherwise. These technologies will impact how humans will live. Their health will improve, their lives will be longer, more fulfilled, and with the potential for great achievements. There is also the hope that with greater abundance for all on Earth, which a potentially vast space economy can provide, the tolerance for wars will decline. This last idea is a bit utopian given the history of the human race, but it is not a fantasy. It is a potential. Space can increase that potential in a major way.”

Dr. David Livingston, creator/host of The Space Show and one of today’s foremost authorities on the New Space economy, had this thought-provoking vision:

“Space settlement is a visionary long-term project.  In addition, I’m confident that be the inevitable outcome pushed by a global humanity wanting to go to space for off-Earth experiences, living off-Earth and eventually creating off-Earth communities.  I see it as a natural outgrowth of innovation, advancements in all walks of life and in our desire to see and check out what lies just around the corner.  Over time this will happen within the private commercial section of our economy with government mostly working to provide enabling rules of the road to mitigate some risks and uncertainty through establishing order and reasonable protocols. To breathe life into this vision so that it becomes reality, collectively we need to anchor our vision in science, engineering, medical development, behavioral science and most likely many more foundational components so that what we build and stands the test of time on solid footing. Having a dream and a vision for space settlement is one thing but to work on it, to enable it, to develop it, to make it come about implies we are a free people able to pursue dreams, to turn them into reality and to create amazing outcomes that were not even in existence yesterday. But its not enough to just have a good dream or vision for the future. We need to be able to make it happen which to me implies having a solid foundation not Bay Mud, plus realistic, plausible outcome expectations that are only possible when we can explore, build, and develop as we see fit. When we can take risks.  Being free to push forward to what lies beyond Earth is as essential as all the other ingredients that will go into making space settlement happen because without that freedom, we will have our dreams but without the ability to make them real.

“I’m fully aware that the settlement discussions like to focus on operational timelines, rockets, engineering, medical, food, and all sorts of challenges.  While all of this is critical to developing space settlement, these discussions must not sidetrack us into a world of hypotheticals and perspectives suggesting this or that technology is best given our present state of settlement R&D. Since I firmly believe that the private sector should make settlement happen, more so than the government, I would like to see viable commercial projects and startups designed to enable and support the goal of settlement. Government too has an important role in establishing space settlement. Rules of the road and policies are needed to provide order, structure, and safety.  One of our primary relationships with government must be oversight so that we enable not curtail settlement development.

“Space Settlement is fraught with challenges, with naysayers and those that think they know best for others.  I have every confidence that we will in time be overcome these obstacles.  By showing and doing, not by talking and promising.  I’m in less of a hurry to see the first settlement than I am in seeing us get started with essential precursors such as long-term commercial project financing as an example.  Space settlement will likely evolve because of a step-by- step methodical approach to information and fact gathering, problem solving, testing, development, and more testing. Risk taking will play a very large role in our ability to move forward.  As for risk taking, it can only be taken by those with the freedom to do so. As we advance step by step, innovation and forward thinking by those on the front lines will play an increasingly valuable role in turning our vision into reality.

“Space settlement is and should be a global endeavor with unlimited motivating and inspiring reasons driving thousands if not millions of us to our goal. As we move forward, we are sure to uncover and use many of the tightly held secrets of our universe. For sure it will be a very exciting and rewarding adventure as we figure out how to live, work, and play off-Earth, all the while making sure the process and our off-Earth communities are sustainable and independent on an ongoing basis.  This will happen if we remain focused and avoid distraction. Having patience will help us stay the course and to develop and maintain our needed drive into the future.  A future that to me lies ahead of us with as much certainty as does our daily sunrise and sunset.”

Tom Marotta, CEO of The Spaceport Company and Brett Jones, Strategic Marketer and Frontier Tech investor cowrote this inspiring response:

“Reimagining the Stars: A Multiplanetary Mindset for a Flourishing Future
The challenges humanity faces today are vast. From the instability of our global systems to the dwindling resources and fading hopes, there’s an undeniable sense of stagnation. Yet, within this atmosphere of despondency lies a beacon of hope, a path toward rejuvenation: the cosmos. Imagine a world where resources are not just abundant, but practically infinite. Where our collective potential is not limited by the boundaries of our blue planet, but instead, expanded by the boundless wonders of space. Such a vision is not mere science fiction; it is a future within our grasp.

“Space: An Oasis of Resources and Possibilities
Outer space is not just about twinkling stars and distant planets. It’s a treasure trove waiting to be explored. The vast quantities of materials and energy floating in the cosmic expanse can fuel economies, revitalize our planet, and secure prosperous futures for generations. And it’s not just about physical resources. The challenges of space exploration will drive advancements in healthcare, technological innovation, and even the social fabric of society.

“New Frontiers, New Beginnings
Space offers a fresh canvas, an opportunity to redefine human existence. For those yearning for change, be it a new environment, companionship, or the thrill of exploration, the cosmos holds endless possibilities. It’s not just about survival; it’s about thriving in ways we have yet to envision.

“Redefining NASA’s Mission: From Pride to Purpose
NASA has always been a symbol of American pride. Its achievements, from landing on the moon to exploring the distant reaches of our solar system, are testament to human ingenuity. Yet, its true potential lies not just in exploration, but in transformation.

“For NASA to truly leave an indelible mark on every individual, it needs to shift its vision. Instead of focusing solely on exploration and scientific endeavors, the emphasis should be on providing direct benefits for every citizen. This involves prioritizing space settlements, harnessing energy from space, and leveraging cosmic resources.

“An Invitation to the Stars
As we stand on the cusp of a new era, we must choose the trajectory of our future. By adopting a multiplanetary mindset, we’re not just securing a better life for ourselves but ensuring the continued growth and prosperity of all humankind for millennia to come. The universe beckons, offering hope and possibilities. It’s up to us to answer the call.”

Conceptual illustration of a mobile offshore launch platform as part of a robust launch industry infrastructure servicing thousands of launches in the near future to support space development. Credits: The Spaceport Company

Daniel Suarez, author of Delta-V and Critical Mass, believes we should rephrase the question:

“The question of ‘why’ humanity should settle space has been debated ever since it became technologically possible in the late 1960’s and early 1970’s. And the question has renewed relevance here in 2023 with the launch of a new space race — both public and private. A frequent objection is: “Why should we spend precious resources on space development when we have pressing problems to solve down here on Earth?”

“However, to address that concern I think it’s vital to re-frame the question as not just ‘why’ we should settle space, but why we must urgently settle space. And the answer is compelling: we must settle space in order to deliver economic opportunity and clean energy to all the people of Earth, particularly if we are to have a reasonable chance of resolving the existential threat of climate change. One may question how expanding human society and industry into space accomplishes that, but the answer is straightforward…

“Yes, developed nations have made progress in reducing their carbon emissions in an effort to address climate change. And yes, more consumers are buying electric cars. However, social media and mainstream news reports tend to suggest climate change will soon be under control if we just continue installing solar & wind farms, and keep buying electric cars. However, the truth is that human civilization as a whole is not reducing carbon emissions. In fact, for all our efforts over the past 30 years all we’ve done is slow the growth of emissions. For example, global carbon emissions increased yet again (0.9%) in 2022 and that increase was above the 6% increase from the year before (source: National Oceanic & Atmospheric Administration). Pointedly, carbon emissions have increased almost every year since the dawn of the industrial age in 1850 (a notable exception being 2020, during the height of the pandemic).

“The amount of CO2 in the atmosphere today was last experienced 4.3 million years ago, during the mid-Pliocene epoch when sea levels were 75 feet higher than today, and average temperatures were 7 degrees Fahrenheit warmer than pre-industrial times. Even if we reduced annual global carbon emissions to zero tomorrow, average global temperatures would still continue to rise each year for a century or more because of the trillion tons of CO2 that we’ve already released into our atmosphere since 1850. That CO2 will take a century or more to be sequestered by the natural carbon cycle, which means there will be a surplus of heat absorbed by the planet each and every year no matter how many solar panels, wind turbines, and hydro power stations we install.

“No, in order to truly address climate change, we’re going to need to remove CO2 from Earth’s atmosphere, reducing concentrations from the present 418ppm down to at least 350ppm, a level more suitable to global civilization. But coming up with the terawatts of clean energy required to remove all that CO2 is going to be nearly impossible here on Earth, especially as economic and political turmoil continues to spread in response to climactic chaos.

“Adding to the challenge of resolving climate change is the fact that over 2 billion people currently live in poverty and billions more experience meager living standards. They are eagerly trying to improve their circumstances through economic development and increased energy usage. India, China, nations of Africa, and elsewhere want to improve the lives of their citizens just as developed nations of the West did over the past 150 years. They need energy to do so, and new coal and gas-fired power plants are coming online in the developing even as they continue to roll out solar and wind.

“How can we possibly increase the energy and resources available to the people of Earth without further polluting our already ailing home world — especially in time to stave off the worst effects of climate change, which will itself cause more conflict, uncontrolled migration and food shortages, reducing cooperation on global issues? Earth is a finite system, and the solution to climate change and continued economic development worldwide lies in going beyond Earth’s atmosphere to obtain the energy and resources we need.

“One answer is to expand carbon-intensive industry and energy generation into cislunar space. By using in-situ resource utilization in deep space (as opposed to launching all our working mass from Earth), we can start to rapidly build out an offworld industrial infrastructure & economy, using resources harvested from our Moon and near-Earth asteroids. By refining these materials in space, we can build enormous solar power satellites, place them in geosynchronous orbit, and beam at first gigawatts and later terawatts of clean solar power to rectennas on the Earth’s surface 24-hours a day, rain or shine anywhere in the hemisphere beneath them. The technology to accomplish this has existed since the mid-1970’s. And Earth’s geosynchronous orbit, safely populated with solar power satellites could return well over 300 terawatts of continuous clean energy — and for reference we currently consume a bit over 20 terawatts of energy worldwide.
Plus, the economic growth made possible by expanding industry and energy generation into cislunar space will be critical for all the people of Earth. This could include industries only possible in the microgravity and/or near-perfect vacuum of space, from ultra-clear ZBLAN fiber optics, exotic alloys, pharmaceutical discovery, astronomy — the list goes on.

“So ‘why’ should we settle space? I contend that’s the wrong question. The right question is ‘why should we urgently‘ settle space? And the answer is to avoid an existential catastrophe and instead make possible a promising and dynamic future for countless generations to come.”

Artist depiction of a space-based solar power satellite collecting sunlight and converting the energy to microwaves for beaming to rectennas on Earth to be fed into a country’s power grid. Credits: © ESA – Andreas Treuer

Finally, here are the reasons for space settlement articulated as goals in 1976 by Gerard K. O’Neill from his blueprint for migration off Earth, The High Frontier:

  • Ending hunger and poverty for all human beings
  • Finding high-quality living space for a world population which will double withing forty years, and triple with another thirty, even if optimistic estimates of low-growth rate are realized
  • Achieving population control without war, famine, dictatorship, or coercion
  • Increasing individual freedom and the range of options available to every human being
Cutaway view revealing interior of a toroidal space settlement. Credits: Rick Guidice / NASA Ames Research Center
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Artificial photosynthesis for production of oxygen and fuel on the Moon and Mars

Image of ice in a crater on the Martian plain Vastitas Borealis captured by the European Space Agency’s Mars Express orbiter. Credits: ESA/DLR/Freie Universitat Berlin (G. Neukum)

When we establish outposts and eventually, settlements on the Moon or Mars it would be economically beneficial if we did not have to create supply chains from Earth for water, breathable air and the fuel we will need for our rockets. This is why sources of water ice in the permanently shadowed craters at the lunar poles and in glaciers in the equatorial regions on Mars are so attractive as early destinations. Once we get there what equipment will we need to process this valuable resource? The typical way envisioned for cracking water in situ on the Moon or Mars to produce oxygen and hydrogen is through electrolysis. But this method requires a lot of power. There may be a more efficient way. New ESA sponsored research by scientists* in the UK and Europe examines a novel method that mimics photosynthesis in plants using a photoelectrochemical (PEC) device. The findings were published June 6 in Nature Communications.

PEC reactors are currently being studied on Earth for water splitting to produce green hydrogen from sunlight. Since they only rely on solar energy for power they are ideal for space applications. One type of device consists of a semiconductor photocathode immersed in an electrolyte solution that absorbs solar energy for a reaction to split hydrogen from water molecules. Oxygen is produced at the anode of the cell. PEC devices can be fabricated as panels similar to photovoltaic arrays. For use on Mars, the authors analyze another similar PEC technology using a gas-diffusion electrode to reduce atmospheric carbon dioxide in a reaction producing methane for rocket fuel.

The authors modeled the performance of these devices subjected to the expected environmental conditions on the Moon and Mars. Specifically, they looked at attenuation from the accumulation of dust on the PEC cells caused by micrometeorites pulverizing the lunar surface, coupled with the solar wind inducing an electrostatic charge in the resulting dust. And of course dust storms are relatively frequent on Mars which could significantly degrade performance. To address this problem self cleaning coatings are suggested as a solution. Solar irradiance was also considered as it would be reduced at the orbit of Mars. It was concluded that the PEC performance could be significantly boosted with solar concentrators by a factor of 1000 enabling higher production rates and power densities, especially on Mars.

An added advantage for space-based application of this technology is the elements needed to construct PEC devices are readily available on these worlds obviating the need to transport them from Earth and thereby significantly reducing costs.

“…in-situ utilization of elements on both, the Moon and Mars, is feasible for the construction of PEC devices.”

The technology is ideal to augment the production of oxygen in environmentally controlled life support systems of habitats that may not initially be 100% closed and cannot easily be resupplied with consumables from Earth. A competing technology for oxygen production which was recently demonstrated on Mars is the Mars Oxygen In-Situ Resource Utilization Experiment (MOXIE) which functions via solid oxide electrolysis of carbon dioxide. This process requires high temperatures and therefore, more energy presenting a challenge when increased production of oxygen will be required for large settlements. The author’s analysis show that the PEC devices are more energy efficient and can easily be scaled up.

“Oxygen production via unassisted PEC systems can … be carried out at room temperature … suitable to be housed in temperature controlled space habitats.”

* Authors of the Nature Communications article Assessment of the technological viability of photoelectrochemical devices for oxygen and fuel production on Moon and Mars: Byron Ross at the University of Warwick, UK; Sophia Haussener at Ecole Polytechnique Fédérale de Lausanne, Switerland; Katharina Brinkert, University of Bremen, Germany

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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 Astrosexological 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, 0.5 Earth G, 0.75 Earth G 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.

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The limits of space settlement – Pancosmorio Theory and its implications

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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Making Martian regolith safe for agriculture

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

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

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

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

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

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

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

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

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

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