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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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Greater Earth (GE⊕) Lunar Power Station

Conceptual illustration showing the first iteration of the proposed design of a GE⊕ Lunar Power Station beaming power to facilities on the Moon. Credit: Astrostrom

In response to ESA’s Open Space Innovation Platform Campaign on Clean Energy – New Ideas for Solar Power from Space, the Swiss company Astrostrom laid out a comprehensive plan last June for a solar power satellite built using resources from the Moon. Called the Greater Earth Lunar Power Station (GE⊕-LPS, using the Greek astronomical symbol for Earth, ⊕ ), the ambitious initiative would construct a solar power satellite located at the Earth-Moon L1 Lagrange point to beam power via microwaves to a lunar base. Greater Earth and the GE⊕ designation are terms coined by the leader of the study, Arthur Woods, and are “…based on Earth’s true cosmic dimensions as defined by the laws of physics and celestial mechanics.” From his website of the same name, Woods provides this description of the GE⊕ region: “Earth’s gravitational influence extends 1.5 million kilometers in all directions from its center where it meets the gravitational influence of the Sun. This larger sphere, has a diameter of 3 million kilometers which encompasses the Moon, has 13 million times the volume of the physical Earth and through it, passes some more than 55,000 times the amount of solar energy which is available on the surface of the planet.”

GE⊕-LPS would demonstrate feasibility for several key technologies needed for a cislunar economy and is envisioned to provide a hub of operations in the Greater Earth environment. Eventually, the system could be scaled up to provide clean energy for the Earth as humanity transitions away from fossil fuel consumption later this century.

One emerging technology proposed to aid in construction of the system is a lunar space elevator (LSE) which could efficiently transport materials sourced on the lunar surface to L1. SSP explored this concept in a paper by Charles Radley, a contributor to the Astrostrom report, in a previous post showing that a LSE will be feasible for the Moon in the next few decades (an Earth space elevator won’t be technologically possible in the near future).

Another intriguing aspect of the station is that it would provide artificial gravity in a tourist destination habitat shielded by water and lunar regolith. This facility could be a prototype for future free space settlements in cislunar environs and beyond.

Fabrication of the GE⊕-LPS would depend heavily on automated operations on the Moon such as robotic road construction, mining and manufacturing using in situ resources. Technology readiness levels in these areas are maturing both in terrestrial mining operations, which could be utilized in space, as well as fabrication of solar cells using lunar regolith demonstrated recently by Blue Origin. That company’s Blue Alchemist’s process for autonomously fabricating photovoltaic cells from lunar soil was considered by Astrostrom in the report as a potential source for components of the GE⊕-LPS, if further research can close the business case.

Most of the engineering challenges needed to realize the GE⊕-LPS require no major technological breakthroughs when compared to, for example (given in the report), those needed to commercialize fusion energy. These include further development in the technologies of the lunar space elevator, in situ lunar solar cell manufacturing, lunar material process engineering, thin-film fabrication, lunar propellent production, and a European heavy lift reusable launch system. The latter assumes the system would be solely commissioned by the EU, the target market for the study. Of course, cooperation with the U.S. could leverage SpaceX or Blue Origin reusable launchers expected to mature later this decade. With respect to fusion energy development, technological advances and venture funding have been accelerating over the last few years. Helion, a startup in Everett, Washington is claiming that it will have grid-ready fusion power by 2028 and already has Microsoft lined up as a customer.

Astrostrom estimates that an initial investment of around €10 billion / year over a decade for a total of €100 billion ($110 billion US) would be required to fund the program. They suggest the finances be managed by a consortium of European countries called the Greater Earth Energy Organization (GEEO) to supply power initially to that continent, but eventually expanding globally. Although the budget dwarfs the European Space Agency’s annual expenditures ( €6.5 billion ), the cost does not seem unreasonable when compared to the U.S. allocation of $369 billion in incentives for energy and climate-related programs in the recently passed Inflation Reduction Act. The GE⊕-LPS should eventually provide a return on investment through increasing profits from a cislunar economy, peaceful international cooperation and benefits from clean energy security.

The GE⊕-LPS adds to a growing list of space-based solar power concepts being studied by several nations to provide clean, reliable baseload energy alternatives for an expanding economy that most experts agree needs to eventually migrate away from dependence on fossil fuels to reduce carbon emissions. Competition will produce the most cost effective system which, coupled with an array of other carbon-free energy sources including nuclear fission and fusion, can provide “always on” power during a gradual, carefully planned transition away from fossil fuels. The GE⊕-LPS is particularly attractive as it would leverage resources from the Moon and develop lunar manufacturing infrastructure while serving a potential tourist market that could pave the way for space settlement.

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Spin gravity cities fabricated from Near Earth Asteroid rubble piles

A cylindrical, spin gravity space settlement constructed from asteroid rubble like that from the Near Earth Asteroid Bennu. The regolith provides radiation shielding contained by a rigid container beneath the solar panels. The structure is spun up to provide artificial gravity for people living on the inner surface. Credits: Peter Miklavčič et al.*

Scientists and engineers* at the University of Rochester have conceived of an innovative way to capture a Near Earth Asteroid (NEA) and construct a cylindrical space colony using it’s regolith as shielding. In a paper in Frontiers in Astronomy and Space Sciences they propose a spin gravity habitat called Bennu after the NEA of the same name. Readers will recall that NASA’s OSIRIS-REx spacecraft launched in September 2016, traveled to Bennu, collected a small sample in October 2018 and is currently in transit back to Earth where the sample return capsule will reenter the atmosphere and parachute down in Utah later this year.

Near Earth Asteroid Bennu imaged by the spacecraft OSIRIS-REx. Credit: NASA Goddard Space Flight Center

It would be ideal if an asteroid could be hollowed out for radiation shielding and spun up to create artificial gravity. However, it is shown in this paper that this would not work for larger solid rock asteroids because they don’t have the tensile strength to withstand the rotational forces and smaller rubble pile asteroids (like Bennu) would fly apart because they are too loosely conglomerated.

The problem is solved by containing the asteroid in a carbon fiber collapsible scaffolding that initially has the same radius of the asteroid. As the container is spun up, the centrifugal force will cause the disintegrating rubble to push open the expandable cylinder to its final diameter.

“…a thick layer of regolith is created along the interior surface of this structure which forms a shielded interior volume that can be developed for human occupation.”

The mechanism to initiate the rotation of the structure is interesting. Solar arrays on the outer surface would power mass driver cannons which eject rubble tangentially exerting torque to produce spin.

Detailed engineering analysis and simulations are performed to calculate the stresses on a Bennu sized asteroid to create a cylindrical space colony 3 kilometers in diameter. This structure would have a shielded livable space of 56 square kilometers, an area roughly equivalent to Manhattan.

The authors conclude that the physics of harvesting small asteroids and converting them into rotating space settlements is feasible. They note that this approach would cost less and be easier from an engineering standpoint then fabrication of classic O’Neill cylinders. Concepts for asteroid capture and utilization have already been covered on SSP such as TransAstra’s Queen Bee and SHEPHERD.

The University of Rochester News Center provided a good write up of the paper last December.

* Authors of cited paper: Miklavčič PM, Siu J, Wright E, Debrecht A, Askari H, Quillen AC and Frank A – (2022) Habitat Bennu: Design Concepts for Spinning Habitats Constructed From Rubble Pile NearEarth Asteroids. Front. Astron. Space Sci. 8:645363. doi: 0.3389/fspas.2021.645363

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The case for free space settlements if the Gravity Rx = 1G

Cutaway view of interior of Kalpana One, an orbital settlement spinning to produce 1G of artificial gravity. Credits: © Bryan Versteeg, Spacehabs.com / via NSS

SSP has addressed the gravity prescription (GRx) in previous posts as being a key human factor affecting where long term space settlements will be established.  It’s important to split the GRx into its different components that could effect adult human health, child development and reproduction.  We know that microgravity (close to weightlessness) like that experienced on the ISS has detrimental effects on adult human physiology such as osteoporosis from calcium loss, degradation of heart and muscle mass, vision changes due to variable intraocular pressures, immune system anomalies…the list goes on.  But many of these issues may be mitigated by exposure to some level of gravity (i.e. the GRx) like what would be experienced on the Moon or Mars.  Colonists may also have “health treatments” by brief exposures to doses of 1G in centrifuge facilities built into the settlements if the gravity levels in either location is found to be insufficient. We currently have no data on how human physiology would be impacted in low gravity (other then microgravity).

The most important aspect of the GRx with respect to space settlement relates to reproduction.  How would lower gravity effect embryos during gestation? Since humans have evolved in 1G for millions of years, a drastic change in gravity levels during pregnancy could have serious deleterious effects on fetal development.  Since fetuses are already suspended in fluid and can be in any orientation during most of their development, it may be that they don’t need anywhere near the number of hours of upright, full gravity that adults need. How lower gravity would affect bone and muscle growth in young children is another unknown. We just don’t know what would happen without a clinical investigation which should obviously be done first on lower mammals such as rodents. Then there are ethical questions that may arise when studying reproduction and growth in higher animal models that could be predictive of human physiology, not to mention what would happen during an accidental human pregnancy under these conditions. 

Right now, we only know that 1G works. If space settlements on the Moon or Mars are to be permanent and sustainable, many space settlement advocates believe they need to be biologically self-sustaining. Obviously, most people are going to want to have children where they establish permanent homes. If the gravity of the Moon or Mars prevents healthy pregnancy, long term settlements may not be possible for people who want to raise families. This does not rule out permanent settlements without children (e.g. retirement communities). They just would not be biologically self-sustaining.

SSP has suggested that it might make sense to determine the GRx soon so that if we do determine that 1G is required for having children in space, we begin to shape our strategy for space settlement around free space settlements that produce artificial gravity equivalent to Earth’s.  Fortunately, as Joe Carroll has mentioned in recent presentations, the force of gravity on bodies where humanity could establish settlements throughout the solar system seems to be “quantized” to two levels below 1G – about equal to that of the Moon or Mars.  All the places where settlements could be built on the surfaces of planets or on the larger moons of the outer planets have gravity roughly at these two levels.  So, if we determine that the GRx for these two locations is safe for human health, we will know that we can safely raise families beyond Earth in colonies on the surfaces of any of these worlds.  Carroll proposes a Moon/Mars dumbbell gravity research facility be established soon in LEO to nail down the GRx. 

But is there an argument to be made for skipping the step of determining the GRx and going straight to an O’Neill colony?  After all, we know that 1G works just fine.  Tom Marotta thinks so.  He discussed the GRx with me on The Space Show recently.  Marotta, with Al Globus coauthored The High Frontier: An Easier Way.  The easier way is to start small in low Earth orbit.  O’Neill colonies as originally conceived by Gerard K. O’Neill in The High Frontier would be kilometers long in high orbit (outside the Earth’s protective magnetic field) and weigh millions of tons because of the amount of shielding required to protect occupants from radiation.  The sheer enormity of scale makes them extremely expensive and would likely bankrupt most governments, let alone be a challenge for private financing.  Marotta and Globus suggest a step-by-step approach starting with a far smaller version of O’Neill’s concept called Kalpana.  This rotating space city would be a cylinder roughly 100 meters in diameter and the same in length, spinning at 4 rpm to create 1G of artificial gravity and situated in equatorial low Earth orbit (ELEO) which is protected from radiation by our planet’s magnetic field.  If located here the settlement does not require enormous amounts of shielding and would weigh (and therefore cost) far less.  Kasper Kubica has proposed using this design for hosting $10M condominiums in space and suggests an ambitious plan for building it with 10 years.  Although the move-in cost sounds expensive for the average person, recall that the airline industry started out catering to the ultra-rich to create the initial market which eventually became generally affordable once increasing reliability and economies of scale drove down manufacturing costs. 

What about all the orbital debris we’re hearing about in LEO? Wouldn’t this pose a threat of collision with a free space settlement given their larger cross-sections? In an email Marotta responds:

“No, absolutely not, I don’t think orbital debris is a showstopper for Kalpana.

… First, the entire orbital debris problem is very fixable. I’m not concerned about it at all as it won’t take much to clean it up: implement a tax or a carbon-credit style bounty system and in a few years it will be fixed. Another potential historical analogy is the hole in the ozone layer: once the world agreed to limit CFCs the hole started healing itself. Orbital debris is a regulatory and political leadership problem, not a hard technical problem. 

Second, even if orbital debris persists, the technology required to build Kalpana…will help protect it. Namely: insurance products to pay companies (e.g. Astroscale, D-Orbit, others) to ‘clear out’ the orbit K-1 will inhabit and/or mobile construction satellites necessary to move pieces of the hull into place can also be used to move large pieces of debris out of the way.  In fact, I think having something like Kalpana…in orbit – or even plans for something that large – will actually accelerate the resolution of the orbital debris problem. History has shown that the only time the U.S. government takes orbital debris seriously is when a piece of debris might hit a crewed platform like the ISS. Having more crewed platforms + orbital debris will drastically limit launch opportunities via the launch collision avoidance process. If new satellites can’t be launched efficiently because of a proliferation of crewed stations and orbital debris I suspect the very well-funded and strategically important satellite industry will create a solution very quickly.”

To build a space settlement like the first Kalpana, about 17,000 tons of material will have to be lifted from Earth.  Using the current SpaceX Starship payload specifications this would take 170 launches to LEO.  By comparison, in 2021 the global launch industry set a record of 134 launches.  Starship has not even made it to orbit yet, but assuming it eventually will and the reliability and reusability is demonstrated such that a fleet of them could support a high launch rate, within the next 20 years or so there will be considerable growth in the global launch industry.  If larger versions of Kalpana are built the launch rate could approach 10,000 per year for space settlement alone, not to mention that needed for rest of the space industry.  This raises the question of where will all these launches take place?  Are there enough spaceports in the world to support it?  Marotta has an answer for this as well.  As CEO of The Spaceport Company, he is laying the groundwork for the global space launch infrastructure that will be needed to support a robust launch industry.  His company is building distributed launch infrastructure on mobile offshore platforms.  Visit his company website at the link above for more information.

Conceptual illustration of a mobile offshore launch platform. Credits: The Spaceport Company

For quite some time there has been a spirited debate among space settlement advocates on what destination makes the most sense to establish the first outpost and eventual permanent homes beyond Earth.  The Moon, Mars or free space O’Neill settlements.  Each location has its pros and cons.  The Moon being close and having ice deposits in permanently shadowed craters at its poles along with resource rich regolith seems a logical place to start.  Mars, although considerably further away has a thin atmosphere and richer resources for in situ utilization.  Some believe we should pursue all the above.  However, only O’Neill colonies offer 1G of artificial gravity 24/7.  With so many unknowns about the gravity prescription for human health and reproduction, free space settlements like Kalpana offer a safe solution if the markets and funding can be found to make them a reality.

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Highlights from the International Space Development Conference

Conceptual illustration of Mag Mell, a rotating space settlement in the asteroid belt in orbit around Ceres – grand prize winner of the NSS Student Space Settlement Design Contest. Credits: St. Flannan’s College Space Settlement design team*

In this post I summarize a few selected presentations that stood out for me at the National Space Society’s International Space Development Conference 2022 held in Arlington, Virginia May 27-29.

First up is Mag Mel, the grand prize winner of the NSS Student Space Settlement design contest, awarded to a team* of students from St. Flannan’s College in Ireland. This concept caught my eye because it was in part inspired by Pekka Janhunen’s Ceres Megasatellite Space Settlement and leverages Bruce Damer’s SHEPHERD asteroid capture and retrieval system for harvesting building materials.

The title Mag Mell comes from Irish mythology translating to “A delightful or pleasant plain.” These young, bright space enthusiasts designed their space settlement as a pleasant place to live for up to 10,000 people. Each took turns presenting a different aspect of their design to ISDC attendees during the dinner talks on Saturday. I was struck by their optimism for the future and hopeful that they will be representing the next generation of space settlers.

Robotically 3D printed in-situ, Mag Mell would be placed in Ceres equatorial orbit and built using materials mined from that world and other bodies in the Asteroid Belt. The settlement was designed as a rotating half-cut torus with different angular rotation rates for the central hub and outer rim, featuring artificial 1G gravity and an Earth-like atmosphere. Access to the surface of the asteroid would be provided by a space elevator over 1000 km in length.

* St. Flannan’s College Space Settlement design team: Cian Pyne, Jack O’Connor, Adam Downes, Garbhán Monahan, and Naem Haq

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

Daniel Tompkins, an agricultural scientist and founder of GrowMars, presented his Expanding Loop concept of self replicating greenhouses which would be 3D printed in situ on the Moon or Mars (or in LEO). The process works by utilizing sunlight and local resources like water and waste CO2 from human respiration to grow algae for food with byproducts of bio-polymers as binders for 3D printing blocks from composite concretes. Tompkins has a plan for a LEO demonstration next year and envisions a facility eventually attached to the International Space Station. He calculates that a 4000kg greenhouse could be fabricated from 1 year of waste CO2 generated by four astronauts. An added bonus is that as the greenhouse expands, an excess of bioplastic output would be produced, enabling additional in-space manufacturing.

Diagram depicting GrowMars Expanding Loop algae growing process to create greenhouse blocks and byproducts such as proteins and fertilizer. Credits: GrowMars / Daniel Tompkins.
Illustration of a portion of the Spacescraper tethered ring from the Atlantis Project. Credits: Phil Swan

Phil Swan introduced the Atlantis Project, an effort to create a permanent tethered ring habitat at the limit of the Earth’s atmosphere, which he calls a Spacescraper.  The structure would be placed on a stayed bearing consisting of two concentric rings magnetically attached and levitated up to 80 km in the air.  In a white paper available on the project’s website, details of the force vectors for levitation of the device, the value proposition and the economic feasibility are described. As discussed during the talk at ISDC, potential applications include:

  • Electromagnetic launch to space
  • Carbon neutral international travel
  • Evacuated tube transit system
  • Astronomical observatories
  • Communication and internet
  • Solar energy collection for electrical power
  • Space tourism
  • High rise real estate

Phil Swan will be coming on The Space Show June 21 to provide more details.

Conceptual illustration of a Mars city design with dual centrifuges for artificial gravity. Credits: Kent Nebergall

Finally, the Chair of the Mars Society Steering committee and founder of MacroInvent Kent Nebergall, gave a presentation on Creating a Space Settlement Cambrian Explosion. That period, 540 million years ago when fossil evidence goes from just multicellular organisms to most of the phyla that exist today in only 10 million years, could be a metaphor for space settlement in our times going from extremely slow progress to a quick expansion via every possible solution. Nebergall suggests that we may be on the verge of a similar growth spurt in space settlement and proposes a roadmap to make it happen this century.

He envisions three settlement eras beginning with development of SpaceX Starship transportation infrastructure transitioning to robust cities on Mars with eventual para-terraforming of that planet. He also has plans for how to overcome some of the most challenging barriers – momentum and money. Stay tuned for more as Kent has agreed to an exclusive interview on this topic in a subsequent post on SSP as well as an appearance on The Space Show July 10th.

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Tube Town – Frontier: Living beneath the surface of the Moon

A lunar sinuous rille (probable collapsed lava tube) Credit: NASA/Lunar Reconnaissance Orbiter (LRO)

SSP featured a post in 2020 on the promise of lava tubes as ideal natural structures on the Moon or Mars in which space settlements could be established. Some are quite voluminous and could contain very large cities. Lava tubes provide excellent protection from radiation, micrometeorite bombardment and temperature extremes while being very ancient and geologically stable.

How would a city be established inside a lava tube? What would it be like to live and work there? Brian P. Dunn paints a scientifically accurate picture of such a future in Tube Town – Frontier, a hard science fiction book visualizing life beneath the surface of the Moon. Dunn recently appeared on The Space Show where he provided tantalizing details on his book scheduled to be published later this year. You can also get a taste of the story through excerpts available on his website.

I’ve had the opportunity to get an advanced copy of his book and will be providing feedback to Dunn prior to publication. He agreed to an interview via email, summarized below, answering some of my initial questions:

SSP: Your first chapter of the book takes place in 2028 and starts out with teleoperated “SciBots” networked together in swarms to explore and prospect for resources at the Moon’s south pole.  They are battery powered and need to periodically recharge at stations at the base of solar power towers at the Peaks of Eternal Light, similar to what Trans Astronautical Corp. is planning with their Sunflower system.  This time frame seems overly optimistic given that NASA’s Artemis program won’t return astronauts to the Moon until the mid 2020s and Jeff Foust reported recently that a second landing won’t take place until 2 years later.  Would it be more realistic to move out the timeline 5-10 years?

BPD: As Kathy Lueders at NASA has said, our strategy with both Moon and Mars is ‘Bots then Boots’. There is much scientific and ISRU work that can be done before the humans arrive. (See the article on my blog “The Mother of All CLPS Missions.”)  With the Moon’s close proximity and communications satellites, we can teleoperate rovers much easier than on Mars. Regarding the SLS/Artemis timeline, I don’t believe it will ever reach full fruition. The Artemis/Gateway architecture is too expensive and too slow. There is a paradigm shift happening now as the concept of large, re-usable, re-fuel able, high payload, quick launch cadence rockets is being proven out with SpaceX’s Starship.

SSP: After discovery of the lava tube in which Tube Town is eventually established, the public “was clamoring for more” and the “excitement of the discovery of the tube breathed new life into lunar and space exploration”.  I know that I would be excited, and most space cadets would be as well, but why would the general public be so supportive of space exploration because of the discovery of a lava tube on the Moon?  A recent poll found that a majority of people think that sending astronauts to the moon or Mars should be either low or not a priority.

BPD: Now that we’re starting to get the rockets, the American public will soon see landers and rovers return to the Moon. This time it will be in HD TV. At some point Americans will return to the Moon. This will be must-see TV. Taikonauts will eventually land on the Moon. This will definitely light a fire under the Americans. Interest in the Moon and lunar exploration will go up. The problem will be sustaining interest (We have an incredibly short attention span). After the world record TV event, interest will wane. We will only be able to put a few astronauts in small habitats on the surface for short periods of time. Upon discovery of an intact lava tube people will know that we could actually build a town on the Moon. Even better than that guy described in that book… what was it called?

SSP: Tube Town is operated by an umbrella organization of national space programs led by NASA called the International Space Program.  How do you envision this cost sharing structure getting started?

BPD: Although much cheaper than a comparable sized surface base, outfitting a lava tube for human habitation will not be cheap. Much of the materials can be made in situ, such as aluminum sheeting for the floors and airlocks, waterless concrete, steel for pressure vessels to hold volatile gasses, but much will need to come from Earth such as Factory machines, computers, electronics, medical equipment, etc.

In Tube Town, this cost is spread among the space programs of 27 countries of the International Space Program (NASA, ESA plus 9 countries that signed the Artemis Accords).

US, Canada, Australia, New Zealand, Japan, South Korea, India, Brazil, Israel, United Arab Emirates, and the 17 member countries of the European Space Agency (Austria, Belgium, Denmark, Finland, France, Germany, Greece, Ireland, Italy, Luxembourg, the Netherlands, Norway, Portugal, Spain Sweden, Switzerland and the United Kingdom). Notable holdouts were China (CNSA) and Russia (Roscosmos).

The ISP is a cost and opportunity sharing umbrella organization for building and maintaining a large Moon base and robotic creation of a Mars base and the first crewed mission to Mars.

NASA would be the lead partner of the ISP, but project decisions were approved and administered by the ISP Board of Directors consisting of the member countries of the organization with weighted voting rights proportionate to their contribution. Many countries wanted to get in on the ground floor of a new space economy but couldn’t afford to duplicate the resources and infrastructure that already existed at NASA. With their combined buying power, the ISP could source rockets, landers, robotics, space suits, etc. from the most efficient and innovative private suppliers. In return, ISP countries received habitation services (shelter, atmosphere, food, water) and discounted rates for:

  • leasing habitation space in the Tube for scientific or commercial enterprise,
  • buying propellant and other in situ resources, and
  • payload return to Earth

ISP construction costs of the Tube are initially off-set by lunar tourism and bespoke mining. Tourism licenses are issued by the ISP to private companies. The contracts include revenue sharing, ISP Code of Conduct compliance and Space Heritage sites preservation requirements. In exchange, the licensees get transportation, medical emergency and habitation services on the Moon.

In Tube Town, the first ISP tourism licensee is with Lunar Experience, LLC. LE licensed 50 seats for a seven Earth day stay. They ran two tours per Earth month to take advantage of the Nearside lunar day (in early days, most of the popular attractions were on the Nearside). LE agreed to give away 25% of the seats to people who could not afford the price. So, of the 50 seats per trip, 12 were free and 38 were paying customers. Assuming a ticket price of $5m for a trip to the Moon for a week, a flight made $190m. The revenue sharing agreement with the ISP was 60/40 (LE 60%, ISP 40%) so for that $190m flight, LE earned $114m and ISP $76m. If only two trips were completed per month, the yearly income would be LE $1.3B and ISP $912m. The ticket price would double to watch the uncrewed launches to Mars and the price would triple to be a part of history to witness the crewed launch to Mars.

In addition, the ISP or commercial customers could take advantage of very reasonable freight rates to backhaul refined payload on the returning tourist rockets to Earth. When would the price become affordable for regular people? Probably after the third tube is discovered. I could see an ISP member like UAE opening a large lava tube exclusively as a vacation resort.

SSP: The main product produced by Tube Town’s factory is spacecraft for Mars exploration and the eventual establishment of an outpost on the Red Planet.  Presumably, at least at first, not all electronic components can be made on the Moon so will have to be imported from Earth via a space-based supply chain.  Elon Musk is designing Starship to go directly to Mars from Earth.  Why does building spacecraft on the Moon for a Mars mission make economic sense when compared to “going direct” like Starship, and why isn’t Starship mentioned in the book? 

BPD: The book is a work of fiction so I try not to use real names or products. Although I think Starship is the first of its class of big, reusable rockets, I also think the concept will be replicated (like airliners) and hopefully there will be several options in the Earth to Moon supply chain. If you can make a big re-usable rocket on a beach in Texas, you can make one inside a nice lava tube on the Moon. We will also need to get lots of bots and machinery to Mars before the humans. This can also be manufactured on the Moon. When you launch, you don’t have to fight the giant gravity well of Earth  (12.6 km/s vs 2.6 km/s) and you may not even have to re-fuel to head for Mars. Huge payloads will be much more economical from the Moon.

Artist conception of a spacecraft manufacturer inside a lava tube. Credit: Riley Dunn

SSP: Tube Town has a Farm devoted to food production, waste re-cycling, and ice processing.  However, without insects or wind pollination it is not possible to grow desirable fruits and vegetables like apples, squash, melons and many more.  You devised an innovative way to pollinate the plants.  Tell us about that!

BPD: Nearly all of the technology described in the book is based on existing technology, whether in the lab or in production. Harvey’s pollinating space bees are based on a combination of miniature drone-delivered soap bubble pollination and AI image recognition software.

SSP: In your book, the Apollo 11 landing site becomes a tourist destination.  What steps are taken to preserve this fragile heritage site?

BPD: I think the Apollo 11 site is the must-see tourist attraction on the Moon. Part of that attraction is that you can still see the boot prints of the astronauts in the regolith. On the moon, boot prints are forever- unless another human destroys them. It only takes one knucklehead.

In my book, a regolith wall is built around the site to protect from plume drift from vehicles. The entrance is a good distance away from the site. Access into the site is in a plexiglass pod that is suspended above the surface. A cable system mounted on tall towers maneuvers pods of tourists through the site from above, giving them a close-up encounter, yet not disturbing the artifacts nor the regolith.

There should be multiple Space Heritage Sites on the Moon consisting of artificial artifacts from multiple countries and natural wonders like Schroter’s Valley. They should be identified and preserved by the tourist licensees that will profit from them.

Vallis Schröteri (Schroter’s Valley), believed to be volcanic in origin, is the largest sinuous rille on the Moon seen here as imaged by Apollo 15. Credits: NASA via Wikipedia

SSP: Tube Town has a centrifuge in the Rec Section to provide artificial gravity for residents to maintain their physical health, but very little detail is provided.  How often do residents use this facility, on average, and is it’s radius optimized to minimize Coriolis forces?  You might consider this well thought out design for a centrifuge.

BPD: I love this design for a lunar lava tube environment! The Rec section of Tube Town is over 400m wide so this is the perfect place for a floor mounted Dorais Gravity Train. In my book, this would be used for scientific study of the effects of artificial gravity treatment in a low gravity environment. They would do studies on both animals, plants and humans. I see crewmembers and tourists using the gravity train as a health spa and treatment against ‘gravity sickness’.

SSP: There are a couple of resident dogs in Tube Town and one them actually becomes pregnant.  This has huge implications for biomedical research on mammalian reproduction in lunar gravity and in particular, determination of the gravity prescription for healthy human gestation.  In my opinion, determination of the gravity prescription is one of the most significant questions to be answered for long term space settlement.  Tell us about how this research is carried out in Tube Town in an ethical manner?

BPD: The studies would start with mice. Only when and if the studies show that mammalian reproduction in low gravity is safe, would the crew move up to higher level mammals. If safe, the female dog would be taken off the canine birth control medication she is on. BTW, all the ISP crewmembers and commercial residents must agree to be on birth control medication while living on the Moon. Many may choose to freeze eggs or sperm on Earth before a long deployment in space.

SSP: Where on the Moon should we look for lava tubes?

BPD: Nearly all of the volcanic activity of the Moon was on the Nearside, not the Farside. So we should definitely concentrate on the Nearside. We can see lots of collapsed lava tubes on the surface of the Moon, the intact ones are probably in the same regions.

Global mosaic map of sinuous rilles identified across the Moon by the LRO Wide Angle Camera. Credits: NASA / D. Hurwitz, J. Head, H. Hiesinger, Planetary and Space Science via Semantics Scholar

My suggestion is to look for them where we would like to find them, in other words, lets look in strategic lunar base locations where there is water and power and easy access to other useful minerals (like metals).

 Multiple sinuous rilles (Aristarchus plateau area) Credit: NASA/LRO

I’m sure NASA knows better than me, but my target priorities would be:

  1. North Pole – because its near water and solar power and metals (the Northern Oceanus Procellarum and the highlands between the maria).
  2. South Pole – because its near water and solar power. The South Pole-Aitken basin is a large impact crater but apparently there was some later volcanic activity so it is possible to find tubes in the South Pole area but they may be smaller in size and length than the ones in the Maria.
  3. Marius Hills (southwest of Schroter’s Valley in Oceanus Procellarum) – because there is lots of volcanic activity and collapsed tubes and it is near minerals and metals.

SSP: Thanks Brian for your exciting vision of our future on the Moon and for the opportunity to get a sneak peek. I’m enjoying the story of Tube Town and wish you much success with the release of the book.

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Moon-Mars dumbbell variable gravity research facility in LEO

Conceptual illustration depicting the deployment sequence of a LEO Moon-Mars dumbbell partial gravity facility serviced by SpaceX’s Starship. Left: Starship payloads being moored by a robot arm. Center: 1.6 m ID inflatable airbeams (yellow) play out from spin access and mate with dumbbell end modules. Rectangular solar arrays deploy by hanging at either end as spin is initiated via thrusters at Mars module. Right: Full deployment with Starship and Dragon docked at spin axis hub. Credits: Joe Carroll via The Space Review

There may be no single human factor more important to understand on the road to long term space settlement than determination of the gravity prescription (GRx) for healthy living in less than Earth normal gravity. What do we mean by the GRx? With over 60 years of human space flight experience we still only have two data points for stays longer than a few days to study the effects of gravity on human physiology: microgravity aboard the ISS and data here on the ground. Based on medical research to date, we know that significant problems arise in human health after months of exposure to microgravity. To name a few, osteoporosis, immune system degradation, diminished muscle mass, vision problems due to changes in interocular pressure and cognitive impairment resulting memory loss and lack concentration. Some of these problems can be mitigated with a few hours of daily exercise. But recovery upon return to normal gravity takes considerable time and we don’t know if some of these problems will become irreversible after longer term stays. We have virtually no data on human health at gravity levels of the Moon and Mars, as shown in this graph by Joe Carrol:

Graph of the correlation between human health vs gravity showing the two data points where we have useful data. Whether the relationship is a linear function or something more complex is an unknown of great importance for space settlement. Credits: Joe Carrol presentation at Starship Congress 2019 and Jon Goff post on Selenium Boondocks Nov 29, 2005

The more important question for permanent space settlements is can humans have babies in lower gravity? If we go by the National Space Societies’ definition, an outpost will never really become a permanent space settlement until it is “biologically self-sustaining”. We evolved over millions of years at the bottom Earth’s gravity well. How will amniotic fluid, changes in cell growth, fetal development and human embryos be affected during gestation under lower gravity conditions on the Moon or Mars? There are already indications that problems will arise during mammalian gestation, at least in microgravity as experienced aboard the ISS.

To answer these questions, Joe Carroll suggests the establishment of a crewed artificial gravity research facility in LEO which he described last month in an article in The Space Review. He proposes a Moon-Mars dumbbell with nodes spinning at different rates to simulate gravity on both the Moon and Mars, which covers most of the planetary bodies in the solar system where settlements would be established if not in free space. The facility could be launched and tended by SpaceX’s Starship once the spacecraft is flight worthy in the next few years in parallel with Elon Musk’s plans to establish an outpost on Mars. Musk may even want to fund this facility to inform his long term plans for communities on Mars. If his goal is for the humanity to become a multiplanetary species, surely will want to know if his settlers can have children.

Carroll’s design connects the Moon and Mars modules with radial structures called “airbeams” which will allow crew to access the variable gravity nodes in a shirtsleeve environment. The inflatable members are composed of polymer fiber fabric which can be easily folded for storage in the Starship payload bay. Crews would be initially launched aboard Dragon until the Starship is human rated.

“Eventually, rotating free-space settlements will get massive enough to use other shapes, but dumbbells plus airbeams seem like the key to useful early ones.”

The paper addresses details on key operating concepts, docking procedures, emergency protocols, and the implications for long term settlement in the solar system.

There may even be a market for orbital tourism to experience lower gravity that could make funding for the facility attractive to space venture capitalists, especially if it is located in an equatorial orbit shielded from ionizing radiation by the Earth’s magnetic fields. As the technology matures, older tourists may even want to retire in orbital communities that offer the advantage of lower gravity as their bodies become frail in their golden years.

Humankind’s expansion out into the solar system depends on where we can survive and thrive in a healthy environment. If ethical clinical studies on lower mammals in a Moon/Mars dumbbell clears the way for a healthy life in lunar gravity then we can expand out to the six largest moons including our own plus Mars. If the data shows we need at least Mars gravity, then the Red Planet or even Mercury could be potential sites for permanent settlement. But if nothing below Earth normal gravity is tolerable, especially for mammalian gestation, it may be necessary to build ever larger rotating O’Neillian free space settlements to expand civilization across the solar system. There are vast resources and virtually unlimited energy if we need to do that. But it will take considerable time and careful planning to establish the vast infrastructure needed to build these settlements. If human physiology is constrained by Earth’s gravity then space settlers will want to know this information soon so that the planning process can be integrated into space development activities about to unfold on the Moon and beyond. If Musk finds out that Mars inhabitants cannot have children and wants to establish permanent communities beyond Earth, would he change course and switch to O’Neillian free space settlements?

“If we do need sustained gravity at levels higher than that of Mars, it seems easier to develop sustainable rotating settlements than to terraform any near-1g planet.”

Listen to Joe Carroll answer my questions about his Moon/Mars dumbbell facility from earlier this month on this archived episode of The Space Show.

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Starship changes the space settlement paradigm

Artist rendering of an earlier version of Starship (formerly BFR, Interplanetary Transport System) approaching Mars. Credits: SpaceX

A mission architecture for Starship is described in a preprint open access article published online December 2 to be released in the next issue of the New Space Journal. The paper lays out a proposed strategy for using the yet to be validated SpaceX reusable spacecraft to establish a self sustaining colony on Mars. The authors* are a mix of space practitioners from NASA, the space industry and academia. No doubt Elon Musk may be thinking along these lines as he lays his company’s plans to assist the human race in becoming a multi-planet species.

Starship is a game changer. It is being designed from the start to deposit massive payloads on The Red Planet. It will be capable of delivering 100 metric tons of equipment and/or crew to the Martian surface, and after refueling from locally sourced resources, returning to Earth. This capability will not only enable extensive operations on Mars, it will open up the inner solar system to affordable and sustainable colonization.

Some of the assumptions posited for the mission architecture are based on Musk’s own vision for his company’s flagship space vehicle as articulated in the New Space Journal back in 2017, namely that two uncrewed Starships would initially be sent to the surface of Mars with equipment to prepare for a sustainable human presence.

“These first uncrewed Starships should remain on the surface of Mars indefinitely and serve as infrastructure for building up the human base.”

The initial landing sites will be selected based on where the water is. The priority will be finding and characterizing ice deposits so that humans will eventually be able to locally source water for life support and to produce fuel for the trip home. The automated payloads of these initial missions will be mobile platforms similar in design to equipment planned for upcoming robotic missions to the Moon in the next couple of years. One such spacecraft, the Volatiles Investigating Polar Exploration Rover (VIPER) is discussed with its suite of instruments that will be used to assess the composition, distribution, and depth of subsurface ice to inform follow-on ISRU operations.

“The use of water ice for ISRU has been determined as a critical feature of sustainability for a long-term human presence on Mars.”

VIPER Searches for Water Ice on the Moon
Conceptual depiction of the NASA VIPER rover planned for delivery to the Moon’s south pole in late 2023. A mobile platform with a similar suite of instruments based on this design could be launched to Mars aboard Starship. Credits: NASA

To harvest water from subsurface ice the authors suggest using proven technology such as a Rodriguez Well (Rodwell). In use since 1995, a Rodwell has been providing drinking water for the U.S. research station in Antarctica. The U.S. Army Engineer Research and Development Center’s (ERDC) Cold Region Research and Engineering Laboratory (CRREL)  has been working with NASA to prove the technology for use in space in advance of a human outpost on Mars.

Diagram depicting how a Rodriquez Well works. Credits: U.S. Army Engineer Research and Development Center

“Rodwell systems are robust and still in routine use in polar regions on Earth.”

The next order of business is power generation. The authors suggest using solar power as a first choice because the technology readiness level is the most mature at this time. Autonomous deployment of a photovoltaic solar array would be carried out on the initial uncrewed missions. But due to frequent dust storms that could diminish the array reliability, nuclear power may be a more appropriate long term solution once space based nuclear power is proven. NASA’s Glenn Research center is working on Fission Surface Power with plans for a lunar Technology Demonstration Mission in the near future. A solid core nuclear reactor is also an option as the technology is well understood.

These initial missions will robotically assess the Martian environment at the landing sites to inform designs of subsequent equipment to be delivered by crewed Starship missions in future launch windows occurring every 26 months. Weather monitoring will be performed as well as measurements of radiation levels and geomorphology to inform designs of habitats and trafficability. Remotely controlled experiments on hydroponics will also be performed to understand how to produce food. Testing will be needed on excavation, drilling, and construction methods to provide data on how infrastructure for a permanent colony will be robustly designed.

Starship’s ample payload capacity will allow prepositioning of supplies of food and water to support human missions before self sustaining ISRU and agriculture can be established. Communication equipment will be deployed and landing sites prepared for the arrival of people. Much of these activities will be tested on the Moon ahead of a Mars mission.

Production of methane and oxygen in situ on Mars will enable refueling of Starship for the trip home, as envisioned in 1990 by Robert Zubrin and David Baker with their Mars Direct mission architecture. Zubrin’s Pioneer Astronautics may even play a role through provision of equipment for ISRU as they are already working on hardware that could be tested on the Moon soon. One could envision a partnership between Zubrin and Musk as their organizations have common visions, and Zubrin has written about the transformative potential of Starship. When people arrive on Starship during a subsequent launch window after the placement of uncrewed vehicles, further testing of ISRU and life support equipment will be performed with humans in the loop to validate these technologies that will enable Mars settlements to sustain themselves.

If Musk is successful in establishing a permanent self-sustaining colony on Mars will it be a true settlement? The National Space Society in their definition says that a space settlement “..includes where families live on a permanent basis, and…with the goal of becoming…biologically self-sustaining…”, i.e. capable of human reproduction. The definition is agnostic as to if the settlement is in space or on a planetary surface. Musk wants to established cities on the planet housing millions of people by mid century. But does this make sense if settlers can’t have healthy children in the lower gravity of Mars? SSP explored this question in a recent post. Hopefully, once Starship becomes operational, an artificial gravity research facility in LEO will be high on Musk’s priority list to answer this question before he gets too far down the Martian urban planning roadmap. Would he ever consider a change in space settlement strategy in favor of O’Neill type free space colonies? Starship could certainly help facilitate the realization of that vision.

If all goes according to plan, SpaceX will attempt the first orbital flight of a Starship prototype sometime next year, which also happens to be when the next launch window opens up for trips to Mars. Obviously, nothing in rocket development goes according to plan, so the initial flight ready design is at least a year away optimistically. And we know Musk’s timelines are notoriously aspirational. As ambitious as Musk is in driving his company toward the goal of colonizing Mars, it seems unlikely that an initial uncrewed mission with all its flight ready automated hardware as described above could be ready by the next launch window in 2024. But what about 2026? NASA’s current plans for return to the Moon call for a human rated version of Starship as a lunar lander “…no earlier then 2025”. However, Japanese billionaire Yusaku Maezawathe’s Dear Moon mission sending 8 crew members around Luna with a crewed Starship is still planned for 2023. A lot of details are yet to be worked out and we still have not covered the topic of Planetary Protection nor the granting of a launch license to SpaceX by the FAA, but could a Starship human mission to Mars take place in 2028? Let me know what you think.

“The SpaceX Starship vehicle fundamentally changes the paradigm for human exploration of space and enables humans to develop into a multi-planet species.”

* Authors of Mission Architecture Using the SpaceX Starship Vehicle to Enable a Sustained Human Presence on Mars Jennifer L. Heldmann, Margarita M. Marinova, Darlene S.S. Lim, David Wilson, Peter Carrato, Keith Kennedy, Ann Esbeck, Tony Anthony Colaprete, Rick C. Elphic, Janine Captain, Kris Zacny, Leo Stolov, Boleslaw Mellerowicz, Joseph Palmowski, Ali M. Bramson, Nathaniel Putzig, Gareth Morgan, Hanna Sizemore, and Josh Coyan

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Reproduction off Earth and its implications for space settlement

Launch of the Space Shuttle Atlantis (STS-66) on November 3, 1994. The mission carried an experiment called NIH.Rodent 1, the first of only two study’s to date on rats launched at mid-pregnancy and landed close to full term to study the effects of microgravity on reproduction. Credits: NASA

In a MDPI Journal Life paper, Alexandra Proshchina and a team* of Russian researchers summarize the research that has been performed thus far on reproduction of invertebrates in space. As mentioned in the article, the only data we have on mammalian reproduction in microgravity since the dawn of the space age is from two experiments carried out over 26 years ago. The studies looked at pregnant rats launched aboard the Space Shuttle on missions STS-66 and STS-70 in 1994 and 1995 respectively, and there have never been any births of mammals in space. This huge knowledge gap on reproduction in space is problematic for human space settlement. Yet Elon Musk, The Mars Society, and other groups are charging ahead with plans for cities on Mars. What if we discover that humans cannot have healthy babies in 0.38g? SSP has covered the quest for determining the gravity prescription before looking at JAXA’s effort to at least start experimenting with artificial gravity in space, albeit on adult mammals (mice). We are still waiting for JAXA’s published results of 1/6g experiments carried out in 2019.

The data from the Space Shuttle program only looked at part of the gestation period (after 9 days) and only in microgravity. The results did not bode well for reproduction in space. Some findings “…clearly indicate that microgravity, and possibly other nonspecific effects of spaceflight, can alter the normal development of the brain itself.”

Histological cross section through a representative rat brain from NIH.Rodent 1 experiment from STS-66. Left side (a) is low magnification and right side (b-d) are high magnification. Red arrows show areas of neurodegeneration. 1 – Nasal cavity, 2 – olfactory nerve, 3 – olfactory bulb, 4 – eye, 5 – cortex telencephali, 6 – hippocampus, 7 – fourth ventricle, 8 – cerebellum. Credits: Alexandra Proshchina et al.*

So we have this one piece of data for reproduction in microgravity and nothing in higher gravitational fields except what we know here on Earth in 1g.

Would partial gravity like on the Moon or Mars be sufficient for normal fetal development in rats (or mammals in general, especially humans) during the full gestation period? If problems are identified could it be extrapolated to human reproduction? The fact that homo sapiens and their ancestors evolved on Earth in 1g for hundreds of thousands of years is a big red flag for future space colonists that hope to settle on the surface of planetary bodies and have children.

We don’t know how lower gravity conditions could affect embryonic cell growth. How would the changes in surface tension and embryo cell adhesion be altered in these environments? We have very little data on cellular mechanisms and embryonic alterations that lower gravity may induce that could affect fetal development.

“There are also many other questions to be answered about vertebrate development under space flight conditions.”

A recent report on giving birth in space by SpaceTech Analytics looks at many of the factors that need to be considered for human reproduction off Earth. Most problems could be potentially mitigated through engineering solutions such as radiation protection, medical innovations tailored for space use, life support technology, etc. In this entire presentation the authors gave very little consideration to partial gravity affects on human embryos and child birth. One slide (number 70) out of 85 discusses these issues.

It is clear that more and longer term experiments will be necessary to determine how partial gravity affects the reproduction and development of mammals before humans settle space. Some researchers are actually considering genetic modification to allow healthy reproduction in space, and the ethical considerations associated with this course of action. Obviously, such a drastic methods would come only if there was no other alternative. One would think that building O’Neill type habitats rotating to produce 1g of artificial gravity would be preferable to such extreme measures.

Clearly, we need a space based artificial gravity laboratory to carry out ethical clinical studies on the gravity prescription for human reproduction, starting with rodents and other lower organisms. SSP recently covered a kilometer long version of such a facility that could be deployed in a single Falcon Heavy launch. And don’t forget Joe Carroll’s proposal for a LEO partial gravity test facility. Doesn’t it make sense to invest in such a facility and do the proper research before (or at least in parallel to) detailed engineering studies of colonies on the Moon or Mars intended for long term settlement? This research could inform decision making on where we will eventually establish permanent space settlements: on the surface of smaller worlds or in free space settlements envisioned by Gerard K. O’Neill. Elon Musk may want to consider such a facility before he gets too far down the road to establishing cities on Mars.

* Authors of Reproduction and the Early Development of Vertebrates in Space: Problems, Results, Opportunities: Alexandra Proshchina, Victoria Gulimova, Anastasia Kharlamova, Yuliya Krivova, Nadezhda Besova, Rustam Berdiev and Sergey Saveliev.

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Kilometer long artificial gravity facility could be deployed in a single launch

One kilometer long spinning space station producing 1G of artificial gravity deployed from a single Falcon Heavy launch vehicle. Credits: Zachary Manchester, graphic by Tzipora Thompson

This year’s NASA Innovative Advance Concepts (NIAC) award winners presented their ideas in a virtual poster session last week. Zachary Manchester of Carnegie Mellon University and Jeffrey Lipton at the University of Washington have come up with a rotating habitat to produce artificial gravity. But to do this without causing severe disorientation that would result from a short radius habitat, their novel facility is one kilometer long spinning to produce 1G at both ends. Manchester and Lipton’s innovation is a deployment mechanism that leverages advances in “mechanical metamaterials” to reduce mass while increasing expansion ratios such that the structure can be squeezed into a single Falcon Heavy payload envelope but when deployed, expands to 150 times its stored configuration size. The structure can be erected autonomously and without any assembly in space.

The key enabling technologies are a combination of “handed shearing auxetics” (HSA) and branched scissor mechanisms. HSA is described in a 2018 paper in Science by Lipton and other researchers where they “…produce both compliant structures that expand while twisting and deployable structures that can rigidly lock.”

“The station can…be spun at 1-2 RPM to generate 1g artificial gravity at its ends while still maintaining a microgravity environment at its center near the spin axis, providing the crew with the flexibility of living in a 1g environment while performing some work in microgravity.”

All the NIAC Fellow poster presentations can be found at the 2021 NIAC Symposium Virtual Event website.