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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.

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Space development on the Moon, Mars and beyond featured in 2023 NIAC Phase I Grants

Conceptual illustration of an oxygen pipeline located at the lunar south pole. Credits: Peter Curreri

This year’s list of NASA Innovative Advanced Concepts (NIAC) Phase I selections include a few awards that look promising for space development. For wildcatters (or their robotic avatars) drilling for water ice in the permanently shadowed craters at the lunar south pole and cracking it into hydrogen and oxygen, Peter Curreri of Houston, Texas based Lunar Resources, Inc. describes a concept for a pipeline to transport oxygen to where it is needed. Clearly oxygen will be a valuable resource to settlers for breathable air and oxidizer for rocket fuel if it can be sourced on the Moon. The company, whos objective is to develop and commercialize space manufacturing and resources extraction technologies to catalyze the space economy, believes that a lunar oxygen pipeline will “…revolutionize lunar surface operations for the Artemis program and reduce cost and risk!”.

Out at Mars, Congrui Jin from the University of Nebraska, Lincoln wants to augment inflatable habitats with building materials sourced in situ utilizing synthetic biology. Cyanobacteria and fungi will be used as building agents “…to produce abundant biominerals (calcium carbonate) and biopolymers, which will glue Martian regolith into consolidated building blocks. These self-growing building blocks can later be assembled into various structures, such as floors, walls, partitions, and furniture.” Building materials fabricated on site would significantly reduce costs by not having to transport them from Earth.

A couple of innovations are highlighted in this NIAC grant. First, Jin has studied the use of filamentous fungi as a producer of calcium carbonate instead of bacteria, finding that they are superior because they can precipitate large amounts of minerals quickly. Second, the process will be self-growing creating a synthetic lichen system that has the potential to be fully automated.

In addition to building habitats on Mars, Jin envisions duel use of the concept on Earth. In military logistics or post-disaster scenarios where construction is needed in remote, high-risk areas, the “… self-growing technology can be used to bond local waste materials to build shelters.” The process has the added benefit of sequestration of carbon, removing CO2 from the atmosphere helping to mitigate climate change as part of the process of producing biopolymers.

Graphical depiction of biomineralization-enabled self-growing building blocks for habitats on Mars. Credits: Congrui Jin

To reduce transit times to Mars a novel combination of Nuclear Thermal Propulsion (NTP) with Nuclear Electric Propulsion (NEP) is explored by Ryan Gosse of the University of Florida, Gainesville.

Conceptual illustration of a bimodal NTP/NEP rocket with a wave rotor enhancement. Credits: Ryan Gosse

NTP technology is relatively mature as developed under the NERVA program over 50 years ago and covered by SSP previously. NTP, typically used to heat hydrogen fuel as propellant, can deliver higher specific impulse then chemical rockets with attractive thrust levels. NEP can produce even higher specific impulse but has lower thrust. If the two propulsion types could be combined in a bimodal system, high thrust and specific impulse could improve efficiency and transit times. Gosse’s innovation couples the NTP with a wave rotor, a kind of nuclear supercharger that would use the reactor’s heat to compress the reaction mass further, boosting performance. When paired with NEP the efficiency is further enhanced resulting in travel times to Mars on the order of 45 days helping to mitigate the deleterious effects of radiation and microgravity on humans making the trip. This technology could make an attractive follow-on to the NTP rocket partnership just announced between NASA and DARPA.

Finally, an innovative propulsion technology for hurling heavy payloads rapidly to the outer solar system and even into interstellar space is proposed by Artur Davoyan at the University of California, Los Angeles. He will be developing a concept that accelerates a beam of microscopic hypervelocity pellets to 120 kilometers/s with a laser ablation system. The study will investigate a mission architecture that could propel 1 ton payloads to 500 AU in less than 20 years.

Artist depiction of pellet-beam propulsion for fast transit missions to the outer solar system and beyond. Credits: Artur Davoyan

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ICON awarded $57 Million by NASA to develop lunar 3D printing technology for lunar surface construction

Conceptual illustration of Olympus, a lunar construction system based on in situ resource utilization. Credits: ICON

In a press release, the Austin based company reports how the Phase III award under NASA’s Small Business Innovation Research (SBIR) program will be used to adapt its existing additive manufacturing process for home building on Earth to the Olympus system using lunar regolith for fabrication of structures on the Moon. ICON envisions the system to be integrated into a rover that will be delivered to the Moon via a lander. The rover will then autonomously drive to a target site where the Olympus laser 3D printer will process lunar regolith into useful structures. The system can be used for fabricating roads, landing pads and habitats out of local resources without having to bring building materials from Earth, thereby significantly lowering costs. Once the system is proven on the Moon, perhaps in the later stages of Artemis, the same technology can be applied on Mars as well.

ICON plans to test the system “…via a lunar gravity simulation flight” although no details were revealed on such a mission. Presumably, this would be a parabolic flight in the Earth’s atmosphere. The company would use samples of lunar soil brought back during the Apollo missions and lunar regolith simulant to tune the process variables of their laser 3D printing equipment operating under these conditions. Once optimized, Olympus would be placed on the Moon “…to establish the critical infrastructure necessary for a sustainable lunar economy including, eventually, longer term lunar habitation.”

“The final deliverable of this contract will be humanity’s first construction on another world, and that is going to be a pretty special achievement.”

– Jason Ballard, ICON co-founder and CEO

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Mars as breadbasket for the outer solar system

Artist’s rendering of a farming settlement on Mars. Credits: HP Mars Home Planet Rendering Challenge via International Business Times.

Space settlement will eventually require space farming to feed colonists and to provide life support. It’s clear that we will replicate our biosphere wherever we go. In that spirit, Bryce L. Meyer envisions Mars as the breadbasket of the outer solar system. In a presentation at Archon 45, a science fiction and fantasy convention held annually by St. Louis area fans, he makes the case for why the fourth planet would be the ideal spot to grow crops and feed an expanding population as part of the roadmap to agriculture in space.

Carbon dioxide and subsurface water ice are plentiful on Mars, critical inputs for crop photosynthesis. There is also evidence of lava tubes there which could provide an ideal growing environment protected from radiation, micrometeorite bombardment and temperature extremes. The regolith should provide good nutrients and there is already research on methods to filter out perchlorates, a toxic chemical compound in the Martian soil.

Image of Lava tubes on the surface of Mars as photographed by ESA’s Mars Express spacecraft. Credits: ESA/DLR/FU Berlin/G Neukum / NewScientist

Another advantage that Mars holds as a food production hub for the asteroids and beyond is its placement further out in the solar system. Since it is higher up in the sun’s gravity well, Meyer calculates that it would take less than 43% of the fuel needed to transport goods from Mars outward than from Earth. He even suggests that with its lower gravity and recent advancements in materials research, a space elevator at Mars could be economically feasible to cheaply and reliably transport foodstuff off the planet.

Meyer keeps a webpage featuring space agriculture, terraforming, and closed cycle microgravity farming where he poses the question “Why settle space?” I like his answer: “Trillions of Happy Smiling Babies!!!”

Basic input/output diagram of an environmental control and life support system like what would be expected in a space farm. Credits: Bryce L. Meyer

Meyer is the founder and CEO of Cyan React, LLC, a startup that designs compact photobioreactors and provides expertise in closed-cycle farming and life support especially for space settlement and space habitats. He is also a National Space Society Space Ambassador doing his part to educate the public about the potential benefits to humanity through the use of the bountiful resources in space. In a presentation at this year’s International Space Development Conference, he describes his research on bioreactors explaining how settlers will grow food and recycle waste sustainably on the high frontier.

Diagram depicting the flow of materials in a closed space farm habitat utilizing bioreactors. Credits: Bryce L. Meyer

Complete closure and stability of an environmental control and life support system (ECLSS) is challenging and not without limitations. As launch and space transportation costs come down in the near future and off-Earth supply chains become more reliable, complete closure will not be required at least initially. In situ resource utilization will provide replacement of some ECLSS consumables where available for colonists to live off the land. As missions go deeper into space reaching the limits of supply chain infrastructure and even out to the stars, closure of habitat ECLSS and resource planning will become more important. Meyer has done the math for farms in space to provide food and air for trillions of smiling babies…and their families as they move out into the solar system.

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The role of space ethics on the high frontier

Artist concept of a cutaway view of the Stanford Torus free space settlement. Credits: Rick Guidice / NASA

Can humanity explore and develop space responsibly by learning from some of the mistakes made throughout history while settling new lands? In an article called “To Boldly Go (Responsibly)” on LinkedIn, CEO of Trans Astronautica Corporation Joel Sercel provides a vision for how we should conscientiously manage space settlement in a manner that respects human rights and the rule of law, but also maintains stewardship of the space environment.

“Through space settlement, we have a chance to show that humanity has learned from history and is evolving morally and culturally”

Sercel warns of the “Elysium effect”. In the words of Rick Tumlinson, who coined the term in an article on Space.com, “…as entrepreneurs like Elon Musk, Jeff Bezos and Richard Branson spend billions to support a human breakout into space, there is a backlash building that holds these projects as icons of extravagance.” Ironically, these New Space pioneers actually have the opposite goals of lowering the cost of access to space for average citizens and preserving the Earth’s environment by moving “dirty” industries outside it’s biosphere.

Public space agencies and private space companies can help open the high frontier responsibility through cooperation on development of common standards and international agreements in accordance with the Outer Space Treaty. Sercel believes that an urgent need in this area would be establishment of salvage rights for defunct satellites and dormant orbital debris like spent upper stages which under the OST are the responsibility of the nation that launched the payloads.

“That’s a legal impediment for companies developing satellites to clean up orbital debris and firms eager to recycle abandoned antennas and rocket bodies.”

Some work in the area of orbital debris mitigation has already been started by the Space Safety Coalition, an ad hoc coalition of companies, organizations, and other government and industry stakeholders, through establishment of best practices and standardization for space operations. And just last month the Orbital Sustainability Act of 2022 was introduced in the U.S. Senate that will “require the development of uniform orbital debris standard practices in order to support a safe and sustainable orbital environment.”

Good progress on interagency cooperation in space has also been made with the creation of the Artemis Accords, Principles for a Safe, Peaceful, and Prosperous Future. Signed by seven nations thus far, the agreement provides a legal framework in compliance with the OST for humans returning to the Moon and establishing commercial mining rights.

Sercel thinks that before establishing a permanent human presence on Mars we should first thoroughly explore the planet robotically for signs of life to ensure that we do not disrupt any indigenous organisms if a biosphere is found to be present there.

Another example of space ethics, discussed on SSP in previous posts, is determination of the gravity prescription, especially the human gestation component. The answer to this critical factor may drive the decision on where to establish permanent long term settlements so colonists can raise families. It may turn out that having children in less than 1G may not be biologically possible and therefor, for ethical reasons, may change the long term strategy for human expansion in the solar system favoring free space settlements with Earth normal artificial gravity over surface settlements. Sercel believes that determination of the gravity Rx should be a high priority and suggested on The Space Show recently a roadmap of mammalian clinical reproduction studies starting with rodent animal models producing offspring over multiple generations progressing to primates and then, only if these are successful, initiating limited human experiments. Such studies would prevent ethical issues that may arise from birth defects or health problems during pregnancy because we don’t know how lower gravity would effect embryos during gestation.

Dylan Taylor of Voyager Space Holdings has advocated for a sustainable approach to space commercial activities to ensure “…that all humanity can continue to use outer space for peaceful purposes and socioeconomic benefit now and in the long term. This will require international cooperation, discussion, and agreements designed to ensure that outer space is safe, secure and peaceful.”

Sercel is calling for the National Space Council “…to coordinate private organizations to include think tanks, advocacy groups, and the science community to work together to define the field of space ethics…to guide the development of laws and regulations that will ensure the rapid and peaceful exploration, development and settlement of space.”

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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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Plasma process for in situ production of air, fuel and fertilizer on Mars

Hubble Space Telescope image of Mars showing clouds in atmosphere near the poles and the extinct volcano Olympus Mons at right. The primary constituents of the Martian air are carbon dioxide (95%) and nitrogen (~3%). Credits: NASA

A new technology funded by ESA is under development in Belgium and Portugal that could produce breathable air, oxidizer for rocket fuel and nitrogen for fertilizer out of thin air on Mars. Using a high energy plasma, researchers at the University of Antwerp and the University of Lisbon published independent results that look promising as a source of oxygen for life support and propulsion, plus nitrogen oxides as fertilizer to grow crops.

Team Antwerp heated simulated Martian atmosphere with microwaves in a plasma chamber. The electrical energy cracked the carbon dioxide and nitrogen in the gas into highly reactive species generating oxygen which, in addition to creating breathable air and oxidizer for fuel, was combined with the nitrogen to create useful fertilizer.

The scientists in Lisbon used direct current to excite the gases into a plasma state, literally creating lightning in a bottle. This team focused only on the production of oxygen.

The efficiency of these processes is quite impressive. For example, when compared to the Mars Oxygen In Situ Resource Utilization Experiment (MOXIE) on NASA’s Perseverance rover, the Antwerp system uses the same input power, about 1kWh, but produces 47 g per hour which is about 30 times faster. MOXIE uses solar energy to electrochemically split carbon dioxide into oxygen ions and carbon monoxide, then isolates and recombines the oxygen ions into breathable air.

Image of the toaster-sized Mars Oxygen In Situ Resource Utilization Experiment (MOXIE) being installed on the Perseverance rover at the Jet Propulsion Laboratory prior to launch. Credit: NASA/JPL-Caltech

The research is in early days but has the potential for benefits on Earth too. The amount of energy needed to fix nitrogen in fertilizer for terrestrial crops is significant and releases considerable amounts of carbon dioxide to support worldwide agriculture. This plasma technology, if it can be commercialized, has the potential to reduce the carbon footprint of Earth-based fertilizer production. The fact that the process has duel-use provides a profit motive for development of the equipment and scaling up production, which could lead to improvements in efficiency and reduction in the mass for space applications.

We love ISRU technology that facilitates production of consumables using local resources at space destinations, thereby reducing the mass that needs to be transported to support space settlements and enabling them to become self-sustaining.

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The thorium molten salt reactor for Earth and space applications

Schematic of the Thorium Molten Salt Reactor for space propulsion applications. Credits: Ajay Kothari / The Space Review

President Joe Biden recently signed into law a sweeping climate bill that will have very little (if any) impact on addressing global warming (a reduction of 0.028 degrees F by 2100). While there are tax credits in the bill for construction of new nuclear power plants over the next 10 years, only two are planned to add to the existing 93 facilities operating today which provide 18% of the U.S. energy production. Most of the funding in the bill is targeted at tax credits for EVs and incentives for renewable sources such and wind and solar which are subject to interruption. Nuclear energy holds enormous promise to offset the carbon emissions associated with fossil fuel energy production and can provide reliable base load power, but it is still plagued by negative public perceptions related to safety and the potential for weapons proliferation.

Is it time to reimagine our approach to sourcing clean energy in general, and nuclear power in particular while at the same time addressing climate change? Ajay Kothari thinks so – by research and development and eventual commercialization of nuclear power plants fueled by thorium rather than uranium. Dr. Kothari describes his vision in the August 1, 2022 issue of The Space Review. He believes that this powerful and sustainable power source “…will solve the world’s energy problem a thousand times over with zero carbon dioxide emission during operation, and it may be the cheapest form of energy production for us.”

“One ton of thorium is roughly equivalent to five million barrels of oil”

Thorium is abundant in the Earths crust making it relatively cheap and therefore, more affordable. It is only slightly radioactive, far less so then uranium and does not contain fissile material making it much safer and easier to moderate (i.e. switch off) in the case of an accident. This would prevent meltdowns unlike conventional reactors which have coolants that operate at much higher pressures and need far more complicated engineering safeguards to prevent disasters.

Thorium molten salt reactors are inherently safe. Flibe Energy is designing a Liquid Fluoride Thorium Reactor (LFTR) and according to the company’s website, “…any increase in operating temperature reduces the density of the salt which in turn, causes the reaction to slow and the temperature to fall. LFTR is also designed with a simple frozen salt plug in the bottom of the reactor core vessel. In the event of power loss to the reactor, the frozen salt plug quickly melts and the fuel salt drains down into a storage tank below – causing a termination in the fission process.”

Once developed for energy production on Earth, the same technology has applications in space. While it would not be used in a booster during launch, a molten salt thorium reactor upper stage, like that shown in the illustration above, could provide an efficient 700 second specific impulse by heating hydrogen as fuel for advanced propulsion for the next few decades until fusion energy comes on line. An added benefit would be that the upper stage reactor could also be used to provide energy at the destination, for example on the Moon or Mars.

“One kilogram of thorium taken from Earth [to the Moon] … can support a 2.6 thermal megawatt plant for a year.”

A thorium reactor was developed at Oak Ridge National Laboratory (ORNL) back in the 1960s but was never commercialized after the then Atomic Energy Commission favored plutonium fast-breeder reactors.

Diagram of the thorium fuel cycle in molten salt reactors. Credits: Flibe Energy

There are challenges to overcome. For example, the thorium fuel cycle is complicated and still produces some radioactive waste, but far less and with much shorter half life when compared to conventional uranium nuclear reactors. But the benefits of this clean, abundant and affordable energy source could make investment by the public and private sector worth the effort.

“With US reserves at 595,000 tons of thorium, we have enough to last us 600 years at current rates.”

Kothari has been a long time proponent of Thorium reactors. He recently gave a talk on the molten salt thorium reactor via Zoom for the University of Maryland now available on YouTube. You can also hear an in-depth discussion of the technology on The Space Show when he was a guest back in October 2021 and when he returns to the show September 13, 2022.

Dr. Kothari agreed to take a deeper dive with SSP into what he calls “Thor – The Life-Saver” through an email interview. If you have questions I didn’t cover about thorium molten salt reactors please leave a comment.

SSP: Dr. Kothari, thank you for taking the time to answer my questions. With respect to the public’s fear of nuclear power in general, the safety of thorium molten salt reactors is certainly an argument in favor to the technology. But aren’t there still risks of nuclear proliferation?

AK: We have more than 400 reactors in more than 40 countries worldwide. We found ways to have countries develop their reactors but have proliferation controls. This idea, the TMSR, creates no Plutonium, and would be easier to monitor. Besides, whether we want [to] or not, other countries WILL do it. Many are. Also we can develop the technology for ourselves and [for] friendly countries OR at the very least, USE IT FOR OURSELVES! How can we deny this incredible opportunity for our (US) populace? Is that fair?

SSP: Flibe Energy appears to be the only U.S. company pursuing LFTR technology. Chicago based Clean Core is focusing on thorium-based fuels to be used in existing pressurized heavy-water reactor designs. What do you think of these two company’s approaches and are you aware of any other thorium reactor development efforts in the U.S, either in private industry or academia?

AK: MIT is developing tech to resolve some of the TMSR issues that would be quite helpful [SSP found this story from MIT Nuclear Reactor Laboratory on deployment of its “…nuclear reactor (MITR) and related testing apparatus as a proving ground for the materials and processes critical to molten-salt-cooled reactors.”]. Others are shown in the chart below with some of them being US based (bottom right).

Color coded map showing global molten salt reactor technology development activities and the sponsoring country/entities. FHR= Fluoride salt-cooled high-temperature reactor. LEU = Low Enriched Uranium. HEU= Highly Enriched Uranium. TRU=Transuranic wastes, i.e. heavier elements than Uranium. Credits: Oak Ridge National Laboratory

SSP: How difficult would it be to adapt this technology for space propulsion and power applications and is it so far off that fusion energy may be available by the time development efforts come to fruition?

AK: In my opinion, …. controlled fusion may be 100, 200 or 50 years away. We have a valley of death … between now and then. This TMSR can fill the gap but can also be used for space propulsion as my diagram above shows. Sure, the TRL of it needs to be brought up, but that’s what we are here for. It would be less heavy than [the] NERVA idea, especially if the chemical processing plant is separated and U233 is used for space propulsion rather than Th232. This would be the idea. The rate of fission is then controlled by the graphite rod moderators/controllers.

SSP: China has been working on a LFTR since 2011 and was recently cleared to start operating the reactor which is a direct descendent of the original experimental design that ORNL studied in the 1960s. It would appear that the Chinese have a significant head start. Is this concerning?

AK; Absolutely. All I can say is that we are idiots.

SSP: One of the disadvantages of thorium reactors is that large upfront costs are needed due to the significant amount of testing and licensing work for qualification of commercial reactors. The reactors also involve high fuel fabrication and reprocessing costs. How would you address these issues to attract investors?

AK: This idea really is a golden nugget, so to speak. The way to attract investors is to bring the TRL up with government (DoE, NASA and DoD) funds. When the light at the end of the tunnel is seen by investors, they will jump in with both feet. It may still be 5-10 years away but if we do not do it soon, (1) it will always remain so, and (2) some other country (China) or many other countries will DEFINITELY move ahead of us!

SSP: Another disadvantage is the presence of a significant level of gamma ray emissions due to Uranium-232 in the fuel cycle. How will this be dealt with safely?

AK: The Gamma ray radiation occurs from Protactinium 233 absorbing another neutron (before it Beta decays) to become Pa234 If it is separated in a chemical processing plant, it would remain easier to handle. From Wiki[pedia]: “The contamination could also be avoided by using a molten-salt breeder reactor and separating the 233Pa before it decays into 233U)”.

SSP: What regulatory and policy changes are needed to realize this technology in the U.S.?

AK: [The] NRC and DoE should allow smaller (~2 MW) size experimental reactors at Universities and research institutions right now.

SSP: On a related note, what efforts can leaders in private industry, academia and government undertake to begin the research and technology needed to commercialize thorium molten salt reactors.

AK: There are a few uncertain items in this nuclear process that Universities, small businesses and government research institutions can resolve. Government agencies need to fund SBIR/STTR type of initiatives to address the following technical issues:

  1. The sustainability of the heat exchangers whether they are to be made of Hastelloy-N or some other composite. This characterization is needed w.r.t. neutron flux intensity, temperature reached and time exposed (in months to years)
  2. The same as above for reactor containment vessels and pipes carrying the hot molten salt.
  3. Chemical separation for in-line or off-line work for Protactinium and U233.
  4. Tritium mitigation ideas (probably using CO2 in closed loop for electricity generation) or sequestration of it for later use in fusion when and if available. Designing and demonstrating tritium separators are key elements of DOE’s solid fuel MSR program at both universities and national laboratories
  5. Gamma ray mitigation or reduction

Thorium doesn’t spontaneously undergo fission – when an atom’s nucleus splits and releases energy that can generate electricity. Left to its own devices it decays very slowly, giving off alpha radiation that can’t even penetrate human skin, so holidaymakers don’t need to worry about sunbathing on thorium-rich beaches.

We don’t have as much experience with Thorium. The nuclear industry is quite conservative, and the biggest problem with Thorium is that we are lacking in operational experience with it. When money is at stake, it’s difficult to get people to change from the norm.

Irradiated Thorium is more dangerously radioactive in the short term. The Th-U cycle invariably produces some U-232, which decays to Tl-208, which has a 2.6 MeV gamma ray decay mode. Bi-212 also causes problems. These gamma rays are very hard to shield, requiring more expensive spent fuel handling and/or reprocessing.

Thorium doesn’t work as well as U-Pu in a fast reactor. While U-233 an excellent fuel in the slow-neutron regime, it is between U-235 and Pu-239 in the fast spectrum. So for reactors that require excellent neutron economy (such as breed-and-burn concepts), Thorium is not ideal.

Proliferation Issues

Thorium is generally accepted as proliferation resistant compared to U-Pu cycles. The problem with plutonium is that it can be chemically separated from the waste and perhaps used in bombs. It is publicly known that even reactor-grade plutonium can be made into a bomb if done carefully. By avoiding plutonium altogether, thorium cycles are superior in this regard.

Besides avoiding plutonium, Thorium has additional self-protection from the hard gamma rays emitted due to U-232 as discussed above. This makes stealing Thorium based fuels more challenging. Also, the heat from these gammas makes weapon fabrication difficult, as it is hard to keep the weapon pit from melting due to its own heat. Note, however, that the gammas come from the decay chain of U-232, not from U-232 itself. This means that the contaminants could be chemically separated and the material would be much easier to work with. U-232 has a 70 year half-life so it takes a long time for these gammas to come back.

The one hypothetical proliferation concern with Thorium fuel though, is that the Protactinium can be chemically separated shortly after it is produced and removed from the neutron flux (the path to U-233 is Th-232 -> Th-233 -> Pa-233 -> U-233). Then, it will decay directly to pure U-233. By this challenging route, one could obtain weapons material. But Pa-233 has a 27 day half-life, so once the waste is safe for a few times this, weapons are out of the question. So concerns over people stealing spent fuel are largely reduced by Th, but the possibility of the owner of a Th-U reactor obtaining bomb material is not.

Molten Salt Reactors

See our full page on Molten Salt Reactors for more info.

One especially cool possibility suitable for the slow-neutron breeding capability of the Th-U fuel cycle is the molten salt reactor (MSR), or as one particular MSR is commonly known on the internet, the Liquid Fluoride Thorium Reactors (LFTR). In these, fuel is not cast into pellets, but is rather dissolved in a vat of liquid salt. The chain reaction heats the salt, which naturally convects through a heat exchanger to bring the heat out to a turbine and make electricity. Online chemical processing removes fission product neutron poisons and allows online refueling (eliminating the need to shut down for fuel management, etc.). None of these reactors operate today, but Oak Ridge had a test reactor of this type in the 1960s called the Molten Salt Reactor Experiment [Wikipedia] (MSRE). The MSRE successfully proved that the concept has merit and can be operated for extended amounts of time. It competed with the liquid metal cooled fast breeder reactors (LMFBRs) for federal funding and lost out. Alvin Weinberg discusses the history of this project in much detail in his autobiography, The First Nuclear Era [amazon.com], and there is more info available all over the internet. These reactors could be extremely safe, proliferation resistant, resource efficient, environmentally superior (to traditional nukes, as well as to fossil fuel obviously), and maybe even cheap. Exotic, but successfully tested. Who’s going to start the startup on these? (Just kidding, there are already like 4 startups working on them, and China is developing them as well).

Loss of coolant accident consequences are significantly different than for Light Water Reactors

– Low driving pressure and lack of phase change fluids

– Guard vessels employed on some designs

– Planned vessel drain down to cooled, criticality-safe drain tanks on some designs