Artist’s impression of a lunar landing pad. Credits: SEArch+
When humanity returns to the Moon and begins to build infrastructure for permanent settlements, propulsive landings will present considerable risk because rocket plumes can accelerate lunar dust particles in the bare regolith to high velocities which could result in considerable damage to nearby structures. Obviously, nothing can be done about the first spacecraft that will return to the moon later this decade unless they use their own rocket plume to create a landing pad like the concept proposed in a NIAC Grant by Masten Space Systems (now part of Astrobotic).
Flight Alumina Spray Technique (FAST) instant landing pad deployment during lunar landing. Source: Matthew Kuhns, Masten Space Systems Inc (now Astrobotic)
Therefore, before significant operations can begin on the Moon that require lots of rockets, a high priority will be construction of landing pads to prevent sandblasting by rocket plume ejecta of planned structures such as habitats, science experiments and other equipment. Several methods are currently being studied. Some require high energy consumption. Others could take a long time to implement. Still others are technologically immature. Which technique makes the most economic sense? Phil Metzger and Greg Autry examine options for the best approach to this urgent need in a November 2022 paper in New Space.
A lunar landing pad should have an inner and outer zone. The inner zone will have to withstand the intense heat of a rocket plume during decent and ascent. The outer zone can be less robust as the expanding gases will cool rapidly and decrease in pressure but will still be expanding rapidly, so erosion will have to be mitigated over a wider area.
Landing pad layout showing inner and outer zone measurements proposed in this study (Figure 1 in paper). Credits: Philip Metzger and Greg Autry / New Space – Lunar surface image credit: NASA.
Several processes of fabricating landing pads were examined by the authors. Sintering of regolith is one such technique, where dust grains are heated and fused by a variety of methods including microwave heating or focused solar energy. SSP has reported on the latter previously, but in this study it was noted that that technology needs further development work. Fabricating pavers by baking in ovens in situ was also examined in a addition to infusion of a polymer into the regolith to promote particle adhesion.
An economic model was developed to support construction of landing pads for NASA’s Artemis Program based on experimental data and the physics for predicting critical features of construction methods. Factors such as the equipment energy consumption, the mass of microwave generators compared to the power output needed to sinter the soil to specified thickness, and the mass of polymer needed to infuse the regolith to fabricate the pads were included in the model. Other factors were considered including the costs associated with program delays, hardware development, transportation of equipment to the lunar surface, and reliability.
When varying these parameters and comparing different combinations of manufacturing techniques, the trade study optimized the mass of construction equipment to balance the costs of transportation with program delays. The authors found that from a cost perspective, microwave sintering makes the most sense for both the inner and outer regions of the landing pad, at least initially. When transportation costs come down to below a threshold of $110K/kg then a hybrid combination of microwave sintering in the inner zone and polymer infusion of regolith in the outer zone makes the most sense.
Once astronauts land safely and begin EVAs on the lunar surface, they can keep from tracking dust into their habitat by taking an electron beam shower.
Other lunar dust problems and their risks can be mitigated with solutions covered previously on SSP.
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
Conceptual illustration of a lunar base in Mare Tranquilitatis Hole, believed to be an entrance to a lava tube about 100 meters below the lunar surface. Credits: Dipl.-Ing. Werner Grandl
In a new paper in Acta Astronautica Raymond P. Martin, a propulsion test engineer at Blue Origin and Haym Benaroya, a professor of mechanical and aerospace engineering at Rutgers describe the former’s research he carried out as a graduate student under the latter analyzing the structural integrity of lunar lava tubes after pressurization with breathable air. As reported previously on SSP, subterranean lava tubes on the Moon and Mars hold much promise as naturally occurring enclosures that are believed to be structurally sound, thermally stable and would provide natural protection from micrometeoroids as well as radiation. If they could be sealed off for habitation and filled with breathable air, life could be simplified for colonists as they would not have to don space suits for routine activities.
“This paper makes the argument that … lunar lava tubes present the most readily available route to long-term human habitation of the Moon”
Two views of a lunar skylight revealing a potential subsurface lava tube in Mare Ingenii. Credit: NASA/Goddard Space Flight Center/Arizona State University
Martin opens the paper with a history of the discovery and physical characteristics of lunar lava tubes tapping geological data dating back to the Apollo program. The existence of a lava tube is sometimes revealed by the presence of a “skylight”, a location where the roof of the tube has collapsed, leaving a hole that can be observed from space. Using an engineering simulation software called ANSYS, he developed a computer model to assess the structural integrity of these formations when subjected to internal atmospheric pressure.
Martin creates a model for his simulation based on the morphology of a relatively small lava tube known to exist from imagery taken by the Chandrayaan-1 spacecraft, the first lunar probe launched by the Indian Space Research Organisation . This structure averages 120 meters in diameter and was chosen because it has a rille-type opening level to the surface and could be sealed off at two locations. This approach makes sense as a starting point because the cavern would be easy to access and less energy would be be required to pressurize a smaller enclosure. Thus, the amount of infrastructure needed to establish early settlements would be minimized.
The goal of the simulation was to assess the integrity of the enclosed space under varying roof thicknesses and pressurization levels. Failure conditions were defined using commonly employed methods of assessing stability of tunnels in civil engineering and based on lunar basaltic rock general material properties known from testing of samples brought back from the Moon in the Apollo program and lunar meteorites. Finally, a formula was derived for safety factors associated with the failure conditions to ensure robustness of the design.
When running the simulation over various roof thicknesses and internal pressures, an optimum solution was found indicating that it is possible to pressurize a lava tube with a roof thickness of 10 meters with breathable air at nearly a fully atmosphere while maintaining its structural integrity. This would would feel like sea level conditions to people living there.
Being able to pressurize a lava tube for habitation could significantly simplify operations on the Moon as the infrastructure needed to make surface dwellings safe from radiation, micrometeorite bombardment and thermal extremes would be extensive adding costs to the settlement.
“A habitat within a pressurized tube would offer large reductions in weight, complexity, and shielding, as compared to surface habitats.”
Once a permanent settlement has been established and engineering knowledge advances to enable expansion into larger lava tubes, we can imagine how cities could be built within these spacious caverns, and what it would be like to live and work there. SSP explored just this scenario with Brian P. Dunn, who painted 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 envisions a thriving cislunar economy with factories producing spacecraft for Mars exploration.
Conceptual illustration of a spacecraft manufacturer inside a lava tube. Credit: Riley Dunn
Martin and Benaroya dedicated their paper to the memory of Brad Blair, a mining engineer who was a widely recognized authority on space resources.
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.”
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.”
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.
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:
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)
The same as above for reactor containment vessels and pipes carrying the hot molten salt.
Chemical separation for in-line or off-line work for Protactinium and U233.
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
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.
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
Conceptual illustration of a Moon base composed of inflatable habitats near one of the lunar poles. Credits: ESA / Pneumocell
The European Space Agency (ESA) recently published a report on a design study of an inflatable lunar habitat. The work was done by Austrian based Pneumocell in response to an ESA Open Space Innovation Platform campaign. The concept utilizes ultralight prefabricated structures that would be delivered to the desired location, inflated and then covered with regolith for radiation protection and thermal insulation. The main components of the habitat are toroidal greenhouses that are fed natural sunlight via a rotating mirror system that follow the sun. Since the dwellings are located at one of the lunar poles, horizontal illumination is available for most of the lunar night. Power is provided by photovoltaic arrays attached to the mirror assemblies. During short periods of darkness power is provided by batteries or fuel cells.
Cutaway view of the inflatable lunar habitat. Credits: ESA / Pneumocell
The detailed system study worked out engineering details of the most challenging elements including life support, power sources, temperature control, radiation protection and more. The greenhouses would provide sustenance and an environmentally controlled life support system for two inhabitants recycling everything. The authors claim that “…it appears possible to create in the long term a closed system…” This remains to be validated.
Inflatable space habitats have many advantages over rigid modules including lower weight, packaging efficiency, modularity and psychological benefit to the inhabitants because after deployment, the interior living space is much larger for a given mass. Several organizations and individuals have already begun to investigate inflatable habitats for lunar applications. The Pneumocell study mentions ESA’s Moon Village SOM-Architects concept which is a hybrid rigid and partly inflatable structure. Also referenced is the Foster’s and Partners Lunar Outpost design which envisions a 3D printed dome shaped shell formed over an inflatable enclosure.
Foster and Partners Lunar Outpost constructed from a hybrid of 3D printed modules and an inflatable structure. Credits: Foster and Partners
Illustration of a hybrid lunar inflatable structure. Credits: Rohith Dronadula
The Pneumocell report concludes: “A logical continuation of this study would be to build a prototype on Earth, which can be used to investigate various details of the suggested components … ” Such an approach would be relatively inexpensive and could inform the future design of flight hardware.
Speaking of ground based prototypes, The Space Development Network has been exploring inflatable structures for habitats on the Moon for some time. Doug Plata, president of the nonprofit organization working to advance space development hopes to display an inflatable version of his InstaBase concept at BocaChica, Texas when SpaceX attempts its first orbital launch of Starship, hopefully within the a year or so. When comparing his design to Pneumocell’s, Plata says in an email to SSP, “One difference is that we have the modules directly attached to each other and so avoid the mass of those connecting corridors.”
Conceptual illustration of InstaBase – a fully inflatable lunar base capable of supporting an initial crew of eight. Credits: The Space Development Network
In reference to the greenhouse designs, Plata continues: “As for the GreenHabs, they have a pretty interesting design to take advantage of direct sunlight. We address the shielding conceptually by fully covering the GreenHabs and then use PV solar drapes and transport the electricity into the GreenHabs via wires. By converting sunlight to electricity to LEDs, more surface area of plants can be grown than the surface area of the solar panels powering them. This is due to the full spectrum of the sun being converted to only those frequencies that plants use.”
It is great to see such creativity and variety of designs for abodes on the Moon. When reliable transportation systems such as Starship blaze the trail, we will be ready with easily deployable, safe and voluminous habitats for lunar settlements.
Artist rendering of the interior of an inflatable toroidal greenhouse in a lunar habitat. Credits: Pneumocell
Image credit: NASA/Goddard/Arizona State University
The Cislunar Science and Technology Subcommittee of the White House Office Science and Technology Policy Office (OSTP) recently issued a Request for Information to inform development of a national science and technology strategy on U.S. activities in cislunar space.
Dennis Wingo provided a response to question #1 of this RFI, namely what research and development should the U.S. government prioritize to help advance a robust, cooperative, and sustainable ecosystem in cislunar space in the next 10 to 50 years?
In a prolog to his response Wingo reminds us that historically, NASA’s mission has focused narrowly on science and technology. What is needed is a sense of purpose that will capture the imagination and support of the American people. In today’s world there seems to be more dystopian predictions of the future than positive visions for humanity. We seem to be dominated by fear of “…doom and gloom scenarios of the climate catastrophe, the degrowth movement, and many of the most negative aspects of our current societal trajectory.” This fear is manifested by what Wingo defines as a “geocentric” mindset focused primarily within the material limitations of the Earth and its environs.
“The question is, is there an alternative to change this narrative of gloom and doom?”
He recommends that policy makers foster a cognitive shift to a “solarcentric” worldview: the promise of an economic future of abundance through utilization of the virtually limitless resources of the Moon, Asteroids, and of the entire solar system. An example provided is to harvest the resources of the asteroid Psyche which holds a billion times the minable metal on Earth, and to which NASA had planned on launching an exploratory mission this year but had to delay it due to late delivery of the spacecraft’s flight software and testing equipment.
Artist rendering of NASA’s Psyche Mission spacecraft. Credits: NASA/JPL-Caltech/Arizona State Univ./Space Systems Loral/Peter Rubin
Back to the RFI, Wingo has four recommendations that will open up the solar system to economic development and address many of the problems that cause the geocentrists despair.
First, we should make the Artemis moon landings permanent outposts with year long stays as opposed to 6 day “camping trips”. This should be possible with resupply missions by SpaceX as they ramp up Starship launch rates (assuming the launch vehicle and lander are validated in the same timeframe, which seems reasonable). Next, we need power and lots of it – on the order of megawatts. This should be infrastructure put in place by the government to support commerce on the Moon. By leveraging existing electrical power standards and production techniques, large scale solar power facilities could be mass produced at low cost on Earth and shipped to the moon before the capability of in situ utilization of lunar resources is established. Some companies such as TransAstra already have preliminary designs for solar power facilities on the Moon.
Which brings us to ISRU. The next recommendation is to JUST DO IT. This technology is fairly straightforward and could be used to split oxygen from metal oxides abundant in lunar regolith to source air and steel. Pioneer Astronautics is already developing what they call Moon to Mars Oxygen and Steel Technology (MMOST) for just this application.
Conceptual illustration of the Lunar OXygen In-situ Experiment (LOXIE) Production Prototype. Credits: Mark Berggren / Pioneer Astronautics
And lets not forget the wealth of in situ resources that could be unlocked via synthetic geology made possible by Kevin Cannon’s Pinwheel Magma Reactor.
Conceptual depiction of the Pinwheel Magma Reactor on a planetary surface in the foreground and in free space on a tether as shown in the inset. Credits: Kevin Cannon
Of course there is water everywhere in the solar system just waiting to be harvested for fuel and life support in a water-based economy.
Illustration of an ice extraction concept for collection of water on the Moon. Credits: George Sowers / Colorado School of Mines
Wingo’s final recommendation is industrialization of the Moon in preparation for the settlement of Mars followed by the exploration of the vast resources of the Asteroid Belt. He makes it clear that this is more important than just a goal for NASA, which has historically focused on scientific objectives, and should therefore be a national initiative.
“…for the preservation and extension of our society and to preclude the global fight for our limited resources here.”
With the right vision afforded by this approach and strong leadership leading to its implementation, Wingo lays out a prediction of how the next fifty years could unfold. By 2030 over ten megawatts of power generation could be emplaced on the Moon which would enable propellant production from the pyrolysis of metal oxides and hydrogen production from lunar water. This capability allows refueling of Starship obviating the need to loft propellent from Earth and thereby lowering the costs of a human landing system to service lunar facilities. From there the cislunar economy would begin to skyrocket.
The 2040s see a sustainable 25% annual growth in the lunar economy with a burgeoning Aldrin Cycler business to support asteroid mining and over 1000 people living on the Moon.
By the 2050s, fusion reactors provide power and propulsion while the first Ceres settlement has been established providing minerals to support the Martian colonies.
“The sky is no longer the limit”
By sowing these first seeds of infrastructure a vibrant cislunar economy will enable sustainable settlement across the solar system. A solarcentric development mythology may be just what is needed to become a spacefaring civilization.
Artist’s concept of an O’Neill space colony. Credits: Rachel Silverman / Blue Origin
I met Kent Nebergall during a cocktail reception at ISDC which took place May 27-29. He chairs the Steering Committee for the Mars Society (MS) and gave a fascinating talk Sunday afternoon on Creating a Space Settlement Cambrian Explosion. We had a wide-ranging discussion on some of his visions for space settlement and he agreed to collaborate on this post. We’ll do a deep dive into some of the topics he covered in his talk, which is available on his website at MacroInvent.
In summary, he breaks down some of the key challenges of space settlement and proposes economic models for sustainable growth. His roadmap lays out a series of space settlement architectures starting with a variant of SpaceX Starship used as a building block for large rotating habitats and surface bases for the moon, Mars, and asteroids. Next, he presents his Eureka Mars Settlement design which was entered in the MS 2019 Mars Colony Design Contest addressing every technical challenge. Finally, an elegant system for para-terraforming Martian canyons in multi-layered habitats is proposed, “…with the goal of maximizing species diversity and migration beyond our finite world. We not only preserve and diversify species across biomes, but engineer new species for both artificial and exoplanetary habitats. This is an engine for creating technology and biological revolutions in sequence so that as each matures, a new generation is in place to keep driving expansion across the solar system and beyond.”
Here’s my interview with Kent conducted via email. I hope you enjoy it!
SSP: You created a checklist of the required technologies needed to enable space settlement where each row is sorted by increasing necessity while the columns are sorted by greater isolation from Earth.
Credits: Kent Nebergall
Musk has started to crack the cheap access to space nut and large vehicle launch at upper left with Starship but we’re not there yet. Given that Musk’s timelines always should be taken with a grain of salt, and the challenge of planetary protection (bottom of column 3) could potentially prevent Musk from obtaining a launch license for a crewed mission before scientists have a chance to robotically search for signs of life, what is your estimation of the probability that Humans will land on Mars by 2029, in accordance with your proposed timeline (see below)?
KN: Elon time is real, definitely. My outside analysis implies that SpaceX is using Agile development systems borrowed from the software industry. The benefit of Agile is that technological progress is as fast as humanly possible. The bad news is that it largely ignores things that traditional management styles value, such as being able to predict the date something is really finished. At any rate, my general conclusion is that anything Elon predicts will be off by 43 percent as a baseline, assuming no outside factors are involved. Starship has slid more because the specifications kept changing, much as they did with Falcon Heavy.
We seem to be locked in on the early orbital design, which seems to be purely for getting Starlink 2 satellites in place and providing return on investment while getting the core flight systems refined. It doesn’t need solar panels, crew space, or the ability to stay on orbit more than a day. Crewed Starship may take another few years and use a smaller than expected cabin with a large payload bay. 2029 is the most recent year of a crewed Mars landing from Elon (as of March, 2022). If we allow for Elon Time, we could expect cargo in that launch window. I suspect one vehicle may try to return to prove out that flight range, like return to Earth from deep space. The first mission would largely be watching Optimus Prime robots setting up a farm of solar panels to make fuel for the return trip.
“The irony is that Elon could just pack the ship with Tesla humanoid robots for the first few missions…”
The planetary protection regulatory barrier is quite possible, yes. We just saw the regulatory findings for Bocca Chica. That requires several frivolous preconditions for flight, like writing an essay on historic monuments and accommodating ocelots, which haven’t been seen in the area in forty years. I doubt the capacity of political Simon Says playground games like has been exhausted yet.
What we’ve seen historically is that those who cannot compete will throw up regulatory and legal barriers. However, we’ve also seen that these efforts eventually burn out after a few years. This has been true with paddle wheel river ships, steam ships, railroads, and airlines. It’s playing out with Tesla and the big three domestic automakers now as well. Most of those tricks were already pulled with Falcon 9, so I think that path is largely burned through. I’m nearly certain they will try the planetary protection argument later. We have already seen with the ocelots that they are willing to protect absent species.
The irony is that Elon could just pack the ship with Tesla humanoid robots for the first few missions and build a base while running life searches in the area. The base could be built with nearly the same productivity as a human crew, and the cultural pressure to move humans into it would be quite high if no life is found in the meantime. It would be great marketing for the Tesla robots as well.
SSP: The table seems comprehensive and covers just about everything. Has it changed or been updated in 18 years? I noticed “Spacesuit Lifespan”. Why is this a challenge for space settlement?
KN: The table is fairly solid in terms of subject matter, but I’ve started a project to rebuild it. I only found out recently that NASA’s term for this is RIDGE (Radiation, Isolation, Distance, Gravity and Environment). My slicing into 26 categories is more precise – literally an alphabet of categories.
First, if it were a true “periodic table” analog, it would transpose the columns. But it’s much easier to fit in PowerPoint this way. Second, I have used this principle for other challenge sets and found interesting implications, so I may make a more advanced version in the future with far more depth. I’ll still use this for PowerPoint, though, because it can be read from the back row in under a minute. Third, each “challenge” is actually a family of challenges. There are multiple health problems with microgravity, for example, but one root cause – the absence of gravity. So, while each challenge in the table has many sub-factors, there is a single root cause and a solution that eliminates that cause also eliminates all sub-sets of problems. If a solution cannot fix the root cause, than separate solutions are needed for each child challenge like bone loss.
Spacesuit lifespan for the ISS is an issue because the suits are often older than the station itself. On the moon, the spacesuits picked up abrasive moon dust in the joints and could have eventually lost flexibility or pressure integrity if they’d been used much longer. A Mars suit is in some ways easier because the soil is more weathered and therefore less abrasive. Space settlement hits a standstill if you can’t go outside. Unfortunately, efforts to replace them have cost a billion dollars so far and have just been restarted for an even higher price tag. It seems to be the classic example of doing as little progress as possible while spending as much money as possible. There have been some great technologies developed but there has been no pressure to finish a completed suit. As the old saying goes, “One day, you just have to just shoot the engineer and cut metal”.
At one point, SpaceX outright said, “We can do it.” But NASA showed no interest, and SpaceX apparently didn’t bid on the moon suit designs this time. They have been converting the ascent suit from Dragon to one able to do spacewalks in the 1960’s Gemini sense for launch this year. I wouldn’t be surprised if they develop a moon suit just because they can, and on their own dime. It would be quite embarrassing for all involved, including SpaceX, if we had a 100 tonne payload moon lander capable of holding dozens of people, and not have a single suit capable of letting them leave the ship.
SSP: You mentioned orbital debris being a potential barrier for your plan’s LEO operations and you’ve come up with methods for shielding early orbital habitats, but they may not be effective against larger debris fragments. The X-prize Foundation is considering an award for ideas to solve this problem and there are numerous startups on the verge of addressing the issue. Such a solution would have to be implemented quickly and on a massive scale for your timeline to be achieved. If orbital debris looks like it may still be a problem for larger orbital settlements until they can be established in higher orbits, could your plan be modified to perhaps include debris removal as an economic driver? [SpaceX president and COO Gwynne Shotwell has suggested that Starship could be leveraged to help clean up LEO]
The problem must be sliced up, just as the other grand challenges are sliced up. We need several approaches at once. First, refueling starship is a bit risky, and the risk rises with prolonged exposure to the debris hazard. SpaceX originally wanted to launch the Mars vehicle, then refuel it on orbit over several tanker flights. More recently, they are implying they would fly a tanker up, fill it with several other tankers, then refuel the Mars or Lunar vehicle in one go. This makes a lot more sense. A tanker or depot hit by debris would be a space junk hazard, but it wouldn’t cost lives or science hardware.
We need to de-orbit the largest items, many of which are spent rocket stages. SpaceX has offered to gobble them up with Starship, but that means a lot of delta V in terms of altitude, inclination, elliptical elements, and so on. I could see a sort of penny jar approach where they drop off a satellite, then pick up an old one or two (the satellite and old rocket stage) before returning. Realistically, though, old rocket stages and satellites that haven’t vented every single tank (main and RCS [reaction control system]) will be hazardous to approach.
It seems the best solution would be mass-produced mini-satellites with ion drive and electrodynamic tethers. Each mini-sat would find a spent rocket stage or defunct satellite and add an electrodynamic tether to drag it down using Earth’s magnetic field while also powering an ion engine to assist in de-orbiting. You would have to do a few at a time because the tethers themselves would become a hazard if we had thousands of them cutting through space like razor ribbons.
I could also see a spider robot that would grab larger satellites with propellant still on board, wrap them up like a spider wrapping a bug in silk, and then puncturing the tanks carefully to both refill itself and render the satellite inert. It would then be safe to grab with a Starship or de-orbit with a drag or propellant system [Another concept for debris removal could be Bruce Damer’s SHEPHERD which we covered a year ago. Although originally conceived for asteroid capture, a pathfinder application could be satellite servicing/decommissioning].
We didn’t create the problem in a day, and we can’t solve it quickly either. But we can take an approach of de-orbiting two tons for every ton launched once we have mass produced systems for doing so. Maybe other launch providers can grab defunct satellites with their orbital launch stages before dragging them both into the Pacific.
That said, we can’t get every paint chip and bolt out of orbit this way. We will hit a law of diminishing returns. Anything below that line will require a technology to survive impacts. The pykrete ice shield I proposed could be much smaller, such as just one hexagonal hangar big enough for 2-3 starships in LEO at a time. Once refueled, the craft would go to the much safer L5 point or directly to the moon if that is the destination. Keeping a ring at L5 would not require a massive ice shield or centrifuge habitat to be a useful waystation. But those would be designed into it up front to give room for expansion.
If we decided that a Mars mission had to wait for all the infrastructure I proposed, we’d be in the same trap that Von Braun would have fell into of wanting massive infrastructure before the first crewed lunar mission. You need a balance of infrastructure and exploration to give both meaning.
“We can democratize early if we give some participation method in the initial investments in time, technology, and financing.”
SSP: Musk says he needs 100s of starships to deliver millions of tons of materials to support large cities on Mars by mid-century (his timeline). You’ve created a somewhat more reasonable timeline for Starship round trip logistics for this effort based on Hohmann transfer orbits and Mars orbital launch windows (i.e. every 2 years).
Credits: Kent Nebergall
What will be the economic driver for such an ambitious project besides Musk just “making it so”? I saw later in your presentation that you proposed an initial sponsorship and collectables market followed by MarsSpec competitions. How will these initiatives kickstart sufficient market enthusiasm to support such an enormous fleet of Starships?
KN: It’s a complex topic, and easily a book in itself. To cut to the core of it, any major discovery or invention that is not democratized becomes historic or esoteric rather than revolutionary. Technology revolutions do not take place in particle accelerators any more than music revolutions take place in symphony orchestra pits. Things that don’t impact people constantly are simply curiosities. Even many things taken for granted like GPS and running water are ignored, but they remain transformative. When the furnace filter factory worker sends part of his month’s labor to Mars, we have space settlement. We can democratize early if we give some participation method in the initial investments in time, technology, and financing. But these waves will go from new and novel to basic and ignored rather quickly, and this is especially true if they succeed.
Imagine being a medieval merchant and getting an opportunity to send a bag of grain on a voyage to Cabot or some other explorer. In return you get a rock from the opposite side of the world, a certificate saying what you gave and authenticating what you got back, and a tiny bit of participation in the history of your era that you can share with your children. A decade later, your son is working in a smelting plant in a port city and making hardware for houses in the new world. In another decade your grandchildren are growing crops in Maryland. It’s a bit like that. Each wave will fund and create the industrial and skill base for the next wave before becoming culturally ubiquitous. The last child has no interest in a rock from his Maryland backyard. But to the grandfather living a generation or two beforehand, it may as well be from the moon. The wave of sponsorship, followed by specifications for space-rated products, followed by biological engineering in lower gravity worlds will each create benefits and enthusiasm back on Earth. After that last wave, the economic ecosystem becomes permanently multi-planetary.
Everything else about space is a simple engineering problem. Minds, trends, budgets, and so on are not so well behaved as atoms or heat, but they have a lot of history that we can use to model workable solutions. This is the one I came up with.
“The problem with any grand engineering venture is that every design looks good until it comes in contact with reality.”
SSP: The Eureka Space Settlement concept features dual centrifuges providing artificial gravity equivalent to the Moon and Mars.
Eureka settlement duel centrifuge facility providing lunar gravity on the inner ring and Mars gravity on the outer one. Credits: Kent Nebergall
I like the idea of using variable gravity to study biological effects on plant and mammalian physiology, adapting species to be multi-planetary and prepping for settlements that will need gravity as we move out into the outer solar system, but this can be done more cheaply in LEO or in cislunar space as outlined earlier in your architecture. Why not simplify the Eureka settlement by eliminating the centrifuge and going with normal Mars gravity?
KN: The problem with any grand engineering venture is that every design looks good until it comes in contact with reality. You can’t model every issue up front, and one of the hardest to work out without experience are multi-generational ecosystems. If we build a $100 billion Mars city and the kids have birth defects, we have a huge liability issue and a city that will be turned over to robots or dust.
The advocates assume all will be fine, but they tend to downplay issues. The critics assume all will go poorly, but they never want to venture past the status quo. Reality will be a mixed bag of data points on a bell curve between the two with both unknown threats and opportunities waiting for discovery. This unknown is a big reason for the enthusiasm to try in the first place.
I came up with the steelman methodology by taking all the criticisms and range of danger possibilities and cranking the bell curve values up a few sigma to the nasty side. The idea is that if you can STILL make an affordable design that pays for itself when the universe is coming after you with a hammer, you probably will be fine when the bell curve is realized. You should always have a back-down plan to have surface domes with no centrifuges, or simply use the centrifuges for pregnant mammals and trees that need to fight gravity to have enough limb strength to bear fruit. That said, another beauty of this design is that a Pluto colony or asteroid colony will almost certainly need centrifuges for multigenerational life. Prototyping it on Mars may be overkill for Mars, but perfect for Pluto or Enceladus. This makes it much easier for Mars settlers to think about colonizing the outer solar system. Even the children of our dreams need dreams, after all.
“A space outpost must bring materials to itself, so a system like that without surface outposts or asteroid mining is a dead end.”
SSP: In the proposed first wave of the architecture, rotating settlements are created from Starship building blocks in high orbit to create “…deep space industrial outposts in the O’Neill tradition with a thousand inhabitants each. On the lunar and Martian surface, we simply take a slice of the ring architecture with starships inside as an outpost.” With the amount of investment needed to build the infrastructure to transport materials and people for large settlements on Mars, and given that the biggest grand challenge on your chart is reproduction (which may not be possible in less than Earth’s gravity), why wouldn’t it make more sense to focus efforts on building larger 1G rotating free space settlements where we know having children is possible?
KN: It’s not so much a roadmap of first this structure here, then that one there. It’s a draft set of compatible building standards for everywhere. Think about the standard sizes for bricks, pipes, and wiring and how entire continents use them interchangeably over a hundred years or more. My goal was to lay out what the maximum amount of infrastructure would look like with the minimum number of parts.
There is a false dichotomy between structures like space stations made entirely from material from Earth, and local materials formed with 3D printers that can do everything with complete reliability. Both are impractical extremes, and to some degree strawman designs. Importing everything is prohibitively expensive even with Starship. Conversely, creating structures from random conglomerates of whatever material is at the landing site will be too brittle. By proposing bags that can be made of basalt cloth but that will initially come from Earth, I’m bridging the two extremes. They can be filled with dust, water, sand, or whatever is fine grained enough and can be either sintered or cemented in place. Such structures don’t have to be aligned with absolute precision and can follow soft contours or whatever is needed. You also don’t need four meters of shielding for cosmic rays if you augment it with magnets. They can be scaled in layers or levels as needed, just like bricks or two by four boards are in homes.
A space outpost must bring materials to itself, so a system like that without surface outposts or asteroid mining is a dead end.
Centrifuges for surface settlements are a bit awkward, to be sure. A train system that keeps the floor below you when spinning or de-spinning is a better system at first. Eureka was mainly done with fixed pitch decks just to show that the scale of a centrifuge for a large torus L5 ring could be done on a surface with some clever engineering. My original design goal was to make the cars, car beds, rails, and buildings swappable without stopping the ring rotation. In the same way, the pressure shell has inner and outer walls that can in theory be replaced while the other keeps pressure. It’s probably not necessary, but the goal is to remove all design barriers early in the thought process so that future engineers aren’t painted into corners.
SSP: After the first settlements are established on Mars, you suggest starting to adapt the Mars environment to Earth-like conditions through “para-terraforming” small parts of the planet such as the Hebes Chasma, a canyon the size of Lake Erie just north of Valles Marineris. This feature has the advantage of being right on the equator and closed at both ends so that kilometer sized arch structures could enclose the valley to warm the local environment with many Eureka settlements below.
Top: Artist concept of kilometer scale arches built above space settlements and enclosing a Martian canyon to provide a para-terraformed environment. Bottom: Magnificent view from below depicting these domes at cloud level on a typical summer day. Credits: Kent Nebergall / Aarya Singh
Planetary protection was mentioned as one of the grand challenges to be overcome. Some space scientists are advocating for robotic missions to answer the question of whether life existed (or still exists) on Mars before humans reach Mars. No such missions are planned prior to Musk’s timeline for putting humans on Mars at the end of this decade. Are you assuming that by the time humans are ready for para-terraforming that the question of life on Mars will be answered?
KN: We would certainly know if active, widespread, indigenous life was an issue by the time of building canyon settlements the size of Lake Erie. Even isolated pockets would leave fossil traces in broader zones.
The bigger question is that of whether or not it is possible to settle Mars if there is a risk of crossing into a local biome accidently. Eureka is built entirely on the surface, so it doesn’t cross the sterilized surface soils if it doesn’t have to. We should be able to mine from Mars with sterile equipment and be able to sterilize further after robotic extraction. We can extract water ice, volcanic rock, and surface dust and build the entire settlement from those basic materials. We can avoid sedimentary materials until we are confident they are not biologically active.
I suspect any life on Mars is from Earth, and brought by meteors. The cross-traffic of meteors throughout the solar system may mean bacterial and possibly slightly more complex life all over the solar system from the late bombardments of Earth. We should consider this no more exotic than breathing in Australia or swimming in the ocean. Microbes adapted for those environments would not be adapted to be pathogenic because why spend billions of generations preparing for a food source that may never arrive? We would have a bigger problem with random toxins that hadn’t leached out or reacted to life billions of years ago than with life itself. I respect the work of those who want sterile capsules of pristine soil captured by the current Mars rover prior to human arrival. That certainly makes sense. I like Carol Stoker’s Icebreaker mission concept. I think NASA and universities would be smart to work with SpaceX on simple rack-mount instrumentation that could be flown to planetary destinations en masse and serviced by Optimus Prime Tesla robots.
“My goal is to build the next generation of the quiet heroes of the dinner table. And certainly a few of those will be leaders too.”
SSP: You’re writing a book about creating an inventor mindset to enable a million “mini-Musks” – people who are not necessarily rich, but who shake up the world in constructive and innovative ways. Tell us more about this philosophy.
KN: The core concept is that if you could get a thousand people to do a hundredth of what Elon has accomplished, it would be a tenfold increase in what we’ve seen in terms of his contribution to technology. That’s not a very big ask individually, even if it’s more garage labs than factories for now. I looked deeply into what Elon Musk does and what other inventors like him have done. I’ve looked at technology revolutions and what key things spark the massive growth waves of innovation. Obviously, there are intersections between the two.
I’m writing a short book this summer to document Elon’s methodologies in an approachable and comprehensive reference. If it attracts enough interest, I can take that core module into different directions. One is digging more into how the mind invents. Another is breaking down how technology revolutions work. A third is all this work on space settlement. I’ve also come up with intellectual property around the root of these concepts that would be valuable software and services. I guess we’ll see what reaction the Elon book gets and see where that goes. It’s a bit heartbreaking to see millions spent on NFTs and other random “stupid money” projects when I’m coming up with concepts for trillion-dollar companies as a hobby.
While we talk a lot about Musk, there are thousands of people who work just behind the spotlight. My father was a production test pilot who put his life on the line to ensure that bombers were flyable for national security, and that the technology that became the commercial jet airliner a decade later would be safe for billions of travelers. He worked with some historic figures of aviation, and his dinner stories were amazing. The Mars Society gave me a way to repeat a little of this history for myself in this dawn of the Mars Age.
Technology revolutions may celebrate a few leaders. But without thousands of talented people several feet behind these inventors, they are little more than curiosities – Di Vinci notebooks or Antikythera mechanisms. My goal is to build the next generation of the quiet heroes of the dinner table. And certainly a few of those will be leaders too. That is my hope. To fill the diaries of pioneers that give permanent cultural bedrock to the accomplishments of people like Elon. Otherwise, even a moon landing is a short story written in water.
Don’t miss Kent’s appearance on The Space Show coming up on Sunday July 10 where you can call in and ask him in person your own questions about these and other visions for space settlement.
