Inflatable Biospheres and Bio-Tori for Large Outpost and Colonies on the Lunar Surface

Notional regolith bag covered Kevlar biosphere and  bio-torus next to two solar powered cylindrical SLS propellant tank technology derived lunar regolith habitats on top of a microwave sintered lunar outpost floor.

by Marcel F. Williams 

NASA's Space Launch System (SLS) scheduled to go into operation by 2020 or 2021. But large cargo landing vehicles are going to be required  in order to utilize the SLS for the deployment of  lunar outposts habitats.  Large multilevel pressurized habitats derived from SLS propellant tank technology  could be deployed to the lunar surface on top of cargo landing vehicles designed to fit within a 10 meter in diameter SLS payload fairing. Such multilevel habitats for the lunar surface could be 8.4 meters in diameter, with two to four levels available for habitation. The average apartment in the US provides approximately 82 meters of floor area.  With each 8.4 meter in diameter level providing more than 55 square meters of floor area, a single multilevel SLS deployed lunar habitat could provide lunar astronauts with 105 to 210 square meters of habitation floor area. 

X-Ray of notional SLS propellant tank derived Lunar Regolith Habitat

However, substantially larger lunar habitats would require the deployment of inflatable structures.

Various  types of inflatable  habitats have been proposed by NASA personal since the dawn of the space agency. In the 1980's, M. Roberts of  NASA's Johnson Space Center,  proposed deploying inflatable   Kevlar biospheres to the lunar surface.  Since the lower hemisphere  of such biospheres would be underground, the radius of the inflated habitats would be limited by the depth of the regolith. Depending on the region on the lunar surface, lunar regolith can be as deep as eight meters or as shallow as two meters before encountering bedrock.  Such depth constraints on the lunar surface would limit the diameter of a biosphere to just  4 to 16 meters. A 16 meter biodome pressurized with an Earth-like  nitrogen and oxygen atmosphere of 14.7 psi (101.3 kPa) with a safety factor of four would weigh only 1.76 tonnes.

X-Ray of notional regolith bag shielded biosphere on the lunar surface (Credit: NASA)

However, the constraints of regolith depth could be easily alleviated by inflating a biosphere-- on top of the lunar surface-- and surrounding it with an inflatable bio-torus. An inflated Kevlar torus would be an inherently self supporting structure. So regolith could be deposited within the cavity between the bio-torus and the biosphere, providing structural support for the inner biosphere. Since the surround bio-torus would require substantially more Kevlar material than the biosphere, reducing the diameter of the torus to approximately half that of the biosphere could substantially reduce the amount of mass needed to be deployed to the lunar surface.  A spacious cavity between the bottom of the biosphere and the surrounding bio-torus could accommodate  additional living space in the form a smaller bio-torus about one third the diameter of the external bio-torus.

Inflatable torus extraterrestrial habitat (Credit: NASA, 1961)

Lunar Statistics

Diameter relative to the Earth: 27.3%

Surface area relative to the Earth: 7.4% (Land area not covered by water only comprises ~ 29% of the Earth's surface)

Surface gravity: 0.17g

Regolith depth: 2 to 8 meters 

Annual amount  of cosmic radiation on the Lunar surface during the solar minimum - 38 Rem

Annual amount of cosmic radiation on the Lunar surface during the solar maximum - 11 Rem

(Maximum amount of  radiation allowed for radiation workers on Earth per year - 5 Rem)
(Maximum amount of radiation allowed for adult female during nine months of pregnancy -)

The biodome and the upper and outer exterior of the bio-torus could be covered with regolith bags that are either 2.5 meters or 5 meters in thick, depending on what level of radiation protection is desired for the habitat. At least, 10 centimeters of lunar regolith is required to protect humans from the cell killing heavy nuclei component of cosmic radiation. Thermal fluctuations of the lunar surface may also require as little as 10 centimeters of lunar regolith. Assuming an average regolith density of about 1.5 grams per cubic centimeter, at least 60 centimeters of lunar regolith would be required to protect the habitat from micrometeorites.

Its relatively easy to shield habitats and even humans in pressure suits  from the heavy ion component of cosmic radiation.  But most cosmic ray particles are composed of the smallest ionized atoms: protons (85%) and alpha particles (ionized helium atoms) which are much more difficult to shield against. Most protons and alpha particles streak harmlessly though the vacuous space between the atoms of the human body. But the relentless rain of these cosmic ray components  inevitably results in impacts upon our body tissues.

On average, humans receive about 620 mrem per year of radiation due to a combination of sources from both cosmic and terrestrial radiation sources. The maximum recommended radiation exposure for  a pregnant woman is 50 mrem per month which comes very close to the average radiation exposure that humans on Earth experience in a year.

The maximum level of radiation exposure for radiation workers on Earth is 5 Rem per year. And that would require approximately 2.5 meters of regolith shielding. But the maximum level of radiation exposure allowed for a woman during the term of her pregnancy is just 0.5 Rem. So lunar regolith shielding would probably have to be increased to  5 meters (the same level of radiation shielding provided for humans by the depth of the  Earth's atmosphere). Inflated with an Earth-like atmospheric pressure, biospheres and bio-tori could easily support the weight of 5 meters of regolith.

Of course, there would be no shortage of available regolith on the surface of the Moon.  Just one  hectare of regolith on the lunar surface could provide between  20,000 to 80,000 cubic  meters of shielding material (2 million to 8 million cubic meters per square kilometer) for  large pressurized habitats.  And the excavation and deposition of lunar regolith and even the production of regolith bags could be done by robots teleoperated by personal employed on the surface of the Earth. 

During solar minimum conditions, the maximum radiation exposure on the lunar surface can  exceed 3000 mrem per month. A hardened pressure suit designed to protect against the heavy nuclei component of cosmic radiation could  reduce general cosmic radiation exposure by two thirds. But even 1000 mrem (one Rem) per month would exceed annual radiation levels for radiation workers in less than six months. Pregnant lunar colonist would probably have to remain inside the protective confines of their habitat during nine months of pregnancy. But even if lunar colonist spent only 10% of their time  outside of  pressurized habitats (less than 2 Rem of annual exposure within radiation hardened pressure suits ), that would still avail them to more than 16 hours a week of EVA time on the lunar surface. But I seriously doubt if most lunar colonist will spend more than 5% of their time outside of the comfort of their lunar habits.

So it seems likely that Lunar colonist will spend at least 90 to 95% of their time on the Moon within the confines of pressurized  habitats. So living on the Moon will mostly be about living within the protective confines of pressurized habitats that are also designed to protect its inhabitants from the dangers of micrometeorites, extreme thermal fluctuations, and excessive radiation exposure.

So if future Lunarians are going to have to spend the overwhelming majority of their time-- indoors, such pressurized habitats should be as comfortably-- spacious-- as possible. Once large SLS propellant tank technology derived habitats are on the lunar surface, much larger (inflatable) habitats could be deployed by the SLS.

A single SLS Block I launch could deploy a 27.5 tonne biosphere, plus a 38 tonne external  bio-torus and a 2.5 tonne inner bio-torus to LEO. So a total mass of 68 tonnes would be deployed by the SLS to Low Earth Orbit. A pair of reusable ACES-68 orbital transfer vehicles could transport the payload to NRHO. Reusable lunar cargo vehicles could transport the biosphere and the bio-tori separately to the lunar surface.

X-Ray of 40 meter in diameter lunar biosphere surround by two bio-tori

A second SLS Block I launch could deploy five 3 meter in diameter and 3 meter high airlocks: one to be connected to the bottom of the biosphere and two each to be connected the bottoms of the two bio-tori on opposite sides. Six 3 meter in diameter expandable tunnels will also be deployed to linearly connect the airlocks to each other and to allow astronauts to enter and exit the base of the inflatable habitats. Six expandable regolith walls will be included to provide a firm regolith base for the biosphere and the bio-tori. Six 2.4 meter in diameter ECLSS modules will be included: two to be attached to the a biosphere airlock and individual modules to be attached to each of the bio-tori airlocks. Piping  will be provided to connect the ECLSS modules to external radiators. And wiring will be provided to connect the ECLSS to external solar, nuclear, and chemical power units.  Again, these payloads will initially be deployed to LEO before be transported to NRHO and then to the lunar surface by reusable LOX/LH2 vehicles.

 Once deployed to the lunar surface, the inflated Kevlar biosphere would be 40 meters in diameter. An 18 meter in diameter bio-torus would surround the biosphere. And an additional 6 meter in diameter bio-torus would be placed with the lower cavity between the biosphere and the external bio-torus.The pressurized biosphere and bio-tori would sit on top a regolith base. Airlocks beneath the biosphere and bio-torus would be connected to cylindrical metallic tunnels internally pressurized with cylindrical Kevlar bags would provide astronauts with easy access to the other sections of the habitat while also allowing them to exit the habitat or to connect to exterior habitats. 

The atmospheric pressure within the biosphere and within the bio-torus would be the same atmospheric pressure as on Earth. And this will allow people working in the bio-torus to move easily back and fourth between the bio-torus and the biosphere without the need of to deal with differences in pressure.

Notional biodome recreational floor area of a 40 meter in diameter bio-torus

With a floor area of 1257 square meters within a spacious biodome 20 meters high, the upper hemisphere of the 40 meter biosphere could be used for a variety of recreational purposes (tennis, volleyball, basketball, gymnastics, swimming, etc). The biodome could also provide astronauts with  a spacious area for relaxation if landscaped with grass and trees and other aesthetically pleasing foliage. 

The lower hemisphere would be composed of four expansive habitat floors, 2.4 to 3 meters high, providing apartments, laboratories, and gyms and more than 1200 square meters of habitable floor space.  The floors, rooms, and apartments will be composed of prefabricated sections manufactured on Earth and assembled within on the Moon within the pressurized biosphere. Ceiling, floor, and wall panels and beams and other structural components could be transported to the lunar surface by reusable and expendable  commercial lunar transports.  So the lower half of the biosphere should be able to provide at least four expansive levels for  habitation, with the lower hemisphere alone far exceeding that of the floor area for  SLS propellant tank derived habitat modules.

The surrounding 18 meter bio-torus would also consist of multiple levels that are composed of modular components. But, under this scenario, the   bio-torus would be divided into five levels. The top level would be used for orchards (apple, orange, lemon, cherry, and peach trees) and also for raising large fauna: pigs, miniature cows, sheep, and possibly even ostriches. The second level would be used for poultry. The third and fourth level would be used for growing fruits and vegetables: bananas, pineapples, watermelons, tomatoes, carrots, lettuce, potatoes, corn, wheat, sugar beets, etc. The bottom level of the bio-torus would be used for aquaculture: brine shrimp, fish, oysters, etc.

The inner 6 meter in diameter bio-torus would be largely used for storage and for emergency habitation in case something serious should occur inside of the biosphere.

The entire facility would be designed to comfortably accommodate between 50 to 100 individuals.

 Diameter and mass of Kevlar biospheres and bio-tori pressurized at 14.7 psi (101.3 kPa) with a safety factor of  four without regolith shielding and structural support

40 meter in diameter  biosphere: 27.5 tonnes
Surrounding 18 meter in diameter bio-torus: 38 tonnes
Surrounding 6 meter in diameter interior bio-torus: 2.5 tonnes

Mass of an M1-Abrams Tank - 62 tonnes

100 meters in diameter biosphere: - 430 tonnes
Surrounding 50 meter in diameter bio-torus: 759 tonnes
Surrounding 16 meter in diameter interior bio-torus: 44 tonnes  

Mass of a Boeing 747 - 440 tonnes

200 meters in diameter biosphere:  3438 tonnes
Surrounding 100 meter in diameter bio-torus: 6071 tonnes
Surrounding 32 meter in diameter interior bio-torus: 348 tonnes

 Mass of the Eiffel Tower - 7300 tonnes

300 meters in diameter biosphere:  11,600 tonnes
Surrounding 150 meter in diameter bio-torus: 20,512 tonnes
Surrounding 50 meter in diameter interior bio-torus: 1264 tonnes

Mass of an Ohio-Class atomic submarine - 16,764 tonnes


400 meter in diameter biosphere: 27, 500 tonnes
Surrounding 200 meter in diameter bio-torus: 48, 574 tonnes
Surrounding 60 meter in diameter interior bio-torus: 2478 tonnes

Mass of a cruise ship - 100,000 tonnes

1000 meters in diameter biosphere: 430,000 tonnes
Surrounding 500 meter in diameter bio-torus: 759, 000 tonnes
Surrounding 160 meter in diameter interior bio-torus: 44, 000 tonnes

 Mass of the Golden Gate Bridge - 804, 673  tonnes

Much larger inflatable facilities will probably require the Kevlar material to be exported from Earth in small sections to be woven together by machines deployed to the lunar surface. And, eventually,  Kevlar threads will be manufactured on the lunar surface from lunar materials mostly found at the lunar poles.

Biospheres that are 400 meters in diameter could be very attractive for human colonization of the Moon. The 200 meter high bio-domes of such facilities would be able to provide artificial lakes and lagoons at least 200 meters in diameter with surrounding sandy beaches where you could not only swim but also put on a pair of  wings and fly under the low lunar gravity.  The top half of the surrounding 200 meter in diameter bio-torus could also be used for housing familiar to that on Earth plus recreational parks and 100 meter lakes and lagoons. And with a 100 meter high rooftop, there should also be enough room in the bio-torus to strap on a pair of wings and fly at least 50 meters above the ground within the upper half of the bio-torus.



Links and References

Inflatable Biospheres for the New Frontier

Structural Design of a Lunar Habitat

Inflatable space habitat

Inflatable Habitation for the Lunar Base


Living and Reproducing on Low Gravity Worlds

Information for Radiation Workers

Doses in Our Daily Lives 

Ionizing Radiation

 GLOBAL LUNAR REGOLITH DEPTHS REVEALED


 ECLSS

Inflatable Biospheres for the New Frontier

X-Ray of a notional regolith shielded 16 meter in diameter biosphere (Credit: NASA)

by Marcel F. Williams 

At least 0.1 g is required for  unaided human traction when walking  on a low gravity world. And some studies suggest that some individuals may have difficulty-- non-visually-- perceiving up and down under a gravity that is less than 1.5 g. There are also some questions as to whether rigorous exercise will be enough to prevent human bones from losing  significant amounts of calcium  under low gravity environments that could cause bone fractures-- especially when returning to Earth.


Planets and Moons within the solar system that are potentially suitable for human colonization:


Moon

surface gravity relative to the Earth: 0.17g

diameter relative to the Earth: 27.3%

surface area relative to the Earth: 7.4%


Mars

surface gravity relative to the Earth: 0.38g 

diameter relative to the Earth: 53.1%

surface area relative to the Earth: 28.4%


Mercury

surface gravity relative to the Earth: 0.38g 

diameter relative to the Earth:  38.3%

surface area relative to the Earth:  14.7%


Callisto 

surface gravity relative to the Earth: 0.13g 

diameter relative to the Earth:  37.8%

surface area relative to the Earth:  14.3%

Note: Land area comprises ~ 29% of the Earth's surface with ~71% covered by water


But even if future human colonist  can physically and psychologically  adjust to living and reproducing  on the surfaces of low gravity worlds, its  unlikely that such individuals would spend more than ten percent of their time outside of the protective envelope of their pressurized habitats. Even on the surface of Mars, during solar minimum conditions, cosmic rays could expose colonist to levels of radiation exceeding that legally allowed for radiation workers on Earth in just two months. And on extraterrestrial worlds without atmospheres such as the Moon, Mercury, and Callisto,   pressure suits with more massive radiation shielding would be required to protect the human brain and cardiovascular system from the enhanced dangers of  heavy ions.

Radiation levels on the Moon and Mars


Surface of the Moon:

38 Rem - annual amount  of cosmic radiation on the Lunar surface during the solar minimum

11 Rem - annual amount of cosmic radiation on the Lunar surface during the solar maximum

Surface of Mars:

33 Rem - annual rate of cosmic radiation on the surface of Mars beneath 16 gm/cm2 of Martian atmosphere during the solar minimum

8 Rem - annual rate of cosmic radiation on the surface of Mars beneath 16 gm/cm2 of Martian atmosphere during the solar maximum


Pressurized habitats in extraterrestrial environments can easily be protected from dangerous levels of cosmic radiation and their  heavy nuclei component with just a few meters of  regolith or several meters of water.  However, the fetuses of pregnant women and children growing up on   extraterrestrial  worlds are substantially more vulnerable to higher levels of  radiation exposure and will probably have to spend a lot more time within the protective confines of pressurized habitats.  

Internal configuration of a  lunar habitat derived from  SLS propellant tank technology. A  regolith wall composed of kevlar sandwiched between eight rigid aluminum panels is deployed around the habitat cylinder and filled with regolith to protect astronauts from cosmic radiation, micrometeorites, and fluctuating temperatures on the lunar surface. The airlocks are derived from ETLV propellant tank technology.

So it appears likely that future colonist  living on the surfaces of extraterrestrial worlds will  probably have to spend at least 90% of their time inside of radiation protected pressurized  habitats. Therefore, pressurized habitats that are spacious enough  and aesthetically comfortable enough for people not to mind spending  90% of their lives living and raising their families in indoor environments will probably be necessary.

The deployment of huge— inflatable biospheres— could provide a large variety of aesthetically spacious and comfortable environments for colonist on extraterrestrial worlds-- especially if the upper half of a biosphere is utilized to provide open spaces for parks and recreational activities. 

 
NASA researchers have previously proposed deploying a 16 meter  biospheres to the lunar surface weighing 2.2 tonnes with a safety factor of five. The mass of the inflatable material increases in proportion to the mass of the atmosphere that it envelopes.   Here, I propose using the SLS in combination with large cargo landing vehicles to deploy 28 tonne Kevlar-29 biospheres to the surfaces of the Moon and Mars  with an inflated  pressurized volume of 33,510 m3 and a diameter of 40 meters.  Nitrogen and oxygen environments could be provided in such pressurized biospheres with an Earth-like  14.7 psi (101.3 kPa) of pressure similar to atmosphere aboard the ISS— with a safety factor of four.

Notional Lunar Cargo landing vehicle that could transport regolith habs and deflated Kevlar biospheres to the lunar surface.

An extraterrestrial cargo landing vehicle with 30 tonnes of LOX/LH2 propellant could deploy a deflated 28 tonne biosphere to the surface of the Moon from EML1. Similar biospheres could be deployed to the surface of Mars using lunar landing vehicles coupled with  ADEPT deceleration shields currently being developed by NASA. An ADEPT deceleration shield would be capable of deploying up to 40 tonnes of cargo to the Martian surface.

Notional ADEPT deceleration shield for deploying payloads to the Martian surface. (Credit: NASA)

Possible ADEPT architectures that could deliver up to 40 tonnes of cargo to the Martian surface. (Credit: NASA)

On Mars, the nitrogen component for the pressurized atmosphere of the biosphere could be extracted from the Martian atmosphere which contains nitrogen at  approximately 1.89%. On the moon, nitrogen would have to be derived from possible ammonia deposits at the lunar poles or exported from Earth.

The oxygen component of the biosphere's pressurized atmosphere could be derived from the electrolysis of water extracted from ice deposits from the lunar poles or directly derived from the pyrolysis of lunar regolith. Oxygen derived from water on Mars could be derived from various regions on Mars that are rich in water ice.

Notional 40 meter in diameter regolith bag shielded Lunar biosphere connected to two Lunar Regolith habs

Since the top half of a Lunar  biosphere would be above the surface,   the upper hemisphere would be protected from micrometeorites and extreme temperature fluctuations by covering the upper exterior dome with regolith bags. Regolith bags would also protect humans inside from heavy nuclei while reducing overall cosmic radiation exposure to appropriate levels. Constructing a supporting geodesic dome inside of the upper dome area of the biosphere   could be  protected from a rapid collapse if the Kevlar walls are punctured.   Light fixtures could even be placed on the internal geodesic dome for internal illumination.

Notional 40 meter in diameter biosphere covered with a water filled biodome to protect inhabitants from cosmic and UV radiation. Since there would be no danger from micrometeorites on Mars, regolith shielding the upper dome would be unnecessary.

On Mars, a transparent water filled biodome could be placed on top of the top hemisphere of a transparent Kevlar biosphere to protect the inhabitants from radiation while still allowing in sunlight.  The transparent water filled biodome could be embedded a transparent UV protective film to shield inhabitants from ultraviolet radiation.  This would allow inhabitants occupying the top half of the biosphere to enjoy the Martian sunlight during the day and to view the stars at night. Since the atmosphere of Mars is so thin (~ one percent of the Earth’s atmosphere) the high heat conductivity from the thick Earth-like pressurized biosphere would keep the liquid water in the external water dome from freezing. The water dome could be  replaced if it becomes  soiled with dust from periodic dust storms on Mars or an enormous tent could be  temporarily placed over the water dome to   protect it from being soiled during dust storms. 

The upper half of a biosphere could be used for open space recreational activities and sports while the lower, underground, half of the biosphere could be used for housing and commercial structures.  But,  homes and apartment buildings similar to those found on Earth could also be assembled and  placed on the bottom surface of the top half of the biosphere, if desired,  along with grass and trees and other foliage to enhance the aesthetic environment.

X-ray of a 40 meter in diameter lunar biosphere with a 20 meter circular swimming pool. Multiple levels of habitats could be constructed in the bottom half of the biosphere with some base support by lunar regolith. A central area could utilize scissor elevators to access different floor levels. 

Some biospheres could be specifically dedicated for agriculture, providing space in the upper half for grazing animals used for milk and meat and cheese while the lower half could provide compartments for hen houses and aquaculture. For growing crops, the top half could be used grow fruit trees: apple trees, orange trees, cherry trees, peach trees, pear trees, lemon trees, etc. while underground compartments in the bottom half of the biosphere could be used for growing corn, potatoes, wheat, rice, tomatoes, lettuce, yams, sugar beets, etc.

Much thinner but larger  biospheres could also be deployed to the surfaces of extraterrestrial worlds. But once they are inflated, they would have to be internally thickened with additional adhesive layers of Kevlar in order to provide the same safety factor as the smaller domes. This would probably require the deployment of modular Kevlar manufacturing factories on the surface of these worlds by cargo landing vehicles. But this would make it possible to deploy biospheres that are 100 to 200 meters in diameter in the near future. Once the Moon and Mars become fully industrialized worlds with significant populations then  Kevlar biospheres that are 300 meters to 1000 meters in diameter might eventually be deployed. 

Mass of a Kevlar-29 biosphere for an atmospheric pressure of of  14.7 psi (101.3 kPa) with a structural safety factor of four.
 
40 meters in diameter - 28 tonnes

100 meters in diameter - 430 tonnes

200 meters in diameter - 3438 tonnes

300 meters in diameter - 11,600 tonnes  

1000 meters in diameter - 430,000 tonnes 

Biospheres as large as 200 meters in diameter could allow colonist to enjoy familiar sporting activities such as America football and baseball and international soccer. Some biospheres could be specifically designed for sporting activities, allowing baseball, American football, and international soccer to be played on the bottom surface of the top half of the biosphere while the bottom half, extending nearly 100 meters below, could easily accommodate large variety of  underground stadiums for playing basketball,  hockey, volleyball, and  tennis while also being able to accommodate a few  Olympic sized swimming pools.

Dimensions for professional sporting activities

Volleyball Court - 9 meters by 18 meters

Doubles Tennis Court - 10.97 meters by 23.77

Basketball Court -  15 meters by 29 meters

Olympic sized swimming pool - 25 meters by 50 meters

International Hockey Rink - 30.5 meters by 61 meters

NFL Football field 48.76 meters  by 110 meters (110 m)

Baseball outfield fence from home plate -  91 meters  to 128 meters

But biospheres that are only 100 meters in diameter on the Moon could be spacious enough to allow people to don wings to fly within the upper biodome or even withing the entire biosphere.  This could perhaps initiate of a new era of aerial extraterrestrial sports! Who knows! Someday flying inside of  Lunar biospheres or watching Lunar Aeroball could be a major attraction for space tourist from Earth!


Links and References

Inflatable Habitation for the Lunar Base

The Economic Viability of Mars Colonization

The Architecture of Artificial-Gravity Environments for Long-Duration Space Habitation

Protecting Spacefarers from Heavy Nuclei

Landing on Mars with ADEPT Technology

ADEPT Technology for Crewed and Uncrewed Missions to the Planets

Living and Reproducing on Low Gravity Worlds

Cosmic Radiation and the New Frontier

Pioneering and Commercial Advantages of Permanent Outpost on the Moon and Mars