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