|X-Ray of a notional regolith shielded 16 meter in diameter biosphere (Credit: NASA)|
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:
surface gravity relative to the Earth: 0.17g
diameter relative to the Earth: 27.3%
surface area relative to the Earth: 7.4%
surface gravity relative to the Earth: 0.38g
diameter relative to the Earth: 53.1%
surface area relative to the Earth: 28.4%
surface gravity relative to the Earth: 0.38g
diameter relative to the Earth: 38.3%
surface area relative to the Earth: 14.7%
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.
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)|
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|
|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.|
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.
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 Architecture of Artificial-Gravity Environments for Long-Duration Space Habitation
Living and Reproducing on Low Gravity Worlds
Cosmic Radiation and the New Frontier