Space colony essentials: Shelter

Space colony essentials: Shelter

In May of 1607, English colonists landed in what is now Virginia and established a colony.

I do not know how the colonists chose the location for the Jamestown settlement.  Many reference materials cite recommendations given to the colonists to select a site that was “defensible from other European states.”  However, I am also certain that they must also have thought about selecting a location with essential resources (water, food, etc.), easy access to their transportation (ship), and some provision for shelter.

Similar to the establishment of the Jamestown colony, any space colony must also select a location that provides the essentials of human life (resources, easy access to transportation, and shelter).  In this blog entry, I will discuss some of the shelter requirements of a space colony.

The Jamestown colonists looked Space imposes shelter requirements completely different to our experiences on Earth.  Not surprisingly, the human body adapted to this environment found on Earth.

Compare these number to those found on other major solar system bodies:

	Temp	Gravity	Lum	Radiation		Pressure
	K	Gs	Sols	REMs	Earth Rads	Bars
Mercury	700	0.38	6.57	900.0	3,000	0.0
Venus	735	0.91	1.93	0.0	0	92.1
Earth	290	1.00	1.00	0.3	1	1.0
Moon	290	0.17	1.00	30.0	100	0.0
Mars	208	0.38	0.43	20.1	67	0.0
1 Ceres	131	0.03	0.13	30.0	100	0.0
Jupiter	165	2.53	0.04	1,314,000.0	4,380,000	1.0
Io	130	0.18	0.04	1,314,000.0	4,380,000	0.0
Europa	125	0.13	0.04	197,100.0	657,000	0.0
Ganymede	152	0.15	0.04	2,920.0	9,733	0.0
Callisto	165	0.13	0.04	3.7	12	0.0
Saturn	160	1.07	0.01	0.3	1	1.0
Titan	93	0.14	0.01	15.0	50	1.4
Uranus	57	0.90	0.00	0.3	1	1.0
Neptune	72	1.14	0.00	0.3	1	1.0
Triton	38	0.08	0.00	20.0	67	0.0
Pluto	55	0.07	0.00	20.0	67	0.0
Charon	53	0.03	0.00	20.0	67	0.0

Environment of the major solar system bodies

·       Temperature in Kelvin (273 is 0 C).

·       Gravity in Gs (Earth gravity is 9.8 m/s/s)

·       Luminosity in Sols (Earth Sols = 1)

·       Radiation in REMs (Earth Rads = 1)

·       Pressure in Bars (Earth = 1)

Temperature

The Jamestown colony suffered from severe temperature swings, at least by the standards of Western Europe.  The winter cold directly caused the deaths of many colonists.  In most locations on Earth, we might see a difference in temperature of 30 F between day and night and perhaps 100 F or slightly more through the year.  The colonists adapted by building log homes (wood is a good insulator) and burning wood for fuel.

However, without the moderating effect the Earth’s oceans and atmosphere have on temperatures, many places in space can experience temperature changes of 200 F or more.  Colonists in space will require insulators (to moderate the temperature swings in space).  However, they will not need insulators to keep themselves warm (unless they are located in the outer reaches of the solar system).

The other problem posed by most locations in space is the inability to dump waste heat.  You might have heard that “the temperature of space is very cold” and this is true (the microwave background temperature of the Universe is about 3 K).  However, without fluids for convection or direct contact for conduction, the transfer of energy, the only method of heat transfer is radiation – and radiant heat transfer is the least effective mechanism to transfer heat.

Unless we locate the colony on a large body outside the orbit of Venus, the main effort to maintain temperature will be to dump waste heat.  Giant radiators will likely provide the best method of dumping waste.  The size of the radiators depends upon the amount of power we use.  Therefore, I will include the formulas required for calculating the size of thermal radiators for a given colony power output in my blog entry on power generation.

Locating the colony on a large body significantly reduces the problems with waste heat. 

Radiation

The Jamestown colonists did not experience issues with radiation from the environment.  However, this is one of the most difficult problems faced by space colonists.  Protection from radiation requires shielding and not the SF classic / magic “Scotty, raise shields” shielding.

The surface of the Earth experiences a meager 0.3 REMs of radiation.  The table above shows that most places in the solar system suffer from much higher levels of radiation (mostly solar and cosmic).  Few of these bodies possess a radiation environment hospitable to terrestrial biology.  From a radiation perspective, the large planets possess the most hospitable radiation environments – this is due to their powerful magnetic fields (which deflect solar and cosmic radiation) and thick atmospheres (that block anything not deflected by their magnetic fields).  Jupiter is the exception and most of the Jovian system is very inhospitable to terrestrial biology.  Any other location in the solar system (planet colony, asteroid colony, space station, or space ship) requires significant radiation shielding to protect our space colonists.

Our colony must protect humans from four types of radiation.  These include solar wind (protons), x-ray/gamma ray (high-energy photons), neutrons (from nuclear reactors), and cosmic rays (very high velocity atomic nuclei from interstellar space).  The Earth’s magnetic field and atmosphere protects us from all four types of radiation on Earth.  However, any space colony we could build in the next 100 years will be located in an environment without thick atmosphere and strong magnetic field.  So how do we provide the same level of protection without locating it on Earth?

There is an interesting fact that helps us a lot: on Earth, a column of water 32 feet tall contains the same mass as a column of air from sea level into space.  This means that a wall of water 32 feet thick would work almost as well at blocking proton and neutron radiation as the Earth’s atmosphere.  For a variety of reasons, this wall of water does not block cosmic or gamma & x-rays as well as it blocks neutrons and protons.  However, the amount of radiation attenuation that this quantity of matter provides should be more than sufficient.

This leaves cosmic rays as the remaining issue.  When cosmic rays hit a human body with no radiation shielding, they act like minuscule rifle bullets.  They do damage but only along a very narrow track.  When a cosmic ray hits radiation shielding the “rifle shot” transfers its energy into multiple atoms in the shielding and turns them into a shotgun blast of atomic nuclei and other subatomic particles that does a lot more damage to living tissue than the original cosmic ray.  On Earth, the thickness of the atmosphere provides protection against these blasts.  In fact, the mass of the atmosphere acts a bit like a Kevlar flak jacket slowing the individual atoms while the depth of the atmosphere gives mesons (subatomic particles) a chance to decay before they reach the surface.

You may have already identified the problem posed by providing this level of radiation protection, its mass.  The mass of a radiation shield composed of water 32 feet thick is enormous.  The calculation for the mass for this level of protection for a single 10 ft x 10 ft x 10 ft room is 15.7 pounds / in^2 * 144 in^2/ft^2 * 100 ft^2 / side * 6 sides = 1,356,480 lbs of water!  No spacecraft could afford to provide this level of protection and its crew and still complete its mission.

This means that spacecraft would provide a much lower level of radiation protection but for short periods.  Long-term habitats must provide protection equivalent to the 32 feet thick water shielding.  Since our current spacecraft capabilities dictate months or years long trips to most other solar system bodies.  Luckily, a concept called a cycler bridges this gap.  I will discuss cyclers in a later post but it essentially provides a space colony that orbits between two solar system bodies on a regular basis (e.g. a habitat that orbits between Mars and Earth).  A spacecraft traveling to Mars would boost from Earth, dock with the cycler, the crew would live on the cycler until it approached Mars’ orbit, and then the crew would reboard the spacecraft, and decelerate into Mars orbit.  The crew would spend almost the entire trip in the heavily shielded and more spacious cycler habitat.  Only the spacecraft would accelerate and decelerate at the start and end of the trip, the cycler would require very little fuel once established in its orbit.

Gravity

No location on Earth possesses a surface gravity appreciably different from the Earth normal one gravity (9.8 m/s/s).  The uniformity of Earth’s gravity ensured that the Jamestown colonists did not need to worry about the potential health issues involved with long-term exposure to a different gravity.  Unfortunately, our space colonists do need to worry about living in an environment for long periods with gravity lower than the Earth’s gravity. 

The human body evolved to survive and function in one gravity.  When humans live in microgravity for extended periods, their bodies begin to deteriorate – losing bone mass, muscle mass, and blood volume.  Some studies show that astronauts exposed to microgravity *never* completely recover all of the bone lost during their mission.  Biomedical studies (conducted on Earth) intended to simulate the human body’s response to lower gravity environments, indicate similar responses to low gravity environments (e.g., we will lose muscle, bone, and blood volume).  Right now, we do not know how much gravity is enough for our health.

The table at the top of this page includes the surface gravity of the other major solar system bodies.  It turns out that many bodies share similar surface gravities with other bodies.  The gravities include 3 gravities (Jupiter & Sun), 1 gravity (Venus, Earth, Saturn, Uranus, and Neptune), 1/3 gravity (Mercury & Mars), 1/6 gravity (Moon, Io, Europa, Ganymede, Callisto, & Titan), 1/12 gravity (Triton & Pluto), and negligible gravity (everything else).

Because colonies floating in one of the gas giants or a colony on Venus remain well beyond our current capabilities, any colony on one of the smaller bodies requires provisions for regular exercise in an environment with a higher acceleration/gravity than that provide by the body.  This means rotating habitats along the lines of the space station portrayed in 2001: A Space Odyssey.  If placed upon a body with a substantial gravity of its own (e.g. Mars), the facility would be a cylinder placed on its side with its axis pointing through the center of the body.  Its floors would be tilted in a way to ensure that the center of acceleration.

Cross-section of the colony centrifuge facility.

Shape of the centrifuge / rotating habitat

Colonists must spend some time in this centrifuge but the centrifuge could not contain the entire colony.  Therefore, this facility would contain exercise and recreational facilities and perhaps living quarters.  However, the centrifuge could not contain many of the workspaces.  Furthermore, space craft could not afford to push the mass of extensive centrifuge facilities, so only colonies (non-mobile habitats) would possess extensive centrifuges like those shown.  Spacecraft would only possess the most rudimentary facilities, which might only consist of exercise equipment such as treadmills and weights.  Biomedical research has not determined the minimum time required to ensure humans physical condition did not deteriorate too much.

Some (most?) colonists will not invest the time and pain required to keep their bone and muscle loss within acceptable limits.  Ultimately, this will force them to remain in space for the rest of their lives.  As this population grows, humanity will spawn a sub-culture “stranded” in space, who cannot return to Earth without significant risk to their lives.

Just like the extensive radiation shielding, the rotating habitat imposes huge mass penalties upon any space facilities.  Since the centrifuge would be inhabited, the radiation shielding of that section would pose even greater problems (how do you support millions pounds of radiation shielding necessary to protect the rotating habitat?).  Clearly, spacecraft could not include such luxuries despite their necessity for the long-term health of the crew.  This is another facility limited to just colonies and cyclers.

Summary

Only one celestial body provides an environment suitable to terrestrial (including human life).  The rest of the bodies in the solar system possess one or more feature completely inimical to terrestrial life (temperature, atmosphere, radiation, gravity, etc.).  Some of the locations best suited to humans for reasons such as radiation exposure (e.g. floating in the clouds of Saturn) also pose the most significant technical challenges to building a space colony (how do you float a colony in the Hydrogen atmosphere of Saturn?).  The bodies most accessible to humans and their technology (near Earth Asteroids, the Moon, and Mars) possess environments in which humans could only survive through the extensive use of technology (such as radiation shielding, closed-loop environmental systems, extensive thermal radiators, and nuclear reactors).

Although humans never attempted to build a closed-loop colony of the type necessary for the long-term colonization of another body and we still have a lot to learn, we face no technical hurdles that we could not resolve with our current technology for colonizing many locations in the solar system.

I apologize for not covering the topic in more depth; I should cover it more extensively, however, this entry is already weeks late and six pages long.  I hope to return to it in a future entry after I cover some other issues.