Space colony essentials: Consumables

Space colony essentials: Consumables

Propellant, Fuel, Air, Water, and Food

As British fortune seekers looked for base of operations (that later became Jamestown) back in 1607, they had to consider, at some level, whether the spot they selected provided essentials like fresh water and firewood.  I have not seen any records of how they selected the location of the colony, other than their British backers suggested they select a “more secure location,” meaning one defensible from other European powers.

I have seen many different rational provided for establishing space colonies in all sorts of locations, from low earth orbit (LEO), to geosynchronous orbit (GEO), Lagrange points (L1, L2, L3, L4, L5), the Moon, Mars, and just about any other place in the solar system.  In this entry, I want to add my opinion to that lengthy list of opinions.

Regardless of other reasons for placing a space colony in one location or another, any near-term space colony must include a source for the colony consumables (propellant, fuel, air, water, and food).  If the colony cannot produce them from local resources, then the Earth must ship this huge mass to the colony on a continuing basis.  Any interruption in the supply of these resources would immediately doom the colonists to death.  Simply put, any serious attempt at space colonization could not afford to locate the colony anywhere else.

Air and water

Colonists can easily produce oxygen for breathing and water if they have a supply of water ice.  If they wish to breathe an atmosphere of normal Earth pressure, then they must also find a supply of nitrogen (frozen nitrogen for the outer solar system or ammonia ice closer to the earth).  

Propellant

Colonists could manufacture propellant for rocket engines from water ice by electrolyzing water (separating the oxygen and hydrogen and storing them separately).  However, no storage container can retain hydrogen for long periods of time, the hydrogen molecules simply slip in between the molecular bonds of any other material.  Therefore, after separating the hydrogen, the colonists would likely burn it by combining it with carbon to form methane gas and produce a little energy.  They could easily store methane over long periods.

As an alternative, the colonists could create rocket propellant from aluminum and oxygen.  Certain major bodies in the solar system (such as the moon) possess the raw ingredients for this propellant in abundance.  This alternative is less attractive because aluminum/oxygen rocket propellant is a solid.  Solid rockets are not dynamically throttleable and once ignited do not respond to controls, meaning the rocket burn cannot be stopped.  Therefore, the colonists would preferentially produce methane/oxygen rocket instead of aluminum/oxygen rockets.

Fuel

Nuclear or solar power represent the only realistic power generation capabilities for a space colony.  Any convention fuel choice requires massive resupply or production problems for the colony.  After all, how could we ship a million gallons of gasoline or a million pounds of coal AND the oxygen required to burn that fuel to a space colony in the asteroid belt every year?  In my opinion, nuclear power provides a better return on space launch investment than solar.  I arrived at this position primarily because solar panels degrade in the space environment and require replacement.  The colony would likely not develop the ability to replace solar panels in the early years of its development.  The cost of shipping replacement nuclear fuel would be significantly lower than the cost of shipping replacement solar panels.

Food

Food represents the final consumable required by the colonists.  Unlike the processes used to create air and propellant, we cannot use simple chemical processes to produce the food the colony requires.  Self-contained biospheres remain the only practical method of producing food over very long periods.  However, different types of biosphere (aeroponics, hydroponics, geoponics, etc.) provide different types of benefits.  For instance, hydroponics provides perhaps the smallest physical foot print (the lowest space requirement) while aeroponics (growing plants in the air, while misting their roots with nutrient rich water) provides the lowest mass footprint, meaning this would probably be used for self-contained biospheres on spacecraft.  Geoponics requires the least human attention.

Aeroponics

Hydroponics

The colonists will not find growing food difficult.  However, the colonists could strive for a more ambitious goal of a completely self-contained biosphere, in which food and oxygen consumption by the human colonists balanced that produced by the plants.  All experiments attempting this balance on Earth in a self-contained environment failed.  However, each experiment has taught researchers more about how to configure a self-contained biosphere.

Initially at least the colonists could not afford to raise meat animals.  They consume far more plant food energy than their flesh provides.  Only after the colony expands and becomes successful could the colonists afford the luxury of “wasting” plant food energy on raising livestock.

Prime colony spots

What locations satisfy the resource requirements described above?

	Temp	Gravity	Lum	Radiation		Pressure	Volatiles/water
	K	Gs	Sols	REMs	Earth Rad	Bars	Tonnes	Log10
Mercury	700	0.38	6.57	900.0	3,000	0.0	5.00E+14	14.7
Venus	735	0.91	1.93	0.0	0	92.1	1.00E+03	3.0
Earth	390	1.00	1.00	0.3	1	1.0	1.40E+18	18.1
Moon	390	0.17	1.00	30.0	100	0.0	6.00E+12	12.8
Mars	308	0.38	0.43	20.1	67	0.0	2.00E+16	16.3
1 Ceres	131	0.03	0.13	30.0	100	0.0	2.00E+17	17.3
Jupiter	165	2.53	0.04	1,314,000.0	4,380,000	1.0	4.00E+20	20.6
Io	130	0.18	0.04	1,314,000.0	4,380,000	0.0	1.00E+06	6.0
Europa	125	0.13	0.04	197,100.0	657,000	0.0	2.87E+18	18.5
Ganymede	152	0.15	0.04	2,920.0	9,733	0.0	7.10E+22	22.9
Callisto	165	0.13	0.04	3.7	12	0.0	5.59E+22	22.7
Saturn	160	1.07	0.01	0.3	1	1.0	4.00E+19	19.6
Titan	93	0.14	0.01	15.0	50	1.4	8.07E+22	22.9
Uranus	57	0.90	0.00	0.3	1	1.0	4.00E+19	19.6
Neptune	72	1.14	0.00	0.3	1	1.0	4.00E+19	19.6
Triton	38	0.08	0.00	20.0	67	0.0	7.99E+21	21.9
Pluto	55	0.07	0.00	20.0	67	0.0	6.50E+21	21.8
Charon	53	0.03	0.00	20.0	67	0.0	7.60E+20	20.9

Quantity of volatiles on the major bodies of the solar system (in metric tons)

What the table above shows is that most major solar system bodies, with the exception of Venus, possess usable quantities and concentrations of volatiles (mostly water ice).  For some bodies, such as Mars and the Moon, these volatiles exist only in the shadow regions of polar craters.  Other bodies, such as the moons of the outer planets, consist predominantly of various ices.  This means that any major body of the solar system could be a candidate for a space colony from the perspective of native resources.

However, several asteroid types also possess significant quantities of water ice.  The most common asteroid type (C Type-C for carbonaceous) possess 3-22% water ice by mass fraction.  Since they also possess significant quantities of organic materials and nodules of metals, they represent another interesting possible location for a space colony.  The resources available include organic molecules as feedstock for plastics; water for making air, water, & propellant; and metallic nodules as feedstock for metal components.

 Cross-section of carbonaceous chondrite meteor (thought to come from C-Type asteroids)

Recent observations of the asteroid Ceres (the largest asteroid in the solar system) conclude that it possesses a substantial layer of water ice, perhaps 50% by volume.  This quantity exceeds all of the fresh water on Earth.  Since Ceres is a carbonaceous asteroid, it likely possesses large quantities of organic compounds and metal nodules too.

 

Ceres, as seen by Hubble Space Telescope

 

Ceres cross-section

Perhaps the most interesting and easily reached asteroids would be a class of asteroids called Near Earth Objects (NEO).  These consist of asteroids that cross the Earth’s orbit.  They include the asteroids most easily reached from a propellant expenditure and flight time perspectives.  Since most of these cross within the Earth’s orbit, they will not have concentrations of water as high as that found on Ceres.