One of the most compelling concepts of space travel is the possibility of colonising other worlds; to make them as much our homes as our own Earth. Even today, in fiction this ideal tends to focus on finding an Earth-like planet upon which we can settle and thrive, living as comfortably there as we do on Earth. Even the most conservative estimates predict that there may be literally thousands of such planets throughout the Milky Way galaxy, planets with gravity and atmospheric constituents close enough to our needs to make the planets habitable.
Even so, the distances between such worlds are monstrous. There is no world close enough to Earth in mass and chemistry to support human life anywhere else in our Solar System. Even if, as appears possible, Europa turns out to be another home of life, it's no place for us. The radiation levels from Jupiter's immense magnetic field alone are enough to render it deadly to humans. Still, even apparently empty space offers a wealth of opportunities for inventive beings to make new homes for themselves.
The Wealth Between the Worlds
Planets are, on a cosmic scale, infinitesimal things. Even planets like mighty Jupiter are reduced to points of light by interpanetary distances. However, the space between these dots of matter is far from empty. Interplanetary space is filled with the leftover remnants of the early history of the Solar System, rocky and metallic asteroids as well as icy comets. While tiny when compared to even the smallest planets (not to mention some moons), these bodies represent an immense amount of raw material. Silicates, metals, organic materials and volatiles such as hydrogen, carbon dioxide and water ice are present in stunning amounts in comets and asteroids, and these bodies are scattered throughout the entire system. These raw materials will be vital in establishing a permanent presence in space, as well as minimising or even eliminating the need to mine raw materials from Earth, or clear its wild areas for farming. On a more immediate level, they are sources of near-unimaginable wealth.
Cities in Space
As early as the twenties, scientists and engineers such as J.D. Bernal began thinking about the construction of permanently inhabited artificial structures in space. Experience gained from long-duration missions aboard the space station Mir has shown that life in space is eminently survivable, even comfortable. Also, the construction of a colony on a large asteroid would provide a stable home for the generations of miners who would work its surface or probe its secrets.
Of course, a long-term colony will have to overcome several problems (which can be ignored in the short term) in order to qualify as true lifelong abodes for human beings.
Possibly the most obvious problem is that objects following an orbit are in free-fall and experience no resultant gravity. Microgravity not only weakens limb bones and muscles, but it can lead to weaknesses of the heart, immune and renal systems and advanced osteoporosis. Even if the worst of these effects can be avoided, it's probable that children gestated and reared in microgravity would never be able to visit a planet.
Perhaps the easiest method is for some kind of "gravity making" device to quickly and easily sort out the problem. While the current understanding of science renders such a device impossible, a culture with induction drive technology has already cracked the problem. The trick is to cause objects within the colony to accelerate under a generated force, while keeping the structure itself from accelerating. A kind of double-ended induction engine on a large scale could achieve this.
If you're running a pl6 campaign, or any in which gravity technology hasn't been cracked, then there's another solution. Spinning the station at a constant rate would cause anything within it to experience centripetal forces that would approximate the force of gravity (rather like a stone in a sling, or a motorbike in a "Wall of Death" exhibition). It's important not to spin the colony too quickly, otherwise the coriolis forces would cause the inhabitants to be violently sick! One to two rpm is considered best, with three rpm as an upper limit. Also, the colony must be large enough that the force experienced along the length of a person's body is roughly equal. Too high a difference in force between the head and the legs would result in severe disorientation and circulation problems. It's easier to achieve rotational gravity if the colony is large, but of course a large colony will be more difficult to build. Below is a simple table showing the kinds of speed necessary to produce 1g effective gravity in colonies of a given diameter:
200 metres: 3rpm
450 metres: 2rpm
1800 metres: 1rpm (O'Neill "Island Two" cylinder) or Stanford Torus
6400 metres: 0.5rpm (O'Neill "Island Three" cylinder
19200 metres: 0.3rpm (rotating Bernal Sphere)
Radiation in space comes in three basic types: EM radiation, stellar winds and cosmic rays.
EM radiation comes as starlight, as well as the odd burst of radiation from novae and supernovae. Stellar emissions are active throughout the spectrum, including dangerous wavelengths such as ultraviolet. Earth's atmosphere protects us from the worst of the Sun's UV output by means of a layer of ozone gas in the stratosphere. Planets with little or no ozone content, such as Mars, receive a lethal dose of ultraviolet from the Sun. Depending on the spectral class of the star, the UV flux will differ. A-class stars will have dreadfully strong UV radiation, while low-end Gs and Ks will have quite a gentle level when compared to the Sun. M-class stars will have very little UV light in their spectra. Luckily, ultraviolet radiation is very easy to repel. The opaque walls of the colony will prevent the penetration of UV light, and any transparent sections can be polarised to screen out the UV part of the spectrum.
Stellar wind particles are highly ionised bits and pieces of atomic nuclei that have been accelerated to phenomenal speed by the magnetic fields of a star. These particles have a lot of energy due to their speed, and can cause extensive radiation damage to electronics and living beings. From time to time, even relatively placid stars like the Sun can undergo outbursts called solar storms and Coronal Mass Ejections (CMEs), which expel millions of tons of these particles in dense bursts. The Earth's strong magnetic field intercepts these particles and channels them toward the poles, where their interactions with atmospheric gases cause the beautiful Aurora displays. During strong bursts, however, even this protection is not enough, and can lead to electrical disruptions, like the famous Canadian incident a few years ago, in which whole populations were without electricity for days. This is one reason why computers must be made specially radiation resistant if they are to fly in space (the Space Shuttle crew often carry laptops with them, but they are rarely working properly when they return to Earth).
Resisting these particles is quite difficult, since they have a lot of energy and can penetrate most materials. The Apollo spacecraft stored their water in the vessels' walls to provide some protection, but some still got through. Many of the astronauts saw brief flashes of white light from time to time, even with their eyes closed. The solar wind particles were actually travelling through their eyes, leaving a brief glowing trail in the jelly of the eye on their way through! Even with this protection, the astronauts would have been killed by a CME or storm, which is why the flights took place during the Sun's period of minimum activity. A colony must address this issue. The colony walls must be thick enough to absorb the particles safely, or else the colony must have some kind of magnetic field to channel them away from the inhabited areas. Incidentally, the magnetic field option is probably much more trouble than it's worth, since the mass of machinery needed to generate a strong enough magnetic field would provide pretty good shielding even when switched off!
A rotating colony may have an advantage here. A good thickness of soil (a few metres) would provide very effective shielding, and since such a colony's walls are its "ground", the colony's need for soil and its need for radiation protection would be served by the same measure! A higher-tech colony may have to use thick walls and high-lead glass (like that of a TV screen, but more effective) to keep out the particles.
Cosmic rays are, in essence, the same as stellar winds. However, they are travelling many times faster; close to the speed of light, in fact. They are produced by hyper-energetic events such as supernovae, neutron stars, black holes and similar exotica. As a result, they have a lot of energy (a single proton at that speed, for example, has the same kinetic energy as a tennis ball travelling at 150 kph!), and are capable of doing a very great deal of damage. It's almost impossible to screen these particles out (even on Earth, we receive almost a full dose of these particles; only the mass of rock below us can keep them out), but the same measures as those used for stellar flux protection will help to minimise the dose. Anti-radiation medical techniques are likely to be highly developed on space colonies.
Concrete, Carbon, Slag and Glass
Science fiction often portrays space stations and colonies as being made of bright, shiny metal (usually titanium). However, metal is a dreadful material. It's hideously conductive, being usually too hot or too cold, it attracts condensation, it's slippery and acoustically useless. Even worse, when ionised particles (such as the solar wind) hit metal, the metal emits secondary particle showers that add to the radiation dose. It's also not nearly strong enough to build very large structures. Happily, new materials have been discovered over the last decade that may help engineers to build greater structures than any yet seen.
New crystalline versions of carbon are incredibly strong, and would make a very effective skeleton to support the loads and strains of the colony. Also, readily available silicates, combined with the advantages of microgravity construction, would enable large amounts of high-purity glass to be made to the correct sizes. Even the rough slag left over from refinery processes could be used for radiation shielding. However, one of the most interesting advances is in good old concrete.
Concrete made from Lunar soil is much stronger than that made from terrestrial materials (the fine grained, very pure, sterile makeup of lunar soil is the reason for this). This kind of material should also be common on many asteroids, and would be a very useful resource. Building over a carbon crystal skeleton with reinforced lunar concrete would create a thermally stable, acoustically perfect environment that is also much more homely than bare metal and provides better radiation protection. Such a structure could last for literally thousands of years, whereas a metallic one couldn't hope to last beyond a century or so. A space colony will need to plan on these kinds of timescales, since their futures will be measured in generations rather than missions.
The environmental integrity of a colony is of paramount importance in the long-term viability of a colony. Water and oxygen reclamation have been pioneered by Russian missions, using simple technologies to achieve remarkable efficiency. The descendants of these techniques will be needed to keep the colony stable throughout its existence, and simpler techniques will be preferable. Also, a healthy biosphere will be necessary for the psychological health of its inhabitants. A lack of "natural" scenery has been linked to various phsychological disorders in heavily built-up areas (basically, we're programmed to recognise a certain range of environmental stimuli. Without them, we're subconsciously aware of "something wrong", without any conscious knowledge of what that might be). Also, many colonies are likely to be dedicated as ecological preserves, where populations of wild species can flourish, as well as agricultural colonies. The "Biodome" experiments of the last several years have shown that a closed environment is less stable when it is small. As a result, it's likely that only the larger colonies would have true "wild" environments, the smaller colonies making do with parks and orchards. One advantage of an artificial colony is that industrial and other "heavy duty" structures can be kept beneath ground level, with residences and open spaces dominating the greater part of the visible structure, making for a very pleasant environment in which to live.
The shape of a colony is dependant on several factors. Firstly, the structure must be strong, in order to maintain the structural integrity of the colony. Whether rotating or otherwise, the stresses produced by gravity generation will require strong shapes, as well as strong materials.
The strongest shape in nature is the sphere, and its likely that the largest colonies will be spherical. In fact Phobos, the 60km asteroidal moon of Mars, was at one point considered a possibly artificial structure (its density was found to be less than that of solid rock, and it was theorised that maybe it was less dense because it was hollow!). However, a sphere provides the least amount of area for its volume, which would require a greater amount of air to fill it. Mind you, this extra air could be important in keeping the colony thermally stable.
More cost-effective shapes are cylinders and toruses. Cylinders are probably best suited only to rotating colonies, otherwise the decks could get a bit claustrophobic. However, a rotating cylinder provides the best surface area to volume ratio of any of these shapes. Toruses provide the best diameter (for rotational gravity) to material cost ratio, and would be good "starter" colonies. A compromise shape is the "Demeter" colony. Cylindrical in shape, it has an inner cylinder that lessens the need to fill the whole interior with air. As a side benefit, it also provides a large vacuum facility within the main structure of the colony, and also blocks off the potentially disturbing sight of people walking about on the ceiling! In true artificial gravity colonies, the torus would be better replaced with a flattened dome shape, providing an O'Neill-like combination of large surface area with minimum mass requirement.
The size of a colony can vary, from a few hundred metres or so for a Stanford torus, to eight kilometres long for an O'Neill "Island Two" (think of Babylon 5), to as much as 32 kilometres long for an "Island Three". A Bernal sphere-type colony could range from eighteen to sixty kilometres in diameter, though these larger ones would be real feats of macro-engineering. Perhaps the ultimate artificial colonies would be such structures as larry Niven's "Ringworld", over 2AU in diameter and totally encircling its parent star (although the material to build such a structure would have to be as strong as the forces that hold an atomic nucleus together- quite a feat). The technologist Freeman Dyson went so far as to consider an entire artificial shell at such a distance from a Sun-like star, hoarding its energy output and having the surface area of millions of Earths. Such structures would be truly exotic finds for the heroes, or settings for entire campaigns.
Given the many difficulties, both psychological and engineering, to the creation of these structures, you may wonder why we should bother. After all, you only need space stations to get the work done. Like today's offshore oilrigs, the families could stay at home. The trouble is, there is only so much home to go around. The Earth's resources in terms of living space and ecological stability are very limited, and if we are to continue to expand and thrive, we will need more room than our world, any world, can provide. As an example of the potential of this technology, there is enough raw material in the near-Earth asteroids alone to make enough colonies to house over one thousand times the present population of Earth!
There are also advantages. Providing scattered Human habitats ensures our survival as a species in case of global disaster, many of which have almost ended our existence before now. Earth is a dangerous place, with volcanic activity and earthquakes, floods, new diseases and all the other hazards of a dynamic environment. A space colony would have far fewer of these. Of course, a meteoric impact could destroy a colony and kill all the inhabitants, but a colony is a much smaller target than a planet, while still large enough to readily withstand any micrometorite impacts. Another oft-neglected difficulty is biorhythm disruption. Even an otherwise Earthlike world is unlikely to have a rotation period and orbital period that closely matches that of Earth, and living there would result in world-class jet lag, at least until the inhabitants got used to it. An artificial colony would be able to maintain terrestrial time cycles, making coordination of dates much easier and minimising biorhythm disturbance.
In conclusion, the ability to create our own homes from the raw materials abundant in space will enable us to survive throughout the Universe without having to rely upon Providence to gift us with worlds upon which to live. The roleplaying potential of having dozens or hundreds of colonies within a single system, as well as enabling civilisations to colonise normally uninhabited systems increases the venues for adventure and provides a rich backdrop to interplanetary politics.
Â© Mark Peoples 2000.