As we already discussed the most dangerous and costly side of space colonization is getting people there. We can supply a colony automatically and even with an acceptable fail rate, but the transport of humans will be not only more costly but also more technically challenging, the major issue will be the requirements of the colonist during this stage, considerations need to be made for keeping them healthy and fit to perform on arrival.
Mir and ISS have helped to understand most of the problems humans face in a prolonged stay on a space environment. The major issue continues to be the psychological stress of isolation and time of inactivity. But without the extreme risk of an actual interplanetary spaceflight the psychological data might be limited since the stress of such a risky and prolonged voyage will be impossible to fully replicate in a simulation.
Other physical factors still remain to be fully tested even if most seem that can be counteracted by technological solutions, for instance the problem with zero-gravity (or lower gravity in general) and the levels of radiation exposure.
This of course places a greater burden on the selection of candidates for such mission. Some could be experience astronauts, like the one in the Apollo missions, that had pilot experience but most will require to have a possess a greater set of skills as to enable the successful establishment of a colony.
Regarding minimum size for establishing a self sufficient population, in 2002, the anthropologist John H. Moore estimated that a population of 150-180 would allow normal reproduction for 60-80 generations--equivalent to 2000 years.
A much smaller initial population of two female humans should be viable as long as human embryos are available from Earth. Use of a sperm bank from Earth also allows a smaller starting base with negligible inbreeding.
Researchers in conservation biology have tended to adopt the "50/500" rule of thumb initially advanced by Franklin and Soule. This rule says a short-term effective population size (Ne) of 50 is needed to prevent an unacceptable rate of inbreeding, while a long-term Ne of 500 is required to maintain overall genetic variability. The Ne=50 prescription corresponds to an inbreeding rate of 1% per generation, approximately half the maximum rate tolerated by domestic animal breeders. The Ne=500 value attempts to balance the rate of gain in genetic variation due to mutation with the rate of loss due to genetic drift.
Effective population size Ne depends on the number of males Nm and females Nf in the population according to the formula:
People need air, water, food and reasonable temperatures to survive. On Earth a large complex biosphere provides these. In space settlements, bio-regenerative approaches will be necessary, the use life forms to recycle air, water, and organic waste. Hydroponic gardens and algae tanks are proposed solutions for relatively small, closed system that must recycle all the nutrients without "crashing".
Many space agencies build testbeds for advanced life support systems, but these are designed for long duration human spaceflight, not colonization.
The Biosphere 2 project in Arizona has shown that a complex, small, enclosed, man-made biosphere can support eight people for at least a year, although there were many problems. A year or so into the two year mission oxygen had to be replenished, which strongly suggests that they achieved atmospheric closure.
On celestial bodies, oxygen and liquid water can be obtained from purified water ice. On the moon, oxygen can be made as a byproduct of regolith processing. On Mars, oxygen can be obtained from electrolysis of water (extracted from permafrost) or the Sabatier process (C02 extracted from the atmosphere).
The relationship between organisms, their habitat and the non-Earth environment can be:
- Organisms and their habitat fully isolated from the environment (examples include artificial biosphere, Biosphere 2, life support system)
- Changing the environment to become a life-friendly habitat (a process called terraforming)
- Changing organisms to become more compatible with the environment, ie. integrating the habitat into organisms (See also: genetic engineering, transhumanism, cyborg)
A combination of the above is also possible.
Hydroponics, an ancient technique for growing plants with nutrient-rich water instead of soil, has long been touted as the choice for growing plants in space. It is very space and water efficient and can also be part of a closed-life support loop (oxygen regeneration, water filtering and food production). For instance it has been suggested to incorporate plant respiration (of water vapor) into water purification and recovery systems. Research continues on automated hydroponic systems.
To save energy, it is possible to grow plants with colored light, eschewing frequencies they do not use.
Animals, given their low mass efficiency and high energy and space requirements, are unlikely to be raised in space any time soon. More likely sources of animal protein are insects and synthetic meat ("meat-in-a-dish").
Compared to the other requirements, communication is relatively easy for orbit and the Moon. Much of the current terrestrial communications already pass through satellites. Communications to Mars and further will suffer from significant delays making voice conversation impractical.
Communications is not only depended on infrastructure but energy, it requires also technical maintenance.
On Earth, if one needs a new toothbrush and some toothpaste, it is a simple matter of driving to the corner drugstore to pick some up. On Mars or the Moon, the nearest drugstore will be millions of miles away! At least at first. And more to the point, the manufacturing capability of producing all these products is equally inaccessible, down at the bottom of Earth's gravity well.
Even for Earth orbit colonies, launching materials from Earth is very expensive, so bulk materials should come from the Moon or Near-Earth Objects (NEOs - asteroids and comets with orbits near Earth) where gravitational forces are much less, there is no atmosphere, and there is no biosphere to damage. Our Moon has large amounts of oxygen, silicon and metals, but little hydrogen, carbon, or nitrogen. NEOs contain substantial amounts of metals, oxygen, hydrogen and carbon. NEOs also contain some nitrogen, but not necessarily enough to avoid major supplies from Earth.
Manufacturing Goods In-SituEdit
One thing to consider will be that the absence, or alterations, in "normal" gravity enables completely novel manufacturing techniques. Liquids with surface tension form perfect spheres in the absence of gravity. Massive material may be moved with little energy. The temperature range available may be quite large, and can be achieved by creative use of shadow and reflectors. Unfortunately, it also introduces new challenges, as in space all debris must be accounted for less it become a travel hazard.
Laking the technology to have mater replicators as seen seen in science fiction works, today we have the possibility to do 3D printing, also known as rapid prototyping, this allows parts and even entire machines to be created from a digital blueprint, even food could be replicated in this way. This can makes it possible to greatly reduces the need to transport parts.
Self-replication is an optional attribute, but many think it should be the ultimate goal, because it allows a much more rapid increase in colonies, while eliminating costs to and dependence on Earth. It could be argued that the establishment of such a colony would be Earth's first act of self-replication.
Intermediate goals include colonies that expect only information from Earth (science, engineering, entertainment, etc.) and colonies that just require periodic supply of light weight objects, such as integrated circuits, medicines, genetic material and perhaps some tools.
Cosmic rays and solar flares create a lethal radiation environment in space. To protect life, settlements must be surrounded by sufficient mass to absorb most incoming radiation. Somewhere around 5-10 tons of material per square meter of surface area is required. This can be achieved with left over material from processing lunar soil and asteroids into oxygen, metals, and other useful materials.
In-situ refueling infrastructure across the solar system is one of the highest priorities in space development. By essentially resetting the rocket equation with each stop at a refueling station, fuel for any given mission is tremendously reduced, completely revolutionizing aerospace design. It becomes less desirable to discard a spent stage and more practical to refill it. A Mars spacecraft could exhaust all its fuel reaching Phobos's orbit, refuel at a station on Phobos, and then conduct a propulsive descent - a maneuver that is impractical with fuel brought from Earth. (Source: Greason, J. ISDC 2011 Keynote Speech. http://www.nss.org/resources/library/videos/ISDC11greason.html)
- Electrolysis of water yields Hydrogen and Oxygen, a propellant combination with one of the highest specific impulses. This would be practical on the Moon and asteroids containing water ice.
- The Sabatier reaction has been proposed, notably in the Mars Direct plan, to convert Carbon Dioxide (in situ on Mars) and Hydrogen (brought from Earth) to Methane and Oxygen. Hydrogen must be brought because it is of low abundance on Mars. Thankfully, it has very low mass. (Though there exists abundant water ice on Mars, so this may be another possibility.)
- The ALICE concept, tested at Purdue University, is a solid rocket fuel composed of water ice and nanoscale Aluminum powder. It is attractive because it could be produced on any celestial body with sufficient water and Aluminum, and is much easier to store than cryogenic propellants.
- Nuclear thermal rockets may be able to use water or hydrogen extracted from celestial bodies as reaction mass.
The Mars-500 experimentEdit
The Mars-500 experiment ( http://www.esa.int/SPECIALS/Mars500 ), lasting from 2007 to 2011, divided into three stages. The final, 520-day stage of the experiment, which was intended to simulate a full-length manned mission, ended on 4 November 2011, where a team of six volunteers were locked into a cluster of hermetically sealed habitat modules for 520 days, to simulate a mission to Mars using the available technology. To add to their isolation, communications with mission control were artificially delayed to mimic the natural delays of a Mars flight. During the simulation the volunteers (the crew) performed several experiments, all linked to the problems of long duration missions in deep space. The simulation was a success all the volunteers managed to stay healthy in body and mind indicating that a voyage to Mars can be successfully in regards to the psychological aspect of such endeavor.
One way tripEdit
Any one way trip to colonize outer space will be unlike anything else in human history. As the requirements to archive a way back will if not impossible due to lack of the necessary resources at the destination. They could take generations to archive if at all, making that type of voyage, to the colonist, a form of self-imposed exile from Earth. Of course there can be middle-steps, like using robots to create the necessary infrastructure before sending colonists or establishing a consistent resupply and support structure from Earth, but the costs and the added level of uncertain due to the great distances, possible windows for the lunches and time and economic commitment would be huge at today's level of technology and probably impossible on the political cycles most nations use.
One should think that while a colony is dependent of supplies from Earth or location nearby, it will be politically dependent and unless a more reasonable global governance is created, self sufficient colonies are more likely to become independent. A colony may revolt and pursue its independent self interest. In terrestrial civilizations, this frequently occurs on the order of 10 to 100 years. Even a loyal colony may decide that it is against its economic or political interests to aid a troubled Earth, or to recolonize Earth. Even then the goal is simply survival of the species will be assured and one should hope many independent colonies could be established as to collectively form a safeguard against one government amassing too much power over the fate of the whole human race.
Ecologic and historical preservationEdit
As we colonize other planetary bodies one should consider for the possibility of discovering native life and even remains of its previous existence. Preservation and study of this life and remains should be a priority over the colonization process, much like we do when we discover archaeologically relevant objects in construction sites.
Natural selection occurs when a species is challenged, when there is a threat to its survival, a threat to the continued existence of fertile descendants. Simply sending humans to another location and waiting 100 000 years does not necessarily yield a different species.
If we colonize distant worlds, we are likely to settle more hostile places, like Mars or Europa, than Earth-like places, which seem to be rarer in the universe. It is expected that in colonizing space, humans will at first have restricted direct contact with the hostile worlds they will inhabit; instead, they will live inside domes and use space suits to work on the outside. Humans, humans' pets, humans' parasites and complex life in general are unlikely to be able to adapt for instance to the 95% carbon dioxide atmosphere of Mars or to the -160 ºC temperature of Europa, a so we may even consider altering our genetic material and of other living specimens to permit a better adaptation to the new environments.
Heavy building skeletons can be built from stone blocks cut from the suitable large stones found nearby or mined in a quarry. Buildings such as domes, tunnels, castles, cathedrals, pyramids, storehouses, factories, foundries, pools, houses, and others can be built this way very cheaply. Just few robots are needed to be brought from the Earth.