''This is Chapter 4 of the [[SolSeed book]].''
=== Orbiting mini-worlds ===
Habitats in space, as defined by images that NASA shows us, are traditionally sterile white boxes and tubes with little life other than their human occupants. The only green, or color of any kind, is to be found in some ultra-processed space food we may see the astronauts carefully imbibing, doing their level best to avoid polluting the limited air supply with floating crumbs. If there is any plant life in the public imagination of space, it is also strictly for food (as in the typical depiction of a greenhouse adjoining a future Mars base) and its growth is carefully regimented and constrained.
Such was not always the case. In the 1970s, in the afterglow of our first successful mission to another world, Gerard O'Neill and others developed an ambitious vision of huge orbiting colonies with complete self-sustaining ecosystems inside. Humans would live in ordinary houses built on the inside surfaces of giant spinning spheres and cylinders (the spin creating the effect of a roughly Earth-equivalent gravity or perhaps somewhat less). They would lead lives much like those of their Earthbound brethren, though they would only have to glance at the upside-down forests and rivers arching overhead to remind themselves of where they were.
Many people were disappointed that these ideas did not gain more traction and work their way into NASA's planning, but that doesn't mean the dream is dead. The International Space Station is the largest structure ever built in orbit, and it will doubtless serve as a stepping-stone to far larger ones, whether built by governments or new private space-station manufacturers like Bigelow Aerospace. There is a revived interest in visiting the asteroids, at first only for mining and perhaps to test methods of diverting a potential biosphere-killer like the one whose impact killed the dinosaurs, but these could be the first steps toward hollowing out such a giant rock, filling it with air, and seeding life inside.
It's hard to be optimistic, though, when you think about the size of such a bubble world in comparison to the sum total of all previous objects we've sent into space. Millions of tons of shielding alone would have to go into the design, for defense against damaging solar and cosmic radiation. O'Neill proposed huge mass drivers to launch material from the Moon that would go into shielding, oxygen, and the beginnings of soil for the new colonies' plant life. To date, we've never done any construction work in space, unless you count snapping together pre-built space station modules; it seems too great a leap from where we are today to go straight to establishing a mining rig and other major installations on the Moon. So what stepping-stones can we envision that would take us in that direction?
=== Biospheres 3, 4, 5, etc ===
You've probably heard of the Biosphere 2 experiment: a large glass-walled building containing several miniature ecosystems, completely airtight, with the only input from outside being sunlight. Eight "Biospherians" spent two years inside this sealed structure, researching how well this microcosm of Earth's biosphere could maintain itself, with one main goal being to see if such a system could provide life support for spacecraft and space colonies.
The experiment is best known for its failures, both sociological and technical (particularly oxygen getting absorbed by the concrete supports to the point where it became somewhat difficult to breathe). But that doesn't make it less surprising that few significant efforts have been made since then to study how to get it right. After all, technological life-support systems (air and water purification, oxygen generation, etc) often have single points of failure and can be difficult to repair. By contrast, each element, or niche, of an ecosystem is composed of many self-repairing organisms, making it much more robust, reducing the likelihood that problems will escalate into disaster.
Research in this area may be a key area where SolSeed can make a contribution. Two of the Biospherians started a company, Paragon Space Development Corporation, that has created very small closed-ecosystem experiments for the International Space Station and is planning to send a living flower to the Moon. NASA also has a "bioregenerative life support" research division, relatively poorly funded but with at least one project underway at the University of Arizona to develop a space-rated crop-growing module. Perhaps we can study and expand on their work, starting small as they have, helping this nascent research community work its way up to a closed system that we can more confidently send humans into (which may be a better way than what Biosphere 2 attempted, trying to get it all right on the first try).