The second of the four goals formulated by Gerard K. O’Neill is to find (or rather create) an optimal living climate for all of humanity. Not surprisingly he spends a large portion of his book on orbital space settlements, discussing the internal design of space habitats in order to promote public well-being.
O’Neill’s general layout of the valleys of a cylindrical habitat (called “Island Three” by him, but nowadays mostly referred to as “O’Neill cylinders) as a collection of villages surrounded by forests. Of course, this was just his preference, so we do not need to follow his design, when we will construct the first orbital settlements. Nevertheless, his design shows that O’Neill understood the importance of public green.
Since the early settlements will be relatively small (though still being among the largest objects ever made by mankind), population density will be high. Hence space settlements will essentially cities located in orbit. Consequently the interior of these settlements will be designed as urban zones.
Though we usually see cities as deserts made of concrete and bitumen, this not need to be the case. In fact it would be wise for sociological reasons to make space settlements as green as possible. For instance one study done by a team of researchers of the University of Geneva led by Marlyne Sahakian , shows that public parks play an important role in promoting social and individual well-being. Parks are a place where people can relax, regardless of social-economical class, and hence stimulate social cohesion among the people.
Another reason for urban green within space settlements, is related to food security and hence also with the first one of O’Neill’s goals (the eradication of hunger and poverty). According to a study by the University of Shefield gardens, allotments, parks and even roadside vegetation could provide up to fifteen percent of the food consumption of an urban population . So edibility will be an important criterion of selection of plants we want to import. Also new studies suggest that there is a relation between growing up in a green environment, not only rural area’s but also urban green as a neighborhood park, and IQ (or general intelligence) .
A fourth argument for a green urban design for orbital space settlements, is the management of carbon dioxide. Humans and other non-plant life breath oxygen and produce carbon dioxide, while plants convert carbon dioxide back into oxygen. So without vegetation CO2 levels will sooner or later reach lethal levels. Plants will sequester this excess CO2.
Pekka Janhunen proposes to use this mechanism to manage carbon dioxide levels within closed space habitats. By growing and storing biomass, CO2 levels are reduced and by burning this “green waste” we can increase CO2 levels . As agriculture is in O’Neill’s vision is (to a large extent) separated from residential habitats, CO2 levels in agricultural areas will become low and hence burning green waste from urban areas would help to sustain carbon dioxide levels there. Interestingly urban green seems to store more carbon than forests .
Both local food production and the collection of biomass, will offer opportunities to monetize public green. Fruit and vegetables from parks and roadside vegetation could be sold on the local market, while green waste could be sold to non-urban farmers to be converted into carbon dioxide. A third way of monetization of public green would be urban honey . Bees are crucial in pollination and hence bee-keeping would be an important activity within space habitats. This way, local governments could, at least partially, fund the maintenance of public green through non-tax revenue.
One might ask why this is actually important. The answer is clear: maintaining public parks and roadside vegetation cost money but we do not want to make parks only accessible on condition of paying an entrance fee. If public green is a source of income for the authorities, they will less likely inclined to pursue cuts on the budget of managing public green.
By turning the management of public green into a (hopefully) profitable business, the enjoyment of it will be a positive externality.
 ScienceDaily: Public parks guaranteeing sustainable well-being https://www.sciencedaily.com/releases/2020/05/200527105025.htm (Checked: 2020-08-25)
 ScienceDaily: Urban land could grow fruit and vegetables for fifteen percent of the population https://www.sciencedaily.com/releases/2020/03/200317130713.htm (checked 2020-08-25)
 The Guardian: Children raised in greener areas have higher IQ, study finds https://www.theguardian.com/environment/2020/aug/24/children-raised-greener-areas-higher-iq-study (checked 2020-08-25)
 Janhunen, Pekka, Control of habitat’s carbon dioxide level by biomass burning, https://space.nss.org/wp-content/uploads/NSS-JOURNAL-Control-of-Habitat-Carbon-Dioxide-Level.pdf, NSS Journal (Checked 2020-08-25)
 ScienceDaily: Green space in cities help control floods, store carbon: https://www.sciencedaily.com/releases/2018/03/180306101706.htm (checked 2020-08-25)
 The Atlantic: Urban Hives Make Better Honey, https://www.theatlantic.com/health/archive/2010/09/urban-hives-make-better-honey/62251/ (checked 2020-08-25)