Many consider space the ‘final frontier’, the ultimate proving ground for humanity’s will of expansion and endurance. After the Moon landings in the late 1960s and early 1970s, humanity has focused on human spaceflight in its immediate vicinity, i.e. Low Earth Orbit (LEO), e.g. by usage of several space stations such as Skylab, MIR and currently the International Space Station (ISS). All ISS partners (United States, Europe, Canada, Japan, Russia) and China plan to send humans to the lunar environment in the next decade, e.g. to the Lunar Orbital Platform Gateway (LOP-G) or also the lunar surface.
Others regard spaceflight, especially human spaceflight with criticism, often for the seemingly high costs involved and lack of immediate applicable, visible results for everyday life. Furthermore, one might argue that the current final frontier, at least the most important one, is making living on Earth sustainable.
Living on Earth and living in space have been generally regarded as two different challenges. On the former resources are abundant and readily available and for the latter, resources are scarce, need to be recycled and uprated to minimize the cost of space missions.
The connection between sustainability and a prosperous existence has been communicated in development strategies for several decades. Economic growth has been shown to be not a guarantee for societal improvement in developing countries, in fact causing new problems, e.g. due to environmental pollution. In the 1980s development programs have shown to be ineffective on a long-term and ideas of sustainability were discussed, defining sustainability as satisfying the needs of the current generation while keeping up a society’s ability to meet needs of future generations [1]. This eventually led to the United Nations Conference on Environment and Development in Rio de Janeiro in 1992, often referred to as Rio92, which agreed e.g. about the Agenda 21, setting a strategy for achieving sustainability in the twenty-first century. Follow-up conferences defined further steps, e.g. Rio + 20 in 2012, which eventually led to the official formulation and ratification of the United Nations Sustainable Development Goals (SDGs) [2] in 2017.
Awareness for the need of sustainable development resp. sustainability, although discussed for several decades, is spreading and thus now actions are taken with more urgency. Humanity is beginning to realize widely that Earth’s resources are not limitless and that humanity’s use of resources is endangering ecosystems worldwide and thus our own basis of living [3]. While Earth’s “life support system” is by far more complex, robust and capable than any artificial life support system developed for e.g. space applications, it is strained and getting out of balance. Actions from multiple angles are necessary to keep Earth’s “life support system” intact for our own well-being and that of future generations.
This paper explores the relation between technologies, processes and principles developed for and used in human spaceflight, and sustainability on Earth. Sustainability has ecological, economical and societal dimensions. With spaceflight technology especially the first two dimensions can be influenced and as the societal dimension is not independent of the former two, thus to some extent also the latter.
Requirements on a closed loop for human spaceflight are far more stringent compared to living on Earth. On the lunar surface the ecological footprint must be close to zero as there is no ecology, which can be exploited, except for water ice [4] and generally lunar regolith. Similarly, while there are resources on Earth, they have to be conserved and not exploited.
For instance, water, especially potable water, is limited in various regions on Earth. About 2 billion people do not have access to clean drinking water [5]. Technology can improve the sanitation situation as cleaning and saving water is an important part of a closed-loop system for e.g. long-term human spaceflight missions as well.
Paper outline
This guideline paper lines out, how human space exploration and sustainability on Earth are related in their challenges and thus also in their solutions concerning technology. We discuss the implications and recommend making use of synergy effects, by coordinating exchange of know-how between both fields.
In the remaining part of the introduction three concepts will be explained: that of lead users in technology development, which are drivers for new technologies, the meaning of closed loop as defined for human spaceflight systems and the idea of transferring technology from a spaceflight application to a terrestrial.
In the second section we will present the fundamental functions associated to human habitation on planetary bodies such as Moon or Mars and how they are also applicable for describing human life on Earth, underlining the similarity of the tasks of “settling” Earth and settling on Moon or Mars.
Afterwards examples for technology applications are given and how the respective space technologies can be beneficial for improving sustainability. This is done by presenting the general potential of the respective applications and at the same time show what current developments are in the sector of human spaceflight – pinpointing possible benefits from cooperation.
The fourth section then presents one possible approach of coordinating sustainability technology research within a research infrastructure designed by the authors. The infrastructure’s purpose is closed-loop technology development and thus can act as furnace for technologies supporting long-term human spaceflight missions and sustainability on Earth. This chapter contains the approach, an overview of the purpose and design of the infrastructure, which includes lessons learned from prototype tests.
Before concluding the paper, the fifth section discusses the previously made statements, obstacles acting as barriers for technology adoption and proposes to coordinate space habitation research in closer alignment with sustainable development to improve the gain for both. A set of guidelines is presented as an outcome.
The space sector as lead user for technology development
To understand the role human spaceflight has in technology development in general, the following paragraphs will focus on the concept of lead users – a concept applicable to (human) spaceflight concerning many technological advances. This concept relates how human spaceflight can be a driver for development of technologies which are subsequently applied in other areas.
In management or economy theory, lead users are advanced users specialized in a certain area of application. They possess two characteristic properties [6, 7]:
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Lead Users are the first with certain needs or requirements, which other users, resp. market participants, even early adopters, will only have some time later.
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Lead Users benefit significantly from innovation and are possibly even working on innovations themselves.
Lead Users can be individual experts, companies or organizations. They are participating in the innovation process earlier than other users and are contributing, e.g. by supporting innovation processes with scientists, manufacturers, and engineers or even conduct the innovation process wholly on their own.
A typical example for lead users is the Formula 1 racecar sector. It is a testbed and breeding ground for car technology later used by ordinary consumers of the car industry but advanced initially by the steep demands on racecars, e.g. concerning aerodynamics or engine technology.
Often lead users are active in a more extreme environment than ordinary users. Consequently, their needs surpass those of ordinary users and the solutions for their needs are often based on out-of-the-box thinking, pushing the limits of the state of the art further ahead. Therefore, innovations are tested and matured in the lead user sector, before being introduced into the general market for widespread use [6, 7].
Spaceflight and human spaceflight especially represent a lead user situation. Requirements concerning e.g. robustness, performance, autonomy, reliability, and radiation hardness are usually exceeding those for terrestrial applications, due to the harsh space environment, the costs associated with space missions (and therefore the need for low risk operations) and the fact that often human life is relying on flawless operation of technical equipment.
One example for a lead user situation in the space sector, which led to terrestrial application, is solar cell technology. Solar cells are one major contributor to sustainable power generation on Earth. In the early 2000s solar power had not been a relevant contribution to world-wide power generation. In 2005 the actually installed total capacity of photovoltaic power had been 5 Gigawatts (GW) [8]. In just 10 years, this had increased by a factor of almost 50. In 2015 the total capacity was almost 230 GW, with the major shares associated to Europe (97 GW) and the Asia-Pacific area (96 GW) [8].
The first actual solar cell has been developed by Bell Labs in 1954 [9] – but lacked a practical application. This came in 1958 with Vanguard 1 [10], the second US satellite and fourth satellite altogether. Solar cell technology became more and more prominent for usage on satellites and remains a major element of today’s spacecraft of various types, e.g. landers, interplanetary probes and Earth satellites. The major advantage of solar cells over the batteries used exclusively on early satellites has been their capability to harvest energy in space, allowing missions to last longer than with just primary batteries and to design lighter spacecraft, because rechargeable batteries meant they could be smaller than for previous missions, i.e. mass was saved.
At the same time, the new and expensive solar cell technology was affordable for the space budgets of the competing nations in the space race [10]. The space application boosted their development, despite the relatively large price (100$/ Watt compared to 0.5$/ Watt for typical terrestrial power sources), which was mostly associated to the high level of robustness and radiation hardness required for space missions [10]. This gradually reduced in the 1970s when terrestrial application began in a larger scale e.g. for navigation buoys and especially oil companies invested in this alternative power generation method after the oil crisis of 1973, e.g. Exxon [10]. Similarly, solar power generation became a major element in human spaceflight technology, e.g. for Skylab and even today’s ISS.
Today solar cells are one important element for sustainable energy generation not just in space, but also on Earth – initially funded by the lead users of the space sector, requiring sustainable energy supply for their spacecraft. A similar approach can be adopted and should be facilitated e.g. for closed-loop technologies aiming at supporting humanity’s sustainable living through development of sustainable technologies.
Definition of closed-loop technologies
But what exactly are closed-loop technologies? What is the closed loop regarding space habitation?
The closed loop concerns all resources and materials within the artificial habitat. Just like there is e.g. a carbon cycle on Earth, there is a loop of material fluxes in a habitat ensuring that all materials are present in their required amount for processing. This could e.g. be oxygen for breathing or water for drinking and watering plants. The closed loop should also include materials needed for building and construction, e.g. new parts for the habitat, equipment, furniture, clothing – otherwise these commodities would have to be regularly supplied from Earth.
The closed loop ensures that resources required by one element of it, are recycled from its output by other elements until the original resource is available again. Referring to human spaceflight systems the needs of different consumers (e.g. plants or humans), materials (e.g. CO2 and O2 & C) are exchanged and transformed (e.g. CO2 and H2O into O2 and carbohydrates), e.g. by a bio-regenerative life-support system based on edible plants. Such systems are currently being developed by e.g. the German Aerospace Center [11] and other space entities.
The concept of a closed loop is sketched in Fig. 1, showing three conditions for the materials oxygen, carbon and hydrogen, transformed between CO2, H2O, O2, Carbohydrates and waste products. Transformation from the original condition could e.g. occur via plant growth. Out of H20 and CO2 are created, i.e. O2 and carbohydrate production (via using light, i.e. energy which could be coming from outside via sunlight/ solar power generation). The plants’ edible parts can be consumed by the human crew, again producing CO2, H2O and waste (e.g. feces and non-edible biomass), which has to be transformed into its original constituents as well to arrive at the original condition.
The actual loop is more complex than presented in Fig. 1 and includes further materials, e.g. nitrogen or other nutrients and energy, e.g. in the form of light for plant growth. Especially the latter is difficult to keep in a closed loop (unless using methods for energy harvesting, see Section 3), yet if sustainably used, e.g. by using solar power generation, there is no strain on the closed loop.
Closed-loop technologies are technologies, which are required to artificially create a closed loop and thus establish e.g. a planetary habitat, which is sustainable, i.e. it can operate without external input of resources, especially those transferred from Earth. Therefore, long-term human spaceflight missions have to achieve on their small scale, what Earth’s population has to achieve on a large scale: sustainability. It is therefore prudent to assume that technologies developed for sustainable habitation in space can support sustainable development and sustainability on Earth.
Sustainability supported with spaceflight technology
Sustainable development is not possible with just a sustainable use of resources. Instead societal changes have to be initiated leading to more justice and equality, as defined by the United Nations Sustainable Development Goals (SDG) [2]. These goals even stand in a certain competition with each other – fighting poverty can include economic growth or lead to more consumption, which can contradict the idea of environmental sustainability [3]. In optimization theory, this is a typical case of a Pareto optimum, i.e. a complex system, to be optimized in several dimensions, has a state, where you cannot improve the system’s value in one dimension, without reducing those values of other dimensions. Thus, there is a compromise where all values reach a maximum (or minimum, depending on the goal of the optimization) which cannot be further improved even in one dimension without deviating from the maxima of the other values.
The SDGs have a similar property, where once a relative maximum is reached in one goal, you cannot further improve one goal without degrading the others [12] in our current forms of society and economy. Concerning SDG 7, technical solutions for even cheaper energy supply might exist, but they could be less sustainable or e.g. polluting water and thus are not eligible selections for sustainability.
Technology cannot be the ultimate solution for overall sustainable development, as it only addresses certain SDGs. It can improve living conditions (e.g. via telemedicine for remote areas), ease e.g. working situations or education, but its function per se, does not promote the non-environmental related SDGs. While the SDGs are interlinked and depend on each other, certain SDGs are more susceptive for approaches of problem solving with technologies from human spaceflight programs, e.g.:
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Goal 2: Zero Hunger: Improving crop yield through artificial means while at the same time reducing the induced environmental impact can be achieved by adopting human spaceflight technologies for planetary greenhouse food production (e.g. reducing water consumption and pollution).
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Goal 6: Clean water and sanitation: Both are also a major concern for human spaceflight missions and thus recycling technology, often associated with food production, or water are a major development branch.
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Goal 7: Affordable and clean energy: Human spaceflight has a high need for energy due to the life support systems involved, but in general spaceflight missions rely on regenerative power sources as resources are scarce. Developments, e.g. more efficient solar cells, directly benefit similar energy generation strategies on Earth.
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Goal 11: Sustainable cities and communities: This goal is a general link to human spaceflight, as any human spaceflight mission aiming at a long-term presence, has to be a sustainable community.
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Goal 12: Responsible consumption and production: This goal can benefit from recycling technologies and processes as well as overall production strategies benefiting recycling and resource efficiency developed from human spaceflight missions, e.g. additive manufacturing using recycled material.
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Goal 17: Partnerships for the goals: Facilitating cooperation between human spaceflight and sustainable development would be directly addressing this goal. Furthermore, spaceflight activities themselves already involve international partnerships, partnerships between public and industry, science and engineering.
Other goals, e.g. Goal 1: No poverty, can be addressed indirectly e.g. by improving access to food and water. Less effort and resources spent on food and water supply allows more resources to be spend on e.g. education to reduce poverty.
In general, technology – and especially human spaceflight technology – can improve the ability to attain a Circular Economy, if defined as “realization of (a) closed loop material flow in the whole economic system” [13]. The closed-loop material flow is the paradigm for a long-term human spaceflight mission to Moon or Mars. Thus, closed-loop technologies are developed for the lead-user application of human spaceflight, but can be adapted for terrestrial use, promoting sustainable development as part of science and technology for sustainability (STS).
The subsystems of the aforementioned greenhouses (Section 1.3) are resource efficient, e.g. using aeroponic nutrition with little water loss. The used water is also recycled. These technologies are not only applicable to food production for a human space exploration mission, but can be adapted to terrestrial application, e.g. in vertical farms located in urban areas. This would improve food security, lessen stress on existing agriculture areas and lessen the demand in agriculture resources such as water. Furthermore, local food production would reduce CO2 emissions associated with food transport from rural areas to urban. To close the loop of bio-regenerative life-support systems, non-edible plant products are reused and recycled.
At the same time, energy is a precious commodity in a closed habitat, especially for a lunar base, where e.g. the lunar night can last up to 14 days, due to the Moon’s slow rotation. Thus, solar power generation is not sufficient for power supply and efficient energy storage is needed to provide electrical power during lunar night. Elaborating energy-efficient habitat technology, e.g. by energy harvesting of radiated heat, can in the long run be used for terrestrial housing as well, reducing energy consumption.
As usable resources are scarce on Moon and Mars, especially those needed for human habitation, waste is a non-affordable loss. Any used materials and resources have to be treated to allow them to be reused, recycled or up-cycled. Similarly, reduction of using primary resources on Earth will benefit from such technology developed for human spaceflight.
While development of technologies aiding in sustainability is not unique to human spaceflight programs, they can nonetheless contribute to sustainable development on Earth. If humanity masters closed-loop technologies for living on other planetary bodies in the solar system, it can use the same techniques on Earth.
Especially in the area of fighting climate change and adapting human settlement towards the aggravated environmental challenges, the space community is already contributing towards solutions on Earth. Generally, the data used for evaluating climate change and its impacts are often gathered by space based systems. Furthermore, the research of space actors is also focusing on this current challenge, e.g. NASA’s Goddard Institute for Space Science has a program investigating impacts of the climate change on human life and the environment and contributed to the Climate Change and Cities report of the Urban Climate Change Research Network [14]. This also stresses the already existing link between research concerning human settlement on Earth and space, highlighting the potential to learn also from Earth settlement for settlements on other bodies such as Moon or Mars. Challenges, faced by Earth communities, e.g. waste management, water security [14] are similar in nature to those of a sustainable space community.