The trouble with plants on the moon
Plants need 17 essential chemical elements, delivered in the right way and in the right combination to grow vital and healthy. If one of these elements is missing, the natural life cycle of the plant cannot be completed, and deficiency symptoms will occur. The elements needed in larger amounts are called macronutrients. They are carbon, oxygen, hydrogen, nitrogen, phosphorus, potassium, calcium, magnesium and sulphur. Micronutrients are elements that are needed in smaller amounst and eight elements are included: boron, iron, manganese, zinc, copper, molybdenum, chlorine, and nickel.
On earth, these nutrients are derived from soil, in which they originate from mineral or organic compounds being broken down by biochemical and physical processes.
Organic components with elements such as calcium, magnesium, nitrogen, potassium, phosphorus, iron and others must be first broken down into into the inorganic matter in order to be available to the plants.
Subsequently, the salts dissolve in water in the soil from where they are absorbed by the roots of the plants. 
Growing vegetables in moon soil is well below optimal: First, moon soil rarely contains organic matter and therefore many of the essential nutrients for the plants are not provided. Secondly, growing tests on a simulated moon soil conducted for a Master’s thesis by former SWAG-Member Broes Laekeman showed that the presence of toxic heavy metal concentrations harm plant growth and can eventually accumulate in its consumer. Therefore, an alternative to moon soil is needed.
Hydroponics: Growing food without soil
Hydroponic is defined as alternative plant growth by using only a nutrient solution and an inert medium instead of soil . It is also known as “soilless culture” and is already practiced in the agriculture industry in parts of the world like the Netherlands.
These hydroponic farms are also facilities that can be thermally insulated and almost completely airtight. LEDs and other necessary equipment like air conditioners, air circulating fans, CO2 and nutrient solution supply units provide the right conditions for plants to grow indoors in vertical stacked trays or tubes.
Indoor vertical farming systems are efficient and sustainable due to advantages over conventional food production. Some examples are:
How to bring the organic matter to the plants in an inorganic environment
The nutrient solution given in a hydroponic system uses minerals mostly produced industrially. Hence, the essential chemicals will have to be transported from earth to the habitat, especially those originating from organic matter.
A more sustainable approach would be to use excrements, like the urine and faeces of the humans living on the moon. This would not only bring valuable essential plant nutrients back to the plants, it would also reduce waste. By doing this, food could be provided in a sustainable way for the inhabitants while optimizing another waste stream in order to achieve the utopia of a perfectly closed system.
However, excrements can be contaminated and are therefore dangerous if they are not sterilized. This can be achieved by heating the faeces to 300-400 degrees Celsius, which turns them into a carbonaceous material called biochar that is also believed to be completely sterile. The whole process, called pyrolysis, is an energy-intensive way to reuse human waste and bring back the valuable nutrients back into the cycle.
Research about the optimal use of biochar and urine in hydroponic systems is being conducted at our University applied science Zürich (ZHAW) in Wädenswil, Switzerland.
First design of the SWAG-System
The first Swag-system that was built for IGLUNA 2018/2019 functioned with an aeroponic system. The nutrients solution was constantly sprayed on the tips of the roots by a pump. This system is highly efficient because there was less water required than in other hydroponic systems.
The nutrient solution consisted of water and 1% of “Aurin”, a solution with high urine concentration, in which the cultivated garden radish grew. Unfortunately, numerous nutrient deficiencies were apparent on the plant’s leaves and attracted our attention.
This informed the way our second model has been designed. This time around, we are trying to avoid nutrient deficiency by making sure that all the essential nutrients are provided to the plants in the right dosage.
New design for IGLUNA 2020
This year’s SWAG-System will be in an almost airtight case in which sensors will constantly monitor essential parameters that influence plants growth like temperature, air humidity, CO2, pH value and more. On the basis of the data collected, the system will be adapting the environment into the right conditions for the plants to grow.
Together with our partner FINK, we designed the optimal SWAG-system that does not only enable good vegetable growth, but is also pratical and elegant.
Designing our own lamp for the SWAG-System
The sun is the plant’s energy source. With photosynthesis the plant converts the energy of light into chemical energy that is used for growth, reproduction and survival. Moreover, different plant species require different amounts of light and intensity as depending on their environment. In a moon habitat, light will be scarce. So, artificial light will be necessary.
The SWAG-Team built for this reason its own lamp whose LEDs are completely individually adjustable and adaptable to the plant. These can be used as programs for the cultivation of different plant species, depending on their natural environment.
The LEDs are hung into the system where the distance to the plant is measured by TOF (Time of Flight) sensors and automatically adjusted so that the right amount of light reaches the plant. Additionally, the spectrum and the lighting period is also controllable with a self-written mobile phone application. Five different pre-installed and ready to use lighting packets have already been created. Overall, the lamp is technically able to imitate the sun at any climate zone – with its radiation as well as its diurnal cycle.
There is water on the moon beneath the surface and this can be drilled for and pumped out. Even so, water will still be a valuable resource on the moon and must be used sustainably. In the SWAG-System, water will be cleaned with a membrane filter and reused once it has finished its cycle. Water is pumped up to the top and gravity makes it flow back into the water reservoir. The stream provides the plants with nutrients and only the tips of the roots are in contact with the water in order to provide a high level of oxygen to the roots. This technique is called the nutrient film technique (NFT) and is well applicable to systems in limited spaces that want to achieve a rapid growth rate.
 Toyoki Kozai, Genhua Niu, and Michiko Takagaki, Plant Factory – An Indoor Vertical Farming System for Efficient Quality Food Production, 1 (London: Academic Press, 2015), p. 165.
 Howard M. Resh, Hydroponic Food Production – A Definitive Guidebook for the Advanced Home Gardener and the Commercial Hydroponic Grower, 7 (New York: CRC Press, 2013), p. 15.
 Kathie L. Thomas-Keprta and others, ‘Organic Matter on the Earth’s Moon’, Geochimica et Cosmochimica Acta
Howard M. Resh, Hydroponic Food Production – A Definitive Guidebook for the Advanced Home Gardener and the Commercial Hydroponic Grower, 7 (New York: CRC Press, 2013), p. 2.
 Toyoki Kozai, Genhua Niu, and Michiko Takagaki, Plant Factory – An Indoor Vertical Farming System for Efficient Quality Food Production, 1 (London: Academic Press, 2015), p. 4.