In general, the idea of providing a space station or spacecraft with oxygen through photosynthesis looks logical, but in reality, it is difficult to implement it.
Calculations show that approximately 10,000 leaves are required to provide one person with oxygen through photosynthesis. The ISS has a crew of 6 people, i.e. approximately 60,000 leaves will be needed. There is nowhere to grow trees on the ISS, so most likely, these leaves should grow on some small plants, such as tomatoes.
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On one tomato bush, there are around 30 leaves, i.e. the ISS will need to put somewhere 2,000 pots of tomatoes.
Light is needed for photosynthesis, but sunlight cannot obviously be used. Firstly, the ISS only 50% of the time is on the sunny side, and secondly, the ISS has very few windows, so the sunlight hardly enters it.
They can use artificial lighting, but this will require additional energy, and besides, somehow it will be necessary to dissipate and remove the heat created by the lighting elements.
In addition, water, soil, and nutrients (fertilizers) for plants should also be taken from somewhere.
However, there is a good alternative. In the 1960s, a series of experiments BIOS-1, BIOS-2, BIOS-3 was conducted in the USSR to create closed ecosystems. During the BIOS-1 experiment, using 20 kilograms of chlorella (green algae), it was possible to completely provide the person with oxygen, while the aquarium with algae had a volume of only 8 cubic meters.
In theory, a sufficiently large algae farm can satisfy the oxygen requirements of the ISS crew or another space station. Subsequent experiments, both in the USSR and in the USA (Biosphere-1, Biosphere-2, etc.), showed the fundamental possibility of creating a closed ecosystem that provides itself with oxygen.
It doesn’t make sense to deploy algae tanks on the ISS to provide people with oxygen. The Earth is close enough, and it’s not difficult to replenish the oxygen supply from our planet, and shifting the care of the crew’s breathing to plants that may die is a deliberate decrease in reliability. A chlorella tank is less reliable than a compressed oxygen tank. But for long flights to other planets, as well as for potential colonies on Mars, the Moon, etc, algae can become a truly irreplaceable replenished source of oxygen.