Station workers say that what they miss the most on long missions is the usual uncanned food. We will learn how to properly water seedlings in zero gravity, whether it is possible to fertilize the soil of other planets with excrement, and how scientists propose to make Mars habitable with the help of algae.
Why do astronauts need fruits and vegetables?
We remember from childhood that “an onion from seven ailments”, and “an apple for dinner - and a doctor is not needed”, in other words, fruits, vegetables and herbs are the basis of a healthy diet and a source of vital substances. The World Health Organization advises adults to eat about 400 grams of fruits and vegetables every day. Of course, vegetables are in the canned food of astronauts, but they cannot be compared with fresh crispy fruits on Earth.
In addition, over time, frozen packaged food just gets boring.
It's not just sad - astronauts often lose weight due to lack of appetite, says Norwegian biologist Silje Wolf. These problems can largely be solved by own beds on board.
Space gardens are also useful for the psyche of astronauts. They have plenty of sources of constant stress: high risk, non-standard situations at work, and even the closed space of the station, where it is difficult to be alone for a while. Gardening is known to help reduce depression and anxiety, and improve subjective feelings of well-being. Scientists from the University of Florida collected testimonies from Soviet and American cosmonauts and concluded that this also works in orbital stations. For example, American Peggy Whitson, who conducted an experiment with soybeans on the ISS, was amazed by her own reaction to sprouts in the onboard greenhouse: “I think the opportunity to see something green for the first time in a month and a half on the station made a really strong impression on me.”
Astronaut Don Pettit was so impressed by his work with plants that he published an entire diary on his blog from the perspective of an orbiting zucchini: “Nothing compares to the smell of living greens in this forest of engineering machines.”
Today, space farming technologies are being developed for stations in Earth orbit, but biologists have other goals that are much more ambitious. Researchers and enthusiasts are increasingly talking about the colonization of other planets. Specific figures appear in plans and projects: how long the flight will last and how many people will be able to become the first colonists. The road, for example, to Mars will take many months, even longer people will have to settle in a new colony. According to Julie Robinson, an expert on the ISS program at NASA, even the most modern preservation and freezing technologies will not allow all the necessary nutrients to be preserved in the food of immigrants for so long.
A new settlement cannot survive on canned food alone, relying on supplies from Earth is risky, so methods are needed that will allow them to grow plants on their own. They will have to be tested in the most severe conditions - after all, on the same Mars, the colonists are waiting for dust instead of fertile soil and hard ultraviolet instead of gentle sunlight filtered by the earth's atmosphere.
Why is gardening in space so difficult?
Mankind made its first steps towards space plantations back in the early 1980s, when the astronauts of the Salyut-7 station managed to get the seeds of Tal's resicum. This small plant from the cabbage family has become for plant researchers what the Drosophila fruit fly is for animal biology: the full development cycle of Tal's clover can take as little as 6 weeks. Since then, many crops have been grown in orbit, from lettuce to wheat, but these crops are at best a pleasant addition to food: it will not be possible to fully provide the inhabitants of space stations with vegetables for a long time.
What exactly prevents the creation and cultivation of "six acres" outside the Earth? The authors of the review article in Botany Letters cite several reasons. The most obvious of these is microgravity: both in Earth orbit and on potential colony planets, gravity is less than we are used to. Weak gravity affects many features of the development of organisms, and plants are no exception. In experiments where the same crops were planted on Earth and on the ISS, some species in orbit noticeably lost in taste and nutritional value. For example, in the "cosmic" embryos of the turnip Brassica rapa, there was much less starch and protein (by 24%). The air temperature, humidity and light levels around the plants at the station almost coincided with the earth, so scientists believe that low gravity is to blame. Perhaps the fact is that in zero gravity, plants begin to "suffocate": water in such conditions envelops the roots in a thicker layer, causing oxygen starvation.
At closed stations, there is another problem - violations of convection (heat transfer), which occur if the enclosed space is poorly ventilated. At the same time, volatile organic substances accumulate around the plant, which can slow down its growth.
Don't forget about radiation. Observations show that constant radiation can cause DNA damage and mutation, and also affects the level of gene expression [how hereditary information from genes is converted into RNA or protein]. Given all this, it is impossible to predict how plants brought from Earth will change over time. Experiments with radiation have already forced the roots, stems and leaves of Tal's clover to “lose weight”.
Speaking about the "gardens" on space stations, scientists are rather optimistic: most of these problems can be solved by studying what conditions plants need and which species best tolerate the absence of their usual environment.
It will be more difficult for future colonists of other planets, because the "soil" of new worlds can bring many unpleasant surprises.
Our terrestrial soil, which gives life to plants, is a complex system where both minerals and organics are equally important. On Mars, for example, the situation is quite different. The surface of the Red Planet is covered in regolith — fine sand and dust that forms when rocks are eroded by wind, temperature fluctuations, and meteorite impacts. This dust is not just lifeless, it is dangerous for plants: it contains toxic compounds, including perchlorates - salts of perchloric acid.
Chinese scientists have figured out how a similar concentration of perchlorates in water affects several types of plants: toxins noticeably reduced both stems and roots. In addition, perchlorates accumulated in the leaves, so including such plants in the diet will not work. And also salts of perchloric acid will not allow to populate the surface of Mars with terrestrial bacteria in order to create a fertile layer of humus. The experiments of Scottish astrobiologists have shown that perchlorates enhance the germicidal effect of ultraviolet radiation, so the bacteria in our soil simply cannot survive on the surface of Mars.
It is possible that the idea of vegetable gardens on the Martian regolith will have to be abandoned altogether, focusing on other methods, primarily hydroponics and aeroponics technologies.
What can replace the soil.
Today's space gardening methods can be broadly divided into those that require a relatively dense substrate (say, soil or clay) and those where water and liquid solutions play a major role.
The Vegetable Production System (Veggie), which has been supplying the ISS with fresh herbs since 2014, is closer to the first type.
In Veggie, the seeds germinate in special pads where calcined clay is mixed with fertilizer capsules. The polymer shell of the capsules is gradually destroyed, releasing the next portion of top dressing in time. The structure is illuminated by green, red and blue LEDs - during the experiments, the astronauts periodically change the lighting mode to find out what works best for certain plants. The installation has an automatic watering system using capillaries, but sometimes the astronauts water the orbital garden themselves. For example, Scott Kelly had to do this to save zinnia flowers from an unexpected drought.
When Veggie has served its purpose, it is planned to be replaced by a larger installation - a fully automatic "greenhouse" Advanced Plant Habitat (APH). It will be able to adjust many parameters, including humidity, pressure, light, the amount of oxygen and nutrients supplied, and even measure the temperature of individual leaves. NASA loves speaking abbreviations, so the system for monitoring many parameters was called PHARMER (Plant Habitat Avionics Real-Time Manager in Express Rack). Researchers at the Kennedy Space Center have already thought about the first experiments involving APH.
The researchers intend to bring seeds ripened on the ISS to Earth, germinate them in the laboratory and return a new generation of seeds to the station to find out how such strong gravity drops will affect them.
The cosmonauts of the Russian segment of the ISS also carried out many experiments. From 2002 to 2011, two varieties of barley, radish, "Japanese cabbage" mizuna, dwarf wheat and dwarf peas were grown in the Lada automatic greenhouse. These experiments showed that many of the most important functions of plants, such as fertilization and the formation of embryos, do not change in space.
A few years ago, a new greenhouse, Lada-2, was created at the Institute of Biomedical Problems (IMBP) of the Russian Academy of Sciences, in which they planned to grow wheat, lettuce and sweet peppers. Unfortunately, "Lada-2" died in the accident of the cargo ship "Progress MS-04" in 2016. There are no plans to create a new greenhouse to replace the lost one at the IBMP: the process will take several years, by which time the ISS operation cycle may come to an end. Now Russian cosmonauts are conducting experiments on the equipment of the American segment of the station. Perhaps in the future, another Russian development will go into space, the Vitacycle-T greenhouse with a rotating cylinder inside.
Just Add Water: Hydro and Aeroponics
The need to use soil or clay for "beds" is rather a disadvantage in space flight conditions. Solid substrate weighs a lot, the capacity of cargo ships and compartments is always limited, in addition, particles of earth can get into the ventilation at the station, and suitable soil cannot be found on future colony planets. Therefore, researchers are increasingly looking towards methods in which greens and vegetables grow in water - hydroponics and aeroponics.
"Garden" in a nutrient-rich liquid solution is far from a new idea; Francis Bacon wrote about this method at the beginning of the 17th century. Since then, there have been a plethora of soilless gardening techniques, so space tech makers have plenty to choose from. For example, you can keep the roots in the water all the time or use the ebb and flow technique, as well as use a variety of substrates that retain the right amount of liquid.
Even more promising may be aeroponics: in this case, the roots of plants are not in water or substrate, but in the air. Sprayers are installed nearby, which from time to time envelop the roots with a light haze of tiny drops of nutrient solution. So the plants get both nutrition and a sufficient amount of oxygen - the risk of suffocating the crop with a layer of water is much lower than in the case of classical hydroponics. The risk of plant disease is also reduced, as dangerous microorganisms often settle in water or a moist substrate.
Hydroponics and aeroponics have long been successfully used on Earth. They allow you to harvest even in extreme conditions - for example, in Antarctica.
Scientists from the German Institute for Polar and Marine Research. Alfred Wegener has been growing cucumbers, tomatoes, sweet peppers and herbs for several years at the Antarctic station Neumayer-Station III.
The aeroponic greenhouse has been set up in a separate building, and when a snowstorm prevents scientists from getting there from the main building, their German colleagues can remotely control the irrigation and lighting. Biologists say that one of the main tasks of their work is to prepare new horticultural techniques for testing in space conditions.
Another find for closed life support systems is anthroponics, when the waste of the crew becomes a source of water and fertilizer for hydroponic installations. For example, the urine of astronauts can become the basis of nitrogen fertilizers, Italian scientists have already carried out such an experiment on Earth. It all looks like the famous scene from The Martian, but in reality it is not so easy to switch to this technology. Excrement of astronauts can be found, for example, an excess of some metals, so following the example of Mark Watney will succeed (or, conversely, fail) only after much research
Like on a volcano: experiments with analogues of regoliths
Despite the prospects of hydroponics, there are also supporters of gardening based on the soil of other planets among scientists. Such experiments have been going on in the Netherlands since 2013. Biologists from Wageningen University are growing vegetables in artificial soil that resembles the composition of regolith from the surface of Mars and the Moon. "Martian" soil is made from volcanic ash and sand from Hawaii, and "lunar" soil is made from desert sand in Arizona. To repeat the texture of the regolith, the material is additionally ground into dust..
Scientists have already harvested more than a dozen crops; their food basket includes tomatoes, peas, radishes, rye, green onions and other plants. The first tests showed that the level of toxic heavy metals in vegetables does not exceed the permissible limits (however, new crops will still be tested many times).
In 2017, worms were placed in a Martian soil sample, and they not only survived, but also gave birth.
Project manager Wiger Vamelink says that earthworms can become the most important link in agriculture on other planets: they enrich the soil with vermicompost, and their passages help water and air to better penetrate the soil.
Of course, Vamelink's forecasts are very optimistic. The conditions on the Red Planet are harsh: plants will not only have to survive in dusty soil, but also resist the onslaught of ultraviolet radiation - the level of radiation on Mars is much higher than on Earth, since our planet is protected by the ozone layer. Do not forget about toxic perchlorates: it is not known whether there is a way to clean the soil and how much it will cost. However, even if planting gardens on Mars using the Wamelink method does not work, the results of his work will be useful on Earth - for example, they will help identify plants that give a stable crop on volcanic soils.
New Earth: Terraforming Projects for Other Planets
Each of these experiments is a small step towards the future of space gardening, but there are some scientists who think big. Supporters of the idea of terraforming propose not to be limited to small gardens and greenhouses: they intend to create from scratch on some other planet conditions suitable for the life of terrestrial plants and animals. The problem is that finding a second Earth is not easy: you will have to start not even from scratch, but from a serious “minus”.
The most popular candidate for Earth 2.0 is, of course, Mars. It is not far from us by space standards, has reserves of water ice and an atmosphere - very rarefied, but still capable of at least a little protection from radiation. Terraforming projects mostly focus on thickening the atmosphere. For example, the group of Jim Green, Director of NASA's Planetary Science Division, proposed surrounding the Red Planet with a shell of an artificial magnetic field. According to Green's plan, it will be created by a spacecraft located at the Lagrange point L1 between the Sun and Mars. How exactly this device should work, the astrophysicist did not specify.
According to Greene, the magnetic shield will "melt" the frozen carbon dioxide in the ice caps at the poles of Mars, this will start a greenhouse effect, and the temperature on the planet could rise by several degrees. This is enough to melt some of the water ice, as well as gradually raise atmospheric pressure, bringing Mars closer to Earth conditions. However, in 2018, NASA experts said that it would not work to “warm up” Mars with CO2, at least with today’s level of technology. According to Bruce Jakoski and Christopher Edwards, there is not enough carbon dioxide on Mars to implement such projects.
Another bold idea is to change the Martian atmosphere with cyanobacteria (blue-green algae). These small organisms are capable of photosynthesis: it is believed that they "breathed" a significant part of the oxygen that contributed to the "oxygen revolution" at the beginning of the Proterozoic. In 2018, an international team of scientists found that cyanobacteria can produce gas in very low light levels.
Blue-green algae are able to withstand very harsh conditions, some of them are extremophiles - perhaps some of them will survive on Mars.
For now, terraforming remains more of a dream than a concrete strategy. But the authors of these concepts agree: terrestrial technologies are developing rapidly, and decades later we will be able to talk about the development of other planets much more specifically. Who knows, suddenly the Martian apple trees will become a reality?
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