How plants are grown in space 

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In order to travel into deep space, such as a mission to Mars, astronauts must be able to grow their own food rather than relying on pre-prepared food. Experiments to discover if plants can be grown in space on the International Space Station are paving the way to making these trips a reality.

 

The idea of humans colonising another planet has captured the imagination of sci-fi fans for years, and central to every plot is how to survive in a barren, unearthly environment. This makes the ability to grow plants in space one of the most exciting and talked about areas of the science behind space exploration.

Scientists have started trying to grow plants on terrain similar to Mars, like in the Utah desert.1 But the surface of Mars is more like volcanic rock and ash rather than soil and it contains chemicals that are toxic for humans.2 Scientists are working on a way to clean the toxins out of the rocky surface, but it does not look very promising as a solution to growing food in space.

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Growing Food from Waste

To survive, plants need carbon and nitrogen-rich soil, as well as a regular supply of water and carbon dioxide. It might sound odd, but humans in some way create each of these products as waste. What's more, storing and transporting waste safely and hygienically is a big problem on a spacecraft. One solution is to create a system that recycles human waste products to grow plants for food, just like on Earth. This is called a bio-regenerative life support system.

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Fun Fact: There is a closed-loop water recycling system onboard the International Space Station (ISS). Wastewater is captured from urine, sweat and even moisture from breath, then the impurities are filtered out. The water produced is used by crew members in food, as drinking water and for bathing.3 As strange as it sounds, famous ISS Astronaut Chris Hadfield insists "it's cleaner than the water we drink at home".4

 

Growing Vegetables on the International Space Station

For nearly 20 years humans have been living in space on the International Space Station (ISS). In this time, NASA has worked hard to provide food for their astronauts that is both nutritional and tasty. But, there is only so much pre-packaged food someone can take before they miss the fresh produce of home. This has pushed researchers at NASA to form the ‘Veggie' experiments, which aim to grow fresh fruit and vegetables on the space station. And they have been successful: since 2017, astronauts of the ISS have managed to grow varieties of lettuce, radishes, peas, zinnia flowers and sunflowers.5

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How do they do it? Seeds are sown into ‘plant pillows', a small package containing calcined clay - this is a soil that has been heated to just below the melting point to remove moisture and microbes.6 Each pillow contains a controlled-release fertiliser, and serves as a place for the seeds to take root.

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Once in flight, dried seeds are placed into these plant pillows, and watered. This is installed into ‘Veggie', a chamber similar to a miniature greenhouse, which provides the right conditions for the plants to germinate and grow.7 The aim is to grow normal sized plants in as little soil as possible. Water is administered precisely to the roots. To grow other plants, they use methods of hydroponics, where water is supplied directly to the roots, or aeroponics, where water is supplied to the roots and lower stem of the plant as water vapour. Aeroponics provides a particular advantage for some plants as it reduces the need for soil and a large root system to absorb water, rather the plant gets it through water vapour which is enriched with the nutrients it needs.

 

The Veggie chamber has pre-programmed LED lights to create conditions optimal for the plants, and daily light cycles. The red and blue lights are used primarily in the plants “daytime” as these are the light frequencies they absorb to photosynthesise - green light is reflected away which is what gives them their distinctive colour.7 In zero gravity (weightless conditions experienced in space), gases gather in parts of the Veggie chamber rather than circulating.  Stationary air means the stomata (pores on the surface of leaves that allow movement of gases in and out of the plant) cannot get the carbon dioxide they need to grow and photosynthesise. So, fans in the chamber are crucial to keep the air circulating.8 

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NASA researcher and plant physiologist, Ray Wheeler, explains more about growing plants in space:

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Fresh food means a happy crew

As part of ‘Veg-04', the most recent experiment on the ISS, crew members have a more hands-on approach to nurturing the plants. They help seedlings emerge from the pillows, water the plants and monitor their progress. As well as the astronaut's opinions on the taste and smell of the vegetables, they are also asked about their overall mood following cultivating the plants.9

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 The findings of the Veg-04 experiment are not yet known but evidence suggests that having something new and fresh in the diet, with a different flavour and texture, has a great effect on the crew by helping them get past ‘dietary fatigue’ and adding enjoyment to their meal. Also, the occupation of gardening, something that reminds the crew of home, has a hugely positive psychological impact. Just imagine being in a spacecraft where every surface is plastic, metal, control panels and buttons: it has been described as an “extreme and hostile environment.”7 Green foliage, and nurturing something that reminds you of home can make a massive difference in such a place, especially if you were to spend months or even years there. After all, ISS crew member Scott Kelly loved the zinnia flowers he grew so much that he took selfies with them all over the space station, before finally harvesting the bouquet for his fellow crew-mates on Valentine’s Day 2016.2

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