Astronauts in 2023 take almost everything they eat with them. Future space travellers will need to grow plants in space without regular supply rockets. What’s happening in space agriculture today that I can throw forward a hundred years for my WIP, In Machina?

Escaping the gravity well

Getting anything into space is governed by “the tyranny of the rocket equation”. The payload that a rocket can carry is limited because you need more fuel to carry cargo, so the weight goes up even more and the fuel consumption goes up with it.

For astronauts today and in the near future that means making everything as light as possible, and finding novel ways to create your own food in space and on other worlds. Andy Weir’s stranded astronaut in The Martian grew potatoes in poop — and it’s a well-researched story. What sort of advances are the space community looking at for travellers who don’t have to start from scratch? And will they need to use space poop? (Spoiler: the answer is probably yes.)

Things should look a lot better when you get off Earth by 2120. My universe has no artificial gravity but you can choose to fly slow and light with things like ion drives and solar sails, or go faster with nuclear engines. Your ship is still mostly fuel, engines and life support, but you can scale up to carry a lot more. Habitats often have spin gravity though it’s rarely more than Moon-strength, and settlements around the outer planets come with whatever gravity is present naturally.

NASA astronauts Scott Kelly and Kjell Lindgren on the International Space Station are getting their taste buds ready for the first taste of food that's grown, harvested and eaten in space, a critical step on the path to Mars.
NASA astronauts Scott Kelly and Kjell Lindgren on the International Space Station, looking like two men caught in a bar when they said they were working late. Copyright: NASA

The seeds of space plants

Seeds are about as light as it gets and robust enough to survive both launch and radiation. Plants survive on the things humans excrete — nutrients in our physical waste, carbon dioxide in our breath — and turn them into things we need to survive — food and oxygen. Growing plants might not provide enough oxygen to keep people alive on a spaceship, but a space station or a habitat on a moon, asteroid or other planet could have enough space to grow an effective oxygen farm.

Astronauts first experimented with growing plants in space on a 1984 Soviet Salyut mission. Those on the International Space Station (ISS) now regularly eat a portion of their small harvests.

The Veggie and Advanced Plant Habitat experiments have cultivated three types of lettuce, chilli peppers, pak choi, mizuna mustard, red kale, dwarf wheat and tomatoes. These plants were chosen to provide a variety of vitamins and other micronutrients, grow well on the ISS and have rich tastes that are easier for astronauts to enjoy. Future trials will grow berries, beans and other antioxidant-rich foods, which may counteract some effects of the higher radiation encountered in space.

Taikonauts on the Chinese space station, Tiangong, have grown and consumed rice, lettuce and thale cress.

The light stuff

Growing plants in space requires the same conditions as Earth — water, nutrients, light, air, warmth and something to grow in — but it faces unique challenges.

Sunlight is abundant but rarely available in the right amounts or qualities: low Earth orbit sees a sunrise every 90 minutes and deep space missions will see either too much or too little. Artificial light needs power that’s readily available from the sun if you’re close enough, but travellers going beyond Earth orbit will need nuclear power to keep their greenhouses lit. Mars has an Earth-like day/night cycle, but its seasons are twice as long and the Sun is only half as bright.

Water is essential but it’s likely to be rationed aboard spacecraft. The lunar poles, Mars, some asteroids and the ice moons of the outer planets are so water-rich that thirsty crops like cotton could be viable. Space settlers may find themselves wearing cotton from Callisto. Water transports not only nutrients but also oxygen to plants and the bacteria which help them to fix nitrogen. However, in zero-gravity it forms bubbles which can both starve and drown the plants’ roots.

In closed spaces, air needs to be moved around with fans so that plants and people don’t suffiocate, particularly in zero-gravity where there’s no convection. Spaceships today operate at lower pressure than on Earth, with a mix that’s rich in carbon dioxide, yet some plants have grown surprisingly well on the ISS. However, the materials used to make spaceships safe can give off chemicals that plants don’t like, and if they make too much oxygen it would be bad for both plants and people.

Brown gold

Plants will be able to draw some of their nutrients from astronauts’ bodily waste, but it won’t be able to supply everything. Agriculture on Earth requires industrial levels of fertiliser to maintain productivity, with careful management of soil ecology. Nutrients for space agriculture could be a major export from Earth to space on day. Prospectors who find nitrogen and phosphates amidst the moons and asteroids may find them as lucrative as precious metals.

Even small amounts of gravity could solve a lot of problems for growing plants off-Earth, but it’s yet to be attempted for any length of time. China’s Chang’e-4 lander took an experiment to the dark side of the Moon in 2019, grandly-named the Lunar Micro Ecosystem. It contained seeds of potato, cotton, rapeseed and arabidopsis thaliana (a weed popular in botanical studies), along with yeast and fruit fly eggs. The cotton seeds sprouted two leaves, but the LME wasn’t heated, so everything died after a few weeks, when the lunar night fell and temperatures plummeted.

Martian and lunar soils are not ideal candidates for growing our food. They’ve been sterilised by millennia of solar radiation, the abrasive qualities of lunar regolith may kill plants and Martian soil is full of toxic peroxides. Soil is also heavy, so if you can do without it, all the better.

Cotton seeds sprouting on China's Chang'e-4 lunar rover.
Cotton seeds sprouting on China’s Chang’e-4 lunar rover. Copyright: CNSA.

Growing with air and water

Hydroponics and aeroponics (often called airponics) don’t need soil and make highly efficient use of water. Hydroponics bathes plant roots in a nutrient-rich solution, recycling it to remove waste and add nutrients. Aeroponics is even more efficient, using a mist to keep plants fed and watered.

On the ISS, Veggie is hydroponic and the Advanced Plant Habitat (APH) is aeroponic, but both use porous clay media to support the plants and make sure they get a steady feed of water, air and nutrients in zero-g. Veggie uses “pillows”, pre-loaded with nutrients that release slowly so no one needs to refill the system. It’s open to the air, which enabled Scott Kelly to clean fungi from the leaves of zinnia on the ISS and nurse them back to health. Gardeners on the ISS and the ground monitor the fully-enclosed APH through 180 sensors, which reduces the chance of disease.

Modern LEDs can supply different wavelengths and mimic a complete range of daylight conditions, from sunrise to midday, but those aren’t always the bright lights that people need. Plants reflect a lot of green light and use more red and blue wavelengths, so the Veggie chamber typically glows magenta pink. APH can deliver more colours, including white and even infrared for night-time imaging.

XROOTS — the eXposed Root On-Orbit Test System — tested different hydroponic and aeroponic techniques that didn’t need clay pockets to hold plants. The goal is to improve the next generation of ISS experiments and pave the way to larger systems.

These experiments pave the way for more ambitious projects. Vertical Future is a British company that builds “vertical farms” using hydroponics to grow food in cities and harsh environments like deserts. They’re now working with Axiom Space and Plants for Space (P4S), an academic spin-off from Australia, to develop systems for space.

NASA astronauts Jessica Watkins and Bob Hines work on XROOTS on the ISS in 2022.
Jessica Watkins and Bob Hines, NASA astronauts, work on XROOTS on the ISS in 2022. Copyright: NASA

Plants on demand

Annual and biannual harvests will leave space habitats with unacceptable gaps in their food supply, even with refrigeration and dehydration. The advantage of hydroponics is that you can grow a rolling cycle of crops so that you’re never short of food, waiting for the next harvest.

On the other hand, if space residents grow sugar cane or beet, or culture sugar from microorganisms, someone will try to make jam from a fruit crop (provided they also have pectin). Pickles and chutney are more difficult because they require vinegar and that gets into the uncharted territory of space brewing…a blog post of its own.

NASA operates a long-running competition to find the best ways to feed its astronauts: the Deep Space Food Challenge. Now in its third round, the challenge funds companies and researchers working to improve hydroponics and grow fungi, a potential source of protein that I’ll look at in my next post.

Spaced in space

Growing plants in space is also great for morale. They provide colours, shapes, smells and textures that will be a welcome relief from the tough materials and technology we need to survive beyond Earth’s atmosphere. Lots of Earth-bound urbanites enjoy growing their own food as an antidote to the pressures of modern life. It’s easy to imagine that space travellers will look forward to part-time gardening as well as becoming full-time farmers.

The first ISS Veggie experiment grew Zinnia, an inedible flowering plant. Flowers may be harder to cultivate because they require pollination, there’s no doubt that seeing them will give people a huge psychological boost. The smells of fruiting plants can be overwhelming, but there will undoubtedly be demand for access to the rich atmosphere of a habitat’s growing rooms as different crops ripen.

Research in hydroponics and aeroponics owes a debt to its use among cannabis growers. It’s easy to imagine that future space travellers will also grow recreational crops and relax with a vape amidst the colourful lights of their agriculture chambers.

Artist's impression of a hydroponic vertical farm on Mars.
Artist’s impression of a hydroponic vertical farm on Mars. Copyright: Vertical Future

Next course: let’s meet the meat

Humans also need protein in our diets, whether plant or animal. Next time, I’ll look at the off-Earth opportunities for satisfying the dietary and psychological needs for this part of our diet.

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