Growing Plants in Alien Soil: How Will Future Missions Feed Astronauts

To realize these objectives, NASA is busy developing and testing all the components that will take astronauts beyond Low Earth Orbit (LEO) for the first time in half a century — like the Space Launch System (SLS) and the Orion spacecraft.

Beyond NASA, space agencies like the European Space Agency (ESA), Roscosmos, the Chinese National Space Agency (CNSA), and the India Space Research Organization (ISRO) all have plans to send astronauts to the Moon. Some even plan on building a permanent lunar settlement in the Moon's southern polar region (like the ESA's International Moon Village).

Aside from that, NASA and other space agencies are also deep into researching how humans can live and work for extended periods off-world. This means coming up with designs for habitats that can provide astronauts with a breathable atmosphere, warmth, and protection from the environmental elements.

Given that missions to the Moon, Mars, and beyond will not be able to rely on regular resupply missions, these habitats will also need to be as self-sufficient as possible. This means that water and air will need to be recycled and cleaned on an ongoing basis and that some food will need to be grown in-house.

This could be problematic, since space is a very harsh environment for all living things. And beyond the usual hazards, there's a lot that we don't know about food-production in space. But with a new era of human space exploration on the horizon, we are determined to find out!

The Challenges of Living Off-World

Space is an extremely inhospitable place. Anywhere beyond Low Earth Orbit (LEO), there are multiple hazards that make exploration incredibly challenging. Consider the Moon and Mars as examples, both of which are destinations for future exploration missions (and even settlement).

The Moon is Earth's closest celestial neighbor, making it the easiest, fastest, and cheapest to get to. Mars, meanwhile, is considered to be the second-most habitable body in the Solar System. And yet, living and working on either for extended periods of time is not possible without some serious technological intervention!

Atmosphere:
To begin, the Moon is an airless body. While there is a tiny amount of pressure created by outgassing from the surface, it is negligible to the point of being near-vacuum. Mars, on the other hand, has an atmosphere, but not one that could sustain life (as we know it).

For starters, atmospheric pressure on the surface of Mars is less than 1% of what we experience at sea level here on Earth (0.655 vs. 101.325 kPa). This extremely thin air is also predominantly composed of carbon dioxide (96%), with 3% nitrogen, 1.6% argon, and only trace amounts of oxygen, and water vapor. So, not only is Mars' atmosphere too thin to breathe, it's a toxic fume as far as humans and animals go!

Temperatures:
On Earth, our dense atmosphere, the dynamics that drive it (aka. "climate"), and the levels of carbon dioxide and other greenhouse gases ensure that temperatures are relatively stable over time. There are regional and annual variations, of course, but overall, the level of variation is not extreme.

Based on data from the World Meteorological Organization (WMO), temperatures on Earth average around 14 °C (57 °F). However, they also go from a minimum of -128.6 °F to a maximum of 134 °F (-89.2 to 56.7 °C ) — which works out to a total range of 262.6 °F (146 °C)

On the Moon, surface temperatures average at around with an average of -9.4 °F (-23 °C) and range from -280 °F at night to 243 °F (-173 °C to 117 °C)  in direct sunlight. From extremely cold to boiling hot and a total range of 523 °F (290 °C). That's intense!

Once again, the situation on Mars is a bit better. On the Red Planet, temperates average at around -82 °F (−63 °C), going from −226 °F at night to 95 °F (-143 to 35 °C) during midday in the summer. From extremely cold to warm and balmy (well, sort of) and an overall range of 321 °F (178 °C).

Radiation:
On Earth, people who live in developed nations are exposed to about 620 millirems (6.2 mSv) of radiation a year on average, which works out to 1.7 millirems (0.017 mSv) a day. According to a recent study, with no atmosphere or magnetic field to protect it, the Moon's far side is exposed 200 to 1,000 times as much radiation!

Once again, the situation is better on Mars, but certainly not peachy! In 2008, NASA conducted a study that showed how astronauts (or colonists) on Mars would be exposed to an average of 2667 millirem (26.67 mSv) a year or 0.073 mSv per day — that's 4.3 times as much.

Low-G:
Whereas there are pre-existing strategies for all of the aforementioned challenges, there remains the issue of gravity. Ongoing research aboard the International Space Station (ISS) has shown that long-term exposure to microgravity can have a detrimental effect on astronaut health — from muscles and bones to heart health and psychological disorders.

What is not well-understood, however, is the long-term effects of lunar gravity and Martian gravity on the health of terrestrial life. On the Moon and Mars, the gravity is about 16.6% (0.166 g) and 38% (0.376 g) of what we experience here on Earth, respectively.

Food, Glorious Food

While it is safe to assume that the effects would be similar, a considerable amount of research still needs to be done. We need to learn how and when they will take effect, how long they may last, how (or if) they can be reversed, and what can be done to mitigate them over the long haul.

All of these hazards are a potential risk to plants as well, which astronauts will be reliant on to provide much of their nutrition. Plant-based proteins have the benefit of being much more sustainable and much less resource-intensive, and many green vegetables also contain minerals and nutrients we can't live without.

But if future generations of off-worlders also intend to have animal proteins in their diet, that means livestock, which means their health will have to be assured as well. A lot of research needs to happen before we can figure out how to do this. Luckily, that research is well-underway!

Past Experiments

Biomass Production System (BPS):
The BPS environmental control subsystem provides a growing environment that studies the effects of microgravity on wheat photosynthesis and metabolism. The purpose of this experiment, which ran from December 2001 to June 2002, is to investigate whether regenerative life support systems can be incorporated into future missions to the Moon and Mars.

The 73-day experiment produced a total of eight harvests, and the results suggest that microgravity is not a significant stressor for plant growth. However, comparisons between immature seeds grown aboard the ISS and on the ground showed that it could affect the flavor and nutritional value of the plant.

CARA:
The Characterizing Arabidopsis Root Attractions (CARA) experiment, conducted between March 2014 and September 2014, examined the mechanisms at the molecular and genetic level that influence the growth of a plant’s roots in microgravity (and how they can change based on the absence of light).

The experiment consisted of exposing one set of seedlings to light while keeping another in the dark and examining how each environment influences the patterns of root growth. The results showed that microgravity has some effects on plant growth hormones, as well as the genes that regulate the size and shapes of cells that influence root growth.

Gravity Perception Systems:
On Earth, plants respond to light and gravity to direct the orientation of their roots. The GPS experiment, which ran from September 2017 to October 2018, investigated how plants would perceive gravity and light in a microgravity environment.

This involved normal and mutated research plants (thale cress) being placed in the ISS' European Modular Cultivation System, which contains a centrifuge for simulating gravity. This allowed researchers to subject the plants alternately to microgravity and simulated gravity (0.006 g to 1 g) in the dark.

PESTO:
The Photosynthesis Experiment and System Testing and Operation (PESTO), conducted between December 2001 to June 2002 (in conjunction with the BPS), investigated the effects of microgravity on dwarf wheat plants.

Compared to samples grown on Earth, wheat plants aboard the ISS grew 10% larger while showing a similar leaf growth rate. The experiment also found that microgravity alters leaf development, plant cells, and chloroplasts (the cell structures that conduct photosynthesis) but is not harmful to the plants.

PGBA:
The Plant Generic Bioprocessing Apparatus (PGBA), which ran from June 2002 to December 2002, investigated the effects of microgravity on an important part of plant cell walls (lignin). It consisted of a self-contained plant growth chamber that provided temperature, humidity, nutrient delivery, and light controls.

The experiment found that plant material did not develop normally and identified the need for greater air quality regulation within the plant growth chamber. The lessons learned from this led to improved space flight plant chamber designs for all future plant growth experiments.

Current Experiments

Because of its proximity to Earth, its advanced facilities, and its microgravity environment, the International Space Station (ISS) is able to host multiple experiments. In addition to investigating the effects of space travel on human beings, multiple plant experiments are taking place as well. These include:

Advanced Plant Habitat:
The APA, which began operations aboard the ISS in April of 2017 (and will continue until Sept. of 2021), is a fully-automated, closed-loop system designed to conduct plant bioscience research. The system was developed by NASA and Orbital Technologies Corporation (ORBITECH) and managed by NASA's Kennedy Space Center (KSC).

The system employs a series of LED lights and an environmentally controlled growth chamber equipped with over 180 sensors. This allows the APA to grow plants under optimal light conditions while relaying real-time information (temperature, oxygen content, carbon dioxide content, and water content of both plants and soil) back to the team at the KSC.

Aleph Zero:
In 2019, the Israel-based company Aleph Farms (in collaboration with the Russian company 3D Bioprinting Solutions) grew the first meat in space. Using a process of bioprinting meat directly from bovine (cow) cells, the company produced a small quantity of beef aboard the ISS.

Looking to build on this success, the company announced a new program in late-October of 2020 to grow meat in space on an industrial scale. The program is Aleph Zero, for which the company is looking to secure strategic partnerships with technology companies and space agencies.

Biolab:
The Biological Experimental Laboratory (Biolab) experiment, which was delivered to the ISS as part of the ESA's Columbus module, conducted research into the role "weightlessness plays at all levels of an organism, from the effects on a single cell up to a complex organism including humans."

Using an incubator equipped with centrifuges to simulate varying levels of gravity, Biolab has investigated the effects of microgravity on small plants, invertebrates, microorganisms, animal cells, and tissue cultures since Columbus was launched in 2008.

Soil Health in Space:
Also known as the Determination of Gravitational Effects on Soil Stability for Controlled Environment Agriculture (Soil Health In Space) experiment investigates another often overlooked aspect of plant cultivation and health — the aggregation of soil and nutrients.

The experiment is based on scientific research performed by Morgan Irons and Dr. Johannes Lehmann, from the College of Agriculture and Life Sciences at Cornell University, and Dr. Matthias Rillig of Freie Universität Berlin.

Sponsorship was provided by the Norfolk Institute, Rhodium Scientific, LLC, NASA, Center for the Advancement of Science in Space, with funding from Deep Space Ecology LLC Rhodium Scientific, bio365, and the Zwillenberg-Tietz Foundation.

It consists of the three types of soil samples (fibrous, organic-rich, and silt/clay-rich) distributed into twelve 0.135 oz (4 ml) vials. These samples were provided by Cornell University (silt/clay-rich sample), bio365 (BIOALL, the fibrous sample), and the Rillig Lab's Berlin soil (sand-rich, organic sample).

These are subdivided into two groups of six, known as the “free-floating” and “restricted movement” group. Last, these two groups of six are subdivided into two groups of three and administered water at 60% and 30% of their respective holding capacities.

The aim of this experiment is to identify the effects of microgravity on fungal and bacterial growth and activity, which is essential if humans ever want to grow food beyond Earth. Morgan Irons, a Soil and Crop Sciences Ph.D. candidate at Cornell University, the inventor of the experiment,  explained:

"Microorganisms within a living soil rhizosphere help create soil aggregates, an important soil structure that supports the biogeochemical reactions agricultural plants need to acquire nutrients for growth. The results from post-flight soil analyses of the Soil Health in Space experiment will enhance our knowledge of how spaceflight affects soil microbial activity and the bioregenerative capacity of space-based agricultural systems. Such knowledge will allow us to improve the efficiency and production of food crops grown in controlled environment agricultural systems on short- and long-term space missions."

Veggie Series:
The Veggie Production System (aka. Veggie) has been operating aboard the ISS since March of 2013 and supports a variety of experiments designed to see how plants sense and respond to gravity. In addition, a portion of the crops is generally harvested and consumed by the crew while the rest are returned to Earth for further analysis.

Of all plant experiments aboard the ISS, Veggie's growth volume is one of the largest, which enables growing larger plants that could not be grown before due to size restrictions. Its adjustable LED light bank also allows for other experiments where a temporary light source is required.

To date, four major experiments (harvests) have been conducted aboard the ISS (Veggie-01 to Veggie-04). In February of 2018, Veggie was enhanced with the addition of the Veggie Passive Orbital Nutrient Delivery System (PONDS), a system designed to deliver water and nutrients efficiently in a microgravity environment. 

The PONDS units are designed to mitigate the effects of microgravity on water distribution, increase oxygen exchange, and provide sufficient room for root zone growth. This will allow for the cultivation of more crops, including larger leafy vegetables, fruit crops, and new types of lettuce and mizuna greens.

Other Experiments

Not all experiments into producing food in space are conducted aboard the ISS. Some of them are done here on Earth or in even more exotic locations (like the Moon!)

Chang'e-4:
In January of 2019, China's Chang'e-4 mission became the first robotic lunar explorer to land on the far side of the Moon. In addition to a suite of scientific instruments, the lander element also carried the Lunar Micro Ecosystem — which was designed jointly by 28 Chinese universities.

It consisted of a 6.6 lbs (3 kg) sealed module containing potato, tomato, Arabidopsis thaliana seeds, and silkworm eggs. The purpose of this was to test if plants and insects could grow together in a microgravity environment. On January 15th, 2019, it was reported that cottonseed, rapeseed, and potato seeds had sprouted, which became the first plants sprouted on the Moon.

Nine days later, the experiment was terminated when a sudden temperature drop (caused by lunar night) and failure to keep the biosphere warm caused the sprouts to die. Nevertheless, the experiment was the first of its kind and provided valuable data.

EuCROPIS:
In December of 2018, the German Aerospace Center (DLR) launched the Euglena and Combined Regenerative Organic-Food Production in Space (EuCROPIS) satellite into low Earth orbit. This mission tested plant growth in simulated gravity using human waste as a nutrient source.

The satellite, which was designed to rotate to simulate gravity, contained two greenhouses equipped to grow tomatoes. Two experiments were conducted by EuCROPIS where Lunar and Martian gravity (16.6% and 38% of Earth gravity) were simulated and the effects on plant growth investigated.

Lunar Greenhouse:
Commissioned in 2009, the LGH is a hydroponic plant growth chamber and technology demonstrator. The LGH is an example of a Bioregenerative Life Support System (BLSS), which are designed to provide a closed-loop, sustainable life-support system for living and working beyond Earth.

In addition to providing a continuous supply of food for astronauts, it also provides air revitalization, water recycling, and waste recycling for the crew. The LGH was designed and built by researchers at the University of Arizona's Controlled Environment Agriculture Center (UA-CEAC) — with support from NASA's Goddard Earth Sciences (GES).

Future Experiments

There are currently several experiments in the development process, or which are complete and waiting to be sent to the ISS. There are also incentive competitions to inspire additional experiments, ideas, and strategies.

BIOWYSE:
The Biocontamination Integrated cOntrol of Wet sYstems for Space Exploration, developed by the Centre for Interdisciplinary Research in Space (CIRiS) in Norway, will investigate different methods for ensuring a sustainable and renewable supply of drinking water for astronauts.

This integrated system is designed to store freshwater, monitor it for signs of contamination, and decontaminate it with UV light (rather than chemicals). It is also capable of monitoring the level of bacterial contamination in various humid areas inside of a space station or spacecraft.

This is necessary since about 80% of the water aboard the ISS comes from airborne water vapor, as well as recycled shower water and urine. Future habitats designed for living in LEO or off-world will similarly need to harvest water in a closed-loop system for drinking and irrigation.

Currently, the ISS relies on chemicals to cleanse recycled water, but this is unlikely to be sustainable over the long haul. A system that can sense contamination in airborne water vapor and on humid surfaces will also be a neat perk for crew health and safety.

EDEN ISS:
In May of 2015, an experimental greenhouse facility was established in Antarctica to test a new method for growing plants in space. Its name is EDEN ISS, a multinational project launched in 2015 by 15 companies and research institutes (including the German Aerospace Center) and funded by the European Union‘s Horizon 2020 research and innovation program.

This system combines advanced nutrient delivery, high-performance LED lighting, bio-detection, and decontamination to grow a variety of plants in a limited volume of space. In addition to validating this type of system for operation aboard the ISS, EDEN ISS was also intended for applications here on Earth, providing fresh produce for wintering crews at the Neumayer Station III in the Antarctic.

OBAM:
In February of 2020, the Tomsk Polytechnic University and their partners in central-Russia announced the creation of a prototype for an orbital greenhouse — known as the Orbital Biological Automatic Module. This device would allow plants to be grown and cultivated in space with minimal human supervision.

The OBAM combines smart lighting for accelerated plant growth with specialized hydroponics, automated irrigation, and robotic harvesting. Indiscipinary researchers are also working on a scaled-up version of the prototype for the ISS that will be cylindrical in shape and contain a cultivation area measuring ~320 ft² (30 m²).

TIME SCALE:
Short for Technology and Innovation for development of Modular Equipment in SCalable Advanced Life support systems for space Explorations, this three-year program is also being developed by a consortium of eight research institutes from six European countries (with funding provided by the EU's Horizon 2020 program).

This technology is also being developed by researchers at CIRiS and is designed for recycling water and nutrients for the sake of growing plants. Like its predecessors, it relies on a spinning centrifuge to simulate Lunar and Martian gravity and measures the effect this has on the ability of plants to absorb nutrients and water.

Deep Space Food Challenge

NASA has a long tradition of hosting incentive competitions, the purpose of which is to crowdsource solutions to particular challenges. Given the high-priority that food production systems will have in the coming years, NASA (in partnership with the Methuselah Foundation) and the Canadian Space Agency (CSA) have come together to launch the Deep Space Food Challenge.

As part of NASA's Centennial Challenge Program, the competition will award cash prizes for the development of food production technologies or systems for long-duration missions. The winning entries will be those that can provide safe, nutritious, and appetizing food that requires minimal resources and produce minimal waste.

The competition was announced in January of 2021 and will remain open to applications until July 30th, 2021. NASA will award a prize purse of up to $500,000 to winning proposals submitted by American citizens for Phase 1 of the competition.

The Canadian Space Agency will host a parallel competition for participating Canadian teams and issue awards from its own prize purse. Teams from other countries may also compete and will gain international recognition for their proposals but will not be eligible for monetary prizes.

Depending on the technologies presented, a possible second phase, involving a kitchen demonstration, could follow. Grace Douglas, an advanced food technology lead scientist at NASA’s Johnson Space Center, explained the aims of the competition thusly:

"We need to provide food that meets the caloric and nutritional requirements for our astronauts, but we want to go a step further. The variety, acceptability, and nutritional content of the food system have the potential to go beyond just sustaining the human body to promote psychological and physiological health."

Solve for Space, Solve for Earth

In addition to fostering innovative ideas for growing food in space and on other celestial bodies, this research aims to create more sustainable food practices for use here at home. In the near future, the global population is expected to exceed 10 billion, which will coincide with increased levels of drought, extreme weather, coastal and inland flooding, and environmental destruction.

In short, our population will be swelling while the very systems we rely on for our survival and livelihood will be in danger. In order to meet this challenge head-on, human beings need to find ways to feed more people in a way that is sustainable and doesn't increase our impact on the natural environment.

As Morgan Irons, who is also the co-founder and Chief Science Officer at DSE and a Research Fellow with the National Science Foundation (NSF), the Carl Sagan Institute, and the Norfolk Institute, summarized:

"Soil health is inextricably linked to agricultural health and is crucial to producing nutritious food that promotes environmental and human health on Earth and in space. Whether we are on the Moon, Mars, or another planetary body, the local soil or regolith is a valuable in situ resource that could be processed and used to develop resilient and adaptable habitats for extreme environment living, such as quasi-closed agroecological systems."

Becoming a "multi-planetary species" (as Elon Musk says) doesn't just entail learning to live on other planets. It also means finding better and more sustainable ways to live here on Earth, well into the indefinite future. While we may someday venture out and put down roots elsewhere in the cosmos, Earth will always be the cradle of life as we know it.

If going to space has taught us anything, it is how rare and precious planets like Earth are and how we should not take it for granted. It has also taught us that the only way we will ever colonize space is to understand our planetary environment and appreciate it for the life-giving, life-sustaining system it is.

Further Reading:

• Habitat Marte
• The Mars Society
• Deep Space Ecology
• Grow Mars/Green Moon
• NASA - Growing Plants in Space
• NASA - Experiments: Veggie Pond
• NASA - Deep Space Food Challenge
• NASA - Experiments: Plant Habitat
• NASA - Experiments: Plant Gravity Perception
• NASA - Experiments: Vegetable Production System
• NASA - Houston We Have a Podcast, Ep. 172: Plants in Space.
• Tomsk Polytechnic University - Orbital Biological Automatic Module
• University of Hawai'i - Hawai’i Space Exploration Analog and Simulation (Hi-SEAS)