NASA plant physiologist Ray Wheeler, Ph.D., and fictional astronaut Mark Watney from the movie “The Martian” have something in common — they are both botanists. But that’s where the similarities end. While Watney is a movie character who gets stranded on Mars, Wheeler is the lead for Advanced Life Support Research activities in the Exploration Research and Technology Program at Kennedy Space Center, working on real plant research.
“The Martian movie and book conveyed a lot of issues regarding growing food and surviving on a planet far from the Earth,” Wheeler said. “It’s brought plants back into the equation.”
As NASA prepares the Space Launch System rocket and Orion spacecraft for Exploration Mission-1, it’s also turning its attention to exploring the possibilities of food crops grown in controlled environments for long-duration missions to deep-space destinations such as Mars.
Wheeler and his colleagues, including plant scientists, have been studying ways to grow safe, fresh food crops efficiently off the Earth. Most recently, astronauts on the International Space Station harvested and ate a variety of red romaine lettuce that they activated and grew in a plant growth system called Veggie.
Wheeler, who has worked at Kennedy since 1988, was among the plant scientists and collaborators who helped get the Veggie unit tested and certified for use on the space station. The plant chamber, developed by Orbitec through a NASA Small Business Innovative Research Program, passed safety reviews and met low power usage and low mass requirements for use on the space station.
Aside from the chamber, the essentials needed for growing food crops, whether on the Earth or another planet, such as Mars, are water, light and soil, along with some kind of nutrients to help them grow.
What kind of crops could be grown in space or on another planet? Potatoes, sweet potatoes, wheat and soybeans would all be good according to Wheeler because they provide a lot of carbohydrates, and soybeans are a good source of protein.
Also, potatoes are tubers, which means they store their edible biomass in underground structures. Wheeler said potatoes could produce twice the amount of food as some seed crops when given equivalent light. After salad crops that are now being studied, they are the next category of minimally processed food crops and could be consumed raw.
“You could begin to grow potatoes, wheat and soybeans, things like that, and along with the salad crops, you could provide more of a complete diet,” Wheeler said.
Wheeler has spent a lot of time studying different ways to grow potatoes. Most of his studies took place during the late 1980s through the early 2000s inside Hangar L at Cape Canaveral Air Force Station in Florida. The lab was relocated to the Space Life Sciences Laboratory in 2003. A major portion of the labs were then relocated to the Space Station Processing Facility in 2014 to become part of the Exploration Research and Technology Programs Directorate at Kennedy.
Many of the early potato crop studies were done at the University of Wisconsin, where Wheeler worked prior to coming to Kennedy. Plant scientists at Kennedy used these fundamental findings as a starting point for their studies, and in particular, a variety called Norland red potatoes, using a large plant chamber called the Biomass Plant Production Chamber.
The Biomass Production Chamber originally was a hypobaric test chamber used during the Mercury Project. Including its pedestal, the chamber is 28 feet tall. It was later modified to grow plants in the mid-1980s. Air circulation ducts and fans, high pressure sodium lamps, cooling and heating systems, and hydroponic trays and solution tanks were added. The chamber provided a tightly closed atmosphere for plant growth, which simulated what might be encountered in space.
“Providing food is a complex issue,” Wheeler said. “We have to think about nutritional issues, what’s acceptable and what tastes good. If nobody wants to eat it, that won’t work.”
Water – A Precious Resource
In the movie, the character chooses to use the regolith, or Martian soil, to grow the plants. In reality, the soil on Mars is essentially broken rock material, and lacks most of the nutrients needed to sustain plant growth.
Much of what Wheeler did in his potato studies involved growing the plants in shallow, tilted trays using a hydroponic recirculating system.
“With potatoes, it was a little bit more interesting in the sense that you can’t use systems that require a lot of standing or deep water—potatoes don’t like to be submerged,” Wheeler said, “and we kept the nutrient water film very thin.”
They did very well, as do many crops grown this way, according to Wheeler. But traveling in a spacecraft to another planet will put constraints on the quantity and weight of commodities that could be brought along. You can’t pack everything you need for a long-duration spaceflight. Some resources will need to be recycled, acquired or made at the destination, a process called in-situ resource utilization.
“The recent discovery of water on Mars is a positive development,” said Rob Mueller, senior technologist for Advanced Projects Development in the Exploration Research and Technology Program at Kennedy. “It can be used for making propellant, sustaining human life and growing crops.”
But, Mueller noted, the water will not be pure and will have a brine composition. Perchlorates and other impurities are known to exist in the regolith on Mars, so these must be accounted for and mitigated before the water can be used.
Wheeler said one scenario could be that provisions such as water pumps and fertilizer salts are brought along on deep-space trips, and the plants are grown hydroponically inside a protected environment. Martian soils might be used later as the growing systems expand.
“Growing plants on Mars is not a trivial matter,” Mueller said.
Plants Need Light to Grow
In open fields on Earth, light is plentiful. But out in space, use of direct sunlight for plant growth could be challenging. Yet having sufficient light will be required for growing plants quickly in space.
In 2007, a graduate student at the University of Colorado mapped the light intensity at the surface of Mars over two Martian years. Results showed that the Red Planet gets 43 percent of the sunlight that Earth receives due to its distance from the sun, but has numerous areas at low latitudes that receive adequate light to grow plants.
“Mars gets significant dust storms, which could block a lot of sunlight, and that must be considered,” Wheeler said. “That’s an issue, even if we’re using a photovoltaic system.”
That’s the reason why planetary probes and spacecraft that travel farther away from the sun, like Cassini, Galileo and New Horizons, didn’t use photovoltaic type systems. Just like in the movie, they use radioactive thermal generators, also called RTGs, as power generators. It’s a form of radioactive decay that generates heat, which is converted to electrical power.
“An alternate approach to sunlight would be to use electric light sources. High intensities of efficient LED lights could be used to help push the plants hard,” Wheeler said. “This is an area where NASA has been really right up on the edge of research and development.”
The Veggie plant growth system, currently on the space station, uses blue and red LED lights. Wheeler said using LED lights to grow plants was an idea that originated from a NASA-funded effort at the University of Wisconsin in the 1980s. The technology was patented with NASA-supported funds.
Kennedy Space Center’s plant scientists also were one of the first groups to demonstrate vertical farming — layers of plant trays with a water source and LED lighting. This type of farming is now being used in Japan, Korea, and China, and several facilities in North America.
Protection from Radiation
As if finding the right soil, water and lighting wasn’t enough of a challenge, food crops also would need to be protected from ultraviolet radiation and kept inside a pressurized environment with adequate nutrients and appropriate lighting. The shelter would have to be able to withstand radiation and the extreme temperatures of a Martian environment.
“That’s a big challenge for materials for a greenhouse-like structure. The thermal issues could be alleviated by having either a cover or clamshell that would go over it at night and open in the daytime,” Wheeler suggested.
When nuclear power was emerging in the 1970s, there was a lot of interest in understanding the potential effects of radiation on living organisms, including plants. There are limits to what plants can take, and Wheeler said more research needs to be done on the tolerance of food crops to radiation.
The “Eyes” Have It
How do you regenerate your food source? If you consume everything over a period of time, you will eventually run out.
But there’s something special about potato tubers. Potatoes have “eyes” or buds. If given enough time, the eyes sprout. Sections of potatoes containing at least one “eye” could be replanted so they can sprout and produce new plants. This process was illustrated in The Martian, and actually is used by seed potato growers in field settings on Earth who then take their crops and sell them to production companies.
During the 1990s, NASA’s potato studies with hydroponics got the attention of the Frito-Lay Company in Wisconsin. Wheeler consulted with the company on ways to produce clean, disease-free seed potato stock.
A Source of Recycling
Growing crops in space or on another planet could provide other benefits besides food. Plants could serve to provide oxygen and remove carbon dioxide from air sources.
While plants grow, they generate oxygen through photosynthesis, and they would scrub carbon dioxide out of the air inside a cabin environment. Wheeler said if you co-utilize them in the right manner, they could help process wastewater.
And as odd as it sounds, using wastewater, or even urine, as a source of nutrients for plant growth could be an option. Aboard the space station, U.S. astronauts use the Environmental Control and Life Support System — a system that collects and recycles used water, wastewater and urine.
While the recent movie made it seem like growing potatoes on Mars was a no-brainer, a lot of research has gone into making that a real possibility. With humans expected to plant boots on Mars in the next couple of decades, solving the challenges of growing plants in space today is critical to our journey to the Red Planet.
