The dream of sending humans to Mars presents a number of scientific challenges, not the least of which is: what do you eat on a planet where nothing grows?
Last month's announcement that NASA had discovered very strong evidence of flowing water on Mars renewed excitement over the possibility of humans living on Mars, as we prepare to send astronauts there within the next few decades. But if humans are going to survive on Mars, even temporarily, we need more than salty, cold water—we need food.
That's why, for almost eight years, researchers based out of the University of Arizona have been working on a design for a martian greenhouse that would allow astronauts to grow food and, just as importantly, produce oxygen.
"We operate it like a greenhouse, but it's not just a food production device. It's a fresh water generator, and the plants also keep us alive because plants make oxygen and we give the plants carbon dioxide," explained Gene Giacomelli, a horticultural engineer and co-principal investigator for the project, part of UA's Controlled Environment Agriculture Center. "It's a small, bio-regenerative life-support system and that's what NASA has, for many years, tasked us to develop."
Giacomelli explained that the project has actually been underway since 2000, but it wasn't until 2008 that NASA could provide the team of 20 researchers with a Steckler Space Grant to fund the project and start building the greenhouse. Now, they've got a fully-functional prototype of the kind of structure that could sustain life for astronauts on Mars. The collapsible, lightweight, tube-like greenhouse is 5.5 meters long and 2 meters in diameter, and would actually just be one part of a larger habitat structure the researchers have designed.
"We said, 'well we can't make a greenhouse unless we build a habitat around it,'" Giacomelli said. "It's an appendage at the end of a 30 meter long appendage that is enough to allow one astronaut to survive, and there would be four appendages."
The entire habitat is designed to be autonomously unfurled and assembled (possibly with robotic assistance) upon landing so that everything would be growing and ready to go by the time astronauts arrived several months later. The greenhouse would create a kind of micro, hydroponic version of the Earth systems required to support life.
The hydroponics system allows the plants to grow without soil, while artificial light ensures the plants are able to grow efficiently. A composter unit reclaims water from astronaut waste and plant material, and reuses it to feed and water the plants. An HVAC device pulls moisture out of the air to give the astronauts clean drinking water. But the greenhouse isn't entirely self-sufficient: it would require very specific planning and cultivation by the astronauts in order to sustain life, both plant and human, Giacomelli said.
"You have to go in there and grow in some logical order and procedure so that you're harvesting and transplanting at the same time, never having open space, because it's expensive and energy-intensive space that you'd be wasting if there's no plant there growing," Giacomelli said in a phone interview. "And then you have to be careful that you don't eat too much or else your oxygen production won't be sufficient. You could have a big party tonight, overeat too much, and the next day not have enough oxygen for everyone to survive."
But he said that's not likely to happen, because that's what the team's research is for. There are a lot of challenges to consider: how much water can astronauts drink each day without running out? How do you balance the amount of food an astronaut needs to survive with the number of plants that need to be alive to produce enough oxygen to breath? What crops would be the most efficient, both for growing and for providing nutrients to astronauts? Giacomelli and the rest of the team are considering all of these factors to make sure we know exactly what we need to do to survive before we ever set foot on Mars.
So far, the team has only built one working prototype of the greenhouse, but they plan to build three more to give a true idea of what the greenhouse layout on Mars could look like. They've experimented with different crops, including strawberries, basil, sweet potatoes, and tomatoes. Giacomelli said that since the unit is all self-contained, they don't have to fuss much with the environment on Mars—the habitat would be isolated from the harsh atmosphere of the Red Planet. The only variable that would still affect the habitat is Mars's gravity, which is a little more than a third of Earth's gravity. But when astronauts on the International Space Station enjoyed fresh-grown lettuce in zero gravity this summer, it showed you don't need any gravity to grow at least one crop.
Giacomelli said the next steps will be expanding the prototype and, eventually, sending a testing unit to Mars to make sure everything functions properly. He said there's been a renewed interest in the research in the wake of NASA's announcement and with the film The Martian hitting theaters, but their team has been living with the idea of greenhouses on Mars for more than a decade.
"It's not so exciting, to be truthful. What we're doing is growing plants in a logical sequence and order to meet our market demands," Giacomelli said. "Of course our market demand is four people on Mars that need oxygen to breath, water to breath, and energy from food."