Space organizations like NASA and SpaceX say a mission to Mars carrying a crew could happen in the next couple of decades. Scientists need to solve a lot of problems before that can happen. What kind of vehicle will carry astronauts that far (about 56–64 million km)? Once on the surface of the Red Planet, where will they live? What will they breathe?
Those are complex, daunting challenges that will take teams years to solve. But scientists have another, equally fundamental question they must answer for astronauts heading to Mars, one we ask ourselves every day: what are they going to eat?
Scientists have learned a lot about feeding astronauts over the past 60 years of space travel. Still, the longest an astronaut has been in space on a single mission is only 14 months. A Mars mission would take about 2 years, so scientists are studying the molecules in food and exploring new approaches and new technology to keep astronauts on long-duration missions healthy and happy.
Because weight of the cargo on board is a major concern for any rocket launch, it’s unlikely a Mars crew would carry 2 years’ worth of food with them. Some of their food will probably travel ahead of them on a separate rocket, meaning it will have to be processed and packaged so it stays fresh until the crew shows up. But Mars astronauts may also need to supplement these meals with another source of food, one earthbound humans have relied on for millennia: agriculture.
Scientists have been growing food in space for almost as long as astronauts have been living there. Soviet cosmonauts successfully grew Chinese cabbage, flax, leeks, and onions in 1971 on the first space station with a crew, Salyut 1. Scientists wanted to know if plants could grow in space, and they were already thinking about how they would feed astronauts on a moon base or on other long-duration missions.
Fresh vegetables could be key to maintaining astronauts’ health over years in space. Researchers anticipate nutrient deficiencies in astronauts who’ve spent months in space. NASA’s Matt Romeyn says crops grown in space could help plug nutrition gaps. (Even though C&EN wishes his name were pronounced like the lettuce, it’s pronounced “row-mine.”) He works on NASA’s Vegetable Production System, called Veggie, a sort of high-tech greenhouse that’s flying now on the International Space Station (ISS).
Plants can provide nutrients that our bodies take up more easily than those in multivitamins, Romeyn says. Plants also contain many nutrients beyond the essential vitamins that one might take in pill form.
Fortunately, scientists have found that it’s not too hard to grow plants in space. “Plants grow more or less the same in space as on Earth,” Romeyn says. One challenge is watering them. Watering cans don’t work in microgravity, for one thing. More important, water in space doesn’t absorb gases like oxygen, which plants take up from water via their roots. So rather than growing plants in soil or even hydroponically, without soil, plants in NASA’s Veggie system grow with their roots in an enclosed system—in pillows filled with a porous growth medium that provides everything they need. Polyurethane-coated pellets inside the pillows have been designed to release nutrients over months. And the pillows supply water to the plants and allow air to get to their roots.
Astronauts have demonstrated Veggie by growing red leaf lettuce on the ISS. Romeyn says scientists now want to know how space changes the chemical nutrients produced by plants grown there, compared with those the plants possess on Earth. NASA will be sending up kale plants to study how growing in space might change their levels of sulfur-containing glucosinolate compounds, also found in broccoli and brussels sprouts. Although these compounds may have health benefits, too much of them can produce an off-putting taste, as many kids could probably tell you. If the levels change too much, these vegetables might not be right for space missions. Romeyn says NASA will also grow peppers to look at levels of capsaicin, the molecule that makes them spicy.
Growing vegetables isn’t all about nutrition, though. Those first cosmonaut farmers discovered that tending and nurturing their plants had important psychological benefits as well. Romeyn says ISS crews derive enjoyment from growing their plants and having more color in the drab space station. Plants could make even more of a psychological difference on the 9-month journey to Mars, when there might not be much to keep astronauts busy, Romeyn says. “Having something productive to do is beneficial.”
Once a crew reaches Mars, gravity will solve some of the growing problems seen on the ISS. Martian gravity is less than half that of Earth’s, but it still lends weight to things, in contrast with the weightless conditions on the ISS. Romeyn says astronauts should be able to grow plants in martian soil, too, according to past studies. And any agricultural structures built on Mars could play a bigger role than just housing food, including treating wastewater and converting carbon dioxide to oxygen for astronauts to breathe.
Vegetables are great, but they’re not enough for a whole meal. Astronauts on long-duration missions are probably going to rely heavily on processed, packaged foods to provide the rest of the nutrients they need. These aren’t freeze-dried foods like so-called astronaut ice cream (which, for the record, has never actually been eaten in space). They’re similar to the meals ready to eat (MREs) that US soldiers snack on: sealed pouches of precooked food that can be reheated or eaten as is. ISS crews already eat a lot of their food like this, and NASA is now trying to apply the short-term lessons learned from those astronauts to missions lasting years.
NASA scientists are focused on three parameters in their search for long-duration mission foods: acceptable nutrition, acceptable quality, and variety. The second and third speak to a fundamental challenge for space programs: making sure astronauts eat enough.
Scientists know astronauts get less healthy in space. Many lose weight and muscle mass, and the risk of nutrient deficiencies grows with mission length. And astronauts on early missions to a Mars outpost might spend more time in space suits than ISS crews do now, meaning they’ll need to be getting a lot of calories. So it’s important that they want to eat the food that’s available, according to Grace Douglas, the lead scientist for NASA’s Exploration Food System project, which is tasked with finding ways to feed crews on years-long missions. She points out that the military limits troops to 21 days eating only MREs because it has found that after that time, soldiers are so sick of them that they just start eating less.
ISS crews can choose from a menu of about 200 items, including drinks, which Douglas says isn’t as many choices as you might think. NASA and its partners send food and other cargo on resupply missions to the ISS every couple of months or so. Before the ISS, astronauts flying on space shuttles could pick exactly what they wanted to eat on their missions. But Douglas says NASA moved to the 200-item menu to simplify the logistics of feeding crews. She adds that making a menu for a Mars mission will be even harder. For one thing, the food might be launched to the Red Planet before the mission crew has even been selected. NASA hasn’t found perfect foods that all astronauts will like, she says, so the agency has focused on providing variety.
If getting astronauts to eat is half the battle, the other half is making sure their food is safe. Ensuring that food stored on a spacecraft or sitting on a martian plain is both appetizing and nutritious when an astronaut opens the package will depend on how it’s processed and stored. For that, NASA turned to the experts: the US Army.
NASA picked researchers Ann Barrett, Danielle Froio-Blumsack, and others with the US Army Combat Capabilities Development Command Soldier Center to study how packaged, vitamin-fortified foods’ nutrient content and edibility endure years of storage. Barrett’s group studied low- and high-fat versions of a blueberry granola bar and a chocolate-hazelnut drink mix, both of which are low-moisture-content foods. Froio-Blumsack’s team studied higher-moisture creamy Cajun chicken. The foods were all formulated specifically for these space studies.
Both teams periodically tested samples of these foods stored in a room-temperature warehouse for 3 years, as well as samples subjected to accelerated aging at 38 °C. The warehouse conditions are likely similar to what food headed to Mars would experience, with the exception of gravity, although without shielding they might also receive cosmic and solar irradiation, which the army groups did not study.
Barrett’s group found that vitamins A, B-1, B-9, C, and E were adequately stable over that period in the low-moisture foods (J. Food Sci. 2018, DOI: 10.1111/1750-3841.14218). Vitamin B-9 degraded the most, about 25–30%, but it stayed within the range NASA has deemed acceptable for sustaining its astronauts. Some vitamins, like B-1, degraded differently in the low- and high-fat versions of different foods. Froio-Blumsack’s work isn’t published yet, but she says her team found vitamins were stable in higher-moisture foods too. Barrett extended her study to 5 years and found similar stability, and Froio-Blumsack plans to do the same.
Both groups also measured how enticing the food was after sitting in the warehouse. Trained testers found the different foods maintained their quality, although Barrett’s low-fat bars got crumbly—which can be a problem in space, where floating crumbs might get into equipment. Froio-Blumsack says testers didn’t find the Cajun chicken all that tasty at the start of the experiments but that it thankfully didn’t get much worse.
Barrett’s group stored its foods in standard MRE packaging, but Froio-Blumsack’s team also tested different packaging and preservation options. Military MREs use plastic-coated aluminum foil, which is a strong barrier to air and moisture that can degrade food and encourage microbe growth. NASA, however, would like to move away from this packaging to increase the tastiness of its foods. Because of the packaging, military MREs are preserved by pressure-cooking them. Moving to a different method, like microwave-assisted thermal sterilization, which uses short, powerful microwave bursts to kill microbes in food, could in theory lead to higher-quality food. But aluminum foil can’t go in the microwave, so Froio-Blumsack’s group tested layered plastic packaging with an aluminum oxide coating.
The researchers’ tests showed that more oxygen penetrated these plastic pouches relative to foil, but they did not find any microbe growth over the 3-year study. They also tested preservation by irradiation, which NASA uses on fresh cuts of meat sent to the ISS, but that process destroys most of the vitamins in food.
The ISS aside, it has been decades since NASA or any other space organization has attempted a crewed mission on the scale of a moon or Mars trip. And even if the political will and budgets align to make one happen, it will take years more to get it off the ground. But astronauts will need to eat no matter where they’re sent, and the researchers working on their menus know they need to keep working to get their offerings right.
The Mars crew, faced with pouches and pouches of creamy Cajun chicken, will probably thank them.
This article was updated Oct. 7, 2019, to correct a statement about astronauts' nutrient deficiencies. Researchers anticipate deficiencies on long-duration missions but have not observed them yet.