This is the first of a two-part series on preparations for upcoming human space missions to the Red Planet.
Mark Watney has found himself stranded on Mars. It’s 2035 and his crewmates, thinking him dead, have left him behind in their evacuation of the Red Planet. He faces years, all alone, trying to survive in the face of radiation, storms and little food.
That last problem turns out to be a solvable one. Watney is a botanist. And he figures out how to grow potatoes. The potato seedlings come from his Thanksgiving dinner. Water is derived from leftover rocket fuel. And his own poop becomes fertilizer.
This scenario, from the book and movie The Martian, is science fiction. It is, however, based on fact. NASA studied potatoes in the 1980s and 1990s as a potential crop for human space missions. And though no one is yet growing potatoes on Mars, scientists are already developing tools to grow food in space.
Why? People will likely travel to Mars sometime in your lifetime. NASA has said it plans to send people to Mars in the 2030s. And the private space company SpaceX may send its first crewed mission to Mars as early as 2024.
But ferrying humans to Mars would be a much bigger challenge than getting them to the moon. To pull it off, we first need to solve a lot of problems. Getting to Mars is just one of them. Then we have to figure out where our food and water will come from. Planners also must figure out how space travelers will get any tools they may suddenly need when they’re millions of miles from the nearest hardware store. It’s a huge undertaking, but researchers around the world are already on the job.
Today’s space travelers don’t go to the moon or Mars; they head to the International Space Station (ISS). It’s orbiting 381 kilometers (237 miles) above Earth’s surface. There, astronauts live for weeks to months. Among their tasks are conducting experiments and testing equipment that could be useful for future missions to the moon, an asteroid, Mars or beyond.
If you visited the ISS today, nearly every bit of food you ate would have been shipped up from Earth. The exception: leafy greens. Those are the first foods being grown on the ISS.
There are many reasons NASA wants to learn to grow vegetables in space. Besides providing fresh food for astronauts, plants can provide life support by recycling air and water. “There’s also the psychological benefit that growing plants may have,” says Gioia Massa. She’s a plant scientist and the head of NASA’s Veggie Project at Kennedy Space Center in Cape Canaveral, Fla.
As Mark Watney learned on Mars, potatoes might be good survival food. They’ve got decent amounts of protein, some vitamins and other nutrients. They’re also rich in carbohydrates (sugars and starches). You couldn’t survive on potatoes alone. They could, however, help to keep you from starvation.
There are some downsides, though. Potatoes need to be cooked before they can be eaten. And potato plants need a lot of room to grow. So Massa and her colleagues started with something easier: lettuce.
In 2014, they sent ISS astronauts a garden. Lettuce seeds were packed into “plant pillows” with baked clay and fertilizer. Add water, some artificial light and voila! The lettuce grew!
But the astronauts couldn’t eat it.
They had to send every bit back to Earth to be studied. The next year, after NASA scientists confirmed this food was safe, the astronauts grew a second crop. This time they were allowed to chow down.
The astronauts used their lettuce to garnish hamburgers. They also made lettuce wraps with lobster salad inside. “They got really creative,” Massa says.
Not surprisingly, gardening is different in space than it is on Earth. Without gravity, plants don’t know which way is up. But they adapt. They send their shoots toward light and their roots in the opposite direction. Fans must circulate air. Otherwise, oxygen would gather in a ball around the plants, and they wouldn’t have enough carbon dioxide to do photosynthesis.
The scientists also had trouble providing the plants enough water. The fabric plant pillows containing the seeds, clay and fertilizer were designed to draw water from a reservoir. But they didn’t work fast enough. The astronauts ended up needing to water the plants by hand. Massa and her team are now redesigning the watering system.
ISS astronauts also have grown Chinese cabbage as well as flowers. In addition to being pretty, astronaut Scott Kelly’s garden of zinnias helped scientists study whether plants flower in space. They do! That’s important to know, because flowering is how some plants reproduce. It’s also part of how some plants make fruit.
Future crops will include a bitter Asian green called mizuna and cherry tomatoes, which astronauts will have to pollinate by hand using a tiny brush. “We don’t have bees up there,” notes Massa. One day, they might also grow peppers and herbs.
While the veggie garden is small for now, eventually it could someday help feed astronauts on long-distance space missions — or a colony on Mars. “Everything we do is a stepping stone,” Massa explains.
Building a faster engine
Reaching the ISS from Earth takes less than a day. A trip to Mars might take nearly a year — and a huge amount of fuel. The chemical engines used to launch a rocket into space with a fiery blast are not good at propelling a spacecraft to another planet. With no gas stations between here and Mars, “You pretty much have to take all your fuel with you,” says Bill Emrich. He’s a nuclear engineer with NASA at the Marshall Space Flight Center in Huntsville, Ala. “If you’re going to do that, you want an engine that’s going to get a lot of miles per gallon.”
To do that, he says, you have to go nuclear. The right engine can take a very light gas, such as hydrogen, and heat it to extremely high temperatures in a nuclear reactor. That super-heated gas is sprayed out the back through a nozzle to propel the spacecraft forward. “The hotter you can make the gas coming out of the nozzle, the more efficient it is,” Emrich explains. “Also the lighter the gas, the more efficient it is.”
Nuclear engines aren’t just efficient, they’re fast. Unmanned spacecraft have been sent to the outer solar system using what’s known as ion propulsion. It works by accelerating electrically charged atoms, or ions, to push a spacecraft forward. Such a system could take a year to deliver people to Mars. In contrast, a nuclear thermalengine might shorten that journey to just four or five months, Emrich says.
To get to Mars that quickly, a large spacecraft would need about 230 grams (a half pound) of uranium fuel. Uranium is radioactive, but the uranium fuel isn’t dangerous. “You could easily hold it in your hand and it wouldn’t hurt you,” Emrich notes. But once the reactor starts to operate, the uranium is split into other elements through fission. That’s when you have to be careful. “Those [fission products] are really very radioactive. And that’s where the deadliness comes in,” he says — “not from the uranium itself, but from the byproducts [of fission].”
This system would get rid of one big worry: Even if there were an explosion at lift-off, humans and Earth’s environment would be safe. Why? The spacecraft would use conventional rocket fuel for lift-off. The nuclear-heated engine would not be turned on until the rocket was already in space. Then if there were any explosion, any radioactive material would be spewed into space.
Emrich and his colleagues are working on testing the uranium fuel for this engine. Others are working on different parts. Some are looking to develop and test the reactor. Others are designing a way to integrate the reactor into the propulsion system.
Building this next generation of space engines takes time. “If we have plenty of funding, it could probably be done in 10 to 15 years,” Emrich says.
Astronauts headed to Mars will have to take along almost everything they’ll need. They might be able to harvest some raw materials from the Red Planet. But afterward they’ll need some way to use them. “We have to be much more Earth-independent” than on missions closer to home, says Niki Werkheiser. Like Emrich, she too works at NASA’s Marshall Space Flight Center.
Astronauts on the ISS have similar problems. If someone needs a special tool, they might have to wait months or longer for the next resupply mission. Werkheiser hopes to change that. She’s the lead scientist for a program that is bringing 3-D printing to space. With 3-D printing, astronauts could build the tools they need with the push of a button.
A 3-D printer works a bit like a hot-glue gun. Following a pattern on a computer, the printer squirts out a layer of polymer onto a tray. After this hardens into a plastic, the printer will add another layer. Then another. And it will keep this up until it has built a three-dimensional object. “You can do some really complex designs,” Werkheiser says. “You can build things with gears inside and moving parts — all in one print.”
On the ISS, printing tools could save time and money. But such printers also offer other benefits. Many of the tools and gadgets sent to space on rockets are made from strong materials. To survive the stresses of launch, they also are heavily reinforced. If they were printed in space, they could be made lighter and thinner, with more room in them for electronics, scientific instruments or other pieces. Such make-your-own tools may even be a necessity on a mission to the moon or Mars, where the delivery of spare parts may not be possible.
Printing in space doesn’t work exactly as it does on Earth. For instance, fans are needed to circulate air around the object to cool it during printing. But there are some advantages, too. “On the ground, gravity can actually cause some problems with 3-D printing,” Werkheiser says. Since hot plastic is flexible, earthbound printers sometimes need to add support structures to hold an object upright as it cools. I space, a printer can build in any direction.
Werkheiser's team sent its first 3-D printer to the ISS in 2014. It printed paddle-shaped objects as a test. These were then compared to ones printed on Earth. “We really did not see any meaningful difference,” she says.
Next, Werkheiser hopes to launch a printer this coming spring that can recycle plastic wastes into the material for printing new objects. And in the future, NASA hopes to develop a fabrication laboratory (the “Fab Lab,” for short) that will be able to print things — even electronics — out of metal.
So now that the astronauts can print tools on demand, what was their first request? “We designed them a little back scratcher,” Werkheiser says. It turns out, the dry air on the space station causes astronauts skin to get itchy. Sometimes, at least, the problems of space exploration have very simple solutions.