Lettuce and LEDs: Shedding New Light On Space Farming
By Todd Halvorson
CAPE CANAVERAL, Fla. -- Ask most astronauts and cosmonauts what type of food they miss most on the International Space Station and they'll tell you fresh salads are a culinary commodity craved in orbit.
That situation, however, soon could change.
Researchers here at NASA's Kennedy Space Center are parlaying the technology used to develop the latest traffic signals into a salad machine that could enable station crews to grow and harvest their own greens within the next three years.
What's more, the type of advanced lighting systems now used in sprawling airplane maintenance facilities, automotive assembly lines and semiconductor clean rooms are being tested for potential use at Martian greenhouses.
And while a human expedition outside Earth orbit still might be years away, the space farming efforts are ultimately aimed at developing artificial light sources that promise to help make future explorers self-sufficient at space colonies on the moon, Mars or beyond.
"We know for a long-duration mission, say going to Mars, that there will be too much launch mass involved in order to take everything you need," said Gregory Goins, a research scientist with Dynamac Corp., the life sciences contractor here at NASA's coastal Florida spaceport.
"You just can't put enough in the picnic basket to survive."
So Goins and other Space Age gardeners are testing two high-efficiency light sources that future space colonists might use not only to grow food but also to generate and purify oxygen and water -- key sustainers of human life.
The removal of carbon dioxide from a closed environment is another added benefit.
"Plants are the only way we know of where we can generate enough food, water and oxygen to support humans for such a long flight because we know re-supply is not an option. And so plants are a very appealing approach to use," Goins said.
"But in order to use plants, you must have an energy source, and that energy source is light," he added. "And the lights we use in our homes are not energy efficient enough to get the job done. So that's why we're developing these innovative technology lights."
Take the common incandescent bulb invented by Thomas Edison more than a century ago, or the type of fluorescent lamps first developed in the 1920s.
Both contain electrodes that burn out, so the lights must be periodically replaced. And both gobble up electrical power -- a precious commodity in space -- while generating heat, which must be dispelled from closed environments such as spaceships and space stations.
"Standard light sources that we use in homes and in greenhouses and in growth chambers for controlled agriculture here on Earth are not efficient enough for space travel. Not only that, they don't last a very long time," Goins said.
"And in space, heat is like trash. You make it, and you've got to get rid of it, so we don't want heat. We want light."
In recent years, dramatic improvements in lighting technology have provided NASA and its support contractors with new means to develop low-power space-farming systems that will last the life of a building -- or a greenhouse on the surface of Mars.
Working in plant growth chambers the size of walk-in refrigerators, Goins and other plant physiologists here are experimenting with blue and red Light Emitting Diodes, or LEDs, to grow salad plants such as lettuce and radishes.
Similar to devices now used to manufacture advanced traffic lights, the LEDs enable researchers to eliminate other wavelengths found within normal white light, thus reducing the amount of energy required to power the plant growth lamps.
The LEDs generate less heat, and while leaves take on a black hue due to the lack of green light to reflect, the plants grow normally and taste the same as those raised in white light.
"What we've found basically is that we are able to limit the amount of color we give to the plants and still have them grow as well as with white light," Goins said.
"Being plant physiologists, we know the chlorophyll molecule well enough that we know which wavelengths most efficiently stimulate plant growth, and it turns out to be blue and red. So I don't have to devote energy to green light, and my plant will grow just as well."
Nevertheless, green light can be added for aesthetic purposes.
"So if you're in orbit for a long time, not only do the plants taste good but they actually appear as plants do on the ground," Goins said. "But we also know we can eliminate the green light if energy costs are a concern -- and they usually are in space travel."
Another bonus: The LEDs can last the length of a round-trip mission to Mars, unlike incandescent or fluorescent bulbs, which require frequent replacement.
A second long-lasting light source being tested here: Sulfur Microwave Lamps.
Now used to light up large airplane hangars, shopping malls and gymnasiums, these high-performance lamps were first developed in 1991 and one day might be used to light conservatories on the surface of Mars. "The microwave lamp is a technology where we're thinking about a large-scale system like a greenhouse on Mars, where we can illuminate a large growth area," Goins said. "It is the most efficient electric lighting source known to man."
Twice as efficient as other high-intensity sources, the microwave lamps can generate as much light as the noonday sun. The light in fact is so bright that it can be funneled through pipes and then distributed over large areas, such as a hothouse on the Martian highlands.
The lamps also are dimmable, so space colonists would be able to attenuate light within their greenhouse to match the growing cycles of their crops.
"When there are small seedlings, you don't want a very bright light," Goins said. "But then you could turn the lamps up accordingly as the plants got bigger."
The bulbs, meanwhile, are simple hollow quartz spheres with sulfur and argon gasses that are energized with microwaves. And with no filament to burn out, researchers think the lamps could prove to be the perfect light source for a space colony.
"Theoretically, the microwave lamps should last for years and years, and we've found that to be the case," Goins said.
With an investment of just $80,000 to $100,000 over the past three years, the high-tech lighting systems here have been used to grow potatoes, sweet potatoes, lettuce, spinach, radishes, wheat onion and a whole plethora of herbs such as marjoram and parsley.
The plants typically are grown hydroponically, or without soil. Water laced with a nutrient solution is circulated within plant growth chambers that are lit up with either the LEDs or the Sulfur Microwave Lamps.
And while greenhouses and space colonies on Mars are still a long way off, Goins said a specially designed LED plant growth chamber should be ready for launch to the international station within the next three years.
"I would probably call it a salad machine," Goins said.
About half the size of a tall file cabinet, the plant growth chamber would enable station astronauts and cosmonauts to grow and harvest salad greens, herbs and vegetables during typical four-month tours on the outpost.
"Now this salad machine wouldn't be built on a scale large enough to actually give the crew all the food they need," Goins said. "It would be just a supplemental endeavor in the near term."
But it would have psychological benefits for station crews, too.
"When you're inside a can for several months, I can see where having something green and living onboard would be very appealing," Goins said.
"So to have an herb garden or a salad machine actually on the space station would make the stays in space more pleasurable," he added. They would just love that."