Gardens may be an unruly mess on Earth, but in space, we’ll need our vegetable patches to run like well-oiled machines. That’s why researchers at Purdue University are working out the scientifically perfect cocktail of LED light to grow bumper crops in total confinement.
“Everything on Earth is ultimately driven by sunlight and photosynthesis,” said Cary Mitchell, a professor of horticulture at Purdue University in a statement. “The question is how we can replicate that in space. If you have to generate your own light with limited energy resources, targeted LED lighting is your best option.”
It’s long been known that light emitting diodes (LEDs) use far less electrical power per growing area than conventional high-pressure sodium lamps. But if we could figure out exactly what proportions of the visible spectrum plants are happiest guzzling down, we could in theory reduce our space garden power consumption even further. For lettuce, at least, the magic elixir seems to be a 95-to-5 ratio of red and blue LEDs placed close over the canopy. That’s according to a new scientific study led by Mitchell, which finds that this particular cocktail of light achieves the same growth yields using 50 percent less energy than full coverage LEDs, and a full 90 percent less power than traditional lights.
As the conversation about sending humans to live on Mars takes a more serious tone, so does the need to perfect techniques for growing plants off-Earth. If we’re ever to set up a self-sustaining colony on the Red Planet, or send astronauts further afield on a deep space mission, we’ll need space gardens, not only to feed our settlers, but to create self-contained ecosystems that recycle carbon dioxide, oxygen and water. NASA has recognized this need and identified ‘bioregenerative food systems’ as a research priority in a recent draft technology road map.
But life in space is going to be nothing like life on Earth. Out there, resources we take for granted, such as sunlight and air, will become incredibly precious and limited. One of the big challenges facing would-be space farmers, for instance, is the staggering energy cost of the 600- to 1,000-watt lamps traditionally used to mimic sunlight and stimulate plant growth in closed environments. Conventional lighting also creates excess heat, which can dehydrate or scorch plants if growers aren’t careful.
“Lighting was taking about 90 percent of the energy demand,” study co-author Lucie Poulet said. “You’d need a nuclear reactor to feed a crew of four people on a regular basis with plants grown under traditional electric lights.”
As weed growers and future space farmers alike are discovering, we can do a lot better with LEDs, which can be programmed to only emit the choicest parts of the visible spectrum. Plants throw away a large portion of the sun’s energy, preferring for evolutionary reasons to use red and blue light above all other colors. After some tinkering in the lab, the researchers discovered that feeding lettuce a red-heavy diet with a dash of blue led to the highest yields, while slashing energy consumption by a factor of ten.
There’s plenty more work to be done—Mitchell’s group, for instance, is now focusing on fine-tuning when to increase and decrease lighting throughout a plant’s life cycle. Once we get this process optimized for leafy greens, scientists will move on to more light-demanding plants, such as tomatoes and corn. Others are taking a broader perspective, prototyping bioregenerative systems in which plants recycle water, nutrients, and atmosphere.
It may be shrink-wrapped meals on the cosmic menu for now, but by the time you’re taking a Virgin Galactic cruise to Europa, ordering a fresh salad might not sound so crazy.