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It’s been 40 years since the first human walked on another world, and 37 since the last. From 1969 to 1972, before public interest and political will fizzled, the United States’ Apollo program ferried 12 American men to the surface of the Moon and back to Earth. Today, the list of moonwalkers is set to become much more diverse. China is poised to send crews in coming decades, and explorers from India, Japan, Russia, and the European Union may not be far behind. The US is also planning to return, this time in a more sustained fashion: NASA engineers have ambitious plans for lunar outposts, followed by human missions to Mars.
Most space agencies in this burgeoning Moon race are understandably focused on rocketry. Plans for human interplanetary missions will be moot without powerful (and very expensive) launch vehicles and spacecraft capable of reaching beyond low-Earth orbit. But even if new rocket armadas are built, their missions will be just as fleeting as Apollo’s—unless technologies are developed and deployed to allow human beings to live off-planet for lengthy, perhaps indefinite, periods of time. As NASA occupies itself creating a new generation of rockets, other space agencies are stepping in to meet this separate challenge, crafting advanced life-support systems that may ultimately enable interplanetary colonization and the human exploration of deep space.
Staying alive is quite hard without the help of a benevolent world like Earth. Each breath you take depletes oxygen and releases carbon dioxide, and your body quickly converts all food or water you consume into liquid and solid waste. Earth’s ecosystems process and purify all this, essentially for free. In a sealed container traveling through the interplanetary vacuum, freed from Earth’s weighty pull and protective magnetic field, you’d also have to contend with microgravity and high levels of cosmic radiation, but at least you’d be unlikely to freeze—instead the waste heat from your metabolism would build up within the unventilated enclosed space until you overheated and died.
To survive, astronauts need food, water, and air, all sent from the Earth at a very high price—each pound of material lofted into space costs upward of $10,000. To maximize these precious resources, a spacecraft’s “physicochemical” life-support system recycles water through purifying membranes and uses electrochemical processes to replenish air with oxygen and scrub it of carbon dioxide. Bodily waste is typically sequestered and jettisoned to burn up in Earth’s upper atmosphere.
These practices work reasonably well for the International Space Station, only some 300 kilometers above the Earth’s surface, or even for the three-day trip to the Moon. But for extended space voyages or long-term bases on other worlds, even if all the air and water is efficiently recycled and purified using physicochemical systems, bringing along enough food can prove problematic.
“Food is what limits the equation in terms of long-term human space exploration,” says Mike Dixon, an environmental scientist at the University of Guelph in Ontario, Canada. For a lunar base with dozens of people, supplying food from Earth is feasible, Dixon says, but still prohibitive because “you’ll spend all your payload mass just supplying dinners for lunar explorers.”
Dixon and other researchers think the solution to the food problem is for astronauts to grow their own. In collaboration with the Canadian Space Agency, Dixon directs multiple initiatives to investigate how to cultivate plants and maintain ecosystems off-planet. One of his projects is a greenhouse in the Canadian Arctic. His Controlled Environment Systems Research Facility at Guelph is considered the world’s best for investigating plant growth in unearthly low-pressure atmospheric conditions.
“For extended human activities on the Moon or Mars, you must have self-sustaining biological systems, systems that are regenerative,” Dixon says. In other words, green plants. “They give you oxygen, consume your carbon dioxide, and recycle your water. And you can eat them. As life-support machines, they have no equal.” The problem is, plants require “life-support systems” of their own.
“The infrastructure and power required to support plant-based regenerative life support is actually quite large,” says Sherwin Gormly, an environmental engineer developing physicochemical life-support systems at NASA’s Ames Research Center in northern California. “When you examine how much material you’d need to launch to establish the system and keep it going, it’s hard to justify,” he says. “And then you have to actually spend time working with the plants. If you invest the money to put people on Mars, it’s going to be tough to justify crew time to tending tomatoes.”
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