A version of this article appears in the July 7 edition of Aviation Week & Space Technology.

International Space Station crewmates are looking forward to a little more fresh food with their processed nutrition, thanks to a new plant-growth chamber delivered by the most recent SpaceX Dragon to reach the orbiting outpost. Developed by Orbitec in Madison, Wisconsin, the “Veggie” unit is a very small farm—11.5 X 14.5 in.—that will allow the crew to grow red romaine lettuce for researchers to evaluate and them to eat. Like much of the work on the ISS, the “Veg-01” experiment is aimed at the thorny problem of keeping deep-space explorers alive on long-duration missions to Mars.

“Those plants can help with carbon dioxide removal and generating some other products that are beneficial to us, as well as providing a food source,” says William Gerstenmaier, associate NASA administrator for human exploration and operations (HEO).

Engineers working for the HEO and space-technology NASA mission directorates have a huge task ahead of them in environmental control and life support systems (Eclss) as they prepare for a Mars mission, and Veggie is just a part of it.

“When we go to Mars, this will be a definitively closed system,” says Sam Scimemi, the ISS program director at NASA headquarters. “There will be no resupply. There will be no repair parts. There will be no ground analysis. It will all be closed within the spacecraft and the humans together to go to Mars.”

The unique station environment is the only place to test Eclss hardware for that long journey. The ISS has “dissimilar redundancy”—a key concept in exploration architecture (AW&ST June 23, p. 29)—in its U.S. and Russian life support, but it must rely on its proximity to Earth for the consumables that make the systems work.

“Our life support system is about 86% closed now,” says Gerstenmaier. “We recycle urine. We recycle moisture out of the atmosphere. We take waste carbon dioxide and generate more water from that, and then the waste gas that comes out of it is methane. So everything is fairly closed cycle.”

That is not good enough for a Mars mission. On top of the recycling shortfall, station engineers are learning that today’s Eclss hardware has an engineering oversight that must be corrected before the life-support loop can close. The problem centers on the urine recycling system, which processes the human waste into potable water. It is a complicated piece of gear that requires careful maintenance (see photo), but it works—up to a point.

“With the urine processor, we can only recycle so much of the urine because we end up where, essentially, the brine that’s generated clogs up all our pumps, and stops the system from working and operating,” Gerstenmaier says.

NASA engineers are trying to find ways to wring the last drops of moisture from the brine, Gerstenmaier says, but that addresses the symptom instead of the underlying problem: the humans who drink the recycled water, and what happens to their bodies when their bones no longer have to support them in Earth’s gravity.

“It turned out, when we were having all the bone-loss problems, [that] the biggest constituent of the urine was actually bone, or calcium,” Gerstenmaier says. “And that was causing all our pumps to clog up. So here the humans [are] destroying the mechanical system that’s supposed to provide water for them. It’s the ‘perfect system the engineers built,’ because we tested with reference urine on the ground, which didn’t have the high calcium content because nobody had that high a calcium content on the Earth. So the standard urine that you get to practice with wasn’t really urine that was on board [the] station.”

For Gerstenmaier, the lesson is to pay more attention to the crew’s biological output as well as the air, water and other inputs Eclss must provide for their survival. “I think we need to look at it as more of a system than we have before,” he says. “It’s intriguing when I think about this; the human is really now a piece of the spacecraft.”

NASA and its ISS partners are paying close attention to lessons like this, which illustrate the station’s utility as a laboratory for deep-space exploration. The upcoming year-long stay by astronaut Scott Kelly and cosmonaut Mikhail Kornienko will be a chance to learn more.

Of course, there is another lesson in the urine-calcium discovery, and it is as plain as the changing blue Earth spinning below the windows of the station cupola. In the 60-plus years that we have been observing Earth from space, the human impact has been on view in the growing urban sprawl, dwindling forests and melting polar ice. Sophisticated instruments that view the invisible effects of human activity on the planetary Eclss only underscore what the astronauts see. As an engineer, Gerstenmaier gets it.

“It couples right back here to the Earth,” he says. “The Earth is the ultimate closed system, and how do we do things that perturb the Earth? And don’t realize what they do? And they have long-duration impact.”