Interactive model simulates keeping house on Mars

New computer platform for citizen scientists investigates potential closed-loop life support systems for Mars habitat

Illustration of Mars habitat

It’s 2040. You are on the first team to settle on Mars. You live in a habitat that has been designed by the finest minds on Earth. Keeping you all alive is a physicochemical system that produces oxygen, scrubs carbon dioxide and trace contaminants, and regulates pressure. There is also a biological life support system with a full vegetable garden.

You monitor these systems because survival depends on it. Earth is six months away. But humans and plants have different needs and different life cycles. One day the carbon dioxide and methane levels are spiking. You add more oxygen into the hab. But it doesn’t work. The levels climb. The plants die. Months later the resupply ship arrives to find the hab has become a tomb.

Living off world will not be as simple as a science fiction movie. SIMOC — a new scalable interactive model of an off-world community — drives this home. The model is a pilot project from Arizona State University’s School of Earth and Space Exploration Interplanetary Initiative.

A research-grade computer model and web interface for citizen scientists of all ages to design and operate a human habitat on the red planet, SIMOC is anything but a game. It was built on published data for mechanical life support systems (like those used on the International Space Station) and bioregeneration (sustaining human life with plants) with guidance from experts at NASA, Paragon Space Development, ASU and the University of Arizona.

The web interface enables citizen scientists to test Mars habitats of their own design. The objective is to find the minimum complexity required to sustain human life off-world, for long duration missions. And the minimum complexity is not minimal at all.

“It is difficult to find the careful balance of humans, machines, plants, food and electrical power,” said Kai Staats, project lead and a veteran developer of platforms for science research and education.

SIMOC dashboard

“Water and air must be recycled,” Staats said. “In a completely sealed system there is no such thing as ‘throw it away’ nor can you just run down the street to buy more — of anything! Every breath you take, every drink of water you enjoy, every bit of nutrition you consume must find its way back to you over and over again. … The questions SIMOC helps us answer are: How do we transition from mechanical life support systems to something plant-based such that our air, water, and waste are in part, if not in full, recycled by plants? How do we supply locally grown food for long-term, permanent habitation in places far, far from home?”

That’s never been done. All life support systems have been tailored to specific missions.

“From Gemini to Apollo, from the Space Shuttle to the International Space Station, the machines that recycle air and water and process human waste are designed for a finite number of astronauts and a specific mission duration,” Staats said. “To rely entirely on Earth-launched cargo is not only cost prohibitive, but keeps the habitats from becoming self-sufficient and able to expand based on resources available to them, in situ.”

Grant Anderson is the president, CEO and co-founder of Paragon Space Development Corporation and has led the systems and conceptual design of multiple spacecraft. Paragon, which designs and delivers integrated life support systems for aviation and aerospace customers and currently is part of the team developing NASA’s new moon lander for the Artemis program, is a consultant on SIMOC.

According to Anderson, there are two ways to close systems now.

The first is a physicochemical system like the Environmental Control and Life Support System aboard the International Space Station. It provides and controls atmospheric pressure, fire detection and suppression, oxygen levels, waste management and water supply. Water and oxygen is shipped up from Earth and onboard technology regenerates them.

The other is a biological life support system like what SIMOC simulates. It’s essentially a little mini biosphere, not unlike the complex north of Tucson.

“That one is … more complex to some degree because you now are having to keep plants alive that then facilitate — I should say your life support system, but they're all part of the same thing, which is closed life support,” Anderson said. “It's just a matter of how much biology you throw in. … The difficulty is really in the implementation of the growing and control systems for the plants.”

Plants process different amounts of oxygen and carbon and carbon dioxide out of the air in different phases of their life. They tend to grow rapidly and then they mature. Their chemical systems don't slow down necessarily, but they redirect chemicals to start producing seed so they can recreate the next generation.

But humans always exhale carbon dioxide, and they always need about the same amount of oxygen.

“So what you have to do is stagger your growth of plants and stuff to produce oxygen and to take carbon dioxide out of the air, so that there's always plants in the right stage of growth,” Anderson said.

Plant-based systems are tricky because you have to have a backup system if they die. You need a physicochemical system to bridge the gap until you solve whatever biological problem you have.

Ray Wheeler has been working on this problem for decades. A plant physiologist by discipline, Wheeler has been head of advanced life support research and development at NASA for years. Currently there’s nothing biological on the International Space Station except a small garden producing a few leafy greens.

A closed biological system is a wicked problem, Wheeler said. Any off-world missions are going to have some amount of resupply involved.

“When you start looking at all the mass balances that are involved as you get more and more tightly closed in terms of the materials and masses, then yeah, you have a lot of these recycle loops that you have to think about,” Wheeler said.

“And they're sort of an esoteric objective of, 'What does it take to get to full closure?' There's one that's maybe a little more practical for space missions. That's, 'How do you become reasonably autonomous with a high degree of closure, but you're not doubling or tripling your complications by getting every last ounce of whatever recycled?' Where you have a kind of a hybrid system where you might import a little bit of really high-value commodities. … Is it more cost effective to have occasional resupply of a small amount of materials versus trying to make everything and recycle everything on-site? A hundred percent closure is interesting, but it's sort of a farther out call in my opinion.”

Paragon did a study about seven years ago for Mars One, the European organization planning to establish a colony on the red planet. Their question was how fast could a purely biological system be created.

The answer was never, Anderson said.

“We said, 'Well, you'll never get a pure biological system. And second of all, it will take at least a decade to set up the systems, make sure they're running correctly, make sure you understand them before you can start trusting them for longer periods of times, but you will always have the problem of eventually something goes wrong.'

"One of the things I'm famous for saying is we'll have a biological-based environmental control system on Mars when we can plunk a small- or a medium-size nuclear reactor on the surface because you need the light. You can't rely on light from the sun because the dust storms can block out the sun for two months.”

Creating an integrated system, let alone a completely closed life support system, is a huge challenge in itself, said Judd Bowman, founding ASU associate lead on the project and an experimental cosmologist in the School of Earth and Space Exploration.

“After 60 years of spaceflight, we know a lot about the things humans need to consume in order to stay alive in space — exactly how much water to drink, oxygen to breathe, protein to eat in our food, etc. — and we know exactly what we give off in return through breathing, shedding dead skins cells, and things like that,” Bowman said.

“NASA has even compiled a giant list of all of this, like how many milligrams of fingernails the average human grows per day — it’s crazy!  Over the same period, NASA and others have also studied in exquisite detail the rate at which plants can produce the things we need and consume the things we give off, like carbon dioxide. … What I’ve learned from working with Kai and through SIMOC is that, despite all of this knowledge, we are still pretty inexperienced with putting all of the pieces together. We literally can’t make a forest from the trees. We really don’t understand, yet, how to maintain a balanced system over a long term.”

SIMOC is not only an educational tool, but a research tool as well, Staats said. Absolutely everything in space — every rocket, every spacesuit, every habitat — has years of research and validation in models behind it.

“If SIMOC can play a part, supporting PhD researchers while engaging middle school students in habitat design, data generation and analysis, then we will be a part of the next big human adventure story,” he said.

When our species reaches for the stars, we will take the bare necessities to survive, just as past explorers did. Learning how to survive in space will make humans better stewards of Earth.

“And when we come home again, we carry a totally new perspective with which to approach old issues,” Staats said. “Going to Mars is not about abandoning Earth or ignoring the problems we face here, it’s about unifying around a new, great adventure and giving the next generation something bold to aspire to.”

Running simulations on SIMOC, you quickly realize that everything affects everything else. The same holds true for life on Earth, Bowman said.

“Awareness is imperative if we are to climb out of this climate change conundrum we have created,” he said. “SIMOC is a tool for designing Mars habitats, but it is also a means for learning about the large yet closed ecosystem that we already occupy.”

Teaching that to students is one of the reasons the National Geographic Society got behind the project and co-sponsored it, said Tyson Brown, director of the society’s resource library.

“One of the ways I saw SIMOC as a value to students is because though it’s representing a relatively simple environment with just a fixed number of variables, it produces an incredibly complex modeled environment,” Brown said. “If students see how they can scale that up to what’s on Earth where you have an infinitely more complex model, I think they’re going to gain a lot of value and hopefully some empathy for the planet and the ways they can help protect our resources and other species that live on it.”

Developers hope SIMOC will become a valuable tool for researchers. A real hab on Mars or the moon might have its foundation in the simulation. Last year a student team from Dartmouth won a NASA lunar greenhouse challenge using the SIMOC engine for its plant growth models. Staats and his team published a paper at the International Conference on Environmental Systems about their experiment in plant physiology to guide the plant growth model.

That’s a big part of the reason SIMOC consulted with top experts in academia, NASA and New Space companies, and used real NASA data.

“We often talk about video games and movies as incredibly realistic, but that doesn’t make them authentic,” Staats said. “To be immersed in an alternative reality can be wonderfully engaging, but our goal was to build a platform for research and education built on the real thing — expertise in human-in-the-loop closed ecosystems and decades of data. … Three years of studying literature, collecting data, building and testing our models resulted in the platform we have launched — a high-fidelity simulation of a habitat on Mars.”

Understanding the dynamics of running a life support system with all of the different variables and sources and sinks for water and hydrogen, oxygen and carbon dioxide and waste materials is very important, Anderson said.

“If you don't run those simulations, you don't know what you're up against. And you can do 'what if?' analysis without hurting anybody,” he said. “You need to do a lot of that before you get to Mars to understand. Do you have enough contingency to take care of all the potential problems?”

Brown has run simulations many times on SIMOC.

“It’s definitely a complicated task,” he said. “Even when you’re just trying to provide the bare minimum to these folks traveling so far from the reserves we have . … The difference between being 250 miles above Earth and being on Mars is just incredible.”

SIMOC is an ASU School of Earth and Space Exploration Interplanetary Initiative pilot project, funded June 2017 through June 2019. It is now licensed by National Geographic from April 2020 through March 2021, for inclusion in their Education Resource Library.

Top image: Courtesy of Bryan Versteeg of

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