Creating a life-supporting ecosystem in space
Posted: March 22, 2002

Tiny light strips, such as ones Cary Mitchell displays in his Purdue University lab, may one day provide the growth source for plants grown and consumed by astronauts during extended space missions. Mitchell, a professor of horticulture at Purdue, is director of the NASA Specialized Center of Research and Training for Advanced Life Support. Photo: Tom Campbell
The National Aeronautics and Space Administration has announced that Purdue University will head a center to develop "advanced life support" technologies for sustaining human colonies on Mars and elsewhere in space.

Purdue received a $10 million, five-year grant to lead the NASA Specialized Center of Research and Training for Advanced Life Support. The center will include 24 researchers from Purdue and two historically black universities, Alabama A&M in Normal, Ala., and Howard in Washington, D.C.

The center's director, Cary Mitchell, said Purdue will help design a self-sustaining environment for future space colonies. Residents will grow their own crops and live inside fully enclosed habitats in which all wastes are constantly being recycled and purified. Plants will provide foods and oxygen for humans, microbes will be used to break down wastes, and other technologies will be needed to remove impurities from the air and water.

"There will be a closed-loop synergy, meaning the wastes of one system are taken in, used and processed by another system," said Mitchell, a professor of horticulture at Purdue.

The habitats will be largely "bioregenerative," meaning biological organisms will help to sustain a life-supporting environment. But engineered systems also will be critical in maintaining that environment. Various devices will be needed to recycle air and human wastes and to purify dirty water from bathing, dish washing and other sources.

"It's exactly duplicating what happens on earth," Mitchell said. "But to make sure that things cycle fast enough, you need some physical and chemical processes to help along the biological systems."

Perhaps people will be living in such "biospheres" on Mars or the moon within only a few decades, Mitchell added.

"Because Purdue is so strong in engineering and agricultural research, it is the ideal institution to lead this kind of center," said Purdue President Martin C. Jischke. "Besides the exciting goals associated with human space exploration, this effort also is very valuable for its potential social impacts gained through educational outreach and developing partnerships with minority universities." U.S. Sen. Richard Lugar, R-Ind., said this research is important for the nation's space program.

"This federal research grant for Purdue demonstrates the university's valuable role in ensuring that the United States continues to lead the world in space-related research," Lugar said. "I commend Purdue officials for their hard work to secure funds for this worthwhile initiative and wish them success in this endeavor."

The NASA advanced life support center is the only one of its kind in the nation. Purdue had led the center for five years beginning in 1990, when Mitchell also was its director. Rutgers University has led research efforts for the past five years. Purdue will again head the center as of Oct. 1, the start of the next federal fiscal year.

"Although there have been differences in emphasis among the three centers, they are all working toward the same goal: that of enabling self-sustaining human colonization of planetary surfaces beginning during the late second or early third decades of the 21st century," Mitchell said.

Universities competing for the NASA center were encouraged to include a minority university with expertise in the appropriate technical fields in agriculture and engineering. Purdue selected not one, but two minority universities as partners --one with exceptional engineering researchers and the other with world-class agricultural scientists, Mitchell said.

"Purdue conducted a nationwide search for minority partners," Mitchell said. "We found the best engineers at Howard, and we found the best food scientists and agriculturists at Alabama A&M."

Research teams will integrate scientists and engineers from all three universities.

Half of the center's funding and efforts will be directed toward research in waste management in space. Twenty percent will go toward systems analysis, and another 20 percent is earmarked for food technology and biomass production, which includes food crops. Ten percent will provide educational outreach.

Kathy Banks, a professor of civil engineering at Purdue University, views a "bio-trickle system" that is part of her work with NASA to develop advanced life support technologies for self-sustaining space colonies. Banks is designing a single system to treat both air and water, which has never been done before. Her system is called BREATHe, for bio-regenerative exhaust air treatment for health. The system will purify both water and air by using microbes. Photo: David Umberger
The center's associate directors, Purdue civil engineering professors James Alleman and Kathy Banks, will oversee the solid waste management and outreach projects, respectively. Banks also will lead research to develop an air-and-water treatment system. Joseph Pekny, a professor of chemical engineering at Purdue, will be in charge of the systems analysis portion of the research.

Alleman said a key strength in the Purdue proposal to NASA was an emphasis on interdisciplinary "team spirit."

His research will focus on systems that break down human solid and liquid wastes. Alleman is developing a "solids thermophilic aerobic reactor," or STAR, which will use bacteria inside a "reactor" to break down solid human wastes. The bacteria will generate so much heat as they break down wastes that the inside of the reactor will approach 90 degrees Celsius, or more than 190 degrees Fahrenheit. Because the bacteria thrive in a hot environment, they are said to be thermophilic, and because air will be circulated through the reactor, the process is aerobic.

Alleman also is developing a system that freezes liquid wastes to remove the salt and leave behind pure water crystals, enabling the salt to be strained out. The technique consumes far less energy than other NASA attempts to purify liquid wastes by boiling.

"It's hugely more cost-effective from an energy point of view," Alleman said.

Banks will lead the water and air treatment research team and is working to design a single system called BREATHe, for bio-regenerative exhaust air treatment for health. The system will purify both water and air by using microbes.

"This combined approach to air and water treatment has never been done before," Banks said.

The system uses microbes in "biofilms" to treat the air and so-called "gray water," or water that has been soiled from bathing, washing dishes and similar uses.

"If you walk across a stream and you slip on a slimy rock, you just stepped on a biofilm," Banks said. "A biofilm is a gelatinous matrix, where the microbes actually grow. Microbes excrete an extracellular polymer, and grow in that slimy matrix. The matrix allows them to attach to surfaces."

Banks' research team will grow specialized biofilms on plastic devices, such as spherical structures, through which air and water pass.

"The microbes will eat, actually degrade, the organic contaminants in the water and the air," Banks said.

Another Purdue researcher is designing a system that will use ultraviolet light to further cleanse the air and water before it is used by the crew.

Other technologies will be needed to recycle plant wastes.

"The human inhabitants are going to be eating mainly a vegetarian diet," Mitchell said. "They are going to have a lot of crop waste -- roots, stems, leaves, things you don't eat. Microbes will digest these wastes with natural enzymes."

The plant wastes, which are inedible to humans, might be ground up and fed to Tilapia fish.

"Thus, the mostly vegetarian diet will be supplemented by small but important amounts of fish protein, which also will have important psychological value for humans living for long periods of time in confinement in space," Mitchell said.

Scientists at Alabama A&M are studying the ability of fungi to degrade crop waste that is inedible by humans, producing shitake, oyster and other exotic mushrooms in the process.

Space diets might be more varied than some people would expect, said Mitchell, who in addition to directing the center will be in charge of research dealing with food production.

People living in space will grow a variety of crops, including legumes such as cowpeas, peanuts and soybeans, and cereal crops such as wheat and rice.

"An important consideration in vegetarianism is to have a mixture of a legume and a cereal," Mitchell said. "Legumes and cereals are deficient of certain amino acids, but if you put the two together, then you end up with a protein that's pretty good."

Space faring farmers also will likely grow other foods, including herbs for seasoning, potatoes and salad crops, such as tomatoes and lettuce.

"We will investigate energy-saving ways to light food crops in space using vertical strips of colored, light-emitting diodes," Mitchell said. "Light strips will hang right in the crop stand with plants growing all around them. These lights are cool enough that plants can even touch them. The colors will match the absorbance of the photosynthetic pigments in the plants. This is a modification of the commercial 'pathlights' you see in movie theaters and in airline exit rows."

Researchers are studying about 15 crops for possible use in the advanced life support system. The work will address a range of issues.

"How are we going to store foods in space so they don't degrade microbially or get spoiled?" Mitchell asked. "How can we grow crops hydroponically, because we are not going to be bringing soil with us? How are we going to grow crops in a reduced gravity environment?"

The moon's gravity is only one-sixth that of Earth's, while Mars' gravity is slightly more than one-third as strong as Earth's.

Sophisticated analytical models will be needed to properly design and maintain the space habitats.

"For example, how much food-crop area do you need to grow to sustain a crew of six people on Mars?" Mitchell said. "Since the crops will be putting out oxygen that people need to breathe, you can't have all the crops maturing at once. When wheat turns brown it stops photosynthesizing and making oxygen. So you've got to have everything staggered. You have to have growth curves, models for each crop, and to stagger them so that there is a continuous minimum amount of oxygen and then to provide a balanced diet."

Pekny's systems analysis component will develop mathematical models critical to helping develop the best possible designs. Using models helps to reduce the amount of experimentation needed by predicting how specific designs will function before they are built.

"One function of the systems analysis group is to develop models of each of the components of the advanced life support system and to hook them together to make sure the system functions overall," Pekny said.

Banks' outreach component will strive to educate schoolchildren and the general public about NASA research and the center's work.

She will combine her outreach efforts with the Indiana Space Grant Consortium, based at Purdue and directed by Barrett Caldwell, an associate professor of industrial engineering. Space Grant is a group of universities and institutions that works with schoolchildren, teachers, college students, industry and museums to increase the public's knowledge about science and space exploration.

The outreach effort will include developing materials and programs for lessons in the public schools.