Fresh lettuce or a vine-ripened tomato may seem routine dinner fare to many people. But for future astronauts spending a year or more on the moon or Mars, those simple earthly pleasures become mouth-watering delicacies.
Greenhouses in space hold promise for making astronauts more self- sufficient and cutting costs for long missions. Less freeze-dried food, water, and even oxygen would need to be hauled aboard future spaceships.
Although fresh veggies grown in self-sufficient space greenhouses are at least 15 years away, scientists already are testing experimental greenhouses in laboratories on Earth and in harsh environments like Devon Island in the Canadian high Arctic.
"For a mission of a year, it's possible to pack enough food and water," says Rob Ferl, director of the NASA-affiliated Space Agriculture Biotechnology Research and Education center at the University of Florida in Gainesville. "But for a Martian mission we're compelled to take along a recycling or bio- regenerative life-support system so plants can reproduce food from our waste and vice versa. And in the process of making food, we're also making oxygen and purifying water."
President Bush unveiled a plan in January 2004 to send a manned mission to the moon as early as 2015, and to use the moon after 2020 as a launch point for missions to Mars or beyond.
Mars presents tough challenges for both greenhouses and their plant inhabitants. The Red Planet's temperature extremes - which can range from 50 degrees F. in the day to more than negative 200 degrees F. at night - could crack the shell of a greenhouse, and could make the internal environment too cold to sustain the plants.
The thin Martian atmosphere does not screen out deadly ultraviolet radiation. Also, the atmospheric pressure on the planet's surface is less than 1 percent of that on Earth, a situation that causes plants to react as if they were dehydrated and can affect the structural stability of greenhouses. Mars has only about half the light of Earth, so costly artificial light might be needed for plants to grow.
But scientists remain undaunted as they pursue cutting-edge research in genetically modified plants, such as crops that are tolerant of shade or drought, and new materials for flexible greenhouses in extreme environments.
"One thing is absolutely certain. We're not getting off this planet without plants and the microbial systems that do a lot of the recycling for us," says Michael Dixon, director of the Controlled Environment Systems Research Facility on Devon Island and chair of environmental biology at the University of Guelph in Ontario. "We've got to resolve the management issues, and the mass and energy requirements of the plant production system to give us all the food, water, and oxygen we need, and to consume our carbon dioxide."
The Devon facility, running in its third season and growing mainly hydroponic lettuce that uses a nutrient-rich solution instead of soil, comprises more than 20 different chambers of varying sizes and pressures to study plant growth. Other plants that will be studied include beets, soybeans, tomatoes, and peppers.
In fact, food researchers at Cornell University in Ithaca, N.Y., already have come up with a 10-day menu cycle of vegetarian meals for a crew of six.
While much is known about the lunar surface, no Martian soil has been tested yet, so it's not known whether the soil is dangerous or whether it can grow plants. There also is evidence that water once existed on Mars.
"Whether it's still there ... and in significant quantities that can be easily had is another issue," Dr. Dixon says. "If it isn't, life support on Mars is going to be a very tricky thing indeed."
Dixon is not yet convinced that plants will have difficulty surviving in low- pressure environments.
He and Dr. Ferl are in the process of conducting joint experiments to see whether it is necessary to counteract the effects of low pressure.
Ferl says low pressure causes water to move more quickly through plants, making them act as if they are becoming too dry.
"One of the things we might want to do is breed out this response genetically so plants don't interpret this movement of water as a drought and waste any energy," he says.
Ferl is using DNA microchips and fluorescent dyes to look at precisely what is going on inside a plant. There is one benefit of low pressure: Natural hormones like ethylene that cause ripening also move through a plant more quickly, so fruit and vegetables may last longer.
The move to a plant-based diet probably will come in steps, some experts say.
"It will evolve with first using some smaller plant-growing systems that could supply perishable foods like a salad every three days or strawberries once a week," says Raymond Wheeler, lead scientist for plant research at NASA's Advanced Life Support Program at Kennedy Space Center in Florida.
"As you set up an infrastructure on the surface of Mars," he continues, "you would set up sequential missions with slightly more capacity and continue to expand to the point where you increase the autonomy of your outpost's life-support functions."
Dr. Wheeler says researchers also are looking into more efficient light sources should it be necessary to provide artificial light. One of the key initial test beds for Mars may be the moon.
"The moon could be a place to test concepts before undertaking a more difficult mission to Mars," he says.
Researcher Michael Dixon firmly believes that some space-greenhouse technologies should be applied on Earth. For instance, if plants are genetically modified to thrive in shady environments on Mars, they could also be planted in northern climates on Earth.
"For six months of the year, if you're going to grow a plant in Canada, you have to do it in a glass or plastic box with significant energy costs to maintain temperature and lighting," says Dr. Dixon, director of the Controlled Environment Systems Research Facility on Canada's Devon Island and chair of environmental biology at the University of Guelph, Ontario. "If you put shade-tolerant genetics into every Canadian greenhouse plant you would instantly transform the competitiveness of that industry."
Another potential space application for Earth is the management of plant nutrients. The Canadian subsidiary of Dutch company Priva Computers Inc. is working with Dixon on ion-sensor technology that can provide more details about the nutrients in plants. "You could maintain the quality control of your production system in a much more fine-tuned way.... That's required in space, too, because you're recycling everything," Dixon says.
Industry collaborations are a key part of Dixon's efforts. For example: one space technology making its way into industry is a biofiltration system that works in sealed environments, like office buildings, to manage air quality.
The first company to use the technology, dubbed the "breathing wall," was insurer Canada Life Assurance Co. in Toronto. The biofilter, which looks like a tropical garden, resides in its 1,600-square-foot boardroom on three walls, Dixon says. It pulls air out and recycles it back into the room.