Growing food for space travelers

By: David Morgan

No one said space travel would be easy. President Bush, who is boldly proposing Mars exploration, recognizes that costs will amount to the billions of dollars in research before an astronaut can climb into space gear.

Among the more perplexing problems is how spacemen can generate food for travel that may last three years, too long a period of time for storage. Simply put, tomorrow’s space explorers will have to be self-sustaining farmers, producing enough "salad bar" items - fresh greens and vegetables - to nourish themselves during travel time and exploration.

Consider the obstacles to growing plants for food:

  • Atmospheric pressure - moon = 0; Mars = one hundredth that of the Earth’s.
  • Gravity - moon = one-sixth of the Earth’s; Mars = two-fifths.
  • Mars’ atmosphere is 95 percent carbon dioxide and receives only half as much light as the Earth.
  • There is no carbon on the moon for photosynthesis
  • Poor soil, no water, heat and cold extremes

  • Plant scientists have learned that they can grow almost anything in growth rooms that supply the correct amounts of light, heat, water and nutrients, but the expense of carrying such equipment into space is prohibitive, as much as $15,000 a pound.

    Dr. Fred Davies and his colleagues at Texas A&M University, College Station, have determined that by growing plants in modified growth rooms under lower atmospheric pressures they can attack some of these problems. Growing under low pressure means that:

  • Less structural material for housing and growing plants needs to be shipped into space
  • There is less leakage of oxygen, nitrogen and carbon dioxide gases from a low-pressure crop production atmosphere into the vacuum of the moon or Mars
  • Lower total levels of nitrogen, oxygen and carbon dioxide would be required, which otherwise would have to be transported or produced artificially in space
  • With an external oxygen supply, astronauts could tend crops down to a third of normal atmospheric pressure without having to suit up into cumbersome space suits.

    Davies and his co-workers designed six low-pressure chambers to control atmospheric pressure from ambient to very low pressures, and can also control the partial pressures of nitrogen, oxygen and carbon dioxide. In these chambers, they have been able to germinate seeds and grow seedlings of lettuce and wheat.

    Interestingly, plant growth under low-pressure conditions has been better than ambient conditions, because in a tightly sealed environment ethylene gas levels build up, causing abnormal plant growth and sterility, whereas ethylene production is generally reduced under low-pressure conditions.

    In addition to growing lettuce and wheat, Davies and his associates have shown that:
  • Plant gas exchange is not adversely affected; that is, photosynthesis and stomatal conductance are similar to ambient pressure conditions.
  • Dark respiration, which occurs at night, is reduced in a low-pressure system. This means there is more overall plant "dry mass" accumulation, since not as much carbohydrates and other compounds are consumed during the night. In other words, there is greater plant yield.


    Davies recognized that beside their obvious food use, plants play an important psychological role in human health and well-being.

    "It is known that some of the favorite experiments of the Russian cosmonauts were with plants and seedlings that they could nurture, harvest and eat," he said. "Just biting into something with some turgor to it, and not having a diet limited to reconstituted foods has important psychological benefits. In the Antarctic, which is one of the most desolate places on Earth, there is a small greenhouse at one of the U.S. bases for supplying salad bowl crops. It is also one of the most popular places on the base, where crew members will retreat from the cold, white, barren, snow-capped landscape to recharge, rest and nap in hammocks stretched across the green visual of live, growing, green plants. It is those bright, light colors, aroma, texture and flavor of plants that attract [us] humans.

    "Small wonder that the greatest pastime in the U.S. is gardening. It will also be an important activity as humankind colonizes space during the 21st Century."

    Davies’ research is supported in part by NASA grants. His co-workers include Chunajiu He, Ronald E. Lacey and Que Ngo.
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