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Vegetable Gardening in Space
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# : |
18603 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
4 / 1991 |
2,696 Words |
| Author
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Mark Kliss
Mark Kliss is a research scientist and engineer working for
the Advanced Life Support Division at NASA's Ames Research
Center in California. |
"NASA works on orbiting salad bar" proclaimed a recent newspaper headline. Although this activity initially may sound a bit frivolous, it is just one small part of a much larger and more serious objective: to make future, long-duration space missions less dependent on the supply lines that link astronauts with earth.
Since its inception, the U.S. civilian space program has endeavored to expand human presence and activity beyond earth orbit into other parts of the solar system. One of the requirements critical to achieving this broad objective has been the development of life support systems capable of providing the essentials necessary to sustain human life in space: oxygen, water, and food. During the Apollo missions, life-support systems consisted of little more than storage for these supplies, whose by-products or waste was in turn discarded or returned to earth. For short missions and small crews, the "expendable supplies" approach proved to be both practical and successful.
Because of similar crew sizes and mission durations, the life-support system approach used on the shuttle has not changed significantly from that used during the Apollo missions. Stored oxygen and nitrogen are mixed to simulate the earth's atmosphere. Carbon dioxide exhaled by the astronauts is removed from the cabin atmosphere by circulating cabin air through a canister of lithium hydroxide granules. The used canisters are stored and returned to earth for replenishment with fresh absorbent. All food is supplied, and drinking water and electrical power are provided by combining hydrogen and oxygen in fuel cells. Liquid wastes, such as perspiration, water vapor exhaled by astronauts, and urine, are either vented into space or stored in waste tanks. Solid wastes are exposed to the vacuum of space to remove water before being stored for return to earth.
In the past few years, however, both the National Commission on Space and the NASA task force led by Sally Ride have recommended building systems that support human settlement in space. President Bush has pledged to ensure American leadership in space, calling for the launching of space station Freedom during the coming decade and for a long-term program of human exploration on the moon and Mars. After a point, due to the longer mission durations and potentially larger crew sizes required by these ambitious goals, the expendable-supplies approach is neither economically advantageous nor logistically rational. For example, it currently costs $2,000 to $5,000 to bring a pound of cargo from earth to orbit on the shuttle. At a minimum, each astronaut requires approximately 9.5 pounds of consumables each day: 2
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