Someday, astronauts may grow food efficiently in space and use plants to clean spaceship air, thanks to a two-year experiment scheduled aboard the International Space Station.

The next space shuttle mission, STS-121, will carry the Tropi experiment's apparatus into space when the shuttle hurtles into orbit after its July 1 scheduled launch. Scientists will study a weed in the cabbage and mustard family, to see if its roots grow more readily toward red or blue light, according to scientists.

"Arabidopsis thaliana is a common weed, which we've found in our parking lots," said Mike Eodice, the experiment's project manager at NASA Ames Research Center, located in California's Silicon Valley. "NASA has selected this plant as a model specimen for space research since the plant's genetic structure has been fully mapped. The plant is also a good research specimen because it is very hearty," Eodice explained.

Researchers will use a small video camera to observe the roots while they grow inside seed cassettes. The cassettes will be housed within a special plant research facility, called the European Modular Cultivation System (EMCS), developed by the European Space Agency.

For three days, the dry seeds will be given water and light, which will allow them to grow to a size of about 1.2 inches (3 centimeters). At that point, the plants are large enough to begin the experiment.

"Plants have several mechanisms to perceive and respond to light stimuli. Their ability to sense specific wavelengths (color) of light is why we are studying both the blue- and red-light-sensing system in the Tropi experiment," said Dr. John Kiss, project principal investigator at Miami University, Oxford, Ohio. "These issues are important for the use of plants to support life on long-term space missions such as spaceflights to Mars," Kiss said.

Researchers also will study how combinations of gravity levels and light affect plant growth. To create different levels of artificial gravity, researchers will spin plants at various speeds on a centrifuge.

The mustard plant experiment is the third part of a comprehensive study of how crop yields could be increased for missions that could last many months or even years. Plants that will be used for food may well be used to filter spaceship air and produce oxygen.

Scientists discovered in previous missions that spaceship parts emit ethylene gas, the same emission that creates the new car smell that consumers notice in automobiles and other new products. Earlier experiments also showed that exposure to the gas produced less starch in the roots of the affected mustard-family plants, and reduced their growth.

"In space, materials off-gas (new car smell) and these emissions can be harmful to plants. We design hardware to eliminate these toxic gasses," said Eodice.

To eliminate emissions of ethylene and other toxic gases, a team of NASA Ames engineers designed and manufactured the most highly sophisticated plant hardware ever built for a space shuttle mission, called the Tropi Experiment Unique Equipment. Engineers designed this machine to prevent the build-up of toxic gases harmful to plants. Ethylene removal is accomplished by special equipment inside the EMCS facility.

After astronauts return the space-grown plant samples from the experiment to Earth, scientists will examine the plants' genes to learn how the space environment has affected plant growth.

According to scientists, further understanding of how plants grow and develop at a molecular level can lead to significant advancements in agricultural production on Earth.

"A better understanding of the role light and gravity play in plant growth has the potential to improve crop yield in arid regions that have fewer resources to support plant life, such as space, water, light, air, or soil," concluded Eodice.

For more information about the Tropi experiment on the Web, visit:

http://exploration.nasa.gov/programs/station/Tropi.html

For more information about NASA and agency programs on the Web, visit:

http://www.nasa.gov/home