Left
to right: Chuan J. He, Fred T. Davies Jr., and Ronald E. Lacey grow lettuce
in low-pressure chambers that are prototypes of a bioregenerative life
support system for astronauts living on the moon and Mars. (Photo
courtesy of the Texas Engineering Experiment Station)
(College Station)—Three Texas A&M University System
researchers have discovered that lettuce can grow bigger in low atmospheric
pressure in confinement than it can in earthlike atmospheric pressure in
confinement—a finding that may apply to other plants grown in, say,
greenhouses.
Fred T. Davies Jr., a professor in Texas A&M University’s Department
of Horticultural Sciences; Chuan J. He, a research scientist with the Texas
Agricultural Experiment Station; and Ronald E. Lacey, a professor in Texas
A&M’s Department of Biological and Agricultural Engineering,
have grown lettuce in low-pressure chambers that are prototypes of a bioregenerative
life support system for astronauts living on the moon and Mars.
Lettuce is a very sensitive plant. That it can grow so well in low atmospheric
pressure, 25 percent that on earth, in confinement encourages Davies to
think other plants can too, Davies said.
"Just to demonstrate that plants can be grown in low pressure was important," he
said.
The low atmospheric pressure in the chambers has slowed down so-called "dark-period" respiration,
the process that yields carbon dioxide and energy from carbohydrates and
oxygen in the night, in the lettuce, Davies said. The slower the dark respiration,
the fewer the carbohydrates burned, the bigger the plant.
And the low atmospheric pressure has reduced the ethylene the lettuce produces,
he said. Ethylene is a growth hormone in plants.
"A little bit of ethylene is good: It's needed for growth," Davies
said. "But a lot of ethylene is bad."
Too much ethylene retards the growth of plants. The researchers had predicted
that the low atmospheric pressure in the chambers would stress the lettuce,
the lettuce would produce more and more ethylene, the chambers would trap
the ethylene, and the ethylene would stunt the lettuce, Lacey said. The
opposite of that has happened. And Davies, He and Lacey intend to answer
why, he said, in addition to their first and foremost question.
"The real problem, the real goal, is the less mass you send to space,
the better," Lacey said.
The bioregenerative life support system in the prototypical low-pressure
chambers means the lettuce is not only edible, but also produces oxygen
through photosynthesis and potable water through transpiration and then
condensation. The result may be a lightened payload of a spacecraft bound
for the moon or Mars, he said.
Lacey and three of his graduate students designed the chambers so that
the researchers can lower atmospheric pressure by reducing the levels of
carbon dioxide, oxygen and nitrogen in the chambers. The resultant life
support system may require less of these atmospheric gases. Less atmospheric
gases and fewer containers of them among the payload result in a lighter
payload. And a lighter spacecraft will cost less to launch to outer space,
Lacey said.
"Reducing the pressure is the solution—there's no alternative," he
said.
NASA Advanced Life Support funds Davies, He and Lacey's research. 