Every year around this time northern school children begin
sowing seeds and tending classroom gardens. It’s a familiar springtime
tradition. But if NASA scientists have their way, this annual
gardening ritual could turn into something much more — astronaut
training!
For future spacefarers gardening will be a matter of survival.
Not only will plants provide food when deliveries from Earth aren’t
possible, but plants will also work to make air breathable and
water drinkable. Plants and people — two very different kinds
of astronauts — will eventually live together in balanced, sustainable
habitats where contact with Earth is a luxury, not a necessity.
This vision of self-contained colonies in space — or even
on other planets — has existed for decades in the pages of countless
science-fiction novels. The growing International Space Station
(ISS) brings that vision closer to reality, but the ISS isn’t
self-sufficient. Its life support systems are strictly mechanical
so food must be ferried from Earth.
"In order to have affordable — and even doable — long-term
exploration (of space), you need to incorporate biology into the
life support system," said Chris Brown, director of space
programs at the Kenan Institute for Engineering, Technology &
Science at North Carolina State University.
NASA researchers at the Kennedy Space Center (KSC) and the
Johnson Space Center (JSC) are figuring out how to do just that.
They’re exploring technologies that could wed people, plants,
microbes, and machines into a miniature "ecosystem"
capable of supporting space travelers indefinitely. This type
of life support system — called "bioregenerative" —
would be fully self-contained, creating an ecologically sound
microcosm where each element supports and is supported by each
of the others.
"If we really want to leave (the Earth) on a permanent
basis, we need to figure out how this blue ball in space supports
all of us, and somehow replicate the parts that are necessary
so that we can move on," said Jay Garland, principal scientist
for the Bioregenerative Life Support Project at Dynamac, Inc.,
at KSC.
Humans and planets are ideal space traveling companions. Humans
consume oxygen and release carbon dioxide. Plants return the favor
by consuming carbon dioxide and releasing oxygen. Humans can use
edible parts of plants for nourishment, while human waste and
inedible plant matter can — after being broken down by microbes
in tanks called "bioreactors" — provide nutrients for
plant growth. Plants and microbes can also work to purify water,
possibly with help from machines. The only input needed to keep
such a system going is energy in the form of light.
This is a simplified portrayal, of course. For scientists and
engineers who are trying to design a real system, the devil is
in the details.
For example, finding just the right plant varieties for the
"space garden" is a painstaking process.
"Plants are going to be central linchpins of the life
support system — or at least the biological part of the life
support system," Brown said.
The ideal space-plant would have short stalks to save room,
would have few inedible parts, would grow well in low light, and
would be resistant to microbial diseases. Research is underway
at KSC to choose varieties of wheat, rice, lettuce, potatoes and
other plants that meet these criteria.
Researchers are also working to develop a "greenhouse"
that will function properly in space.
In an orbiting greenhouse, freely-falling plants don’t feel
the constant downward pull of gravity. As a result, water spreads
out evenly in the soil-like material around their roots, which
makes it harder for both air and water to reach the roots. Researchers
had to choose the size of the granules in the "soil"
very carefully. If the grains are too big, the roots won’t get
enough water; if they’re too small, not enough air. (The right
size turns out to be 1 to 2 millimeters; for more information,
see the editor’s note at the end of this article.)
Also, there is less natural air circulation in an orbiting
outpost — plants can therefore suffocate on their own "exhaled"
oxygen! Designers have to provide fans to keep the air moving.
Researchers caution that ironing out these sorts of details
won’t guarantee a working system when all the pieces are assembled.
"There’s a question of how the complete system will develop
with time," Garland said. "On top of the ecological
concerns of how the various microbe species will undergo succession
(i.e., a sequence of replacements of one species by another
species), you’ve got evolutionary effects. For microbes, with
their short generation times, you’re talking about real evolutionary
time scales for prolonged missions."
To test how the humans, plants, and microbes fare when sealed
together for extended periods of time, JSC is building a test
chamber called BIO-Plex. This facility will incorporate all of
the elements of a bioregenerative life support system — including
the people.
And just in case self-contained bubbles of life outside Earth’s
atmosphere aren’t "sci-fi" enough for you, NASA researchers
are also considering how biotechnology and nanotechnology could
be used to improve such "bubbles" in mind-boggling ways.
For example, foreseeable advances in biotech and nanotech could
make it possible to alter plants’ genes so that their cells produce
little molecular sensors, transmitters, and receivers. These would
monitor the plants internally and report on their health to ensure
a good crop, and could even make the plants controllable, sprouting
and flowering on cue.
Another idea is to engineer plants to produce chemicals that
protect them from the increased radiation in space and on planets
with thin atmospheres, such as Mars. Brown also suggested that
nanotech devices in the plants’ cells could deliver light directly
to the cell parts that perform photosynthesis, making the plants
more efficient.
"There are feasibility issues, but … none of them should
stop us completely," said Brown, who wrote a study on the
potential uses of nanotechnology for these life support systems.
"Maybe we can’t quite do it now, but nothing we are considering
is against the laws of physics or chemistry or nature," he
said.
A bioregenerative life support system will probably never fully
replace the mechanical one on the International Space Station,
Garland added. At most, a small crop might be grown there to provide
fresh food. But eventually, with the help of plants and microbes,
future space stations — or outposts on the Moon or Mars — will
truly become worlds unto their own.
