Seed pods from a commercial gardening experiment aboard the ISS are back on our planet. The far-out pods could hold the key to long-term habitation of space.

by Dr Tony Phillips and Patrick L. Barry

When the space shuttle Atlantis returned to Earth in July 2001, it brought home some unusual cargo - seed pods grown in space. They were the harvest of an 8-week-long commercial gardening experiment on board the International Space Station (ISS). Astronauts on the ISS have been tending a batch of fast-growing Arabidopsis plants (better known as "mustard weed") to discover whether plants can complete their entire seed-to-seed life cycle in a weightless environment.

Video from the experiment shows that seed pods were produced by the space-borne plants. But scientists aren't yet certain what's inside the pods.

"We are waiting for retrieval of the payload to see whether or not seeds are indeed inside the seed pods," says Weijia Zhou, Principal Investigator for the ADVANCED ASTROCULTUREtm plant growth chamber that harboured and nourished the seedlings on the ISS. "Personally, I have a very high confidence level that they will have seeds," he added.

Zhou is the Director of the Wisconsin Centre for Space Automation and Robotics (WCSAR), a NASA Commercial Space Centre that built the growth chamber. "This research is a joint endeavour between WCSAR and Space Explorers, Inc. (SEI)," explains Zhou. SEI is a private company specialising in the development of educational products for schools. Data from the ADVANCED ASTROCULTURE^TM experiment will allow SEI to complete an Internet-based multimedia program called Orbital Laboratory, which students and educators can use to study plant biology in classrooms.

If normal, healthy seeds were produced as Zhou suspects, the experiment will be a good sign that future astronauts can grow multiple generations of plants in space. Such self-perpetuating gardens will be a practical necessity for humans as they explore and colonise the solar system. Hardy space plants could provide fresh food, oxygen, and even clean water for explorers living for long stretches aboard orbiting outposts or on the Moon and Mars.

Image courtesy NASA Marshall Space Flight Centre. A top-down view of the ADVANCED ASTROCULTURETM plant growth chamber on the ISS, 28 days into the experiment. The leafy heads of the Arabidopsis plants are visible in the reddish light, which is a frequency (colour) of light that plants can utilise for photosynthesis.

Now that the plants are back on Earth, scientists at WCSAR will analyse them to learn if growing in the weightless environment of free-fall had any ill effects

"Most importantly, we need to see how many seeds were produced," Zhou says. Comparing the fecundity of the space-grown plants to a control group grown under identical conditions on the ground will tell researchers whether the conditions of growth - such as temperature, moisture, and fertiliser concentrations - were indeed optimal.

"The second thing we need to do is conduct a final chemical analysis of the seeds to find out if there was a different phytochemistry involved," Zhou says. (Phytochemistry is a term for the chemical make-up of a plant.) If there is a difference, it would likely be caused by the weightless environment where the plants were gardened, he added.

These seeds will be preserved for use in a similar experiment to be flown to the ISS by a shuttle flight currently scheduled for November 2001. Half of the seeds in that experiment will be from this space-grown batch, and the other half will be regular Earth-grown seeds. Comparing the plants and seeds produced in this follow-up experiment will tell scientists whether the conditions of space have any effect on subsequent generations of plants.

Eventually gardens could become a routine part of space travel. "NASA has announced a plan to sustain a long-term human presence in space," notes Zhou. What are those astronauts going to eat? "Are they going to eat all dehydrated food, or are they going to get some fresh salad crops?" he asks.

Salads and vegetables are not only good nutrition, but they could also offer an important psychological boost to diners who have spent a long time in space. Eating reconstituted foods from plastic bags is bound to grow tiresome eventually. Fresh lettuce or broccoli might be a welcome change - even for kids.

Plants in space won't only be a source of food -- they'll have other jobs to do as well, playing a critical role in cutting-edge life support systems.

An Arabidopsis plant with tiny seed pods at the top. The small size of the plant was part of the reason researchers chose it for the experiment aboard the ISS, where physical space is at a premium.

On Earth, photosynthetic organisms like plants and algae provide a natural life support system for the planet's many life forms. Plants and algae use energy from light to split water molecules into hydrogen and oxygen. Then they combine the hydrogen with carbon dioxide to make sugars, which serve as food. Oxygen is released into the air as "waste." This serves as a perfect compliment to other life forms such as animals and fungi, which use the oxygen and respire carbon dioxide.

Taking a cue from nature, scientists at NASA's Johnson Space Centre and Kennedy Space Centre are pioneering next-generation "bioregenerative" life support systems, which use plants rather than machines to perform the chemistry of life support.

Not only do plants release precious oxygen, they can also help recycle drinking water. After some processing, nutrient-rich waste-water can be used to water and fertilise the plants. Much of the water absorbed by the roots will evaporate from the leaves as pure water vapour. Condensing this water vapour. out of the air creates virtually pure, distilled water that can be used for drinking.

While elegant in theory, the fine details of such a system must be worked out before plants and people can live in a successful space-symbiosis. Learning to grow many generations of plants in space is an early step toward that goal.

Many research teams at NASA and NASA-sponsored university projects are experimenting with plant growth for space missions, but Zhou's team is the only one at the moment that's actually growing plants in space from seed to seed.

By mimicking the cycles of nature, "bioregenerative" life support systems may someday provide food, oxygen, and water to spacefarers for long-term missions.

"What WCSAR and industry are doing is rather unique," Zhou says. But researchers hope it will soon be common. Fast-growing plants that thrive from generation to generation in orbit will surely produce the seeds from which human exploration of space will spring.