WHEN Nigel Packham climbed out of a sealed tank in Texas last week, the first thing he did was order a Mexican meal. It was not much to ask for after 15 days incarcerated in one of NASA鈥檚 experimental chambers with only 30 000 wheat plants for company.
Packham, a British-born chemist who works for Lockheed Martin Engineering and Sciences, one of NASA鈥檚 contractors, volunteered to spend two weeks in the sealed chamber, measuring 3 metres by 3 metres, at NASA鈥檚 Johnson Space Center in Houston, to help prove that plants can provide enough oxygen to support astronauts on a trip to Mars.
During the experiment Packham breathed oxygen given off by the wheat, while the plants survived on the carbon dioxide he exhaled. 鈥淭he experiment went off flawlessly,鈥� says Packham.
Advertisement
Don Henninger, who heads NASA鈥檚 research into regenerative life support systems, says: We鈥檙e trying to mimic the functions the Earth provides in terms of human life support.鈥� Regenerative life support systems, which continually recycle the necessities of life 鈥� such as oxygen and water 鈥� are vital for flights to far-off planets such as Mars because a spaceship cannot carry enough supplies for the whole trip.
The NASA experiment took place in a vacuum chamber with two connected compartments. Packham lived in one section, where he worked at a computer terminal, exercised and ate. The wheat plants grew in the other.
The wheat produced more oxygen than Packham needed, and some had to be vented from the chamber. But Packham was not quite so productive: he failed to breathe out enough CO2 for optimal plant growth, so extra had to be pumped in.
However, the experiment showed that plants can be 鈥渢hrottled up鈥� to produce more oxygen during periods of high demand, when Packham was exercising, for instance. This was achieved by increasing the brightness of the lights over the plants, increasing the rate of photosynthesis. The plants started to release more oxygen within 10 minutes, says Henninger.
Packham鈥檚 two weeks of isolation was the first experiment in a series of tests designed to develop a life-support system based on both plants and chemical processes. Next summer, NASA plans to seal four people into a larger chamber, in which air and water will be recycled through chemical processes alone. Carbon dioxide from the air will be converted into methane and water, and the water molecules will then be electrically cleaved to release oxygen.
That experiment will last 15 days, but in 1997 NASA intends to lock up four people for three months. They will have the benefit of both plants and chemical recycling systems. By the end of the decade, Packham says, NASA鈥檚 guinea pigs could be spending up to a year in a larger chamber in which they would grow food and recycle their solid wastes as well as recycling the air and water.
According to Henninger, even then NASA鈥檚 experiments will be far less complex than those of Biosphere 2, the 鈥渁lternative Earth鈥� in the Arizona desert. But Biosphere 2 is a poor model for a future spacecraft. 鈥淲e could never fly something that big.鈥�
While scientists have studied the way ecosystems recycle gases, water and nutrients, many of the details of the processes remain a mystery. 鈥淲e really don鈥檛 have a very good handle on Earth鈥檚 biosphere itself,鈥� says Henninger.
One detail that could be important on a long flight is whether people or plants release trace gases that have so far escaped detection because they are so diluted in the atmosphere. The NASA experiments will reveal the presence of any problematic trace gases, and allow NASA to develop ways of getting rid of them. 鈥淭here still are many unknowns,鈥� says Henninger.