Interplanetary spacecraft could run on the crew's organic waste
"I'm trying as hard as I can, Captain," exclaims Scotty, the strain etching lines in his forehead. "I can't give you any more!" But unlike Star Trek's Enterprise, future spacecraft might use a less savoury energy supply than Scotty's beloved dilithium crystals: human waste.
NASA is enlisting the aid of Advanced Fuel Research of Connecticut in a new $600 000 project to turn astronaut waste into a power source for spaceships. The process might also yield other useful chemicals that are in short supply aboard an interplanetary spacecraft or on an extraterrestrial base. The secret is pyrolysis: breaking down the waste by heating it in the absence of oxygen.
Normally when you burn organic molecules such as those found in faeces or in plastic, they combine with oxygen in the air, producing carbon dioxide and water. But in pyrolysis, there is no oxygen to combine with, so the molecules break their bonds and rearrange themselves into smaller molecules. "Things start breaking down at about 350 °C, and what you start making includes a lot of liquids," says AFR scientist Mike Serio. "At 600 °C or 650 °C, you break down the liquids into gases. It does give you flexibility."
You could burn these liquids or gases to release energy, or turn them into plastics or other organic materials, says Jim Markham, the company's chief executive officer.
"[Pyrolysis] can produce heavier molecules such as benzene or toluene, and can be a source of raw materials to make plastics or rubber," says John Fisher, a chemical engineer at NASA's Ames Research Center in California. And pyrolysis would also create ammonia for fertiliser.
Since the pyrolytic process works on many different organic compounds, it will consume many types of fuel. "You can use human waste as well as other waste, like scrap plastic bags," says Markham. And you don't have to worry about variations in the consistency and content of the waste material, the pyrolysis unit should be able to handle them all. "It's tailored to unpredictable mixtures," he says. "Ideally, you'd dial in the desired outcome and it would compensate."
Though a Mars base is still a pipe dream, there might be a use for the process back on Earth-just dump your plastic or other organic waste in a home pyrolysis unit and reap the energy. But in the meantime, Scotty will have to continue milking his dilithium crystals.
This latest idea follows in the wake of a Russian project, announced last year, which aims to use equally bizarre methods of recycling waste in order to maximise available power. The Russian plan, intended to be ready for their first crewed interplanetary mission, is to employ bacteria to break down the astronauts' used underwear to make additional methane, which could then be used to power the spacecraft (New Scientist, 12 December 1998, p 5)
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