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A team from NASA, the military and academia has developed and tested a simple solid rocket fuel of fine-grained aluminum and water ice that the researchers say could provide a cleaner alternative to propellants now in use.
The propellant, known as ALICE (for aluminum and ice), showed its stuff by shooting a nine-foot test rocket a quarter of a mile into the sky this month, according to NASA.
Mitat Birkan, program manager for space power and propulsion at the U.S. Air Force Office of Scientific Research, one of the agencies working on the fuel, says that ALICE is more environmentally friendly, before and after burning, than conventional fuel. The only by-products of ALICE combustion, Birkan says, are gaseous hydrogen and relatively innocuous aluminum oxide.
Those exhaust products would be much gentler on the environment than the ones generated by some of the rockets NASA uses now. For instance, when space shuttle Discovery lifts off under power of its solid rocket boosters later this week (assuming no further delays), several tons of hydrochloric acid will be spewed onto and above the launch site as the propellant burns.
Hydrochloric acid, highly hazardous to human health and the environment, results from the use of perchlorate oxidizers, which make up the bulk of the shuttle's solid fuel. (The second most prevalent component in the boosters' propellant is aluminum.) The beauty of ALICE, Birkan says, is that its oxidizer is both built-in and harmless—it's water.
To be fair, the latter portion of the shuttle's ascent is already pretty benign. The orbiter's main engines, which take over completely after the solid boosters are jettisoned two minutes into flight, are much greener than the booster rockets, relying on fuels of liquefied hydrogen and oxygen. "That creates only water," says Birkan, who calls them "the cleanest engines in the world."
Photo of ALICE test flight: Steven F. Son/Purdue University