The Engineer reported that researchers in the US are developing a more environmentally friendly rocket propellant made of a frozen mixture of water and nanoscale aluminum powder.
Mr Steven Son an associate professor of mechanical engineering at Purdue University in Illinois of US said that the Aluminum ice or ALICE, propellant could be used to launch rockets into orbit and for long distance space missions and could also generate hydrogen for fuel cells.
Purdue is working with NASA, the Air Force Office of Scientific Research and Pennsylvania State University to develop ALICE which was used earlier 2009 to launch a 2.7 meter tall rocket. The vehicle reached an altitude of 396 meters over Purdue's Scholer farms.
Mr Timothee Pourpoint a research assistant professor in the Purdue’s School of Aeronautics and Astronautics said that the tiny size of the aluminum particles which have a diameter of about 80nm is key to the propellant's performance. The nano particles combust more rapidly than larger particles and enable better control over the reaction and the rocket's thrust.
He said that “It is considered a green propellant, producing essentially hydrogen gas and aluminum oxide. In contrast, each space shuttle flight consumes about 773 tonnes of the oxidizer ammonium per chlorate in the solid booster rockets. About 230 tonnes of hydrochloric acid immediately appears in the exhaust from such flights.”
ALICE provides thrust through a chemical reaction between water and aluminum. As the aluminum ignites, water molecules provide oxygen and hydrogen to fuel the combustion until all of the powder is burned.
Researchers have used aluminum particles in propellants before but those propellants usually also contained larger, micron size particles. The new fuel contains pure nano particles. The research team explained that the fuel needs to be frozen so that it can remain intact while subjected to the forces of the launch. It must also be frozen to ensure that it does not slowly react before it is used.
The fuel which is initially a paste is packed into a cylindrical mould with a metal rod running through the centre. After it is frozen, the rod is removed, leaving a cavity running the length of the solid fuel cylinder. A small rocket engine above the fuel is ignited, sending hot gasses into the centre hole which causes the ALICE fuel to ignite uniformly.
Mr Son said that “This is essentially the same basic procedure used in the space shuttle's 2 solid fuel rocket boosters. An electric match ignites a small motor which then ignites a bigger motor.”
In the future, the research team plan to explore the possibility of creating a gelled fuel using the nano particles. Such a gel would behave like a liquid fuel, making it possible to vary the rate at which the fuel is pumped into the combustion chamber to throttle the motor up and down and increase the vehicle's distance.
