|MadSci Network: Earth Sciences|
Pollution caused by space launches: The magnitude of space launch combustion products can be illustrated by a comparison of the amount of fuel consumed by a space shuttle launch with the amount of gasoline consumed in the United States in one day: Space shuttle fuel consumed in a launch: 3.5 million pounds Gasoline consumed in one day in the US - 2,500 million pounds In other words, one space shuttle launch is equivalent to about two minutes of gasoline consumption in the United States. There were 78 space launches worldwide in 1999, almost all much smaller than the space shuttle. The pollution caused by space launches depends not only on the total quantity of the fuels used, but on their chemical composition.. Propellants used for powering space launches are of four types: 1. Solid - Propellants that are a mixture of solid chemicals - a fuel and an oxidizer - that burn at a rapid rate when ignited, expelling hot gasses from a nozzle to achieve thrust. Fireworks are an example of the use of this kind of propellant. The combustion products depend on the chemicals used. The space shuttle uses potassium perchlorate (KClO4) and powdered aluminum. The combustion products are potassium chloride and aluminum oxide 2. Cryogenic - In space propellants, this refers to liquid hydrogen (LH) and liquid oxygen (LOX), which burn when mixed and ignited. LOX is a liquid below -298 degrees F and LH is a liquid below -423 degrees F. They are stored in the space vehicle in insulated tanks and pumped into the rocket engines where they burn to expel hot gases. The LOX/LH combination is by far the most efficient in the amount of thrust per pound of fuel. The combustion product is water vapor. 3. Petroleum - Instead of liquid hydrogen, a purified kerosene is used as the fuel and is mixed with liquid oxygen and burned in the engine. The combustion products are carbon dioxide and water vapor. This fuel system is usually used in launches of smaller rockets where the complications of handling liquid hydrogen are not justified. 4. Hypergolic - fuels and oxidants that ignite on contact without an ignition source. These are generally used for maneuvering after the soak vehicle has reached orbit. The combustion products depend on the chemicals used. The space shuttle uses monomethyl hydrazine (N2CH6) and nitrogen tetroxide (N2O4). The combustion products are nitrogen, water vapor and carbon dioxide. The pollution effects of the four types of fuels are: Solid fuel - The major combustion products of potassium chloride and aluminum oxide and relatively innocuous. Potassium chloride is used as a fertilizer and has medicinal uses. Aluminum oxide is an unreactive compound and is used as an abrasive. Cryogenic - The only combustion product of LH/LOX is water. Petroleum - The combustion products of water and carbon dioxide are harmless except of any possible contribution of carbon dioxide to global warming, but the carbon dioxide from this source would be infinitesimal compared to the energy produced by burning coal and petroleum Hypergolic - The combustion products of this kind of fuel are not a pollution problem. In any event this fuel is used only in small quantities for maneuvering. The space shuttle uses about 2.3 million pounds of solid propellant in the launch boosters and about 1.2 million pounds of LH/LOX in the main engines. A relatively small amount of hypergolic fuel is used for controlling the shuttle once in orbit. Kerosene/LOX propellant is not used. With regard to possible effect on the ozone layer, the only combustion product that would be suspect is the chloride ion of potassium chloride. Studies have shown that in contrast to organic chlorine (as in banned refrigerants) inorganic chloride does not persist in the altitudes of the ozone layer and is not a factor in ozone depletion. References: Ozone Depletion FAQ Part II: Stratospheric Chlorine and Bromine http://www.faqs.org/faqs/ozone-depletion/stratcl/ 1999 Space launch report http://www76.pair.com/tjohnson/log99.html Space Shuttle Solid Rocket Boosters http://www.shuttlepresskit.com/STS-106/REF137.htm Propellants http://www-pao.ksc.nasa.gov/kscpao/nasafact/count2.htm
Try the links in the MadSci Library for more information on Earth Sciences.