Anne Minard, for National Geographic News 14 Apr 09;
Plumes from rocket launches could be the world's next worrisome emissions, according to a new study that says solid-fuel rockets damage the ozone layer, allowing more harmful solar rays to reach Earth.
Thanks to international laws, ozone-depleting chemicals such as chlorofluorocarbons (CFCs) and methyl bromide have been slowly fading from the atmosphere. But when solid-fuel rockets launch, they release chlorine gas directly into the stratosphere, where the chlorine reacts with oxygen to form ozone-destroying chlorine oxides.
Increased international space launches and the potential commercial space travel boom could mean that rockets will soon emerge as the worst offenders in terms of ozone depletion, according to the study, published in the March issue of the journal Astropolitics.
If the space tourism industry alone follows market projections, rocket launches are "going to run up against Montreal Protocol," said study co-author Darin Toohey of the University of Colorado at Boulder. The Montreal Protocol on Substances that Deplete the Ozone Layer, an international treaty, prescribes measures intended to hasten the recovery of Earth's depleted ozone layer.
"This isn't urgent," Toohey said. "But if we wait 30 years, it will be."
Rocket Pollution
Currently the U.S., European, and Indian governments power their rockets with a mix of liquid and solid fuels, which generally take the form of powder or crystals. Russia and China use liquid fuels almost exclusively.
In general, the liquid rocket propellants havent yet undergone the level of scrutiny that solid propellants have, noted study leader Martin Ross, an atmospheric scientist from the Aerospace Corporation in Los Angeles.
"There is a general assumption that the various liquid rocket engines use 'green propellants,' and this is likely true to some extent," Ross said.
"But how do liquids compare to solids as far as ozone loss is concerned? We do not know for sure.
"What we have shown in the Astropolitics paper is that the rockets of the future will use liquid propellants and that they will fly ten or one hundred times more often than today's rockets," he continued.
"We do not have enough scientific information to predict how these high flight rates will affect the ozone layer in 10 or 20 years."
Further complicating matters, individual mission trajectories pollute to different degrees, he added.
Some launches release chemicals into the lower atmosphere, where most of them "rain out" fairly quickly. Others pollute the stratosphere, where they can linger and react with other chemicals.
Also, "we don't know enough about the real atmospheric impacts of all the various types [of fuels] to say for sure which are best," study co-author Toohey said.
"We need to get some observations in a variety of rockets to start to reduce uncertainties."
Global Warming vs. Ozone
Toohey is also sending out a pollution warning about so-called geoengineering proposals that have surfaced to combat global warming.
Some researchers, for example, want to seed the stratosphere with particles of sulfur dioxide and aluminum oxide to spur global cooling. (Read "Extreme Global Warming Fix Proposed: Fill the Skies With Sulfur.")
But aluminum oxide is one of the chemicals in solid rocket fuel that depletes ozone, Toohey pointed out.
"There are people in the engineering world who think we could address global warming in a way that could destroy our ozone layer," he said.
"If people are going to put particles into the stratosphere, they'd better be careful."
