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Will space tourists be Earth polluters? Scientists sound a warning.

As firms prepare to launch the space tourism business, one study warns that the soot from the suborbital crafts' hybrid rocket motors could collect in the stratosphere and warm the poles.

By Staff writer / October 25, 2010

Virgin Galactic's WhiteKnight Two and SpaceShip Two circle the airfield at Spaceport America in Upham, N.M., on Oct. 22.

Virgin Galactic/2010 Mark Greenberg/Reuters

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Scratching an expensive itch to take a pleasure trip to the doorstep of space might come with an unintended consequence: altering the climate back on Earth.

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A new study suggests that projected increases in so-called suborbital flights – including space tourism launches – will boost the amount of soot in the stratosphere, measurably changing climate. The soot comes from hybrid rocket motors, which burn a rubbery solid fuel, aided by a gas "oxidizer" as a stand-in for oxygen. By contrast, many liquid-fueled rockets burn oxygen and hydrogen, which produces a cleaner exhaust.

According to the results, temperatures in the region around the launch site would likely cool slightly as the high-altitude soot blocked some sunlight. But the soot would spread around the globe, warming the stratosphere and touching off changes in its circulation that would bring additional warming to the poles.

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Growing demand

If demand for suborbital flights grows to levels some in the industry project by 2020, black carbon's climate effect could rival the impact from soot coming from all the world's trains, trucks, and heavy construction equipment, the researchers calculate.

The study represents an initial look at the issue, cautions Martin Ross, a scientist at Aerospace Corp., an independent aerospace research firm in El Segundo, Calif., and the lead author on the research paper reporting the results. Many uncertainties remain, including the validity of traffic projections. And any potential effects, if they appear, are decades away.

"What we want to do is understand this now so nobody makes big investments in systems that are not sustainable in the long run," he says. New aerospace systems – from the US Air Force's aging B-52 bombers to NASA's space shuttle – take roughly 10 years to design and test and then remain in service for decades.

Some entrepreneurs already are making those investments. On Oct. 22, Richard Branson, the adventurer and founder of Virgin Atlantic Airways, among other enterprises, welcomed the space-tourism venture Virgin Galactic's first spaceship to its spaceport near Upham, N.M. The craft, SpaceShipTwo, was delivered by its mother ship, WhiteKnight Two, a twin-fuselaged jet that was designed to carry the rocket to its launch altitude.

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