Why does shuttle Discovery look so dirty?

![At NASA’s Kennedy Space Center in Florida, shuttle Discovery pauses for photos during its move called “rollover” from Orbiter Processing Facility-3 to the nearby Vehicle Assembly Building (VAB) on Sept. 9, 2010. The shuttle is due to launch on its final mission on Nov. 1.][1]They’re big and fast and fly in space, but NASA’s space shuttles are far from being shiny white spaceships straight off the factory floor. Case in point: Space shuttle Discovery, as it nears retirement, wears its age with pride.

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URL: http://www.msnbc.msn.com/id/39872790/ns/technology_and_science-space/