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There's an area of Earth's orbit populated by about 13,000 fragments of man-made objects each traveling at speeds up to 27,000 miles per hour. It's a moving obstacle course for spacecraft carrying things like satellites that feed the popular GPS systems on the dashboards of many new cars or beam Howard Stern to the ears of his faithful audience. Those rockets then also contribute to the growing amount of what is called "space junk". It's not a pressing problem now, but NASA scientists say it's getting a lot worse. Nicholas Johnson is NASA's Program Manager for Orbital Debris. In a recent article for Science Magazine he graphed a 200-year prediction for space junk.