For the first time since the Columbia accident, a space shuttle is scheduled to come directly over the North American mainland as it makes its reentry approaching the Kennedy Space Center. Discovery undocked from the space station early this morning, and the weather for a Wednesday afternoon landing looks good. What’s the issue? Well, it was something of one after Columbia broke up, leaving debris in a long streak over Texas and Louisiana. If the ship had broken up just a moment earlier, the debris zone might well have included the Dallas suburbs. The Columbia Accident Investigation Board, among other recommendations, said shuttles should avoid populated areas on return until NASA was confident it could avoid a repeat of the accident. (The board finished its work in 2003, but its website, still active, is HERE.) That time seems to have come, say mission managers. They now inspect a shuttle’s exterior so thoroughly that while astronauts still face myriad hazards, the odds of a Columbia repeat are very, very small. Wayne Hale, the shuttle program manager, said this afternoon there’s another reason shuttles have not come in from the north on most flights: they’d rather steer clear of noctilucent clouds–a not-very-well-understood type of clouds that appear at high altitudes relatively close to the poles. They may be icy, though scientists are not sure. Most shuttles in the last few years have come up toward Florida from the south, passing over the Pacific and parts of the Central American tropics, making everything simpler. But Discovery’s commander, Pam Melroy, would rather land in daylight, says Hale, and the way to do that involves coming into Florida from the northwest. If you’re in the right place, you may be able to see the streak the shuttle makes in the sky as it descends. One place to look for info is HERE.