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Scientists hope they'll make the best map ever of the planet.
In the biggest challenge of the mission, astronauts turned the system on a half-hour ahead of schedule as they flew over the Maldive Islands and Sri Lanka . In all, Endeavour has 13 tons of radar equipment for the mapping mission. So I think there will be some surprises. Because of the risks, the space agency spent months making sure Endeavour and its crew would be safe if the mast got stuck, bent too much or snapped off. The National Aeronautics and Space Administration even trimmed the number of mapping days from 10 to nine to give the astronauts time to go out and crank the mast by hand if necessary.