For the first time, NASA has begun flying an unmanned aircraft outfitted with scientific instruments to observe the Earth's atmosphere in greater detail. The agency has partnered with Northrop Grumman to outfit three aircraft, called Global Hawks, which were given to NASA by the U.S. Air Force. Unlike manned aircraft equipped with Earth observation tools, the Global Hawks can fly for up to 30 hours and travel for longer distances and at high altitudes; they can also gather more precise data than satellites and can be stationed to monitor an area for extended periods of time.