A Predator drone is joining the 4,000 firefighters working to contain the giant 12-day-old wildfire in the Sierra Nevada. The California National Guard drone will fly 22-hour missions to surveil the fire, allowing officials to study its movement and view far-flung corners of the blaze. It’s not the first drone to be used in firefighting, but it will conduct the longest missions ever attempted. The fire is moving at the pace of a slow walk, and has already burned 192,000 acres of forest. Officials say it is 30 percent contained, and they expect to have it under control in three weeks.