The Department of Defense now wants its first unmanned combat aircraft to able to refuel in the air. This aircraft, the X-45C, weighs 19 tons, has a 2.2 ton payload and is 39 feet long (with a 49 foot wingspan.) Officially, its called JUCAS (Joint Unmanned Combat Air System), because the navy and air force will both use it. The X-45C has a combat radius of 2,300 kilometers, or can go out 1,800 kilometers, hang around for two hours, and return. The X-45C can stay in the air for about six hours on internal fuel. Since it doesnt carry a pilot, aerial refueling can be done several times if theres a need to keep the aircraft up there, and there are no equipment problems. Electronic aids for aerial refueling have made the procedure increasingly automated. The X-45C will demonstrate just how far the automation has come. The engineers believe that robotic aerial refueling won't be a big problem.  The first X-45C is still under construction, and wont fly until 2007. Meanwhile, smaller versions, like the X-45A, are being used to test the new software needed to make UCAVs work in a combat environment. The X-45X is a joint U.S. Air Force/Navy project.