If you think a 16-hour flight is bad, try a five-year flight on the Boeing SolarEagle. The Boeing SolarEagle is a project between DARPA and Boeing to build a UAV (unmanned aerial vehicle) that can stay airborne at an altitude of 60,000 feet for five years!
The Boeing SolarEagle would run on solar power, which should, in theory, be able to keep it up and running for as long as need be. The solar UAV would be used as a mobile communication and reconnaissance satellite. The Boeing SolarEagle is set to be ready for flight by 2014.