August 26,2008:  A British experimental UAV, the Zephyr, recently set an endurance record by staying in the air, at about 60,000 feet, for over three days (82 hours, 37 minutes). The 70 pound aircraft uses solar panels on its 59 foot wingspan to power the propeller, and batteries for keeping the aircraft going at night. All the flying was done under software control. On the downside, the aircraft only has a payload of about four pounds. Any useful payload (camera, or communications transponder so the UAV could act as a local space satellite substitute) would need power, which would reduce endurance.

The Zephyr was partly funded by the U.S. Department of Defense, and the basic design could be scaled up, and make use of low power sensors and communications devices in development. Eventually, this type of aircraft would have a practical use.