The Solar Eagle will operate as a pseudo-satellite, soaring 65,000 feet above Earth.
The U.S. military wants a drone plane that can stay aloft for five years.
Boeing, which is building a prototype, intends to test fly its solar-electric drone called Solar Eagle in 2013.
The plane could serve as a pseudo-satellite for communications, reconnaissance and Earth-monitoring.
Think your last flight was long? The Defense Department's research arm wants a plane ride that lasts five years.
DARPA, the Defense Advanced Research Projects Agency, is paying The Boeing Co., $89 million to build a huge, solar-powered, robotic aircraft that can carry 1,000 pounds of sensors and other payloads for five years at a stretch.
"It's challenging," Boeing project manager Pat O'Neil told Discovery News. "It presents opportunities to do things in the atmosphere that normally we'd associate with satellites. It's quite compelling."
The plane, which Boeing calls Solar Eagle, needs to be virtually maintenance-free and highly energy efficient. Well over half the plane, which spans 400 feet from wing to wing, will be covered with solar arrays to harvest energy from the sun. The power needs to be stored onboard so the plane can fly by night, as well as power payloads.
"They want a capability that's going to be equivalent to a satellite, except with more mobility, and that's easier to get into the air and come back down if they want to work on it," Lindsay Voss, a research analyst with the Association for Unmanned Vehicle Systems International trade organization, told Discovery News.
Solar Eagle is intended to soar 65,000 feet above the planet or higher -- about twice the altitude of commercial jet aircraft. From that vantage point, it can serve as a platform for remote sensing, reconnaissance and communications, as well as stage scientific experiments.
"One of the big challenges is getting the aircraft into the air and understanding how it's going to manage for some time. Will the materials hold together for five years, or three years, or will they fall apart in 30 days?" Voss said.
The longest flight of a drone to date was set in July by an unmanned aerial vehicle called Zephyr, built by Qinetiq, Boeing's partner in the Solar Eagle project.
Boeing plans to begin test flights in 2013, leading up to a 30-day demonstration run during the winter solstice when conditions will be most challenging, O'Neil said. The plane is being designed at Phantom Works, Boeing's main research and development arm.