We've been keeping you up to date on the Solar Impulse, a manned solar-powered plane that just completed its first 24-hour flight.  It was a great milestone for solar-powered air travel, but an unmanned solar-powered plane is attempting an even greater feat.

The Zephyr solar aircraft is not only breaking records for solar-powered aviation, it's breaking them for all unmanned flights.  The aircraft has already spent seven days in the air, twice the duration of the longest recorded unmanned flight, and it's aiming for a total of 14 days.

The craft has been flying above the Army's Yuma Proving Ground in Arizona, which is fitting because the potential applications for this type of solar-powered craft include military surveillance (as well as scientific roles like ecosystem observation).

The Zephyr is a super-lightweight, carbon-fiber craft, weighing only 50 kilograms, with a giant wingspan of 22.5 meters.  The wings are covered in thin-film solar panels that charge its lithium-sulphur batteries, which power the engines when the sun goes down.

via Treehugger