This certainly is an interesting time for solar powered flight. Solar Impulse just returned from a 26-hour manned test flight, and now QinetiQ's Zephyr, a drone who we last saw clocking over 83 hours in-flight is in the air again: this time, it's more like seven days and counting! The craft, which took off from the Army's Yuma Proving Ground in Arizona last Friday, is being billed as an "eternal aircraft," one that can stay aloft for extremely long periods of time for use as recon and communications platforms. The previous world endurance record for a UAV was set by NASA's Global Hawk, which stayed aloft for 30 hours and 24 minutes.