The Zephyr, which has an 18-meter (59-feet) wingspan and weighs just 30 kilograms (66 pounds), smashed the previous best of 30 hours, 24 minutes by nearly a whole day, flying to a maximum height of 58,355 feet.
It then flew a second time, again beating the previous benchmark set by a jet-powered US Air Force plane six years ago with a time of 33 hours, 43 minutes to a height of just-under 16,000 meters.
But the company, whose flight trials from the US military's White Sands missile range in New Mexico were funded by Britain's defence ministry, may not see the times stand as a world record, as there was no official observer.
Paul Davey, Zephyr business development director at QinetiQ, said that even if they do not clinch the new record, the aircraft had secured its place in the annals of unmanned aerial vehicle (UAV) development.
"Both flights were achieved in the face of thunderstorms and debilitating heat in the hostile environment of the New Mexico high desert in the summertime," he said.
"They have proved that an autonomous UAV can be operated on solar electric power for the duration required to support persistent military operations."
By day, the Zephyr is powered by solar panels on its wings. Daylight sun also recharges lithium sulphur batteries that keep it aloft at night.
QinetiQ said the Zephyr could be used in areas like earth observations and communications relay for defense or security operations.
© 2007 Agence France-Presse
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