Britain’s New Spy Planes Are weird looking and fly in the stratosphere - nearly space.

On Aug. 17, the British ministry of defense confirmed it would purchase a third Airbus Defense & Space Zephyr S high-altitude pseudo-satellite in addition to two previously confirmed in February.

High-altitude pseudo-satellites — HAPS, for short — are super-lightweight unmanned aircraft that can linger around the stratosphere for weeks on end and act as localized satellites.

The Qinetiq team returned to Yuma Proving Ground with the new model in July 2010 where it once again smashed the endurance record. The aircraft managed more than 14 days of continuous flight — 336 hours and 22 minutes — at a maximum altitude of 70,740 feet.

Operating at a region of the atmosphere where most aircraft attempt to spend as little time as possible, Zephyr is subject to all sorts of engineering challenges.

At its operating ceiling, Zephyr flies high above the wind and weather, but it’s extremely vulnerable during its ascent and descent through the windy troposphere — the region of the atmosphere we inhabit.

During testing, Zephyr was only launched in perfect weather conditions— although Qinetiq press releases repeatedly played up the ground temperature and storms around the test days. But that is not to downplay the effects of the desert temperatures it faced on the ground.

From around 40º Celsius at launch, Zephyr’s ambient temperature would fall 2º Celsius per 1,000 feet. But the aircraft mostly flies in and around the ozone layer, which absorbs the sun’s ultraviolet light and emits the energy as heat. As a result, the ambient air temperature actually begins to rise once Zephyr ascends past 65,000 feet.

When night falls, the aircraft must descend to 45,000 feet to conserve power by flying in more dense air. Here the temperature falls to as low as -80º Celsius. This extreme cold can cause components to become brittle, affect electronics and cause metal components to contract.

The engineers chose to insulate and heat components to protect them, even though that increased Zephyr’s weight. But given these extreme temperatures, it isn’t possible to fully protect each component from thermally-generated expansion and contraction.

Cosmic rays — energetic particles emanating from space — are an additional threat to the platform’s electronics. Zephyr operates right in the peak region for cosmic radiation. These rays can cause data corruption and critical electronic faults and it is unclear how much shielding Zephyr 7 carried to protect against this threat but it reportedly hasn’t suffered any ill effects … yet.

Zephyr operators will also face challenges resulting from its solar-power generation. The amount of solar energy available to any given surface area varies by latitude and date. The tropics offer the most energy, but the farther from the equator you go, the more significant the drop-off in available energy during winter.