James Darcy/Airbus Group
A glider that aims to soar higher than any other piloted aircraft will begin its first campaign this month in the skies above Argentina. For its pilots and engineers, the Perlan Project holds the excitement of breaking the world altitude record for gliding — and perhaps one day reaching close to the vacuum of space.
But for Elizabeth Austin, the project’s chief scientist, there’s another thrill: the glider will carry scientific instruments for climate, aerospace and stratospheric research that cannot be done using other means. “The possibilities are just so incredible,” says Austin, an atmospheric physicist and the founder of forecasting service WeatherExtreme in Incline Village, Nevada.
The carbon-fibre glider, built with a pressurized cabin, is intended to achieve sustained flight at around 27,000 metres, where the density of air is about 2% of that at sea level. In the series of flights that the craft will begin in mid-August, it will fly to only 15,000–18,000 metres — in part because of weather conditions — but this could still break the glider altitude record of 15,445 metres, set by an earlier Perlan model.
The glider will carry instruments to measure levels of aerosols and greenhouse gases, including ozone, methane and water vapour, and will gather information on the exchange of gases and energy between the two lower layers of Earth’s atmosphere: the troposphere and the stratosphere. Those data, to be collected this year and next, could improve climate models, which account poorly for these atmospheric interactions and contain “horrific” uncertainties about the levels and behaviour of water vapour at stratospheric altitudes, Austin says.
Scientific balloons have already flown at much higher altitudes, but they must follow the wind, Austin adds, whereas a pilot can steer and circle a glider. “We can spend hours flying where we want. A glider is an incredible scientific platform as there’s no other way to get this sort of data.”
“It’s an extremely exciting project,” says Jie Gong, an expert in atmospheric dynamics at NASA’s sciences and exploration directorate in Greenbelt, Maryland. On the basis of its intended flight route, the Perlan glider might be able to provide the first direct observations of polar stratospheric clouds, a unique type of ice cloud that forms in the polar stratosphere and helps to deplete ozone, Gong adds.
Surfing over mountains
The glider is named after those same clouds, which have an iridescent mother-of-pearl appearance (Perlan means ‘pearl’ in Icelandic). They are typically generated at high altitudes by stratospheric mountain waves — when strong winds that blow over the tops of high mountains are driven up towards space. In 1992, a retired NASA test pilot, Einar Enevoldson, founded the Perlan Project with the aim of creating a glider that could surf these waves up to the stratosphere. And in 2006, he and the US adventurer Steve Fossett proved the concept with their record-breaking flight on Perlan 1, a modified conventional glider.
But Fossett’s death the following year in a light-aircraft accident set the project back until July 2014, when European aerospace group Airbus became a major sponsor and contributed its research expertise. The Perlan 2 craft made its maiden flight last year in Oregon, and in March surfed its first mountain waves above the Sierra Nevada range in California.
Its next flights will be over El Calafate on the eastern and southern fringes of the Andes range in Argentina. There, during the South Pole’s winter, a fast-moving, high-altitude jet stream called the polar-night jet extends from the troposphere into the upper atmospheric layers — helping the Andes mountain waves (and the glider) to reach the stratosphere (see ‘Science on a glider’).
Besides its atmospheric chemistry, Perlan 2 will carry instruments to study turbulence in stratospheric mountain waves, and to explore the microphysics of interactions between mountain waves and polar meteorology, which ultimately affect weather variability. Information on how mountain waves break in the stratosphere is “extremely limited”, says Gong, and requires detailed, fine-scale data on temperature, humidity and wind, which the glider is uniquely placed to measure. Airbus says that many of the weather phenomena Perlan 2 will encounter will provide useful information for it and other aircraft makers that are contemplating operating aeroplanes at higher altitudes.
Once Perlan is fully tested, says Austin, she hopes to get funding to use the glider as a long-term scientific platform that would examine how hourly, seasonal or even decadal changes in the stratosphere affect weather and climate.
A drone that could carry more instruments is a future possibility — but for now, a piloted craft is preferable and simpler, says Ed Warnock, the project’s chief executive. Machines cannot yet match the best human pilots when it comes to climbing waves in such demanding flight conditions, he says.
Perlan’s backers hope that it can surpass 27,000 metres in 2017 — and, ultimately, they intend another version of the glider to fly higher than 30,000 metres, where the air density is almost identical to that on Mars’s surface. That might provide insight into how winged aircraft could fly on the red planet.
For now, engineers and scientists alike are just hoping to see the glider soar into the stratosphere above the Andes and take data. “Everything in the aircraft is experimental. It’s a very difficult mission to do right, and to do it safely is not easy,” Austin says.
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