Surfing stratospheric waves in an engineless glider isn’t for the faint of heart, especially when you encounter turbulence. It’s like “being inside a washing machine,” says Jim Payne, who intends to break the current glider altitude record as the chief pilot for the Perlan 2, an experimental mission sponsored by the European aerospace company Airbus. “People don’t believe it until they’ve been there,” says Payne, who is based in Minden, Nevada, and described the mission at a briefing last month in Washington, D.C.
And go there he will. This week, Payne and his co-pilot plan to begin a season of flights near El Calafate, Argentina, riding waves created by powerful gusts of wind over the Andes Mountains. They hope to reach a height of 16,700 meters in a series of flights over 2 months, breaking the current glider record. In the coming years, they may even reach their ultimate goal—a height of 27 kilometers. That would break the record for sustained level flight by any aircraft, which has been held for 41 years by the SR-71, a jet-powered spy plane. Along the way, Payne and his team also hope to do a little science, taking measurements in a place where few sensors have gone. The data could help shed light on atmospheric mixing and the behavior of waves in the stratosphere that play a role in weather on Earth’s surface. The Perlan Project dates back to 1992, when the project’s founder, Einar Enevoldson, a NASA test pilot, became convinced that gliders could reach the stratosphere by riding so-called “mountain waves” as they rise up through the atmosphere. In 2006, Enevoldson and his co-pilot reached a height of 15,460 meters, the current glider record. They were deterred from going higher by the frigid air that leaked into the cabin.
Eleven years later, Payne will ride those same waves in a new, custom glider with a 25-meter wingspan. But the Perlan 2’s most important feature is its pressurized cabin, built to withstand the cold and near-vacuum of the stratosphere, where pressures are low enough for blood to boil. At these altitudes, pilots are usually equipped with big and bulky space suits, but the Perlan 2’s sealed cabin will protect the pilots while still granting them a full range of motion. The aircraft’s first round of flights in Argentina began in 2016, but bad weather prevented pilots from getting higher than 7900 meters.
The key to the Perlan 2’s ambitions are the mountain waves, which occur when strong gusts of wind hit the face of a mountain and rise over it, like the water in a stream flowing over a rock near the surface. These waves propagate upward, although their strength usually diminishes before they reach the stratosphere. However, occasionally, in the wintertime at high latitudes near the North and South poles, these waves can get a boost from something called the polar night jet. Polar night jets are eastward-flowing winds that circle the globe high in the stratosphere in the winter, driven by the stark temperature difference between colder, polar air and warmer air from lower latitude. Sometimes, the polar night jet dips into the warmer air of the lower atmosphere.
The interactions can help boost the mountain waves up into the stratosphere, says Jie Gong, an expert in atmospheric dynamics at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Winter in Argentina lasts from June to September, and so flights from mid-July to mid-September provide the best chance for Payne to use the polar night jet to reach the stratosphere.
There, sensors attached to and within the aircraft will measure humidity, air pressure, and temperature from a relatively unexplored region. Stratospheric balloons are launched to even higher altitudes but they’re at the mercy of the winds. High-altitude jets and sounding rockets also probe the stratosphere, but they travel at incredibly high speeds. A glider provides an opportunity for a slower, more controlled exploration of certain stratospheric regions, says Elizabeth Austin, the project’s chief meteorologist based in Incline Village, Nevada.
Any direct observations at all will help scientists calibrate the weather and climate models that are mostly dependent on satellites observations from above, Gong says. “Direct flight campaign measurements of any of the stratosphere variables … would be valuable to validate the quality of our satellite products,” she says.
Ed Warnock, the Perlan Project’s CEO, based in Portland, Oregon, says meteorologists have to estimate the amount of mixing between the stratosphere and lower parts of the atmosphere when creating weather models. Collecting data from both layers of the atmosphere while riding mountain waves could help scientists better understand how these layers interact and what role the waves play in weather, he says.
After this phase of the project ends in September, Perlan 2 will return to its home base in Minden, where it will continue mountain wave flying in the Sierra Nevada, Warnock says. Warnock says the aircraft will remain active until it reaches its altitude goal, which could take a few years. But he says there are already discussions of building a Perlan 3 glider, which would be designed with wings to withstand the shock waves of supersonic speeds.