“That’s Professor Global Hawk”
A remote-piloted warrior starts flying for science.
- By Kara Platoni
- Air & Space magazine, May 2011
(Page 3 of 3)
For the 2010 hurricane surveillance mission, the Global Hawk carried four instruments—including a radar for profiling wind and rain, and a microwave radiometer for measuring temperature and moisture—and faced new challenges. Because Global Hawk’s endurance allows it such a long outbound leg, it faces a lengthy voyage home, with diminishing fuel and uncertain weather. (Flights to observe Atlantic Ocean hurricanes took about eight hours out, with eight on station, leaving eight to return.) But because the unmanned vehicle can fly only over sparsely populated areas, it has fewer landing options in emergencies. “When you’re coming back and facing weather diverts, you’re always wondering, ‘Do I got enough to make it home, or am I going to have to go into one of these emergency fields?’ ” says Miller.
Hurricane surveillance also involves less-than-friendly skies: turbulence, lightning, and precipitation, all of which the crew was eager to avoid. “If you look at that airplane, with its long wing, it’s designed for a flight envelope that does not have high amounts of turbulence,” says Hall. “So we’re not permitted to fly in moderate or severe turbulence.”
Hall, who was at the controls when the Global Hawk overflew its first full hurricane—Earl, off the South Carolina coast—says the experience was more dynamic than the GloPac demonstration mission: As the team assessed the storm’s severity, they called for more rapid changes. At first Hall avoided the hurricane’s eye, but after the team decided it was calm enough, he transected it, crossing the eye seven times on that mission; he flew near it another two. But Hall still had to keep alert for cloud tops that could provoke turbulence, as well as for lightning—a mission rule forbade coming within 20 miles of it. “It was a fun flight because it was busy and kept us challenged,” says Hall.
Global Hawk proved to be an excellent hurricane observer, says research meteorologist Gerry Heymsfield, one of three GRIP scientists. (On a later flight, over Hurricane Karl in the Gulf of Mexico, the Global Hawk made 20 passes, including 12 over the eye. By contrast, an ER-2 typically does about six passes.) He points out that duration is especially important in studying hurricanes, which can intensify rapidly within 12 to 24 hours. In the past, long-term storm coverage required multiple airplanes.
The hurricane observation mission, which also involved DC-8 and WB-57 aircraft, focused on gathering clues about how tropical storms originate, and why some blow into hurricanes while others fizzle out. The team investigated how temperature, wind, and moisture in the environment around storms affect their direction and intensification; the mechanisms that cause a cluster of clouds to start spinning; and the role of convection in intensifying storms. The mission also studied easterly waves, weather disturbances off the west African coast that trigger thunderstorms, which sometimes become hurricanes. “We’re trying to learn why some waves develop and some don’t, because they all look similar,” says Heymsfield.
NASA officials have a long list of what they’d like to do next with their Global Hawks. A portable ground station, which would allow a pilot to launch and land the aircraft in the East Coast while the payload operators remain at Dryden, is in the works for next year. Cutting out the cross-country transit would allow future missions to observe hurricanes that are farther away and for longer periods, which means earlier in their development. NASA is planning a Hurricane and Severe Storm Sentinel mission for 2012 that will fly two Global Hawks, one over the storm and another to study its environment.
A synthetic-aperture radar pod mounted beneath a wing is also planned, and thanks to an East Coast base, says Naftel, “I can see us going to Greenland from Wallops Island [a NASA rocket launch site in Virginia] to map the ice surface up there, to track the changes that are occurring, and doing the same thing over the North Pole and the South Pole.”
Perhaps most significantly, Northrop Grumman is developing technology for mid-air refueling between two autonomous vehicles, potentially allowing the receiving vehicle to stay aloft for up to seven days. A demonstration program is planned for next year.
With longer-endurance aircraft and perhaps a larger fleet on the horizon, NASA scientists envision autonomous aircraft like Global Hawk playing a routine role in monitoring the world’s weather and studying its atmospheric changes. Chris Naftel calls it “nearly a perfect science platform.” Attention satellite manufacturers: You may want to watch your backs.
Kara Platoni is a freelance science writer living in Oakland, California, and an instructor at the University of California at Berkeley’s Graduate School of Journalism. Her most recent story in Air & Space/Smithsonian was “The Six” (June/July 2009).