Published online 3 March 2010 | Nature 464, 14-15 (2010) | doi:10.1038/464014b

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Unmanned planes take wing for science

Drones will measure ozone and aerosols in the atmosphere.

Nose for science: the Global Hawk will gather data during 30-hour flights.Nose for science: the Global Hawk will gather data during 30-hour flights.T. LANDIS/NASA PHOTO

Later this month a remote-controlled aircraft is scheduled to take off from the Mojave Desert in California and veer west over the Pacific Ocean. The Global Hawk, a slim-winged, high-flying jet, was designed for military reconnaissance and tested in both Iraq and Afghanistan. But this time the plane will fly for science.

Guided by pilots at NASA's Dryden Research Center, north of Los Angeles, the plane will measure concentrations of ozone, aerosols and various trace gases along a 15,000-kilometre loop around Hawaii. At the same time, atmospheric scientists hope that the drone's flight will usher in an era of unmanned scientific aircraft that can probe parts of the sky normally inaccessible to manned planes.

During the past two decades, several teams have developed and tested remote-controlled science planes, and NASA already flies the smaller Predator B — also of military origin — over western US wildfires. Drones never caught on as serious research tools, in part because they could carry so little compared with manned planes. But the Global Hawk is larger and much more capable than its predecessors, lifting a payload of around 900 kilograms to a height of nearly 20,000 metres and covering a distance of some 20,000 kilometres.

That combination "can't even be approached with any other aircraft", says David Fahey, a principal investigator with the drone project at the National Oceanic and Atmospheric Administration (NOAA) in Boulder, Colorado. "Scientists don't really know how to use a platform like this, because we've never had one. You kind of have to let your imagination be unbridled for a bit, and then you rein it back in."

In particular, the Global Hawk will give scientists the ability to stay in the stratosphere for hours, collecting samples in this key region where ozone is being destroyed. The manned ER-2 can tap the lower stratosphere, but it can't fly as far as the Global Hawk or remain up for as long, says Paul Newman, the scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, who is leading this month's mission with Fahey. "Whenever you use these planes it always seems as if the thing that you really want to sample is about 1,000 miles farther than you can go."

Flying instruments on the Global Hawk isn't cheap or easy. NASA charges the same price — US$3,500 per hour — to use the Global Hawk as for various manned aircraft. And although staying in the air for long periods offers many advantages, Fahey says that the team has had to figure out the logistics of rotating crews of scientists to monitor equipment during a 30-hour flight.

Chris Naftel, who manages the programme for NASA, saw the potential of the military reconnaissance drones in 2005, when the Air Force was decommissioning seven Global Hawk prototypes. Naftel secured two of the prototypes in 2007 and a third last year for free. The agency signed an agreement with the plane's producer, Northrop Grumman in Los Angeles, to help convert the aircraft, install new communications equipment, train employees and build an operations centre.

During the summer, a team of NASA scientists will deploy the Global Hawk to monitor Atlantic storms, hoping to peer inside them as some develop from tropical disturbances into hurricanes. Multiple teams are developing other research missions, and NASA is now working on a mobile communications centre that will give the aircraft truly global coverage.

With Global Hawk about to start its science runs, support is growing for unmanned research planes. A report from the US National Research Council last month called unmanned vehicles an "extremely exciting complement" to NASA's current aerial fleet. And NOAA is pondering whether to develop its own fleet of science drones.

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David Parrish, a colleague of Fahey's at NOAA who conducts intensive atmospheric research campaigns with a converted passenger aircraft, the P3, emphasizes that manned missions are unlikely to end any time soon. His team loads a P3 with so much instrumentation that the plane, which is designed to hold 80–90 passengers, can seat just five or six scientists.

"It's very difficult to develop instruments with the needed precision and accuracy, yet small enough to fly on these unmanned platforms," Parrish says. He adds, however, that "the atmosphere is so big and so complex" that there is certainly room for both types of aircraft. 

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