Modernization of U.S. Air Force RQ-4 Global Hawk unmanned aircraft is set to move ahead with the aircraft's program gaining Milestone C approval.

The approval from the Defense Acquisition Executive was granted after the unmanned aerial system achieved a predetermined level of software maturity and operational interoperability with other relevant systems, said Northrop Grumman, maker of the aircraft that first took to the air in 1998 and is in use with the U.S. Air Force, the U.S. Navy and NASA as a surveillance and reconnaissance platform.

It has a cruise speed of 357 miles per hour, an altitude ceiling of 60,000 feet and an endurance of 28 hours.

The RQ-4 was still in development at the time of the Sept. 11, 2001, terrorist attack on the United States and was quickly deployed. Global Hawk and its variants have flown more than 150,000 hours since then in support of operations in the areas of anti-terrorism, anti-piracy, humanitarian assistance, disaster relief, airborne communications relay and information-sharing, Northrop Grumman said.

"It is true testament to the U.S. Air Force and the Global Hawk industry team that we have been able to effectively support the warfighter for over a decade with a variety of sensor payload capabilities," said Mick Jaggers, director of Global Hawk at Northrop Grumman. "In working with the Air Force, we seek to fly a variety of additional payloads within size, weight, power and communication parameters."

Northrop Grumman said a number of other companies are part of its team for the RQ-4. Among them are ATK, Aurora, Curtiss-Wright Corporation, GE Aviation, United Technologies - Goodrich, Harris, Honeywell, L-3 Communications, Macrolink, Raytheon, Rolls-Royce, Sierra Nevada Corporation and Triumph Aerostructures.