The Global Hawk Navigation SystemAn Odyssey in the Development of an Unmanned Aerial Vehicle

Greg Loegering

Abstract:	The Global Hawk UAV was developed as an outgrowth of the Department of Defense's desire to have a high altitude long endurance aircraft capable of carrying a large reconnaissance payload. The system was designed under the auspices of an Advanced Concept Technology Demonstration (ACTD) program, giving the design team an unprecedented degree of freedom to weigh competing requirements. The only “real” requirement levied upon the team was that the production aircraft would price out for no more then $10 Million a copy, and every other “requirement” in the initial solicitation was stated simply as a design goal. The result was a system that gives the customer the most “bang for the buck”. The navigation system had a number of design goals that had to be met. These goals included : a) provide adequate navigation accuracy for autonomous taxi, takeoff and landing; b) support goal of landing on a 5000 foot long by 100 foot wide runway; c) support the goal of 1 aircraft loss in 200 missions where the mission length was assumed to be 42 hours long. Overriding each of these design goals was the requirement to minimize the recurring cost of the navigation system. Early on, it was decided to provide the UAV with its own navigation suite independent of any payload carried by the aircraft. It was thought that the basic navigation needs of the UAV could be supported with a lower performance inertial system, supplemented with differential GPS, thus lowering the cost of the navigation system. It was also assumed that the UAV would carry differing payloads, each with their own navigation system requirements. The basic architecture of the navigation system was to be dual-string in order to support the flight critical reliability goals of the aircraft. The system consisted of dual LN-200 fiber-optic gyro inertial measurement units, dual navigation computers, a SCAT-1 differential GPS data link receiver, and dual flight control computers. A navigation system test pallet was built, and flown in a Beechcraft King Air in order to prove out the hardware and software. Results of this manned aircraft flight test clearly showed that the system could provide the required accuracy to support autonomous taxi, takeoff and landing. Another result of the testing was the checkout of a scheme to integrate and use any other navigation system aboard the aircraft supporting a payload. Thus, if a payload had a requirement for a higher accuracy navigator, the flight control computer software could take advantage of that redundant navigator, thus increasing the flight critical reliability of the system.
Published in:	Proceedings of the 12th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1999) September 14 - 17, 1999 Nashville, TN
Pages:	1107 - 1114
Cite this article:	Loegering, Greg, "The Global Hawk Navigation SystemAn Odyssey in the Development of an Unmanned Aerial Vehicle," Proceedings of the 12th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1999), Nashville, TN, September 1999, pp. 1107-1114.
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