The Use of the Global Positioning System ( GPS ) on an Attack Aircraft to Improve Altitude Accuracy During Weapons Delivery

The A-10 military attack aircraft employs an automated weapons delivery system to improve weapons delivery accuracy for free-fall munitions. The performance of this automated system is largely effected by the accuracy of the aircraft's altitude measurement. Throughout the A-10's tactical altitude range, the nominal performance of GPS represents the most accurate altitude measurement available to the aircraft. A concern with the use of GPS for weapons delivery is the degradation in performance during a degraded GPS mode or a GPS outage. In the absences of a GPS measurement, some form of an atmospheric sensor measurement is required to account for aircraft altitude changes. Depending on the vertical velocity of the aircraft, measurement lag in the atmospheric pressure sensor can represent a significant error source. Different techniques requiring different navigational architecture designs are possible to minimize altitude errors when GPS measurements are not available. Thesis Supervisor: Professor R. John Hansman Title: Associate Professor of Aeronautics and Astronautics, MIT Technical Supervisor: James I. Donna Title: Technical Staff Member, The Charles Stark Draper Laboratory, Inc. Acknowledgments (20 January 1995) I thank Mr. James Donna for all his technical assistance and insight in the writing of this thesis. I truly appreciate his expertise. I also thank Jeff Eggers for all his assistance with this thesis. The writing of this thesis also benefited from the technical assistance of Mr. Arnold Soltz and Mr. Mike Jackson. Thank you both. I am especially grateful for the proofreading of this thesis by Ms. Beverly Tuzzalino. Finally, a special thanks goes to Mr. Jack Stebe, Mr. Dow Hardy, and the entire Cockpit Systems Integration Laboratory team. Thanks a million. This thesis was prepared at The Charles Stark Draper Laboratory, Inc., under CSR C-159. Publication of this thesis does not constitute approval by Draper or the United States Air Force of the findings or conclusions contained herein. It is published for the exchange and stimulation of ideas. I hereby assign my copyright of this thesis to The Charles Stark Draper Laboratory, Inc., Cambridge, Massachusetts.