George M. Siouris, D.Eng.Sc., is Adjunct Professor in the Department of Electrical and Computer Engineering at the Air Force Institute of Technology, and a researcher with the Directorate of Development Planning, Studies and Analysis Division, Wright-Patterson Air Force Base, Ohio. Dr. Siouris has written numerous technical papers, book reviews, and conference papers; contributed a chapter on inertial navigation to the Encyclopedia of Physical Science Technology; and is the author of Aerospace Avionics Systems: A Modern Synthesis. From 1983 to 1993 he was the Editor for Navigation/Tracking Systems in the IEEE Transactions on Aerospace and Electronic Systems. His primary research interests include theory and applications of inertial navigation and guidance systems, modeling of physical systems, and applications of modern control and estimation theory.