Presented to: William A. Feess
Citation: For critical early developments in the field of accurate navigation by satellite, and continuous, sustained improvements to GPS position and timing accuracy for all users.
As a key participant in the Air Force 621B program, the satellite-based navigation predecessor to GPS, Mr. Feess conducted some of the earliest testing and analysis in the early 1970s to prove that the concept of one-way ranging from satellites using Code Division Multiple Access (CDMA) signals was a viable means of navigation. These critical test results were instrumental in obtaining the necessary approvals and funding to proceed with the GPS program. His multiple contributions to the early development of GPS were recognized by Dr. Brad Parkinson in his 2010 two-part article on "The Origins of GPS" in GPS World Magazine.
During the 1980s Bill helped develop the concept of GPS "composite clock," which combined measurements from all the GPS Monitor Station clocks and operational GPS Satellite atomic frequency standards to produce a time reference for the GPS system. Prior to this composite clock, GPS time was referenced to one of the Monitor Stations' operational frequency standards. The use of a composite GPS clock greatly enhanced the accuracy of timing and navigation services to all GPS users. In 1989, he also helped develop rigorous methods for steering GPS time to Universal Time Coordinated (UTC), a development which has enabled GPS to serve as the primary means for distribution of UTC worldwide.
In addition to helping define and improve GPS time, Mr. Feess has made multiple, substantial improvements to the orbit determination process that forms the heart of the GPS Operational Control Segment (OCS). In 1979, he led the adoption of a new "Y-bias" solar radiation pressure model for GPS satellites that improved orbit determination accuracy from 10 meters to 2 meters. Mr. Feess conducted extensive analysis of the ionospheric correction algorithm for single-frequency GPS users, and helped refine the current ionospheric model. The 2005 Accuracy Improvement Initiative (AII) improved GPS accuracy and integrity by adding measurements from National Geospatial-Intelligence Agency (NGA) monitor station receivers and other improvements to the OCS Kalman filter. Mr. Feess played an instrumental role in analyzing and predicting the accuracy and integrity improvements of AII to generate and maintain its support among the Air Force leadership. He also convinced DoD users to exploit the additional accuracy enabled by the Wide Area GPS Enhancement (WAGE) data messages.
Additionally Mr. Feess has shared his extensive knowledge and experience by mentoring dozens of colleagues and junior engineers at the Aerospace Corporation, the Air Force, and throughout the GPS industry.