Alternatives to GPS

The U.S. Navy is currently pursuing several approaches to improving the reliability of precision navigation systems, including those that would still permit precision navigation in the event that the Global Positioning System (GPS) is denied or unavailable. This paper examines two alternatives to GPS: bathymetric and celestial navigation. Bathymetric navigation, a non-deniable source of position, determines a position by correlating real time returns from an echo sounder with a digitally stored bathymetric map of an area being traversed. While used successfully for many years by ballistic missile submarines, neither current attack submarines nor surface ships have taken full advantage of this technology. The SSC-SD has demonstrated that when using GPS-based, high-resolution bathymetric charts, along with narrow beam echo sounders, position fix accuracy approaching that of the reference chart can be achieved. Studies conducted by the U.S. Naval Observatory (USNO) show that using present-day star tracker technology, position accuracy derived from a celestial reference could be within one arcsecond (30 meters or 100 feet on the Earth's surface). The USNO, SSC-SD, and the Naval Research Laboratory are currently conducting a joint feasibility study to assess the technology used in modern star trackers. The goal is the development of small, lightweight, inexpensive, and reliable celestial systems that can be coupled to existing Inertial navigation systems for ship and aircraft navigation. Both of these alternatives to GPS can be used to improve navigation performance, and to provide accurate position in the event of GPS loss or denial.