The Department of Defense (DOD) plans to keep the Global Positioning System (GPS) at the core of its positioning, navigation, and timing (PNT) solution, using other PNT technology to complement GPS or as an alternative for when GPS is degraded or unavailable. DOD’s alternative PNT science and technology portfolio explores two approaches: improved sensors to provide relative PNT information, and external sources to provide absolute positioning and navigation.
Relative PNT technologies include inertial sensors and clocks to allow a platform to track its position and keep track of time without an external signal like GPS. However, relative PNT technologies require another PNT technology to correct errors that can accumulate with such systems. Absolute PNT technologies allow a platform to use external sources of information to determine its position but rely on the availability of those external sources. Absolute PNT technologies include celestial and magnetic navigation as well as the use of very low radiofrequencies or low Earth orbit satellites to transmit information.