Autonomous Celestial Inertial Navigation without GPS

A novel autonomous and portable Celestial Inertial Navigation System (C-INS) is proposed for unmanned surface vessels (USVs). The C-INS is capable of developing and maintaining accurate and continuously updated positional awareness on the Earth's surface without the use of GPS. It seamlessly fuses robotic guided ultra-precise astro-imaging with Earth inertial sensing capabilities to achieve Assured Position, Navigation, and Time (APNT). The C-INS has a mobile observatory that integrates: 1) a Robotic Gimbal Machine (RGM) guided astro-imaging unit that has a full range of freedom to point a telephoto imaging payload to any targeted azimuth and altitude direction with a ~0.01 arcsec angular resolution. The RGM is agile, versatile and programable, providing advanced imaging capabilities for precise celestial and vision navigation; and 2) a RGM North and Latitude Sensing Unit (NLSU) that operates a set of ultra-sensitive Fiber Optic Gyros (FOGs) to measure the Earth’s rotation. For North-finding, the RGM rotates a FOG to align the FOG’s sensing axis with the northing meridian plane of the horizontal coordinate system of the observatory. Similarly, for Latitude determination, the RGM actuates a FOG to recognize its positioning to the Earth’s center. The high-performance FOGs combined with the accurate pointing knowledge provided by the RGM gives the NLSU azimuth and latitude accuracy of sub 1 arcsecond accuracy for the USV, as well as the northing and easting speeds with a 1Hz data rate. Whenever a star becomes invisible because of time or weather, CCU automatically performs dead reckoning with the NLSU to maintain the position determination. Because the four intrinsic PNT parameters that NLSU senses have extremely low drift, without random walk, the dead reckoning is capable of maintaining the position fix within a FOM = 2 accuracy level for up to 72 hours. The C-INS allows USVs to navigate and understand their precise location on the Earth in a fully passive manner without electromagnetic emissions or needing to receive external radar, AIS, or GNSS transmissions. The absolute positioning accuracy that the system can achieve is a direct result of NGIT's R&D and innovation in aerial imaging and mapping. Over the past 15 years, NGIT’s principals have provided NASA and the DoD ultra-precise gimballed aerial hyperspectral, multispectral, thermal and optical mapping systems.