Showing papers on "GPS/INS published in 1973"

Updating Inertial Navigation Systems with VOR/DME Information

Abstract: Updating an inertial navigation system (INS) with VOR/DME information (from one or two stations) by means of a maximum-likelihood filter is shown to result in substantial improvements in navigational accuracy over that obtained by the use of a single VOR/DME (current practice). When continuously updating, the use of a high- quality INS (0.01 °/hr gyro drift) instead of a low-quality INS (1.0°/hr gyro drift) does not substantially improve position accuracy. In-flight alignment (or realignment) of an INS to an accuracy comparable to that of ground alignment can be accomplished by using two DME's. Several reduced-order suboptimal filters were found to perform nearly optimally. HE primary navigation aid for civil aircraft flying in the airspace of most of the developed countries of the world is the VOR/DME system. The VOR (Very high-frequency Omni- Range) and the DME (Distance Measuring Equipment) enable onboard determination of an aircraft's bearing relative to north at the fixed ground station and slant range from the station, respectively. Current use of the VOR/DME system involves primarily radial navigation, i.e., aircraft fly directly to or from the ground stations. However, some beginnings have been made in using the VOR/ DME system for area navigation, i.e., use of the system without being restricted to fly directly to or from the ground stations. The number of commercial airliners equipped with inertial navigation systems (INS's) is steadily increasing. The systems now onboard aircraft utilize a gyro-stabilized platform on which the accelerometers are mounted. The platform is aligned before takeoff to the desired orientation. Due to alignment errors and in-flight random disturbances such as gyro drift, scale-factor errors, and accelerometer bias errors, errors in the desired orientation of the platform increase with time. This results in increasing position and velocity errors. Thus, improving navi- gational accuracy by in-flight realignment of an INS is an interesting possibility. Position errors are generally greater for area than for radial navigation. This comes about because the position error resulting from a VOR angular error increases with distance from the station; and an aircraft is farther, on the average, from the VOR stations for area than for radial navigation. Hence, improved navigational accuracy is required to obtain an accuracy for area navigation comparable to that of present-day radial navigation. The availability of an onboard computer to do the triangulation computations required for area navigation suggests Presented as Paper 72-846 at the AIAA Guidance and Control