Stellar Inertial Navigation Applied to Cruise Vehicles

Basic inertial navigation systems used in cruise applications will, in general, experience position errors that continue to increase with time. A cruise vehicle is considered here to be one which may be expected to operate for periods of time between a few minutes to several months, and at velocities from near zero to Mach 3 near the surface of the earth. Various methods of augmenting the basic inertial system may be applied in order to alter the effect of the error sources by using information derived from external references. Among these are reference velocity, reference position and stellar information. These references may be used individually or in any combination. This paper will deal primarily with the concepts of utilizing stellar information in an inertial navigation system with some consideration given to the aspects of supplementing the stellar inertial system with reference velocity information. The effect of utilizing the stellar information is to eliminate the gyro drift as a major source of error in the system. In fact, the application of proportional plus integral control will maintain the gyro bias compensation in a "tuned-up" condition so that in the event the stellar control is lost due to cloud cover or malfunction, the effect of the gyro contribution to system error will be minimized.