Northrop Grumman Systems Corporation

Edward J Knobbe

Carl L Bose

A strapped down astro-inertial navigator includes a roll outer gimbal, a pitch inner gimbal and a platform coupled to the inner gimbal. An instrument cluster which includes X-axis, Y-axis and Z-axis ring laser gyros (RLGs) and associated accelerometers is mounted to the platform. Also hard mounted to the platform is a stellar sensor which includes a telescope and a solid state focal plane array which views stellar reference objects. In an astro-inertial mode of operation one or more stellar objects are tracked for a period of time. The roll and the pitch gimbals are employed to point the telescope and, periodically, to observe and average out the effects of star sensor and horizontal accelerometer errors. The star sensor error observability is accomplished by periodically rotating the inner and outer gimbals through 180.degree. and the stellar objects once again tracked. Due to the 180.degree. rotation boresight errors within the stellar tracker are observed and compensated for. The 180.degree. rotation also serves to reorient the accelerometer input axes by 180.degree., thereby also beneficially causing accelerometer errors to average out. In a free inertial mode of operation the inner and outer gimbals are both continuously rotated through plus and minus 360.degree. but at different rotational rates to provide 3 axis error averaging of both gyro and accelerometer errors.

Two gimbal error averaging astro-inertial navigator

A navigation system 12 for an evasive maneuvering reentry vehicle (EMRV) 10 includes a three-axes strapdown inertial navigator 14 which includes RLGs or other types of gyroscopes and also accelerometers. An altimeter, such as a radar altimeter 16, which is normally provided on the EMRV 10, provides an output (h) to the navigation system 12, the output being expressive of the altitude of the EMRV 10 from the earth's surface. The altitude measurement output (h) is processed by a statistical filter, such as a Kalman filter 18, in conjunction with the inertial solution (X) from the navigator 14. The output of the filter 18 is an estimated inertial correction which is combined with the inertial position and velocity output of the navigator 14 at a block 20 to yield a corrected position and velocity output. It is shown that a single altitude measurement is sufficient to derive three position and three velocity compensations for the EMRV 10.

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Huntington Beach, CA, United States of America

Edward J Knobbe