The invention is a method and apparatus for updating the attitude of a body byutilizing aplurality of gyros to measure as a function of time the angular rate vector orthe integratedangular rate vector for the body. The method comprises the steps of (1)obtaining measuredvalues of the angular rate vector at a plurality of readout intervals, (2)obtaining a smoothedvalue of each of one or more smoothed representations of the angular ratevector at the end ofeach of a plurality of smoothing intervals, and (3) obtaining the updatedattitude of the body atthe end of an update interval by utilizing the attitude at the beginning ofthe update interval andthe smoothed values of the smoothed representations of the angular rate vectorobtained duringthe update interval. A smoothed representation is a weighted sum of themeasured valuesobtained during a smoothing interval. The attitude is updated at the end of anupdate interval byapplying a rotation vector to the attitude at the end of the prior updateinterval, the rotation vectorbeing a weighted sum of (1) a plurality of the smoothed values and (2) thevalues of a plurality ofcross-products of the smoothed values, the smoothed values having beenobtained during theupdate interval.
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