Inertial Navigation System Error Model Research Articles

On Qualitative Characteristics of the State Variable Observability in Linear Time-Varying Models of Inertial Navigation Systems

A criterion for the degree of observability of state variables in linear time-varying systems is considered. The qualitative characteristics of the observability of the errors in inertial navigation systems are studied with a change in the aircraft flight altitude, the step of computation and in depending with the type of inertial navigation system, that are characterized by the values of the mean frequency of the random change in the drift of the gyroplatform. The results of simulation of navigation system errors, their degree of observability and estimation by the non-stationary Kalman filter are presented. The problem of determining the achievable accuracy of corrected inertial navigation systems in aircraft is investigated. In the models of the estimation algorithms, different values of the average frequency of the change in drift of the gyroplatform are used. A method for studying the achievable accuracy of corrected navigation systems has been developed, which makes it possible to make an informed decision on the use of the system in the design of the aircraft avionics. Based on the analysis of the state variable observability characteristics of navigation systems, it can be concluded that the accuracy of the estimation is dependent on the variable parameters of the inertial navigation system error model.

In-Space Calibration of a Skewed Gyro Quadruplet

Anewapproachtogyrocalibrationispresented,wherethespacecraftdynamicsequation,attitudemeasurements, and the gyro outputs are used in a pseudolinear Kalman e lter that estimates the calibration parameters. Also an algorithm is presented for calibrating a skewed quadruplet rather than the customary triad gyro set aligned along the body coordinate axes. In particular, a new misalignment error model is derived for this case. The new calibration algorithm is applied to the EOS-AQUA satellite gyros. The effectiveness of the new algorithm is demonstrated through simulations. YRO calibration, as well as calibration of other instruments, includes two stages. During the e rst stage, the instrument er- ror parameters are estimated, and in the second stage, those errors are continuously removed from the gyro readings. In the classical approach to gyro calibration, the gyro outputs are used to maintain or compute body orientation rather than used as measurements in the context of e ltering. In inertial navigation, for example, 1 gyro errors cause erroneous computation of velocity and position, and then when the latter are compared to measured velocity and posi- tion, a great portion of the computed velocity and position errors can be determined. The latter errors are then fed into a Kalman e lter (KF) that uses the inertial navigation system error model to infer the gyro errors. Similarly, when applying the classical approach to spacecraft(SC) attitude determination, the gyro outputs are used to compute theattitude, andthentheattitude measurements 2;3 areused to determine the attitude errors, which again using a KF indicates what the gyro errors are. Several ways of treating gyro calibration have been presented in the literature. 4i6 In the approach adopted in this work, the gyro outputs are used as angular rate measurements and are compared to estimated angular rates. However,thisapproachrequires the knowl- edge of the angular rate. In the past, 7 the estimated angular rate was computed in a rather simplistic way, assuming basically that the rate was constant. In the present work, the estimated angular rate is derived using a KF whose input can be any kind of attitude mea- surement; therefore, the angular rate experienced by the SC can be continuously changing, and yet a good estimate of the rate, neces- sary for calibration, can be obtained. The calibration algorithm presented in this work was derived for a set ofquadrupletgyros. This required the derivation of anewerror model,particularly forthe gyro misalignments.Thenewcalibration algorithmwas applied to thegyro package ofthe EOS-AQUA satel- lite. The latter consists of four gyros, which are given the task of measuring the three components of the SC angular velocity vector resolved in the body Cartesian coordinates.