CN113188540A - Inertia/astronomical self-adaptive filtering method based on star number and configuration - Google Patents
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Abstract
The invention discloses an inertia/astronomical self-adaptive filtering method based on the number and configuration of stars, and belongs to the technical field of integrated navigation. The method comprises the following steps: s1, modeling astronomical attitude determination errors; s2, deducing an inertia/astronomical adaptive filtering method based on the star vector number and the configuration; and S3, verifying the effectiveness of the inertia/astronomical adaptive filtering method. The simulation result of the invention shows that the designed inertia/astronomical self-adaptive filtering method is utilized to realize the optimal utilization of the inertia navigation information and the astronomical navigation information compared with the traditional Kalman filtering fusion method, thereby effectively improving the output precision of the integrated navigation system.
Description
Technical Field
The invention relates to an inertia/astronomical self-adaptive filtering method based on the number and configuration of stars, and belongs to the technical field of integrated navigation.
Background
The astronomical navigation system has high output precision and errors are not accumulated along with time, so that the astronomical navigation system is very suitable to be used as an inertia/astronomical combined navigation system together with inertial navigation, and the inertia/astronomical combined navigation system is widely applied to spacecrafts, long-endurance airplanes and the like. However, the attitude accuracy of the astronomical navigation also changes dynamically along with the change of the star observation condition, the measurement noise of the kalman filter determines the trust degree of the filter on the measurement of the quantity, the fixed measurement noise cannot realize the optimal observation on the astronomical navigation attitude, and an adaptive kalman filter with the measurement noise dynamically adjusted along with the astronomical observation trust degree needs to be designed to realize the optimal fusion of the inertial navigation information and the astronomical navigation information.
Disclosure of Invention
The invention provides an inertia/astronomical adaptive filtering method based on star number and configuration.
The invention adopts the following technical scheme for solving the technical problems:
an inertial/astronomical adaptive filtering method based on star number and configuration comprises the following steps:
s1, collecting star light vectors through a star sensor, and carrying out astronomical attitude determination error modeling based on the number and configuration of the collected star light vectors;
s2, deducing an inertia/astronomical self-adaptive filtering method based on the star vector number and configuration according to the actual influence of the star light vector on the astronomical attitude determination error;
and S3, verifying the effectiveness of the inertial/astronomical adaptive filtering method by simulating a starlight vector.
Step S1 includes the following steps:
s11, astronomical navigation pose determination;
and calculating the position information of the fixed star unit vector in the star sensor coordinate system according to the image point position, wherein the calculation formula is as follows:
in the formula, skIs the unit vector coordinate, u, of the kth fixed star in the star sensor coordinate systemkProjecting the x-direction coordinate, v, of the image point for the star vectorkProjecting the y-direction coordinate of an image point for the fixed star vector, wherein f is a focal length;
denote the vector coordinate system as Ob-xbybzbAbbreviated as "b" and the centroid inertial coordinate system is "Oi-xiyiziThe coordinate system s of the star sensor is regarded as coincidence with the coordinate system b of the carrier, and the star sensor obtains the coordinate s of the fixed star relative to the carrier coordinate system1、s2、…snWherein s isk=[xsk ysk zsk]T(k ═ 1,2, … n); meanwhile, the coordinates v of the fixed stars relative to the geocentric inertial coordinate system are calculated through the navigation ephemeris1、v2、…vnWherein v isk=[xik yik zik]TThen skAnd vkThe relationship of (a) to (b) is as follows:
in the formula, vkIs the coordinate vector, s, of the kth satellite relative to the Earth's center inertial framekAs a coordinate vector, matrix, of the kth satellite relative to the carrier coordinate systemIs an attitude transformation matrix from a star sensor coordinate system s system to a geocentric inertial coordinate system i systemThe attitude transformation matrix from a carrier coordinate system b to a geocentric inertial coordinate system i is used, the s system is superposed with the b system, and the two matrixes are equivalent;
therefore, when the number n of stars observed by the star sensor is more than or equal to 3, the attitude transformation matrix of the carrier system relative to the inertial system is obtained by least square fitting of each star observation vectorNamely, it is
Wherein the content of the first and second substances,
Q=(VTV)-1VT
q is a conversion coefficient matrix;
s12, modeling astronomical attitude determination errors;
the actual vector information of the star relative to the star sensor coordinate system should be:
wherein, Delta S is astronomical attitude determination observation error,the actual coordinate vector of the fixed star relative to the star sensor coordinate system is shown, and S is an ideal coordinate vector of the fixed star relative to the star sensor coordinate system;
the attitude transformation matrix thus solved is:
wherein the content of the first and second substances,
taking a carrier coordinate system b as a reference coordinate system, and recording an astronomical attitude determination error vector as When the astronomical attitude determination error angles are all small, the attitude transformation matrixExpressed as:
wherein b' is expressed as a calculation carrier coordinate system with errors,for the reality of the carrier coordinate system relative to the inertial coordinate systemA matrix of the attitude transformation is generated,is the actual attitude transformation matrix variation of the carrier coordinate system relative to the inertial coordinate system,is an attitude transformation matrix from an actual carrier coordinate system to an ideal carrier coordinate system,for an error angle of rotation in the x-axis direction,for an error angle of rotation in the y-axis direction,is an error angle of rotation in the z-axis direction;
further obtaining:
wherein the content of the first and second substances,
let the covariance matrix of matrix M be PMAnd then:
further obtaining:
wherein, PMCovariance matrix as matrix MIs a covariance matrix of the attitude determination error vector, and tr () is a trace of a matrix;
when the measurement noise delta S of the star sensor is certain and is Gaussian white noise, the following results are obtained:
thus, the astronomical attitude determination error variance is:
wherein A ═ VTV)*Is a 3 × 3 square matrix, is a matrix VTThe companion matrix of V is the matrix of V,for the mean square error coefficient of astronomical attitude determination errors, det () represents determinant;
and S13, linearly fitting the astronomical attitude determination mean square error and the attitude determination error mean square error coefficient ξ.
Linearly fitting the astronomical attitude determination mean square error and the attitude determination error mean square error coefficient xi to obtain the approximate linear relation of the astronomical attitude determination mean square error and the attitude determination error mean square error coefficient xi
δc=3.32ξ+1.36
Wherein, deltacAnd the astronomical attitude determination mean square error is obtained, observation noise is adjusted in real time through a fitted linear relation, and the combined navigation precision is improved.
The specific process of step S2 is as follows:
the linear Kalman filter is used for combination, and the state equation and the observation equation of the inertia and astronomical integrated navigation system are as follows:
wherein, X (t) is a system state variable;is the derivative of the system state variable; f (t) is a system matrix; g (t) is a system noise coefficient matrix; w (t) is a system noise matrix; z (t) is an observed quantity; h (t) is an observation matrix; v (t) is observation noise;
the inertial/astronomical integrated navigation system adopts a Kalman filtering mode to perform information fusion, and the state equation is as follows:
wherein the state variable X (t) is:
the state transition matrix is:
the noise matrix is:
the system noise vector is:
W(t)9×1=[ωgx ωgy ωgz ωrx ωry ωrz ωax ωay ωaz]T
wherein: phi is aE、φN、φUFor roll, pitch and roll angle errors, δ vE、δvN、δvURepresenting the speed errors of the inertial navigation system in the east, north and sky directions under the geographic coordinate system; delta L, delta lambda and delta h represent errors of longitude, latitude and height of the inertial navigation system in a ground-interior coordinate system; epsilonbx、εby、εbzRepresenting a gyro random constant error; epsilonrx、εry、εrzRepresenting a random error of a gyro first-order Markov process;representing a first order markov process random error of the accelerometer; a (t)18×18A state transition matrix for the system; g (t)18×9Is a noise coefficient matrix; w (t)9×1Is the white noise vector of the system;
FNtransformation matrix for corresponding state quantities of gyro and accelerometer, FSTransforming the state quantities of the gyro and the accelerometer into a matrix of error quantities, FMIs an error amount transformation matrix, O is a null matrix with all elements being 0, O3×3Is an empty matrix of 3 rows and 3 columns, O9×3Is an empty matrix of 9 rows and 3 columns,for transformation of the carrier coordinate system into the geographic coordinate system, I3×3In an identity matrix of three rows and three columns, Trx、Try、TrzComponents of gyro error-related time in three axes, Tax、Tay、TazFor the time of accelerometer correlation, the component in three axes, ωgx、ωgy、ωgzDriving white noise, omega, for a first order Markov process for three axes of a gyroscoperx、ωry、ωrzWhite noise, omega, in three axes of the gyroscopeax、ωay、ωazDriving white noise for a first order markov process for three axes of the accelerometer;
defining the observed quantity as the difference between the attitude angle of the carrier measured by astronomical navigation and the attitude angle of inertial navigation, wherein the observation equation is as follows:
ZC(t)=HC(t)X(t)+vC(t)
at small platform error angles, the observation matrix is represented by the following formula:
in the formula, HC(t) the observation matrixes gamma, theta and psi are respectively roll angle, pitch angle and course angle;
thus, the observation equation is expressed as:
in the formula, gammaI、θI、ψI,γCNS、θCNS、ψCNSRespectively outputting roll, pitch and yaw angles of inertial navigation and astronomical navigation,representing the east, north and sky direction platform error angle v of inertial navigation in the geographic coordinate systemC(t) is attitude error angle observation noise, vC(t) will adapt the size, v, as the observed star vector changesC(t) is represented as follows:
wherein, deltacIs the noise coefficient and alpha is the adaptive coefficient.
The invention has the following beneficial effects:
according to the inertia/astronomical self-adaptive filtering method based on the star number and the configuration, when the star number is small, the noise matrix value measured by Kalman filtering is increased, so that the reliability of astronomical attitude information is reduced; and when the number of stars is large, reducing the noise matrix value measured by Kalman filtering to increase the reliability of the astronomical attitude information. The noise matrix value measured by Kalman filtering is adjusted in real time according to the star number and the attitude determination error mean square error coefficient xi, so that the stability and the integrated navigation precision of the system can be improved to a great extent. Therefore, the studied adaptive filtering method has rationality and correctness.
Drawings
FIG. 1 is a flow chart of the method of the present invention.
FIG. 2 is a method simulation track graph.
FIG. 3(a) is a graph showing the accuracy analysis of the roll angle under the three-star condition; FIG. 3(b) is a graph of accuracy analysis of the pitch angle under the three-star condition; FIG. 3(c) is a diagram of the accuracy analysis of the course angle under the three-star condition.
FIG. 4(a) is a diagram of an analysis of accuracy of a roll angle under a six-star condition; FIG. 4(b) is a diagram of accuracy analysis of the pitch angle under six-star condition; fig. 4(c) is a diagram of the accuracy analysis of the course angle under the six-star condition.
FIG. 5(a) is a view showing an accuracy analysis of a roll angle under a ten-star condition; FIG. 5(b) is a diagram of accuracy analysis of the pitch angle under ten-star condition; FIG. 5(c) is a diagram of the accuracy analysis of the course angle under the condition of ten stars.
FIG. 6(a) is a plot of adaptive filtered versus non-adaptive filtered roll angle error; FIG. 6(b) is a plot of pitch error versus adaptive filtering and non-adaptive filtering; FIG. 6(c) is a plot of a comparison of adaptively filtered and non-adaptively filtered course angle error.
FIG. 7(a) is a graph comparing east position error with adaptive and non-adaptive filtering; FIG. 7(b) is a graph comparing adaptive filtered and non-adaptive filtered north position error; FIG. 7(c) is a graph comparing adaptive filtered and non-adaptive filtered spatial position error.
FIG. 8(a) is a graph comparing east-direction velocity error with adaptive and non-adaptive filtering; FIG. 8(b) is a graph comparing adaptive filtered and non-adaptive filtered northbound speed errors; FIG. 8(c) is a plot of adaptive filtered versus non-adaptive filtered antenna direction velocity error.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments.
As shown in fig. 1, the inertia/astronomical combination filtering method based on star number and configuration of the present invention comprises the following steps:
s11, astronomical navigation pose determination;
the star sensor can be regarded as an information processing system, input information is a starlight direction vector, and output information is the attitude of the aircraft under an inertial coordinate system. The input information comes from two aspects, on the one hand from the navigation star catalogue and on the other hand from the real-time measurement of the star sensor. O iss-xsyszsIs the star sensor coordinate system (abbreviated as s system), OUvw is a CCD array plane imaging coordinate system; o issO is the direction of the optical axis, OsysShaft, OwThe axes are all consistent with the direction of the optical axis; (u)k,vk) The position information of the image point of a certain star on the CCD array surface is obtained. According to the image point position, the position information of the star unit vector in the star sensor coordinate system can be obtained through calculation. The calculation formula is as follows:
in the formula, skIs the unit vector coordinate of the kth fixed star in the star sensor coordinate system, f is the focal length of the optical lens, ukProjecting the x-direction coordinate, v, of the image point for the star vectorkAnd projecting the y-direction coordinate of the image point for the star vector.
Denote the vector coordinate system as Ob-xbybzb(abbreviated as "b" system), the centroid inertial coordinate system is Oi-xiyizi(abbreviated as i series). The star sensor coordinate system s and the carrier coordinate system b are regarded as coincidence, and the star sensor can obtain the coordinate s of the fixed star relative to the carrier coordinate system1、s2、…snWherein s isk=[xsk ysk zsk]T(k ═ 1,2, … n); meanwhile, the coordinates v of the fixed stars relative to the geocentric inertial coordinate system can be calculated through the navigation ephemeris1、v2、…vnWherein v isk=[xik yikzik]TThen skAnd vkThe relationship of (a) to (b) is as follows:
in the formula, vkIs the coordinate vector, s, of the kth satellite relative to the Earth's center inertial framekAs a coordinate vector, matrix, of the kth satellite relative to the carrier coordinate systemIs an attitude transformation matrix from a star sensor coordinate system s system to a geocentric inertial coordinate system i systemThe attitude transformation matrix from a carrier coordinate system b to a geocentric inertial coordinate system i is adopted, the s system is superposed with the b system, and the two matrixes are equivalent.
therefore, when the number n of stars observed by the star sensor is more than or equal to 3, the attitude transformation matrix of the carrier system relative to the inertial system can be obtained by least square fitting of each star observation vectorNamely, it is
Wherein the content of the first and second substances,
Q=(VTV)-1VT
q is a conversion coefficient matrix.
S12, modeling astronomical attitude determination errors;
due to the existence of observation errors of the star sensor, errors of a star observation vector are caused, and the actual vector information of the star relative to the star sensor coordinate system is as follows:
wherein, Delta S is astronomical attitude determination observation error,the coordinate vector of the fixed star relative to the star sensor coordinate system is S, and the coordinate vector of the fixed star relative to the star sensor coordinate system is S.
The attitude transformation matrix thus solved is:
wherein the content of the first and second substances,
taking a carrier coordinate system b as a reference coordinate system, and recording an astronomical attitude determination error vector as When the astronomical attitude determination error angles are all small, the attitude transformation matrixCan be expressed as:
wherein the content of the first and second substances,is the actual attitude transformation matrix of the carrier coordinate system relative to the inertial coordinate system,is the actual attitude transformation matrix variation of the carrier coordinate system relative to the inertial coordinate system,is an attitude transformation matrix from an actual carrier coordinate system to an inertial coordinate system,is an attitude transformation matrix from an actual carrier coordinate system to an ideal carrier coordinate system,for an error angle of rotation in the x-axis direction,for an error angle of rotation in the y-axis direction,is the error angle of rotation in the z-axis direction.
Further, it is possible to obtain:
wherein the content of the first and second substances,
wherein:an attitude transformation matrix from an inertial coordinate system to a carrier coordinate system;
let the covariance matrix of matrix M be PMAnd then:
further, it is possible to obtain:
wherein: pMCovariance matrix as matrix MIs the covariance matrix of the attitude determination error vector, tr () is the trace of the fetch matrix.
When the measurement noise delta S of the star sensor is certain and is Gaussian white noise, the following can be obtained:
wherein, PΔIs an error matrixE () is expressed as a mean value,to observe the variance of the noise Δ S.
Thus, the astronomical attitude determination error variance is:
wherein A ═ VTV)*Is a 3 × 3 square matrix, is a matrix VTThe companion matrix of V is the matrix of V,to the astronomical attitude determination error mean square error coefficient, det () represents a determinant.
And S13, linearly fitting the astronomical attitude determination mean square error and the astronomical attitude determination error mean square error coefficient ξ.
And performing linear fitting on the astronomical attitude determination mean square error and the error weight coefficient k to obtain an approximate linear relation between the astronomical attitude determination mean square error and the error weight coefficient k.
δc=3.32ξ+1.36
Wherein, deltacThe astronomical attitude determination mean square error is adopted, observation noise can be adjusted in real time through the fitted linear relation, and the combined navigation precision is improved.
Further, step S2 is specifically: the linear Kalman filter is used for combination, and the state equation and the observation equation of the inertia and astronomical integrated navigation system are as follows:
wherein X (t) is a system state variable,is the derivative of the system state variable; f (t) is a system matrix; g (t) is a system noise coefficient matrix; w (t) is a system noise matrix; z (t) is an observed quantity; h (t) is an observation matrix; v (t) is observation noise;
s21, equation of state
The inertial/astronomical integrated navigation system adopts a Kalman filtering mode to perform information fusion, and the state equation is as follows:
wherein the state variable X (t) is:
wherein: phi is aE、φN、φUFor roll, pitch and roll angle errors, δ vE、δvN、δvURepresenting the speed errors of the inertial navigation system in the east, north and sky directions under the geographic coordinate system; delta L, delta lambda and delta h represent errors of longitude, latitude and height of the inertial navigation system in a ground-interior coordinate system; epsilonbx、εby、εbzRepresenting a gyro random constant error; epsilonrx、εry、εrzRepresenting a random error of a gyro first-order Markov process;representing a first order markov process random error of the accelerometer; a (t)18×18A state transition matrix for the system; g (t)18×9Is a noise coefficient matrix; w (t)9×1Is the white noise vector of the system.
The state transition matrix is:
wherein: fNTransformation matrix for corresponding state quantities of gyro and accelerometer, FSBeing gyros and accelerationsConversion matrix from state quantity to error quantity of the meter, FMIn order to transform the matrix for the amount of error,for converting the carrier coordinate system to the geographic coordinate system, O is a null matrix, O3×3Is a 3-row and 3-column empty matrix, Trx、Try、TrzComponents of gyro error-related time in three axes, Tax、Tay、TazThe components of the accelerometer correlation time in the three axes.
The noise matrix is:
wherein: o is9×3An empty matrix of 9 rows and 3 columns, O3×3Is an empty matrix of 3 rows and 3 columns, I3×3Is an identity matrix of 3 rows and 3 columns,and converting the vector coordinate system into a geographic coordinate system.
The system noise vector is:
W(t)9×1=[ωgx ωgy ωgz ωrx ωry ωrz ωax ωay ωaz]T
wherein: omegagx、ωgy、ωgzDriving white noise, omega, for a first order Markov process for three axes of a gyroscoperx、ωry、ωrzWhite noise, omega, in three axes of the gyroscopeax、ωay、ωazWhite noise is driven for the first order markov process for the three axes of the accelerometer.
S22, observation equation
Defining the observed quantity as the difference between the attitude angle of the carrier measured by astronomical navigation and the attitude angle of inertial navigation, wherein the observation equation is as follows:
ZC(t)=HC(t)X(t)+vC(t)
when the platform error angle is small, the observation matrix can be represented by the following formula:
wherein gamma, theta and psi are roll angle, pitch angle and course angle respectively.
Thus, the observation equation can be expressed as:
in the formula, gammaI、θI、ψI,γCNS、θCNS、ψCNSRespectively outputting roll, pitch and yaw angles of inertial navigation and astronomical navigation,representing the east, north and sky direction platform error angle v of inertial navigation in the geographic coordinate systemC(t) is attitude error angle observation noise, vC(t) will adapt the size, v, as the observed star vector changesC(t) is represented as follows:
wherein, deltacIs the noise coefficient and alpha is the adaptive coefficient.
And S31, verifying and analyzing the influence of the noise matrix observed by the filter on the navigation precision.
TABLE 1 sensor simulation parameter settings
In order to effectively explain the influence of observation noise on the navigation precision of the whole inertia/astronomical combined navigation system under different sidereal vectors, simulation verification analysis is carried out in the section, flight path and sensor parameters are shown in a figure 2 and a table 1, Kalman filtering observation matrix noise simulation parameters are shown in a table 2, and simulation results are shown in a figure 3, a figure 4, a figure 5 and a table 3.
Table 2 measured noise simulation parameter settings
Number of stars | Astronomical attitude measurement noise (second) |
3 | 3、5、15 |
6 | 3、5、15 |
10 | 3、5、15 |
TABLE 3 statistical results of the influence of astronomical attitude observation noise on the error RMS
It can be known from the statistics of the error curve and the RMS (root mean square error) error, when the number of the fixed star observations is 3, the mean square error coefficient ξ of the astronomical attitude determination error is larger, so that the astronomical attitude determination error is larger, the reliability is poor, the larger observation noise of the kalman filter can improve the precision of the integrated navigation system, and the output precision can be reduced if the observation noise matrix value is too small. When the observation quantity of the fixed stars is 6, the astronomical attitude determination precision is gradually improved along with the increase of the number of the fixed stars, and the combined navigation precision can be improved by properly reducing astronomical observation noise. When the number of stars observed is 10. The astronomical attitude determination precision is remarkably improved, the attitude output of the astronomical navigation system can be trusted, and the astronomical observation noise is reduced, so that the precision of the whole navigation system is further improved.
According to preset carrier track and navigation sensor parameters, under the condition that the number and the configuration of simulated star vectors are different, the influence of observation noise on the navigation precision of the whole inertia/astronomical combined navigation system is simulated, and the simulation result can obtain that when the observation number of the star vectors is 3, the mean square error coefficient xi of the astronomical attitude determination error is larger, so that the astronomical attitude determination error is larger, the reliability is poor, the larger observation noise of the Kalman filter can improve the precision of the combined navigation system, and if the observation noise matrix value is too small, the output precision can be reduced. When the observation quantity of the fixed stars is 6, the astronomical attitude determination precision is gradually improved along with the increase of the number of the fixed stars, and the combined navigation precision can be improved by properly reducing astronomical observation noise. When the number of stars observed is 10. The astronomical attitude determination precision is remarkably improved, the attitude output of the astronomical navigation system can be trusted, and the astronomical observation noise is reduced, so that the precision of the whole navigation system is further improved.
S32, self-adaptive filtering verification analysis under the condition that the star number is time-varying;
when the visible number of stars dynamically changes, simulation verification analysis is respectively carried out on the navigation performance of adaptive filtering and non-adaptive filtering for comparing the navigation performance of the adaptive filtering with the navigation performance of the non-adaptive filtering, and when the number of stars is small, a Kalman filtering observation noise matrix value is increased so as to reduce the reliability of astronomical attitude information; when the number of stars is large, the Kalman filtering observation noise matrix value is reduced to increase the reliability of the astronomical attitude information, and simulation curves are shown in FIGS. 6, 7 and 8 and Table 4.
TABLE 4 navigation error RMS statistics for dynamically changing sidereal numbers
When the number of fixed stars is small, a Kalman filtering observation noise matrix value is increased so as to reduce the reliability of astronomical attitude information; and when the number of stars is large, reducing a Kalman filtering observation noise matrix value to increase the reliability of the astronomical attitude information. It can be seen from the error curve diagram and the error RMS (root mean square) statistical result that the Kalman filtering observation noise matrix value is adjusted in real time according to the star number and the error weight k thereof, the stability and the integrated navigation precision of the system can be improved to a great extent, and the reasonability and the correctness of the researched adaptive filtering algorithm are verified.
Claims (3)
1. An inertial/astronomical adaptive filtering method based on star number and configuration is characterized by comprising the following steps of:
s1, collecting star light vectors through a star sensor, and carrying out astronomical attitude determination error modeling based on the number and configuration of the collected star light vectors;
s2, deducing an inertia/astronomical self-adaptive filtering method based on the star vector number and configuration according to the actual influence of the star light vector on the astronomical attitude determination error;
and S3, verifying the effectiveness of the inertial/astronomical adaptive filtering method by simulating a starlight vector.
2. The method of inertial/astronomical adaptive filtering based on star number and configuration according to claim 1, wherein step S1 comprises the steps of:
s11, astronomical navigation pose determination;
according to the image point position, calculating to obtain the position information of the fixed star unit vector in the star sensor coordinate system, wherein the calculation formula is as follows:
in the formula, skIs the unit vector coordinate, u, of the kth fixed star in the star sensor coordinate systemkProjecting the x-direction coordinate, v, of the image point for the star vectorkProjecting y-squares of image points for star vectorsDirectional coordinates, f is focal length;
denote the vector coordinate system as Ob-xbybzbAbbreviated as "b" and the centroid inertial coordinate system is "Oi-xiyiziThe coordinate system s of the star sensor is regarded as coincidence with the coordinate system b of the carrier, and the star sensor obtains the coordinate s of the fixed star relative to the carrier coordinate system1、s2、…snWherein s isk=[xsk ysk zsk]TK is 1,2, … n; meanwhile, the coordinates v of the fixed stars relative to the geocentric inertial coordinate system are calculated through the navigation ephemeris1、v2、…vnWherein v isk=[xik yik zik]TThen skAnd vkThe relationship of (a) to (b) is as follows:
in the formula, vkIs the coordinate vector, s, of the kth satellite relative to the Earth's center inertial framekAs a coordinate vector, matrix, of the kth satellite relative to the carrier coordinate systemIs an attitude transformation matrix from a star sensor coordinate system s system to a geocentric inertial coordinate system i systemThe attitude transformation matrix from a carrier coordinate system b to a geocentric inertial coordinate system i is used, the s system is superposed with the b system, and the two matrixes are equivalent;
therefore, when the number n of stars observed by the star sensor is more than or equal to 3, the attitude transformation matrix of the carrier system relative to the inertial system is obtained by least square fitting of each star observation vectorNamely, it is
Wherein the content of the first and second substances,
Q=(VTV)-1VT
q is a conversion coefficient matrix;
s12, modeling astronomical attitude determination errors;
the actual vector information of the star relative to the star sensor coordinate system should be:
wherein, Delta S is astronomical attitude determination observation error,the actual coordinate vector of the fixed star relative to the star sensor coordinate system is shown, and S is an ideal coordinate vector of the fixed star relative to the star sensor coordinate system;
the attitude transformation matrix thus solved is:
wherein the content of the first and second substances,
taking a carrier coordinate system b as a reference coordinate system, and recording an astronomical attitude determination error vector as When the astronomical attitude determination error angles are all small, the attitude transformation matrixExpressed as:
wherein b' is expressed as a calculation carrier coordinate system with errors,is the actual attitude transformation matrix of the carrier coordinate system relative to the inertial coordinate system,is the actual attitude transformation matrix variation of the carrier coordinate system relative to the inertial coordinate system,is an attitude transformation matrix from an actual carrier coordinate system to an ideal carrier coordinate system,for an error angle of rotation in the x-axis direction,for an error angle of rotation in the y-axis direction,is an error angle of rotation in the z-axis direction;
further obtaining:
wherein the content of the first and second substances,
let the covariance matrix of matrix M be PMAnd then:
further obtaining:
wherein, PMCovariance matrix as matrix MIs a covariance matrix of the attitude determination error vector, and tr () is a trace of a matrix;
when the measurement noise delta S of the star sensor is certain and is Gaussian white noise, the following results are obtained:
thus, the astronomical attitude determination error variance is:
wherein A ═ VTV)*Is a 3 × 3 square matrix, is a matrix VTThe companion matrix of V is the matrix of V,for the mean square error coefficient of astronomical attitude determination errors, det () represents determinant;
s13, linearly fitting the astronomical attitude determination mean square error and the attitude determination error mean square error coefficient xi
Linearly fitting the astronomical attitude determination mean square error and the attitude determination error mean square error coefficient xi to obtain the approximate linear relation of the astronomical attitude determination mean square error and the attitude determination error mean square error coefficient xi
δc=3.32ξ+1.36
Wherein, deltacAnd the astronomical attitude determination mean square error is obtained, observation noise is adjusted in real time through a fitted linear relation, and the combined navigation precision is improved.
3. The method for inertial/astronomical adaptive filtering based on star number and configuration according to claim 1, wherein the step S2 is implemented as follows:
the linear Kalman filter is used for combination, and the state equation and the observation equation of the inertia and astronomical integrated navigation system are as follows:
wherein, X (t) is a system state variable;is the derivative of the system state variable; f (t) is a system matrix; g (t) is a system noise coefficient matrix; w (t) is a system noise matrix; z (t) is an observed quantity; h (t) is an observation matrix; v (t) is observation noise;
the inertial/astronomical integrated navigation system adopts a Kalman filtering mode to perform information fusion, and the state equation is as follows:
wherein the state variable X (t) is:
the state transition matrix is:
the noise matrix is:
the system noise vector is:
W(t)9×1=[ωgx ωgy ωgz ωrx ωry ωrz ωax ωay ωaz]T
wherein: phi is aE、φN、φUFor roll, pitch and roll angle errors, δ vE、δvN、δvURepresenting the speed errors of the inertial navigation system in the east, north and sky directions under the geographic coordinate system; delta L, delta lambda and delta h represent errors of longitude, latitude and height of the inertial navigation system in a ground-interior coordinate system; epsilonbx、εby、εbzRepresenting a gyro random constant error; epsilonrx、εry、εrzRepresenting a random error of a gyro first-order Markov process;representing a first order markov process random error of the accelerometer; a (t)18×18A state transition matrix for the system; g (t)18×9Is a noise coefficient matrix; w (t)9×1Is the white noise vector of the system;
FNtransformation matrix for corresponding state quantities of gyro and accelerometer, FSFor conversion of gyroscope and accelerometer state quantity into error quantityMatrix, FMIs an error amount transformation matrix, O is a null matrix with all elements being 0, O3×3Is an empty matrix of 3 rows and 3 columns, O9×3Is an empty matrix of 9 rows and 3 columns,for transformation of the carrier coordinate system into the geographic coordinate system, I3×3In an identity matrix of three rows and three columns, Trx、Try、TrzComponents of gyro error-related time in three axes, Tax、Tay、TazFor the time of accelerometer correlation, the component in three axes, ωgx、ωgy、ωgzDriving white noise, omega, for a first order Markov process for three axes of a gyroscoperx、ωry、ωrzWhite noise, omega, in three axes of the gyroscopeax、ωay、ωazDriving white noise for a first order markov process for three axes of the accelerometer;
defining the observed quantity as the difference between the attitude angle of the carrier measured by astronomical navigation and the attitude angle of inertial navigation, wherein the observation equation is as follows:
ZC(t)=HC(t)X(t)+vC(t)
at small platform error angles, the observation matrix is represented by the following formula:
in the formula, HC(t) is an observation matrix, and gamma, theta and psi are respectively a roll angle, a pitch angle and a course angle;
thus, the observation equation is expressed as:
in the formula, gammaI、θI、ψI,γCNS、θCNS、ψCNSAre respectively provided withRoll, pitch and yaw angles output for inertial navigation and astronomical navigation,representing the east, north and sky direction platform error angle v of inertial navigation in the geographic coordinate systemC(t) is attitude error angle observation noise, vC(t) will adapt the size, v, as the observed star vector changesC(t) is represented as follows:
wherein, deltacIs the noise coefficient and alpha is the adaptive coefficient.
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