RU2607197C2 - Astronomical navigation system - Google Patents

Abstract

FIELD: instrument making.

SUBSTANCE: invention relates to instrument making and can be used in high-precision astroinertial navigation systems of aircrafts (AC). For this purpose, astroinertial AC system is additionally introduced with gravimeters, altimeters unit for measuring vertical acceleration of aircraft, gravitational acceleration processing unit and adders, the gravimeters are mounted on a separate platform, made with possibility of synchronous movement with aircraft and parallel to horizontal plane, the outputs of gravity meters and altimeter unit for measuring of vertical acceleration of aircraft are connected to computer inputs of gravitational acceleration meter which outputs are connected through adders to navigation computer of gimballess inertial navigation system, and outputs of accelerometers are connected to second inputs of adders.

EFFECT: technical result consists in increase of accuracy of output parameters by taking into account during measurements in real time of change of gravitational components of gravity acceleration.

1 cl, 1 dwg

Description

The invention relates to the field of instrumentation - high-precision astroinertial navigation systems for use in manned and unmanned aerial vehicles.

A known method and device for astroinertial navigation, including a stable platform with three cardan suspensions, on which an astroizing device with two degrees of freedom is installed, designed to track the stars day or night. The calculator stores positioning data for 61 stars, implements the algorithms of the platform inertial system, and corrects the navigation parameters determined by the inertial system according to the results of astronomical measurements. High accuracy of astroinertial measurements is determined by the quality of binding the axis of sight of stars to the local vertical, which is implemented by an inertial navigation system by setting the platform in a horizontal position. Astro correction reduces the error in determining the true course and the error in its positioning, regardless of the flight time of the Northrop star tracer aboard B-1B. Julian Moxom. Air Force Association Show. October 1983 ", as well as the work of" NAS-21 astro / inertial navigation system (United States). Jane's Avionics, July 1997 ".

However, these systems have significant disadvantages. The accuracy and reliability of systems is limited by a large number of rotating frames (at least five), the need for precision converters, and the need for regular ground calibrations.

The closest technical solution is the strapdown astroinertial navigation system (RF Patent No. 141801 of December 13, 2013, IPC G01C 21/02). It consists of:

- a strapdown inertial navigation system (SINS), which is a monoblock containing laser gyroscopes, accelerometers, an integrated GLONASS / GPS SNA navigation receiver, a power supply, a processor module for processing digital information and performing computational processes in accordance with the work program stored in the built-in memory a device (type flash), which provides the determination of angular position parameters and the solution of navigation problems;

- Astrovizing device (AVU), which includes a star sensor, an electronics unit, a protective housing, a solar sensor;

optical interface unit, which includes an artificial light source, a prism and a photodetector.

The star sensor, in turn, consists of: a base, a CCD sensor assembly, a video path assembly, a lens with a built-in shutter, and a lens hood. The electronics unit consists of a processor unit and a secondary power supply board.

The disadvantages of this device are the limited accuracy of the output parameters due to the use of the calculated cartographic data in the SINS processor module, and not the actual values of the gravitational component of gravity acceleration.

The technical task of the present invention is to improve the accuracy of the output parameters by taking into account in the process of measurement in real time changes in the gravitational components of the acceleration of gravity.

To accomplish this task, an astronautical system installed on an aircraft and containing a strapdown inertial navigation system, including accelerometers, gyroscopes, a satellite radio navigation system receiver, a navigation computer, an astrovization device with a computer that determines the angular parameters of star sighting and is connected to a free navigation navigation calculator system, while the outputs of the satellite radio navigation receiver with The systems and gyroscopes are connected to the inputs of the navigation computer of the strapdown inertial navigation system, gravimeters, a block of altimeters for measuring the vertical acceleration of the aircraft, a gravity calculator and adders are introduced into the system, while the gravimeters are installed on a separate platform that can synchronously move with the movement of the aircraft apparatus and parallel to the horizon plane, and the outputs of the gravimeters and the altimeter unit for measuring the vertical Oren aircraft connected to the inputs of calculating the acceleration of gravity, the outputs of which are connected via a combiner to the navigation calculator strapdown inertial navigation system and outputs of the accelerometers connected to the second inputs of the adders.

As you know, in the BINS software and algorithms, gravitational field models are used that correspond to the selected model of the Earth’s figure, for example, Krasovsky’s reference ellipsoid. This leads to a methodological error in determining the navigation parameters associated with the uncertainties of the Earth's gravitational field. According to available estimates of domestic and foreign experts, insufficient information on the parameters of the Earth's gravitational field introduces the following errors:

for serial inertial navigation systems - 10% in determining coordinates and up to 50% in determining speed;

for developed inertial navigation systems - 40% in determining coordinates and up to 5-75% in determining speed;

for advanced systems - 60% in determining coordinates and up to 90% in determining speed.

Currently, the company Singer (USA), while developing a high-precision inertial system SKN-2440 HAINS for the strategic bomber B-1 B, has proposed a solution to the problem of compensating gravitational disturbances using a digital map - an onboard model of the Earth's gravitational field. This system uses gravity data from the United States Department of Cartography's Cartography Office.

The reason that impedes the development of such navigation systems for aviation purposes using digital maps - airborne models of the Earth's gravitational field is due to the need to recalculate the reference values of gravity anomalies by flight altitude in the process of implementing algorithms for correlation-extreme navigation systems (CENS). Otherwise, due to the attenuation of gravity anomalies with increasing altitude, there will be a significant decrease in the signal-to-noise ratio of observations, which, when using the well-known correlation-extreme navigation algorithms, will lead to a decrease in the estimation accuracy and, ultimately, to a complete loss of CENS operability.

One way to solve the problem of converting gravity anomalies to flight altitude is to use the Poisson formula, which is discrete written as follows:

where Δx, Δy are the sampling intervals for setting the values of gravity anomalies at the height of the sea level (or other level surface); m = -M / 2 ... M / 2, n = -N / 2 ... N / 2 are the serial numbers of spatial samples of Δg _z values in the eastern Ox and northern Oy directions, respectively, Δg is the change in the acceleration of gravity at zero height, h - height.

An empirical rule has been established experimentally, which states that in order to accurately convert gravity anomalies to a height h, it is necessary that Δx-M / 2> 10⋅h and Δy-N / 2> 10⋅h [Bernstein U., Hess R. The effect of vertical deflections on aircraft INS / AIAA v. 14, No. 10, s / 43-46]. Otherwise, the conversion errors will be too high due to the neglect of the influence of the middle zones. In the case where the sampling intervals are the same and equal to 250 m, for calculating each value of the gravity anomalies at an altitude of 5000 m according to the above formula, it is necessary to take into account at least 160,000 values at sea level. Thus, the procedure for converting the values of gravity anomalies to the current flight altitude when implementing any of the known correlation-extreme navigation algorithms will require excessively high performance that is not implemented by the computer, especially considering the need for real-time navigation definitions. Thus, the conclusion is obvious that it is necessary to use real gravity acceleration values in the navigation system calculator.

Modern astroinertial systems have four modes: fully autonomous (inertial), astro-inertial, inertial-satellite and astro-inertial-satellite. The inertial-satellite mode consists in correcting the coordinates and speeds of aircraft by measuring the receiving equipment of the GLONASS / GPS satellite navigation systems. In astro-inertial and astro-inertial-satellite modes, the inertial mode is the main one, since for many consumers on board an aircraft (LA), information about navigation and orientation parameters is required autonomously, regardless of the time of day, weather and seasonal conditions with a high frequency, not provided by satellite navigation and astro correction tools.

The signals received at the output of the gravimeters contain information about both the magnitude of the acceleration of gravity and the magnitude of the acceleration of the aircraft. To isolate the signals of acceleration of gravity, a unit for determining the acceleration of the aircraft’s movement, for example, based on radio altimeters, is introduced. Gravity acceleration signals are obtained by jointly processing the readings of gravimeters and the accelerations of the aircraft’s own motion in the axes of the same name, obtained after differentiating the readings of the radio altimeters. The outputs of gravimeters and accelerometers in the axes of the same name through adders are connected to the inputs of the SINS navigation computer and are used in integration units to calculate the components of the linear velocity and coordinates of the aircraft

Here a _x , a _y , a _z are the readings of the SINS accelerometers oriented in accordance with the axes of the coordinate system Oxyz, V _x , V _y , V _z are the absolute linear speeds of the aircraft, obtained from the solution of equations (2) in the corresponding blocks of the navigation computer of the aircraft , g _x , g _y , g _z - components of the gravity acceleration vector coming from gravimeters at the outputs of gravimeters taking into account the accelerations of the aircraft’s own motion. w _{a x} w _{a y} w _{a z} - projections of the absolute angular velocity vector on the x, y, z axis.

In this case, it is necessary to coordinate the axes of the local horizon defined in the SINS and the block of gravimeters, which is carried out synchronously using a separate platform controlled by the SINS.

In astroinertial and astroinertial-satellite modes, the system operates as follows.

As shown in the prototype, the work of astroinertial systems is based on the relationship between various coordinate systems (SC) used in the work of astroinertial systems. Such coordinate systems include:

ECI - the fundamental inertial SC of the J2000 era;

ECEF - geocentric terrestrial (Greenwich) SC;

ENU - topocentric (local geographical) SC;

B _IMU - instrument SC BINS (right rectangular SC, the axes of which are connected with the construction axes of the BINS);

B _st - instrumental SC of the AVU (right rectangular SK, the axes of which are connected with the optical axis and the plane of the CCD matrix of the AVU).

The relationship between the listed SCs is mathematically convenient to represent in the form of a simple matrix equation that defines the transition from ECI to B _ST :

- матрица, характеризующая угловое положение B_ST относительно ECI;Where

- a matrix characterizing the angular position of B _ST relative to ECI;

- матрица привязки B_IMU к B_ST, определяемая и стабилизируемая блоком оптического сопряжения на этапе технологической юстировки АИНС;

- the matrix of the binding of B _IMU to B _ST , determined and stabilized by the optical interface unit at the stage of technological adjustment of AINS;

,

,

- матрицы переходов от ENU к B_IMU, от ECEF к ENU и от ECI к ECEF соответственно.

,

,

- matrices of transitions from ENU to B _IMU , from ECEF to ENU and from ECI to ECEF, respectively.

и

из состава уравнения (1) могут быть определены в следующем виде:Matrices

and

from the composition of equation (1) can be determined as follows:

Where

matrices of elementary rotations at roll angles γ, pitch ϑ and course ψ, respectively; R _pol is a matrix that takes into account the displacement of the position of the Earth’s pole in the epoch t (at the current time); R _S - matrix of the Earth's daily rotation; N, P are the nutation and precession matrices in the epoch t, respectively.

In view of (3) and (4), equation (2) can be represented as the relation

or

, а параметры матриц

, R_pol известны до начала работы АИНС. На основе представленных соотношений (3), (6) и (7) реализуются различные режимы (варианты) астрокоррекции БИНС, включаемые оператором вручную эпизодически при условии видимости небесных светил.The main information coming from the AVU to the SINS are the elements of the orientation matrix

, and the matrix parameters

, R _pol known before the start of the AINS. Based on the presented relations (3), (6) and (7), various modes (options) of SINS astro correction are implemented, which are manually activated by the operator occasionally provided that the celestial bodies are visible.

The invention is illustrated in the drawing, which shows the astronautical system.

The astronavigation system contains SINS 1 and AVU 2 with a computer 3, which determines the angular parameters of sighting stars, the output of which is connected to one of the inputs of the navigation computer 4 SINS.

BINS 1 includes in its composition quartz accelerometers (at least three) of 5 _1, 5 _2, 5 _3, the laser gyroscopes (at least three) of 6 _1, 6 _2, 6 _3, the power unit 7, the receiver 8 satellite navigation signal system GLONASS / GPS

The astronautical system also contains a block of gravimeters 9 ₁ , 9 ₂ , 9 ₃ (at least three) located on a separate platform 10, controlled by an engine (not shown in the figure), made with the possibility of synchronous movement with the movement of the aircraft and parallel to the horizon plane, block 11 altimeters for measuring the vertical acceleration of the aircraft, the calculator 12 of the acceleration of gravity, while the outputs of the gravimeters and the outputs of the block of altimeters are connected to the inputs of the calculator 12 of the acceleration of gravity, the outputs of which are black Without the adders 13 ₁ , 13 ₂ , 13 ₃ connected to the inputs of the calculator 4 SINS, while the outputs of the accelerometers 5 ₁ , 5 ₂ , 5 _{3 are} connected to the inputs of the adders 13 ₁ , 13 ₂ , 13 _3, respectively.

The system operates as follows.

BINS 1 provides the determination of navigation parameters and parameters of angular orientation, accompanied by the accumulation of errors over time by Schuler. From the SINS output to the input of the astroizing device 2, a priori (unadjusted) information is constantly received about the spatial position of the axis of the AVU and the associated instrument coordinate system of the AVU in the inertial coordinate system.

In the process of observing stars with an astroizing device, images of stars are projected onto a CCD matrix, which is a sensitive element of the AVU.

The AVU reader reads images of stars from a CCD matrix, simultaneously filtering, extracting star-like formations, and selecting them according to configuration and energy features.

AVU searches and recognizes selected objects (stars) based on a comparison of the current image of the starry sky and the star catalog stored in the electronics unit.

, которая передается в навигационный вычислитель 4 БИНС 1.Navigational computer 3 AVU calculates the orientation parameters of the optical axis of the astrovizing device taking into account the era of observation, nutation and precession, aberration and refraction of the atmosphere. Based on the orientation parameters of the optical axis of the astrovizing device, a matrix is formed

, which is transmitted to the navigation computer 4 BINS 1.

There are two modes (options) of astro correction:

1) SINS error compensation mode for determining spatial position angles - astroinertial satellite mode;

2) the mode of compensation of errors SINS to determine the geodetic coordinates and yaw angle - astroinertial mode.

The first correction mode is activated when there is reliable reception of signals from the GLONASS / GPS satellite navigation systems.

In the absence of information from the SNA 7 receiver, the second mode of error compensation SINS 1 is implemented - compensation of errors by determining the geodetic coordinates and yaw angle.

The main mode of operation of the navigation system in question is the inertial mode, which is switched on continuously throughout the flight and functions regardless of the presence of conditions for observing stars and the presence of receiving signals from satellites in the SNA receiver. The modes of astro correction and satellite correction are complementary to the inertial one and turn on for a short time.

In the inertial mode, from the outputs of the accelerometers 5, measurements are received at the adders 13, and the measurements of gravimeters 9, previously processed in the calculator 12 of gravity acceleration, are continuously received there. The second input of the calculator 12 of the acceleration of gravity is connected to the output of the block 11 of the altimeters. From the output of the calculator 12 to the inputs of the adders 13 of the corresponding accelerometers receive data on the components of the acceleration of gravity g _x , g _y , g _z . After integration of equations (2) in the BINS 3 navigation computer, linear velocities and coordinates are determined, refined by gravity acceleration measurements by gravimeters 9. In a first approximation, the expressions for calculating the coordinates can be of the form:

Here r is the radius vector drawn from the center of mass to the point of location of the aircraft, φ, λ is the latitude and longitude of the location of the aircraft, w _W is the angular velocity of rotation of the Earth.

Thus, in the navigation system there are three correction modes for the strapdown inertial navigation system - satellite correction, astro correction and astro-satellite correction. If correction is not possible, an inertial navigation mode is performed. In this case, the main source of inertial errors in determining the navigation parameters of the uncertainty of the Earth's gravitational field is eliminated by measuring the actual values in real time of the gravitational component of gravity by gravimeters.

Claims (1)

An astronautical system installed on an aircraft containing a strapdown inertial navigation system including accelerometers, gyroscopes, a satellite radio navigation system receiver, a navigation calculator, an astroizing device with a calculator that determines the angular parameters of star sighting and connected to the navigation calculator of the first-form navigation informer the receiver of the satellite radio navigation system and gyroscopes are connected to the inputs and a navigation computer of the strapdown inertial navigation system, characterized in that gravimeters, a block of altimeters for measuring the vertical acceleration of the aircraft, a gravity acceleration calculator and adders are introduced into the system, while the gravimeters are mounted on a separate platform that can synchronously move with the aircraft moving and parallel to the horizon plane, and the outputs of the gravimeters and the altimeter unit for measuring the vertical acceleration of the aircraft of the second apparatus are connected to the inputs of the gravity acceleration calculator, the outputs of which are connected via adders to the navigation computer of the strapdown inertial navigation system, while the outputs of the accelerometers are connected to the second inputs of the adders.