Radar satellite three-dimensional attitude guiding method and system

Abstract

The invention provides a radar satellite three-dimensional attitude guiding method and system, and the method comprises the steps: calculating the geocentric distance and geocentric latitude and longitude of a satellite according to satellite orbit parameter information, calculating the height of the satellite and the geodetic latitude and longitude of a droop point through a WGS-84 reference ellipsoid model, and further obtaining the geocentric latitude and the earth radius of the droop point. The position vectors of the droop point and the satellite in a WGS-84 earth-fixed coordinate system are obtained respectively, the position vectors of the droop point and the satellite are compared to obtain the position vector from the satellite to the droop point, then the position vector is converted into a satellite orbit coordinate system, and rolling and pitching guide angles are calculated. Doppler frequency deviation caused by earth rotation is compensated by adjusting the yaw guide angle. According to the method, the problem that loads such as a spaceborne radar altimeter vertically point to the earth surface of the earth reference ellipsoid model is successfully solved, meanwhile, Doppler frequency deviation generated by earth rotation is compensated, and important technical support can be provided for a subsequent radar satellite earth observation task.

Description

Technical Field

[0001] The present invention relates to the field of satellite observation technology, and in particular to a three-dimensional attitude guidance method and system for a radar satellite, and in particular to a three-dimensional attitude guidance method and system for a radar satellite that is perpendicularly pointed to the surface of a WGS-84 reference ellipsoid. Background Art

[0002] Spaceborne radar altimeters can obtain high-resolution altimetry data for both land and sea. To accurately measure the vertical distance from the satellite to the land and sea surface, the satellite's +Z axis (the radar altimeter's pointing axis relative to the Earth) must be controlled perpendicular to the Earth's surface using the WGS-84 reference ellipsoid (World Geodetic System 1984). Furthermore, due to the influence of Earth's rotation, the spaceborne radar will experience a Doppler center frequency shift, requiring yaw guidance control to compensate for this Doppler frequency shift. Therefore, research on three-dimensional attitude guidance methods for radar satellites that are perpendicular to the WGS-84 reference ellipsoid is of great significance for achieving stable three-axis orientation of the payload antenna relative to the Earth's surface (non-Geocentric) and improving the accuracy of radar altimetry measurements.

[0003] This application was compared with existing technologies and the closest technical achievements at home and abroad. The search keywords "vertical pointing to the ground", "ground pointing", "orientation to the ground", "droop point", etc., retrieved a total of 1 related patent.

[0004] Patent document CN108427427B introduces a method for calculating the attitude angle of a target oriented on the surface of the earth, which is based on an earth ellipsoid model and performs iterative calculations according to the principles of spatial analytical geometry. However, this method uses the negative normal vector of the tangent plane at the intersection of the vector pointing from the satellite to the center of the earth and the spherical surface of the earth ellipsoid model as the target vector for orientation on the surface of the earth, thereby calculating the roll attitude angle and the pitch attitude angle of the target oriented on the surface of the earth, and then performing iterative calculations as the satellite orbits. The premise of orientation on the surface of the earth should be that the satellite points to the drooping point on the spherical surface of the earth ellipsoid model, that is, the normal of the tangent plane at the intersection of the satellite pointing vector and the spherical surface of the earth ellipsoid model should pass through the satellite's center of mass. This method uses the negative normal vector of the tangent plane at the intersection of the vector pointing from the satellite to the center of the earth and the spherical surface of the earth ellipsoid model as the target vector for orientation on the surface of the earth. After the attitude points to the target vector, the intersection with the spherical surface of the earth ellipsoid model changes, and at this time, the normal of the tangent plane at the intersection no longer passes through the satellite. As Figure 2 、 Figure 3 、 Figure 4 As shown in the Earth ellipsoid model, the normal to the tangent plane at the intersection of the vector pointing to the Earth's center and the spherical surface of the Earth ellipsoid model does not pass through the satellite and is not parallel to the normal to the tangent plane at the sag point. Furthermore, this method lacks yaw guidance to address the Doppler frequency offset of the radar satellite.

[0005] The search keyword "attitude guidance" retrieved 9 related patents and 19 documents, of which 6 were related to satellite attitude guidance, all of which were SAR satellite attitude guidance to compensate for the Doppler frequency offset caused by the rotation of the earth.

[0006] Patent document CN103674033B introduces a method for attitude guidance of a spaceborne SAR satellite. When the satellite's beam pointing direction is perpendicular to the normal direction of the zero-Doppler plane, the satellite's yaw guidance angle is obtained. However, this method is a one-dimensional yaw guidance method and does not involve attitude guidance perpendicular to the reference ellipsoid surface.

[0007] Patent document CN106843249B introduces a high-precision and stable two-dimensional guidance attitude control method, which decouples the roll direction from the yaw control and can achieve rapid two-dimensional guidance access control at any position of the satellite, but does not involve attitude guidance perpendicular to the reference ellipsoid surface.

[0008] Patent document CN103675760A introduces a method for attitude guidance of a satellite-borne geosynchronous orbit synthetic aperture radar that uses a smaller attitude guidance angle to achieve optimal ground-range resolution. The method achieves optimal resolution attitude guidance by pointing the beam in the direction of the optimal azimuth angle through pitch-roll guidance or roll-pitch guidance. However, this method does not involve attitude guidance perpendicular to the surface of the reference ellipsoid.

[0009] Patent document CN104730506A describes a method that uses instantaneous spacecraft orbit information to eliminate the coupling of the Doppler center frequency to the Earth's rotation and the satellite's orbital ellipticity in the range and azimuth directions, thereby achieving a Doppler center frequency of the synthetic aperture radar beam center echo close to zero Hz. However, this method is designed for pointing toward the center of the Earth and does not address attitude guidance perpendicular to the reference ellipsoid surface.

[0010] In summary, there has been no public report on a method for three-dimensional attitude guidance of a radar satellite that is perpendicular to the surface of the WGS-84 reference ellipsoid, and this application is the first of its kind. Summary of the Invention

[0011] In view of the defects in the prior art, the purpose of the present invention is to provide a radar satellite three-dimensional attitude guidance method and system.

[0012] A radar satellite three-dimensional attitude guidance method provided by the present invention includes:

[0013] Step S1: Calculate the satellite's geocentric distance, geocentric latitude, and geocentric longitude based on the acquired satellite navigation data (including satellite orbit parameter information, satellite position in the WGS-84 coordinate system, etc.);

[0014] Step S2: Calculate the satellite altitude and the geodetic longitude and latitude of the sag point based on the WGS-84 reference ellipsoid model and the satellite's geocentric latitude and longitude;

[0015] Step S3: Calculate the geocentric latitude of the sag point and the radius of the earth at the sag point according to the geodetic latitude of the sag point;

[0016] Step S4: Calculate the WGS-84 ground-fixed position vector of the sag point based on the sag point information;

[0017] Step S5: deriving the position vector of the satellite in the WGS-84 Earth-fixed system based on the satellite's position in the WGS-84 coordinate system;

[0018] Step S6: Calculate the position vector from the satellite to the droop point in the WGS-84 Earth-fixed coordinate system;

[0019] Step S7: obtaining the position vector from the satellite to the descent point in the satellite orbit coordinate system through coordinate conversion calculation;

[0020] Step S8: Calculate the roll steering angle and the pitch steering angle in the orbital coordinate system;

[0021] Step S9: Calculate the yaw steering angle to compensate for the influence of the Doppler frequency shift caused by the rotation of the earth based on the satellite orbit parameter information.

[0022] Preferably, step S1 includes the following sub-steps:

[0023] Step S1.1: Read the real-time orbit parameters of the satellite, which include the current time t, the orbit semi-major axis a, the orbit eccentricity e, the orbit inclination i, the right ascension of the ascending node Ω, the argument of perigee ω, and the mean anomaly M; read the position of the satellite in the WGS-84 coordinate system, which includes X, Y, and Z.

[0024] Step S1.2: Calculate the satellite's true anomaly f and latitude argument u based on the real-time orbit parameters; where:

[0025] f=M+(2e-0.25e 3 )×sin(M)+1.25e 2 sin(2M)

[0026] u=ω+f

[0027] Step S1.3: Calculate the distance r between the satellite and the center of the Earth, where:

[0028]

[0029] Step S1.4: Calculate the satellite's geocentric longitude λ and geocentric latitude φ based on the position in the WGS-84 coordinate system, where:

[0030]

[0031] Preferably, step S2 includes the following sub-steps:

[0032] Step S2.1: Calculate the satellite's altitude h, where:

[0033]

[0034] Where R E is the equatorial radius of the Earth in the WGS-84 reference ellipsoid model, n is the flattening of the Earth in the WGS-84 reference ellipsoid model, and:

[0035]

[0036] Where R p is the Earth's polar radius of the WGS-84 reference ellipsoid model;

[0037] Step S2.2: Calculate the geodetic latitude Φ of the sag point C′ C′ , where the sag point C' is defined as: the earth is a rotating ellipsoid, and the normal line of a certain point of the ellipsoid passes through the satellite, and this point is defined as the satellite sag point; at this time:

[0038]

[0039] Step S2.3: Calculate the geodetic longitude λ of the sag point C′ C′ ,have:

[0040] λ C′ =λ.

[0041] Preferably, step S3 includes the following sub-steps:

[0042] Step S3.1: Calculate the geocentric latitude φ of the sag point C′ C′ ,have:

[0043] φ C′ =arctan[(1-n) 2 tanΦ C′ ]

[0044] Step S3.2: Calculate the radius R of the Earth at the sag point C′ lC′ , that is, the distance from the center of the earth to the sag point, is:

[0045]

[0046] Preferably, the calculation process of step S4 includes:

[0047]

[0048] Preferably, the position vector of the satellite in step S5 in the WGS-84 fixed system is:

[0049]

[0050] Preferably, the calculation process of step S6 includes:

[0051]

[0052] Preferably, step S7 includes the following sub-steps:

[0053] Step S7.1: Translate the position vector of satellite S to the droop point C′ Convert to the J2000.0 geocentric equatorial inertial system and obtain the position vector from satellite S to sag point C′ in the J2000.0 geocentric equatorial inertial system

[0054] Step S7.2: Translate the position vector of satellite S to the sag point C′ in the J2000.0 geocentric equatorial inertial system Convert to the satellite orbit coordinate system and obtain the position vector from satellite S to droop point C′ in the satellite orbit coordinate system have:

[0055]

[0056] Step S7.3: According to the distance from the satellite to the center of the earth, the position vector of the satellite S to the center of the earth in the satellite orbit coordinate system is obtained

[0057]

[0058] Preferably, step S8 includes the following sub-steps:

[0059] Step S8.1: Calculate the angle β between the vertical pointing direction of the spaceborne radar to the ellipsoidal surface and the line connecting the satellite and the center of the earth:

[0060]

[0061] Step S8.2: Calculate the rolling attitude guidance angle In the orbital coordinate system, the position vector of the satellite to the sag point is The angle between the projection on the yoz surface and the track system +Z axis is the rolling guide angle, which is:

[0062]

[0063] Step S8.3: Calculate the pitch attitude guidance angle θ, the position vector of the satellite to the droop point in the orbital coordinate system The angle between the projection on the yoz plane and the position vector is the pitch steering angle, which is:

[0064]

[0065] Preferably, the calculation process of step S9 includes:

[0066]

[0067] Where, ψ is the yaw attitude guidance angle, ω s is the satellite orbital angular velocity.

[0068] A radar satellite three-dimensional attitude guidance system provided by the present invention includes:

[0069] Module M1: Calculates the satellite's geocentric distance, geocentric latitude, and geocentric longitude based on the acquired satellite navigation data (including satellite orbit parameter information, satellite position in the WGS-84 coordinate system, etc.);

[0070] Module M2: Calculates the satellite's altitude and the geodetic longitude and longitude of the sag point based on the WGS-84 reference ellipsoid model and the satellite's geocentric latitude and longitude.

[0071] Module M3: Calculate the geocentric latitude of the sag point and the radius of the earth at the sag point based on the geodetic latitude of the sag point;

[0072] Module M4: Calculate the WGS-84 ground-fixed position vector of the sag point based on the sag point information;

[0073] Module M5: Based on the satellite's position in the WGS-84 coordinate system, the satellite's position vector in the WGS-84 Earth-fixed system is obtained;

[0074] Module M6: Calculate the position vector from the satellite to the droop point in the WGS-84 Earth-fixed coordinate system;

[0075] Module M7: Obtain the position vector from the satellite to the droop point in the satellite orbit coordinate system through coordinate transformation calculation;

[0076] Module M8: Calculates the roll and pitch angles in the orbital coordinate system.

[0077] Module M9: Calculates the yaw steering angle to compensate for the Doppler frequency shift caused by the Earth's rotation based on the satellite orbit parameter information.

[0078] Preferably, the module M1 includes the following submodules:

[0079] Module M1.1: Reads the satellite's real-time orbit parameters, including the current time t, orbit semi-major axis a, orbit eccentricity e, orbit inclination i, ascending node right ascension Ω, argument of perigee ω, and mean anomaly M; reads the satellite's position in the WGS-84 coordinate system, including X, Y, and Z.

[0080] Module M1.2: Calculate the satellite's true anomaly f and latitude argument u based on real-time orbit parameters; where:

[0081] f=M+(2e-0.25e 3 )×sin(M)+1.25e 2 sin(2M)

[0082] u=ω+f

[0083] Module M1.3: Calculate the distance r between the satellite and the center of the Earth, where:

[0084]

[0085] Module M1.4: Calculate the satellite's geocentric longitude λ and latitude φ based on its position in the WGS-84 coordinate system, where:

[0086]

[0087] Preferably, the module M2 includes the following submodules:

[0088] Module M2.1: Calculate the satellite's altitude h, where:

[0089]

[0090] Where R E is the equatorial radius of the Earth in the WGS-84 reference ellipsoid model, n is the flattening of the Earth in the WGS-84 reference ellipsoid model, and:

[0091]

[0092] Where R p is the Earth's polar radius of the WGS-84 reference ellipsoid model;

[0093] Module M2.2: Calculate the geodetic latitude Φ of the sag point C′ C′ , where the sag point C' is defined as: the earth is a rotating ellipsoid, and the normal line of a certain point of the ellipsoid passes through the satellite, and this point is defined as the satellite sag point; at this time:

[0094]

[0095] Module M2.3: Calculation of the geodetic longitude λ of the sag point C′ C′,have:

[0096] λ C′ =λ.

[0097] Preferably, the module M3 includes the following submodules:

[0098] Module M3.1: Calculate the geocentric latitude φ of the sag point C′ C′ ,have:

[0099] φ C′ =arctan[(1-n) 2 tanΦ C′ ]

[0100] Module M3.2: Calculate the radius R of the Earth at the sag point C′ lC′ , that is, the distance from the center of the earth to the sag point, is:

[0101]

[0102] Preferably, the calculation process of the module M4 includes:

[0103]

[0104] Preferably, the calculation process of the module M5 includes:

[0105]

[0106] Preferably, the calculation process of the module M6 includes:

[0107]

[0108] Preferably, the module M7 includes the following submodules:

[0109] Module M7.1: Position vector of satellite S to droop point C′ Convert to the J2000.0 geocentric equatorial inertial system and obtain the position vector from satellite S to sag point C′ in the J2000.0 geocentric equatorial inertial system

[0110] Module M7.2: Convert the position vector of satellite S to the sag point C′ in the J2000.0 geocentric equatorial inertial system Convert to the satellite orbit coordinate system and obtain the position vector from satellite S to droop point C′ in the satellite orbit coordinate system have:

[0111]

[0112] Module M7.3: Based on the distance from the satellite to the center of the earth, obtain the position vector of the satellite S to the center of the earth in the satellite orbit coordinate system

[0113]

[0114] Preferably, the module M8 includes the following submodules:

[0115] Module M8.1: Calculate the angle β between the vertical pointing direction of the spaceborne radar to the ellipsoidal surface and the line connecting the satellite and the center of the earth, which is:

[0116]

[0117] Module M8.2: Calculation of Roll Attitude Guidance Angle In the orbital coordinate system, the position vector of the satellite to the sag point is The angle between the projection on the yoz surface and the track system +Z axis is the rolling guide angle, which is:

[0118]

[0119] Module M8.3: Calculate the pitch attitude guidance angle θ, the position vector from the satellite to the droop point in the orbital coordinate system The angle between the projection on the yoz plane and the position vector is the pitch steering angle, which is:

[0120]

[0121] Preferably, the calculation process of the module M9 includes:

[0122]

[0123] Where, ψ is the yaw attitude guidance angle, ω s is the satellite orbital angular velocity.

[0124] Compared with the prior art, the present invention has the following beneficial effects:

[0125] 1. The present invention successfully solves the problem of vertical pointing of payloads such as satellite-borne radar altimeters to the surface of the Earth reference ellipsoid model. At the same time, it takes into account the compensation of the Doppler frequency offset caused by the rotation of the Earth and proposes a three-dimensional attitude guidance method for satellites to be vertically pointed to the surface of the WGS-84 reference ellipsoid. This method can provide important technical support for subsequent radar satellite earth observation missions.

[0126] 2. The present invention significantly improves positioning accuracy. By combining satellite orbit parameter information with the WGS-84 reference ellipsoid model, the satellite's geocentric latitude, longitude, and position vector of the sag point are accurately calculated, ensuring high accuracy in positioning ground targets and providing data support for earth observation and geographic information systems.

[0127] Other beneficial effects of the present invention will be explained through the introduction of specific technical features and technical solutions in the specific implementation methods. Those skilled in the art should be able to understand the beneficial technical effects brought about by the introduction of these technical features and technical solutions. BRIEF DESCRIPTION OF THE DRAWINGS

[0128] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0129] Figure 1 The figure is a schematic diagram of the calculation flow of the three-dimensional attitude guidance of a satellite pointing perpendicularly to the WGS-84 reference ellipsoid surface according to the present invention.

[0130] Figure 2 Schematic diagram of the satellite sag point under the WGS-84 reference ellipsoid model.

[0131] Figure 3 Schematic diagram of geocentric latitude and geodetic latitude.

[0132] Figure 4 Schematic diagram of the relationship between the satellite position vector and the droop point position vector in the WGS-84 ground-fixed system.

[0133] Figure 5 This is a graph showing how the angle between the vertical direction of the ellipsoid surface and the line connecting the satellite and the center of the earth changes with latitude.

[0134] Figure 6 This is a graph showing the variation of the roll attitude guidance angle with the latitude argument when pointing perpendicular to the WGS-84 reference ellipsoid surface.

[0135] Figure 7 This is a graph showing the variation of the pitch attitude guidance angle with the latitude argument when pointing perpendicular to the WGS-84 reference ellipsoid surface.

[0136] Figure 8 This is a graph showing the instantaneous circular orbit full zero Doppler yaw attitude guidance angle changing with latitude argument.

[0137] Figure 9 A comparison chart of the three-dimensional attitude guidance angles pointing vertically to the surface of the WGS-84 reference ellipsoid. DETAILED DESCRIPTION

[0138] The present invention is described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, without departing from the scope of the present invention, a number of variations and improvements may be made by those skilled in the art. These all fall within the scope of protection of the present invention.

[0139] A three-dimensional attitude guidance method for a radar satellite pointing perpendicularly to a WGS-84 reference ellipsoid surface comprises:

[0140] Step S1: Calculate the satellite's geocentric distance, geocentric latitude, and geocentric longitude based on the acquired satellite navigation data (including satellite orbit parameter information, satellite position in the WGS-84 coordinate system, etc.);

[0141] Step S2: Calculate the satellite altitude and the geodetic longitude and latitude of the sag point based on the WGS-84 reference ellipsoid model and the satellite's geocentric latitude and longitude;

[0142] Step S3: Calculate the geocentric latitude of the sag point and the radius of the earth at the sag point according to the geodetic latitude of the sag point;

[0143] Step S4: Calculate the WGS-84 ground-fixed position vector of the sag point based on the sag point information;

[0144] Step S5: deriving the position vector of the satellite in the WGS-84 Earth-fixed system based on the satellite's position in the WGS-84 coordinate system;

[0145] Step S6: Calculate the position vector from the satellite to the droop point in the WGS-84 ground-fixed system;

[0146] Step S7: Calculate the position vector from the satellite to the descent point in the satellite orbit coordinate system through coordinate conversion;

[0147] Step S8: Calculate the rolling guidance angle and the pitch guidance angle in the orbital coordinate system;

[0148] Step S9: Calculate the yaw steering angle to compensate for the influence of the Doppler frequency shift caused by the rotation of the earth based on the satellite orbit parameter information.

[0149] Specifically, in step S1, the satellite's geocentric distance, geocentric latitude, and geocentric longitude are calculated based on the acquired satellite navigation data (including satellite orbit parameter information, the satellite's position in the WGS-84 coordinate system, etc.), including:

[0150] Step S1.1: Read the satellite's real-time orbit parameters, including the current time t, orbit semi-major axis a, orbit eccentricity e, orbit inclination i, ascending node right ascension Ω, argument of perigee ω, and mean anomaly M; and read the satellite's position in the WGS-84 coordinate system, including X, Y, and Z.

[0151] Step S1.2: Calculate the satellite's true anomaly f and latitude argument u based on the real-time orbit parameters.

[0152] f=M+(2e-0.25e 3 )×sin(M)+1.25e2 sin(2M)

[0153] u=ω+f

[0154] Step S1.3: Calculate the distance r between the satellite and the center of the earth, where

[0155]

[0156] Step S1.4: Calculate the satellite's geocentric longitude λ and geocentric latitude φ based on the position in the WGS-84 coordinate system, where:

[0157]

[0158] Specifically, the satellite altitude and the longitude and latitude of the sag point are calculated from the WGS-84 reference ellipsoid parameters in step S2, including:

[0159] Step S2.1: Calculate the satellite's altitude h, where

[0160]

[0161] Where R E is the equatorial radius of the Earth in the WGS-84 reference ellipsoid model, n is the flattening of the Earth in the WGS-84 reference ellipsoid model, and

[0162]

[0163] Where R p is the Earth's polar radius based on the WGS-84 reference ellipsoid model.

[0164] Step S2.2: Calculate the geodetic latitude Φ of the sag point C′ C′ , where the sag point C' is defined as: the earth is a rotating ellipsoid, and the normal line of a certain point of the ellipsoid passes through the satellite, and this point is defined as the satellite sag point.

[0165]

[0166] Step S2.3: Calculate the geodetic longitude λ of the sag point C′ C′ ,have

[0167] λ C′ =λ

[0168] Specifically, the step S3 of calculating the geocentric latitude of the sag point and the earth radius at the sag point according to the geodetic latitude of the sag point includes:

[0169] Step S3.1: Calculate the geocentric latitude φ of the sag point C′ C′ ,have

[0170] φ C′=arctan[(1-n) 2 tanΦ C′ ]

[0171] Step S3.2: Calculate the radius R of the Earth at the sag point C′ lC′ (the distance from the center of the earth to the droop point),

[0172]

[0173] Specifically, in step S4, the WGS-84 ground fixed position vector of the droop point is calculated based on the droop point information, and there is

[0174]

[0175] Specifically, in step S5, the position vector of the satellite in the WGS-84 fixed system is obtained based on the position of the satellite in the WGS-84 coordinate system, which is:

[0176]

[0177] Specifically, the position vector from the satellite to the droop point under the WGS-84 ground-fixed system is calculated in step S6,

[0178]

[0179] Specifically, the coordinate conversion in step S7 is used to calculate the position vector from the satellite to the droop point in the satellite orbit coordinate system, including:

[0180] Step S7.1: Translate the position vector of satellite S to the droop point C′ Convert to the J2000.0 geocentric equatorial inertial system and obtain the position vector from satellite S to sag point C′ in the J2000.0 geocentric equatorial inertial system

[0181] Step S7.2: Translate the position vector of satellite S to the sag point C′ in the J2000.0 geocentric equatorial inertial system Convert to the satellite orbit coordinate system and obtain the position vector from satellite S to droop point C′ in the satellite orbit coordinate system have

[0182]

[0183] Specifically, the satellite orbit coordinate system O in step S7.2 o X o Y o Z o Defined as: coordinate origin O o is the satellite mass center; O o Z oAxis points to the center of the Earth; O o Y o The axis points to the negative normal direction of the satellite's instantaneous orbital plane; o X o The axis is determined according to the right-hand rule and points in the direction of the satellite's flight. This coordinate system serves as the reference coordinate system for the satellite's vertical pointing attitude relative to the Earth's surface.

[0184] Step S7.3: Based on the distance from the satellite to the center of the earth, the position vector of the satellite S to the center of the earth in the satellite orbit coordinate system can be obtained.

[0185]

[0186] Specifically, in step S8, the rolling guidance angle and the pitch guidance angle are calculated in the orbital coordinate system, including:

[0187] Step S8.1: Calculate the angle β between the vertical pointing direction of the satellite-borne radar to the ellipsoid surface and the line connecting the satellite and the center of the earth,

[0188]

[0189] Step S8.2: Calculate the rolling attitude guidance angle In the orbital coordinate system, the position vector of the satellite to the sag point is The angle between the projection on the yoz surface and the track system + Z axis is the rolling guide angle,

[0190]

[0191] Step S8.3: Calculate the pitch attitude guidance angle θ, the position vector of the satellite to the droop point in the orbital coordinate system The angle between the projection on the yoz plane and the position vector is the pitch steering angle;

[0192]

[0193] Specifically, in step S9, the yaw steering angle is calculated based on the satellite orbit parameter information to compensate for the Doppler frequency offset caused by the rotation of the earth. Here, the yaw steering angle adopts the instantaneous circular orbit full zero Doppler steering method in the document "Doppler properties of radars in circular orbits" (Raney R K. International Journal of Remote Sensing, 1986, 7 (9): 1153-1162.), and the yaw attitude steering angle ψ

[0194]

[0195] Where ω sis the satellite orbital angular velocity.

[0196] The present invention will be further described below with reference to the accompanying drawings.

[0197] like Figure 2 As shown in the WGS-84 reference ellipsoid model, let satellite S be the one whose line with the center of the earth intersects the earth's surface at point C, and the sag point is C', that is, the normal of point C' on the ellipsoid passes through satellite S. The angle between the vertical pointing of the satellite to the ellipsoid surface and the line connecting the satellite and the center of the earth is Figure 2 Middle angle β.

[0198] Under the WGS-84 reference ellipsoid model, the model assumes that the earth is a rotating ellipsoid, and its section through the earth's axis is an ellipse, and the major semi-axis of the section ellipse is the earth's equatorial radius R E =6378.137km, the semi-minor axis is the Earth's polar radius R p =6356.752km, then the Earth's flattening is

[0199]

[0200] The eccentricity of the longitudinal section ellipse is

[0201]

[0202] Due to the ellipsoidal shape of the earth, there are different definitions of latitude, such as Figure 3 As shown:

[0203] (1) Geocentric latitude

[0204] The angle between a radius drawn from the center of the Earth and the equatorial plane.

[0205] (2) Geodetic latitude Φ or geographic latitude

[0206] The angle between the local normal to the ellipsoid (approximately equivalent to the local plumb line) and the equatorial plane.

[0207] The relationship between these two latitudes is as follows:

[0208]

[0209] Here, the satellite S adopts the parameters shown in Table 1, and the simulation test is carried out based on these parameters.

[0210] Table 1 Simulation parameters

[0211]

[0212] Depend on Figure 5It can be seen that the angle β between the vertical pointing of the WGS-84 reference ellipsoid and the line connecting the satellite and the center of the earth varies periodically with the latitude argument, with a period of 180°;

[0213] Depend on Figure 6 It can be seen that the rolling attitude guidance angle j when pointing vertically to the surface of the WGS-84 reference ellipsoid varies periodically with the latitude argument, with a period of 360°, i.e., 1 orbit;

[0214] Depend on Figure 7 It can be seen that the pitch attitude guidance angle θ when pointing perpendicular to the WGS-84 reference ellipsoid surface varies periodically with the latitude argument, with a period of 180°, that is, half an orbit;

[0215] Depend on Figure 8 It can be seen that the yaw attitude guidance angle ψ, which is used to compensate for the influence of the Doppler frequency shift caused by the rotation of the earth, changes periodically with the latitude argument, with a period of 360°, that is, 1 orbit;

[0216] Depend on Figure 9 It can be seen that the rolling and pitching attitude guidance angles are relatively small compared to the yaw attitude guidance angle.

[0217] The method of the present invention successfully solves the problem of vertical pointing of payloads such as satellite-borne radar altimeters to the surface of the Earth reference ellipsoid model. At the same time, considering compensating for the Doppler frequency offset caused by the rotation of the Earth, a three-dimensional attitude guidance method for satellites pointing vertically to the surface of the WGS-84 reference ellipsoid is proposed, which can provide important technical support for subsequent radar satellite earth observation missions.

[0218] The present invention also provides a radar satellite three-dimensional attitude guidance system, which can be implemented by executing the process steps of the radar satellite three-dimensional attitude guidance method, that is, those skilled in the art can understand the radar satellite three-dimensional attitude guidance method as a preferred implementation of the radar satellite three-dimensional attitude guidance system.

[0219] Specifically, a radar satellite three-dimensional attitude guidance system includes:

[0220] Module M1: Calculates the satellite's geocentric distance, geocentric latitude, and geocentric longitude based on the acquired satellite navigation data (including satellite orbit parameter information, satellite position in the WGS-84 coordinate system, etc.);

[0221] Module M2: Calculates the satellite's altitude and the geodetic longitude and longitude of the sag point based on the WGS-84 reference ellipsoid model and the satellite's geocentric latitude and longitude.

[0222] Module M3: Calculate the geocentric latitude of the sag point and the radius of the earth at the sag point based on the geodetic latitude of the sag point;

[0223] Module M4: Calculate the WGS-84 ground-fixed position vector of the sag point based on the sag point information;

[0224] Module M5: Based on the satellite's position in the WGS-84 coordinate system, the satellite's position vector in the WGS-84 Earth-fixed system is obtained;

[0225] Module M6: Calculate the position vector from the satellite to the droop point in the WGS-84 Earth-fixed coordinate system;

[0226] Module M7: Obtain the position vector from the satellite to the droop point in the satellite orbit coordinate system through coordinate transformation calculation;

[0227] Module M8: Calculates the roll and pitch angles in the orbital coordinate system.

[0228] Module M9: Calculates the yaw steering angle to compensate for the Doppler frequency shift caused by the Earth's rotation based on the satellite orbit parameter information.

[0229] The module M1 includes the following submodules:

[0230] Module M1.1: Reads the satellite's real-time orbit parameters, including the current time t, orbit semi-major axis a, orbit eccentricity e, orbit inclination i, ascending node right ascension Ω, argument of perigee ω, and mean anomaly M; reads the satellite's position in the WGS-84 coordinate system, including X, Y, and Z.

[0231] Module M1.2: Calculate the satellite's true anomaly f and latitude argument u based on real-time orbit parameters; where:

[0232] f=M+(2e-0.25e 3 )×sin(M)+1.25e 2 sin(2M)

[0233] u=ω+f

[0234] Module M1.3: Calculate the distance r between the satellite and the center of the Earth, where:

[0235]

[0236] Module M1.4: Calculate the satellite's geocentric longitude λ and latitude φ based on its position in the WGS-84 coordinate system, where:

[0237]

[0238] The module M2 includes the following submodules:

[0239] Module M2.1: Calculate the satellite's altitude h, where:

[0240]

[0241] Where R E is the equatorial radius of the Earth in the WGS-84 reference ellipsoid model, n is the flattening of the Earth in the WGS-84 reference ellipsoid model, and:

[0242]

[0243] Where R p is the Earth's polar radius of the WGS-84 reference ellipsoid model;

[0244] Module M2.2: Calculate the geodetic latitude Φ of the sag point C′ C′ , where the sag point C' is defined as: the earth is a rotating ellipsoid, and the normal line of a certain point of the ellipsoid passes through the satellite, and this point is defined as the satellite sag point; at this time:

[0245]

[0246] Module M2.3: Calculation of the geodetic longitude λ of the sag point C′ C′ ,have:

[0247] λ C′ =λ.

[0248] The module M3 includes the following submodules:

[0249] Module M3.1: Calculate the geocentric latitude φ of the sag point C′ C′ ,have:

[0250] φ C′ =arctan[(1-n) 2 tanΦ C′ ]

[0251] Module M3.2: Calculate the radius R of the Earth at the sag point C′ lC′ , that is, the distance from the center of the earth to the sag point, is:

[0252]

[0253] The calculation process of the module M4 includes:

[0254]

[0255] The calculation process of the module M5 includes:

[0256]

[0257] The calculation process of the module M6 includes:

[0258]

[0259] The module M7 includes the following submodules:

[0260] Module M7.1: Position vector of satellite S to droop point C′ Convert to the J2000.0 geocentric equatorial inertial system and obtain the position vector from satellite S to sag point C′ in the J2000.0 geocentric equatorial inertial system

[0261] Module M7.2: Convert the position vector of satellite S to the sag point C′ in the J2000.0 geocentric equatorial inertial system Convert to the satellite orbit coordinate system and obtain the position vector from satellite S to droop point C′ in the satellite orbit coordinate system have:

[0262]

[0263] Module M7.3: Based on the distance from the satellite to the center of the earth, obtain the position vector of the satellite S to the center of the earth in the satellite orbit coordinate system

[0264]

[0265] The module M8 includes the following submodules:

[0266] Module M8.1: Calculate the angle β between the vertical pointing direction of the spaceborne radar to the ellipsoidal surface and the line connecting the satellite and the center of the earth, which is:

[0267]

[0268] Module M8.2: Calculation of Roll Attitude Guidance Angle In the orbital coordinate system, the position vector of the satellite to the sag point is The angle between the projection on the yoz surface and the track system +Z axis is the rolling guide angle, which is:

[0269]

[0270] Module M8.3: Calculate the pitch attitude guidance angle θ, the position vector from the satellite to the droop point in the orbital coordinate system The angle between the projection on the yoz plane and the position vector is the pitch steering angle, which is:

[0271]

[0272] The calculation process of the module M9 includes:

[0273]

[0274] Where, ψ is the yaw attitude guidance angle, ω sis the satellite orbital angular velocity.

[0275] Those skilled in the art will appreciate that, in addition to implementing the system and its various devices, modules, and units provided by the present invention in purely computer-readable program code, it is entirely possible to implement the same functions of the system and its various devices, modules, and units provided by the present invention in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system and its various devices, modules, and units provided by the present invention can be considered a hardware component, and the devices, modules, and units included therein for implementing various functions can also be considered as structures within the hardware component; the devices, modules, and units for implementing various functions can also be considered as both software modules implementing the method and structures within the hardware component.

[0276] The above describes specific embodiments of the present invention. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. The embodiments of this application and the features in the embodiments may be combined with each other in any manner unless there is a conflict.

Claims

1. A radar satellite three-dimensional attitude guidance method, characterized in that: include: Step S1: Calculate the satellite's geocentric distance, geocentric latitude, and geocentric longitude based on the acquired satellite navigation data; The satellite navigation data includes satellite orbit parameter information and the position of the satellite in the WGS-84 coordinate system; Step S2: Calculate the satellite altitude and the geodetic longitude and latitude of the sag point based on the WGS-84 reference ellipsoid model and the satellite's geocentric latitude and longitude; Step S3: Calculate the geocentric latitude of the sag point and the radius of the earth at the sag point according to the geodetic latitude of the sag point; Step S4: Calculate the WGS-84 ground-fixed position vector of the sag point based on the sag point information; Step S5: deriving the position vector of the satellite in the WGS-84 Earth-fixed system based on the satellite's position in the WGS-84 coordinate system; Step S6: Calculate the position vector from the satellite to the droop point in the WGS-84 Earth-fixed coordinate system; Step S7: obtaining the position vector from the satellite to the descent point in the satellite orbit coordinate system through coordinate conversion calculation; Step S8: Calculate the roll steering angle and the pitch steering angle in the orbital coordinate system; Step S9: Calculate the yaw steering angle to compensate for the influence of the Doppler frequency shift caused by the rotation of the earth based on the satellite orbit parameter information.

2. The radar satellite three-dimensional attitude guidance method according to claim 1, characterized in that: The step S1 includes the following sub-steps: Step S1.1: Read the satellite's real-time orbit parameters, including the current time t, orbit semi-major axis a, orbit eccentricity e, orbit inclination i, ascending node right ascension Ω, argument of perigee ω, and mean anomaly M; and read the satellite's position in the WGS-84 coordinate system, including X, Y, and Z. Step S1.2: Calculate the satellite's true anomaly f and latitude argument u based on the real-time orbit parameters; where: <h2 style=";text-align:left;direction:ltr">f = M + (2e - 0.25e<h2 style=";text-align:left;direction:ltr"> 3 <h2 style=";text-align:left;direction:ltr"> )×sin(M)+1.25e<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> sin(2M) u=ω+f Step S1.3: Calculate the distance r between the satellite and the center of the Earth, where: Step S1.4: Calculate the satellite's geocentric longitude λ and geocentric latitude φ based on the position in the WGS-84 coordinate system, where:

3. The radar satellite three-dimensional attitude guidance method according to claim 2, characterized in that: The step S2 includes the following sub-steps: Step S2.1: Calculate the satellite's altitude h, where: Where R E is the equatorial radius of the Earth in the WGS-84 reference ellipsoid model, n is the flattening of the Earth in the WGS-84 reference ellipsoid model, and: Where R p is the Earth's polar radius of the WGS-84 reference ellipsoid model; Step S2.2: Calculate the geodetic latitude Φ of the sag point C′ C′ , where the sag point C' is defined as: the earth is a rotating ellipsoid, and the normal line of a certain point of the ellipsoid passes through the satellite, and this point is defined as the satellite sag point; at this time: Step S2.3: Calculate the geodetic longitude λ of the sag point C′ C′ ,have: l C′ =l.

4. The radar satellite three-dimensional attitude guidance method according to claim 3, characterized in that: The step S3 includes the following sub-steps: Step S3.1: Calculate the geocentric latitude φ of the sag point C′ C′ ,have: φ C′ =arctan|[(1-n) 2 tanΦ C′ | Step S3.2: Calculate the radius R of the Earth at the sag point C′ lC′ , that is, the distance from the center of the earth to the sag point, is:

5. The radar satellite three-dimensional attitude guidance method according to claim 4, characterized in that: The calculation process of step S4 includes:

6. The radar satellite three-dimensional attitude guidance method according to claim 5, characterized in that: The calculation process of step S5 includes:

7. The radar satellite three-dimensional attitude guidance method according to claim 6, characterized in that: The step S7 includes the following sub-steps: Step S7.1: Translate the position vector of satellite S to the droop point C′ Convert to the J2000.0 geocentric equatorial inertial system and obtain the position vector from satellite S to sag point C′ in the J2000.0 geocentric equatorial inertial system Step S7.2: Translate the position vector of satellite S to the sag point C′ in the J2000.0 geocentric equatorial inertial system Convert to the satellite orbit coordinate system and obtain the position vector from satellite S to droop point C′ in the satellite orbit coordinate system have: Step S7.3: According to the distance from the satellite to the center of the earth, the position vector of the satellite S to the center of the earth in the satellite orbit coordinate system is obtained 8. The radar satellite three-dimensional attitude guidance method according to claim 7, characterized in that: The step S8 includes the following sub-steps: Step S8.1: Calculate the angle β between the vertical pointing direction of the spaceborne radar to the ellipsoidal surface and the line connecting the satellite and the center of the earth: Step S8.2: Calculate the rolling attitude guidance angle In the orbital coordinate system, the position vector of the satellite to the sag point is The angle between the projection on the yoz surface and the track system +Z axis is the rolling guide angle, which is: Step S8.3: Calculate the pitch attitude guidance angle θ, the position vector of the satellite to the droop point in the orbital coordinate system The angle between the projection on the yoz plane and the position vector is the pitch steering angle, which is:

9. The radar satellite three-dimensional attitude guidance method according to claim 8, characterized in that: The calculation process of step S9 includes: Where, ψ is the yaw attitude guidance angle, ω s is the satellite orbital angular velocity.

10. A radar satellite three-dimensional attitude guidance system, characterized in that: include: Module M1: Calculates the satellite's geocentric distance, geocentric latitude, and geocentric longitude based on the acquired satellite navigation data; The satellite navigation data includes satellite orbit parameter information and the position of the satellite in the WGS-84 coordinate system; Module M2: Calculates the satellite's altitude and the geodetic longitude and longitude of the sag point based on the WGS-84 reference ellipsoid model and the satellite's geocentric latitude and longitude. Module M3: Calculate the geocentric latitude of the sag point and the radius of the earth at the sag point based on the geodetic latitude of the sag point; Module M4: Calculate the WGS-84 ground-fixed position vector of the sag point based on the sag point information; Module M5: Based on the satellite's position in the WGS-84 coordinate system, the satellite's position vector in the WGS-84 Earth-fixed system is obtained; Module M6: Calculate the position vector from the satellite to the droop point in the WGS-84 Earth-fixed coordinate system; Module M7: Obtain the position vector from the satellite to the droop point in the satellite orbit coordinate system through coordinate transformation calculation; Module M8: Calculates the roll and pitch angles in the orbital coordinate system. Module M9: Calculates the yaw steering angle to compensate for the Doppler frequency shift caused by the Earth's rotation based on the satellite orbit parameter information.

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