Imaging attitude in-orbit planning method and system for moving target observation by radar satellite

Abstract

The invention provides an imaging attitude in-orbit planning method and system for a radar satellite to observe a moving target. The method comprises the following steps: S1, determining an initial parameter of the moving target and orbit extrapolation duration dt; s2, reading satellite orbit determination data at the T0 + dt moment from a satellite bus; s3, calculating a three-axis attitude angle of the satellite; s4, estimating a position vector of the target under the WGS84 coordinate system according to the initial parameters of the target; s5, calculating an included angle between the satellite-ground vector and the YbOZb surface of the satellite body system; s6, according to the change of the included angle between the satellite-ground vector and the YbOZb plane of the satellite body system, judging whether a top passing moment exists or not; step S7, calculating the satellite-ground distance at the vertex crossing moment and the ground distance from the sub-satellite point to the target, and judging whether there is an imaging opportunity; and S8, calculating an included angle between the satellite-ground vector at the overhead moment and the Yb axis of the satellite body system, and determining an imaging attitude. The method has the advantages of high calculation precision, small calculation amount and short calculation time, and can be deployed on a satellite.

Description

Technical Field

[0001] The present invention relates to the technical field of satellite observation, and specifically, to an imaging attitude on-orbit planning method and system for a radar satellite to observe a moving target. Background Art

[0002] In recent years, the space-based remote sensing demand for sea vessels has grown rapidly. Due to the advantages of all-weather and all-time observation, radar satellites play an increasingly important role in ensuring the navigation safety of ships. Low-orbit radar satellites use left-side viewing attitude or right-side viewing attitude for imaging, so the imaging attitude needs to be specified in the observation task instruction. Traditional satellite observation tasks rely heavily on ground manual operation, with a too long task instruction transmission chain and poor timeliness, becoming increasingly unsuitable for the needs of space-based remote sensing. Sea vessels are moving targets, and the real-time requirement for their observation tasks is higher and the difficulty is greater.

[0003] Based on the above observation requirements, radar satellites must have the on-board autonomous mission planning ability for maritime moving targets, independently estimate the target movement route according to the uploaded information such as the initial position, speed, and heading of the target, and calculate the overpass time and imaging attitude on orbit. Currently, there are few domestic literatures related to the mission planning of radar satellites for observing moving targets.

[0004] The patent document "Autonomous Start Trigger Method and System for a Radar Satellite to Observe a Target" (CN 112607056 A) discloses that by reading the GPS data at time T after the current satellite time, calculating the components of the distance vector between the satellite and the target point in the satellite antenna coordinate system, combining the magnitude of the distance vector, calculating the target depression angle, then determining whether to access the target, and calculating the target transit time and the size of the depression angle. This method cannot perform observation planning for sea moving ship targets, does not consider the two-dimensional guidance attitude control of radar satellites, has certain errors in the calculation results, and does not involve the calculation of imaging attitude.

[0005] The paper "Multi-angle Imaging Attitude Control Strategy for Reflector Antenna SAR Satellites" (Spacecraft Engineering, Vol. 32, No. 4, 2023) addresses the multi-angle imaging attitude control problem of reflector antenna spaceborne synthetic aperture radar, proposes imaging arc segment division rules, first-scene imaging attitude strategies, imaging angle maneuver switching strategies, and calculation methods for the second-scene imaging attitude, and verifies the attitude strategies based on measured scene image simulation data. This method is applicable to the multi-angle imaging problem of a single target during one pass, and is not suitable for solving the imaging attitude of multiple targets during one pass.

[0006] The research paper "Research on Mission Planning Method for InSAR Dual-Satellite Formation Mapping Satellite" (Measurement & Control Technology, Vol. 42, No. 7, 2023) focuses on the characteristics of the dual-satellite formation interferometric synthetic aperture radar mapping mission. Considering the constraint conditions of the dual-satellite formation satellite platform, it adopts multi-objective optimization and a priority-based genetic optimization algorithm to achieve the design of each key step of the dual-satellite formation mission planning, conducts a system simulation of the mapping mission, obtains the mapping mission planning results, and finally obtains the optimal solution of the mission planning. This method does not clearly propose a method for solving the imaging attitude, and using the genetic algorithm to solve it has a large amount of calculation and is not suitable for on-orbit calculation.

[0007] The research paper "On-Orbit Real-Time Mission Planning Design for Agile SAR Satellite" (Spacecraft Engineering, Vol. 29, No. 5, 2020) designs the on-orbit real-time mission planning for an agile synthetic aperture radar (SAR) satellite facing the on-orbit cooperative guidance imaging mission. Considering the cooperative mission process and characteristics, it constructs an on-orbit real-time mission planning operation framework combining rolling planning and dynamic replanning, formulates a planning-decision strategy of rolling forward with a long planning window and a short decision window, and designs an on-orbit real-time mission planning operation process triggered by events or advancing at a fixed period. For the multi-point target imaging planning problem in the operation process, it uses a depth-first tree search algorithm to search for the optimal imaging target sequence, and uses conflict resolution rules and benefit prediction rules to prune the search tree to speed up the search. This method is applicable to agile SAR satellites that achieve beam pointing through satellite platform attitude maneuvers, and the number of observable targets is limited by the satellite platform maneuverability and is not applicable to phased array radar satellites using electronic scanning. Summary of the Invention

[0008] Aiming at the defects in the prior art, the purpose of the present invention is to provide an on-orbit planning method and system for the imaging attitude of a radar satellite to observe moving targets.

[0009] An on-orbit planning method for the imaging attitude of a radar satellite to observe moving targets according to the present invention includes:

[0010] Step S1: Determine the initial parameters of the moving target and the orbit extrapolation duration dt;

[0011] Step S2: Read the satellite orbit determination data at the moment of T0 + dt from the satellite bus, where T0 is the current on-board time;

[0012] Step S3: Calculate the three-axis attitude angles of the satellite;

[0013] Step S4: Estimate the position vector of the target in the WGS84 coordinate system according to the target initial parameters;

[0014] Step S5: Calculate the satellite-earth vector and the satellite body system Y b OZ bThe included angle of the plane;

[0015] Step S6: Determine whether there is an overpass moment according to the change of the included angle between the satellite-ground vector and the Y-axis of the satellite's body coordinate system; b OZ b plane included angle;

[0016] Step S7: Calculate the satellite-ground distance and the ground distance from the sub-satellite point to the target at the overpass moment, and determine whether there is an imaging opportunity;

[0017] Step S8: Calculate the included angle between the satellite-ground vector and the Y-axis of the satellite's body coordinate system at the overpass moment, and determine the imaging attitude. b axis included angle, and determine the imaging attitude.

[0018] Further, in the step S1, the initial parameters of the moving target include: the initial moment of the target, the target heading angle, the speed, and the initial longitude and latitude.

[0019] Further, in the step S2, the satellite orbit determination data are the satellite orbit elements in the J2000.0 geocentric equatorial inertial coordinate system, including the semi-major axis, eccentricity, orbit inclination, right ascension of the ascending node, argument of perigee, and true anomaly.

[0020] Further, in the step S3, the satellite's three-axis attitude angles are the roll angle, pitch angle, and yaw angle at the moment of t; i moment, t; i = T0 + Δt.

[0021] Further, in the step S4, denote the latitude and longitude of the moving target at the moment of t; i moment as; τ; Li respectively, then; τ; Li The calculation formula of is:

[0022]

[0023] τ; Li = τ; L0 + atan(sinLsinθ; L )

[0024] In the formula, L is the geocentric angle passed from the moment of t; L0 ~t; i moment, R; e is the equatorial radius of the earth, t; L0 is the initial moment of the target, V; L0 、θ; L are the initial speed magnitude and heading angle of the moving target respectively, τ; L0 are the initial latitude and longitude of the moving target respectively, and define the heading angle θ of the target; LTaking the local true north as 0° and the local true east as 90°.

[0025] Further, the step S5 includes:

[0026] Step S5.1: Calculate the satellite position vector in the WGS84 coordinate system;

[0027] Step S5.2: Calculate the satellite-to-ground vector in the WGS84 coordinate system;

[0028] Step S5.3: Calculate the satellite-to-ground vector P in the satellite body coordinate system ibody ;

[0029] P ibody = M orb2body (M orb2ECI ) T M ECF2ECI P iECF

[0030] In the formula, P iECF is the satellite-to-ground vector in the WGS84 coordinate system; M ECF2ECI is the transformation matrix from the WGS84 coordinate system to the J2000.0 geocentric equatorial inertial coordinate system at time t i , M orb2ECI is the transformation matrix from the satellite orbit coordinate system to the J2000.0 geocentric equatorial inertial coordinate system, M orb2body is the transformation matrix from the satellite orbit coordinate system to the satellite body coordinate system calculated according to the attitude rotation sequence "one, two, three";

[0031] Step S5.4: Calculate the included angle between the satellite-to-ground vector and the Y b OZ b plane of the satellite body coordinate system, and denote the included angle between the satellite-to-ground vector and the Y i plane of the satellite body coordinate system at time t b OZ b plane as η i , and the calculation formula of η i is:

[0032] X b = [1, 0, 0] T

[0033]

[0034] wherein, it is defined that the included angle between the satellite-to-ground vector and the X b axis of the satellite body coordinate system is positive when it is greater than 90° and negative when it is less than 90°;

[0035] Step S5.5: Calculate the included angle between the satellite-to-ground vector and the Y b axis of the satellite body coordinate system, and denote the included angle between the satellite-to-ground vector and the Y i axis of the satellite body coordinate system at time tb The included angle of the axis is λ i , λ i The calculation formula is:

[0036] Y b = [0, 1, 0] T

[0037]

[0038] Alternatively, the implementation method of step S5.4 is: calculate the included angle η between the satellite-ground vector and the Y b OZ b plane of the satellite's body coordinate system i ;

[0039] X b = [1, 0, 0] T

[0040]

[0041] η i = |γ i - 90°|;

[0042] In the formula, γ i is the included angle between the satellite-ground vector and the X i axis at time t b axis

[0043] Furthermore, the said step S6 includes:

[0044] If the included angle η between the satellite-ground vector and the Y k plane of the satellite's body coordinate system at the current time t b OZ b plane satisfies η k ≥0, and the included angles η k of the satellite-ground vectors at the previous two times t k-1 and t k-2 with the Y b OZ b plane of the satellite's body coordinate system k-1 、η k-2 both satisfy η k-1 <0 and η k-2 <0, then there is an over-the-top moment;

[0045] The calculation method of the over-the-top moment t g is:

[0046]

[0047] In the formula, t m represents t k 、t k-1 and t k-2The mean of the three moments, η m Indicates the star-to-ground vector and Y at three corresponding moments b OZ b The mean of the plane angles, K1 is the time correction.

[0048] Furthermore, the step S7 includes:

[0049] Step S7.1: Using three time points t k-2 , t k-1 and t k The star-to-ground distance and the major semi-axis are calculated, and the star-to-ground distance and the major semi-axis at the time of passing the top are calculated. The star-to-ground distance size p at the time of passing the top is calculated. g The calculation formula is:

[0050]

[0051] p g =p m +K2(t g -t m )

[0052] Where p k-2 、p k-1 and p k t k-2 , t k-1 and t k The modulus of the star-to-earth distance vector at time p m Indicates t k , t k-1 and t k-2 The mean of the moduli of the satellite-to-earth distance vectors at three moments, K2 represents the distance correction;

[0053] The major semi-axis a at the time of passing the top g The calculation formula is:

[0054]

[0055]

[0056] a g =a m +K3(t g -t m )

[0057] Where a k-2 、a k-1 and a k t k-2 , t k-1 and t k The major axis of the moment, a m Indicates t k , t k-1and t k-2 The mean value of the semi-major axis at three moments, and K3 represents the correction amount of the semi-major axis;

[0058] Step S7.2: Calculate the ground distance from the sub-satellite point to the target at the overpass moment. The ground distance L g is calculated as follows:

[0059]

[0060] Step S7.3: If the satellite-ground distance at the overpass moment is less than a given value, and the ground distance from the sub-satellite point of the satellite to the target is within the given range, it is considered that there is an imaging opportunity, and step S8 is triggered; otherwise, it is considered that there is no imaging opportunity, and the calculation ends.

[0061] Furthermore, the said step S8 includes:

[0062] If the included angle λ b between the satellite-ground vector and the Y g axis of the satellite's body coordinate system at the overpass moment is less than 90°, the radar satellite needs to image in the right-looking attitude; when λ g is greater than 90°, the radar satellite needs to image in the left-looking attitude. The calculation formula of λ g at the overpass moment is:

[0063]

[0064] λ g = λ m + K4(t g - t m )

[0065] In the formula, λ k-2 , λ k-1 and λ k are the included angles between the satellite-ground vectors and the Y k-2 , t k-1 and t k axes of the satellite's body coordinate system at the moments of t b respectively. λ m represents the mean value of the included angles between the satellite-ground vectors and the Y k , t k-1 and t k-2 axes of the satellite's body coordinate system at the three moments of t b respectively, and K4 represents the angle correction amount.

[0066] According to an imaging attitude on-orbit planning system for a radar satellite to observe a moving target provided by the present invention, it includes:

[0067] Module M1: Determine the initial parameters of the moving target and the orbit extrapolation duration dt;

[0068] Module M2: Read the satellite orbit determination data at time T0 + dt from the satellite bus, where T0 is the current on-board time;

[0069] Module M3: Calculate the three-axis attitude angles of the satellite;

[0070] Module M4: Estimate the position vector of the target in the WGS84 coordinate system according to the target initial parameters;

[0071] Module M5: Calculate the angle between the satellite-ground vector and the Y b OZ b plane of the satellite's body coordinate system;

[0072] Module M6: Judge whether there is an over-the-top moment according to the change of the angle between the satellite-ground vector and the Y b OZ b plane of the satellite's body coordinate system;

[0073] Module M7: Calculate the satellite-ground distance and the ground distance from the sub-satellite point to the target at the over-the-top moment, and judge whether there is an imaging opportunity;

[0074] Module M8: Calculate the angle between the satellite-ground vector and the Y-axis of the satellite's body coordinate system at the over-the-top moment to determine the imaging attitude. b axis of the satellite's body coordinate system to determine the imaging attitude.

[0075] Compared with the prior art, the present invention has the following beneficial effects:

[0076] The present invention provides an on-orbit planning method for the imaging attitude of a radar satellite to observe a moving target. It predicts the target movement route according to the initial position, speed and heading information of the moving target, calculates the over-the-top moment according to the high-precision orbit and attitude data, and finally autonomously calculates the imaging attitude of the moving target according to the radar satellite coverage area constraint. It has the advantages of high calculation accuracy, small calculation amount and short calculation time, and can be deployed on the satellite.

[0077] 1. Aiming at the space-based observation requirements of moving targets such as sea ships, combining the movement trajectories of moving targets, using the orbit data of the satellite bus, and judging whether there is an over-the-top moment according to the polarity change of the angle between the satellite-ground vector and the Y b OZ b plane of the satellite's body coordinate system, and comprehensively considering constraints such as the satellite-ground distance and the ground distance from the sub-satellite point to the target, the present invention provides an on-orbit planning method for the imaging attitude of a radar satellite to observe a moving target, which can quickly obtain the imaging attitude of the radar satellite in advance for a certain period of time, facilitating the satellite to implement the observation task. The present invention has the advantages of low algorithm complexity, high calculation accuracy, small calculation amount and short calculation time, and can be transplanted and implemented on the satellite, reducing the workload and pressure of the ground operation and control system.

[0078] 2. The present invention can predict the trajectories of moving targets such as sea ships and airplanes, meeting the requirements for imaging moving targets; it makes full use of the high-precision orbit data on the satellite bus for calculation, avoiding complex orbit recursion; it introduces time-varying satellite attitude angles according to the actual radar satellite attitude control law, improving the calculation accuracy; it takes into account the coverage area constraints of the radar satellite, adapting to the imaging characteristics of the radar satellite; it can calculate the overpass time and imaging attitude on orbit only using the data at three time points, greatly reducing the calculation amount and difficulty. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] Other features, objects, and advantages of the present invention will become more apparent by reading the detailed description of the non-limiting embodiments with reference to the following drawings:

[0080] Figure 1 It is a flowchart of an on-orbit planning method for the imaging attitude of a radar satellite observing a moving target.

[0081] Figure 2 It is a schematic diagram of the track of a moving target. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0082] The present invention will be described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that those of ordinary skill in the art can make several changes and improvements without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0083] An on-orbit planning method for the imaging attitude of a radar satellite observing a moving target provided by the present invention, as shown in Figure 1 and Figure 2 includes:

[0084] Step S1: Determine the initial parameters of the moving target and the orbit extrapolation duration dt. The initial parameters of the moving target include the target initial time, target course angle, speed, and initial longitude and latitude. To control the on-board orbit extrapolation error and improve the calculation accuracy, it is required that dt does not exceed 60 min.

[0085] Step S2: Read the satellite orbit determination data at the moment of T0 + dt from the satellite bus. T0 is the current on-board time. To improve the calculation accuracy, it is required that the reading interval is 1 s. The orbit determination data are the satellite orbit elements in the J2000.0 geocentric equatorial inertial coordinate system, including the semi-major axis, eccentricity, orbital inclination, right ascension of the ascending node, argument of perigee, and true anomaly. The orbit determination data at the moment of T0 + Δt are provided by the navigation receiver after orbit extrapolation.

[0086] Step S3: Calculate the satellite three-axis attitude angles. The satellite three-axis attitude angles are t i (ti =T0+Δt) at the time of roll angle, pitch angle and yaw angle. In order to compensate for the influence of the earth's rotation on the radar payload imaging, the attitude of the radar satellite needs to be controlled in two dimensions. Under the two-dimensional guidance law, t i The calculation formula of the satellite three-axis attitude angle at the moment is:

[0087]

[0088]

[0089] Where, θ i and ψ i t i Roll angle, pitch angle and yaw angle at the moment; a i 、e i 、i i 、w i and f i t i The semi-major axis, eccentricity, inclination, argument of perigee and true anomaly of the satellite orbit at this moment; ω e is the angular velocity of the Earth's rotation; μ is the gravitational constant.

[0090] Step S4: Estimate the target's position vector in the WGS84 coordinate system based on the target's initial parameters. i The latitude and longitude of the moving target at any moment are τ Li ,but τ Li The calculation formula is

[0091]

[0092] τ Li =τ L0 +atan(sinLsinθ L )

[0093] Where L is t L0 ~t i The geocentric angle passed by the moment, R e is the Earth's equatorial radius, t L0 is the target initial moment, V L0 ,θ L are the initial speed and heading angle of the moving target respectively. τ L0 are the initial latitude and longitude of the moving target respectively. Define the heading angle θ of the target L The local due north is 0° and the local due east is 90°.

[0094] According to t iLatitude of the moving target at a certain moment and longitude τ Li , with the elevation set to 0, the position vector R of the target in the WGS84 coordinate system can be calculated Li . The specific process has been elaborated in detail in relevant published literature

[0095] Step S5: Calculate the angle between the satellite - earth vector and the satellite's body - fixed Y b OZ b plane. The specific steps include steps S5.1 to S5.5

[0096] Step S5.1: Calculate the position vector of the satellite in the WGS84 coordinate system. At time t i , the position vector R of the satellite in the WGS84 coordinate system SECFi is calculated by the formula

[0097]

[0098] Q i =(R Z (Ω i )) T (R X (i i )) T (R Z (w i )) T

[0099] R sECIi =Q i ·r pi

[0100] R SECFi =(M ECF2ECI ) T R sECIi

[0101] In the formula, Ω i is the right ascension of the ascending node of the satellite at time t i ; R sECIi is the position vector of the satellite in the J2000.0 geocentric equatorial inertial coordinate system at time t i ; M ECF2ECI is the transformation matrix from the WGS84 coordinate system to the J2000.0 geocentric equatorial inertial coordinate system at time t i . The calculation method can be found in relevant literature

[0102] Step S5.2: Calculate the satellite - earth vector in the WGS84 coordinate system. In the WGS84 coordinate system, the satellite - earth vector P i at time t iECF is calculated by the formula

[0103] PiECF = R Li - R SECFi

[0104] Step S5.3: Calculate the satellite-to-ground vector P in the satellite body coordinate system ibody .t i The satellite-to-ground vector P in the satellite body coordinate system at time t ibody is obtained from the satellite-to-ground vector P in the WGS84 coordinate system through a series of coordinate transformations. The calculation formula is iECF

[0105] P ibody = M orb2body (M orb2ECI ) T M ECF2ECI P iECF

[0106] In the formula, M orb2ECI is the transformation matrix from the satellite orbit coordinate system to the J2000.0 geocentric equatorial inertial coordinate system; M orb2body is the transformation matrix from the satellite orbit coordinate system to the satellite body coordinate system calculated according to the attitude rotation sequence "123". The calculation formula is

[0107] V sECIi = Q i ·v pi

[0108] Y a = (V sECIi × R sECIi )

[0109] X[[ID=?]] a = R sECIi × Y a

[0110]

[0111]

[0112] In the formula, β is the yaw angle of the radar satellite; R x (A) represents a rotation of A degrees around the X-axis, R(B) represents a rotation of B degrees around the Y-axis, R(C) represents a rotation of C degrees around the Z-axis.

[0113] Step S5.4: Calculate the angle between the satellite-to-ground vector and the Y b OZ b plane of the satellite body coordinate system. Denote the angle between the satellite-to-ground vector and the Y i OZ b plane of the satellite body coordinate system at time t as η b , η i , η i , η It seems there is an issue with the original text where the "X" variable's formula is incomplete. Please check and correct it if possible for a more accurate translation.i The calculation formula is

[0114] X b = [1, 0, 0] T

[0115]

[0116] where the included angle between the satellite - ground vector and the X - axis of the satellite's body - fixed system is defined as positive when it is greater than 90°, and negative when it is less than 90°. b

[0117] Step S5.5: Calculate the included angle between the satellite - ground vector and the Y - axis of the satellite's body - fixed system. Denote the included angle between the satellite - ground vector and the Y - axis of the satellite's body - fixed system at time t b as λ i b The calculation formula of λ i is i

[0118] Y b = [0, 1, 0] T

[0119]

[0120] where Step S5.4 can also be implemented in the following way: Calculate the included angle η b between the satellite - ground vector and the YOZ b plane at each time point; i

[0121] X b = [1, 0, 0] T

[0122]

[0123] η i = |γ i - 90°|;

[0124] where γ i is the included angle between the satellite - ground vector and the X - axis at time t i b .

[0125] Step S6: Judge whether there is an over - head moment according to the change of the included angle between the satellite - ground vector and the YOZ b plane. If the included angle η b between the satellite - ground vector and the YOZ k plane at the current time t b satisfies η b ≥0, while the included angles η k at the previous two times t k and t k-1 and t​​​​​k-2 The star-earth vector and the satellite's body-fixed system Y b OZ b The included angle η between the planes k-1 、η k-2 Both satisfy η k-1 <0 and η k-2 <0, then there exists an overpassing moment. The calculation method of the overpassing moment t g is as follows

[0126]

[0127] In the formula, t m represents the mean value of the three moments t k 、t k-1 and t k-2 , η m represents the mean value of the included angles between the star-earth vectors and Y b OZ b plane corresponding to the three moments, and K1 is the time correction amount.

[0128] Step S7: Calculate the star-earth distance at the overpassing moment and the ground distance from the sub-satellite point to the target, and determine whether there is an imaging opportunity. The specific steps include steps S7.1 to S7.3:

[0129] Step S7.1: Use the star-earth distances and the semi-major axis at the three moments t k-2 、t k-1 and t k to calculate the star-earth distance and the semi-major axis at the overpassing moment. The magnitude p g of the star-earth distance at the overpassing moment is calculated by the formula

[0130]

[0131] In the formula, p k-2 、p k-1 and p k are the magnitudes of the star-earth distance vectors at the moments t k-2 、t k-1 and t k respectively, p m represents the mean value of the magnitudes of the star-earth distance vectors at the three moments t k 、t k-1 and t k-2 , and K2 represents the distance correction amount.

[0132] The semi-major axis a g at the overpassing moment is calculated by the formula

[0133]

[0134] a g =a m +K3(tg -t m )

[0135] In the formula, a k-2 , a k-1 and a k are the semi-major axes at times t k-2 , t k-1 and t k respectively, a m represents the average value of the semi-major axes at the three times t k , t k-1 and t k-2 , and K3 represents the correction amount of the semi-major axis.

[0136] Step S7.2: Calculate the ground distance from the sub-satellite point to the target at the overpass time. The calculation method for the ground distance L g from the sub-satellite point to the target at the overpass time is

[0137]

[0138] Step S7.3: If the satellite-ground distance at the overpass time is less than the given value and the ground distance from the sub-satellite point to the target is within the given range, it is considered that there is an imaging opportunity, and step S8 is triggered; otherwise, it is considered that there is no imaging opportunity and the calculation ends. The ground distance from the sub-satellite point to the target is related to the coverage range of the radar payload.

[0139] Step S8: Calculate the angle between the satellite-ground vector and the Y b axis of the satellite's body frame to determine the imaging attitude. If the angle λ b between the satellite-ground vector and the Y g axis of the satellite's body frame at the overpass time is less than 90°, the radar satellite needs to image in the right-looking attitude; if λ g is greater than 90°, the radar satellite needs to image in the left-looking attitude. The calculation formula for λ g at the overpass time is

[0140]

[0141] λ g = λ m + K4(t g - t m )

[0142] In the formula, λ k-2 , λ k-1 and λ k are the angles between the satellite-ground vector and the Y k-2 , t k-1 and t k axes of the satellite's body frame at times t b respectively, and λ m represents t k , tk-1 and t k-2 The average value of the angles between the satellite-ground vectors at three moments and the Y-axis of the satellite's body coordinate system, where K4 represents the angle correction amount. b axis, and K4 represents the angle correction amount.

[0143] Regarding the imaging problem of a radar satellite for a moving target, the present invention proposes an in-orbit planning method for the imaging attitude of a radar satellite observing a moving target. By using the high-precision orbit data on the satellite bus for calculation, on the basis of predicting the trajectory of the moving target, constraints such as the satellite-ground distance and the radar coverage range are comprehensively considered, and the imaging opportunity for the moving target is calculated in orbit.

[0144] The present invention also provides an in-orbit planning system for the imaging attitude of a radar satellite observing a moving target. The in-orbit planning system for the imaging attitude of a radar satellite observing a moving target can be implemented by executing the process steps of the in-orbit planning method for the imaging attitude of a radar satellite observing a moving target. That is, those skilled in the art can understand the in-orbit planning method for the imaging attitude of a radar satellite observing a moving target as the preferred implementation manner of the in-orbit planning system for the imaging attitude of a radar satellite observing a moving target. The system includes:

[0145] Module M1: Determine the initial parameters of the moving target and the orbit extrapolation duration dt.

[0146] Module M2: Read the satellite orbit determination data at the moment of T0 + dt from the satellite bus.

[0147] Module M3: Calculate the three-axis attitude angles of the satellite.

[0148] Module M4: Estimate the position vector of the target in the WGS84 coordinate system according to the target initial parameters.

[0149] Module M5: Calculate the angle between the satellite-ground vector and the Y b OZ b plane of the satellite's body coordinate system.

[0150] Module M6: Determine whether there is an overpass moment according to the change of the angle between the satellite-ground vector and the Y b OZ b plane of the satellite's body coordinate system.

[0151] Module M7: Calculate the satellite-ground distance and the ground distance from the sub-satellite point to the target at the overpass moment, and determine whether there is an imaging opportunity.

[0152] Module M8: Calculate the angle between the satellite-ground vector and the Y b axis of the satellite's body coordinate system at the overpass moment, and determine the imaging attitude.

[0153] Those skilled in the art know that, in addition to implementing the system and its various devices, modules, and units provided by the present invention in the form of pure computer-readable program code, the method steps can be logically programmed to enable the system and its various devices, modules, and units provided by the present invention to be implemented in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers, etc. to achieve the same functions. Therefore, the system and its various devices, modules, and units provided by the present invention can be considered as a kind of hardware component, and the devices, modules, and units included therein for implementing various functions can also be regarded as the structures within the hardware component; the devices, modules, and units for implementing various functions can also be regarded as either software modules for implementing the method or structures within the hardware component.

[0154] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. Without conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. An in-orbit planning method for imaging attitude of a radar satellite to observe moving targets, characterized in that, Including: Step S1: Determine the initial parameters of the moving target and the orbit extrapolation duration dt; Step S2: Read the satellite orbit determination data at the moment of T0 + dt from the satellite bus, where T0 is the current on-board time; Step S3: Calculate the satellite's three-axis attitude angles; Step S4: Estimate the position vector of the target in the WGS84 coordinate system according to the target initial parameters; Step S5: Calculate the angle between the satellite-ground vector and the Y-axis of the satellite's body frame b OZ b plane; Step S6: Determine whether there is an overpass moment based on the change in the angle between the satellite-ground vector and the Y-axis of the satellite's body frame b OZ b plane angle Step S7: Calculate the satellite-ground distance at the overpass moment and the ground distance from the sub-satellite point to the target, and determine whether there is an imaging opportunity; Step S8: Calculate the angle between the satellite-ground vector and the Y-axis of the satellite body coordinate system at the over-the-top moment to determine the imaging attitude. b axis to determine the imaging attitude.

2. The imaging attitude on-orbit planning method for a radar satellite to observe a moving target according to claim 1, characterized in that, In the said Step S1, the initial parameters of the moving target include: the initial moment of the target, the target heading angle, the speed, and the initial longitude and latitude.

3. The imaging attitude on-orbit planning method for a radar satellite to observe a moving target according to claim 1, wherein, In the said Step S2, the satellite orbit determination data are the satellite orbit elements in the J2000.0 geocentric equatorial inertial coordinate system, including the semi-major axis, eccentricity, orbital inclination, right ascension of the ascending node, argument of perigee, and true anomaly.

4. The imaging attitude in-orbit planning method for a radar satellite to observe a moving target according to claim 1, characterized in that, In the step S3, the three-axis attitude angles of the satellite are the roll angle, pitch angle, and yaw angle at time t i where t i = T0 + Δt.

5. The imaging attitude on-orbit planning method for a radar satellite to observe a moving target according to claim 4, wherein In the step S4, let t i be the latitude and longitude of the moving target at time τ Li , respectively. Then τ Li is calculated by the formula: τ Li = τ L0 + atan(sin L sin θ L ) where L is the central angle of the earth passed from time t L0 to t i ; R e is the equatorial radius of the earth; t L0 is the initial time of the target; V L0 , θ L are respectively the initial speed magnitude and the course angle of the moving target; τ L0 are respectively the initial latitude and longitude of the moving target. Define the course angle θ L of the target with the local true north as 0° and the local true east as 90°.

6. The imaging attitude on-orbit planning method for a radar satellite to observe a moving target according to claim 1, characterized in that The said Step S5 includes: Step S5.1: Calculate the satellite position vector in the WGS84 coordinate system; Step S5.2: Calculate the satellite-ground vector in the WGS84 coordinate system; Step S5.3: Calculate the satellite-ground vector P in the satellite body coordinate system ibody ; P ibody = M orb2body (M orb2ECI ) T M ECF2ECI P iECF Wherein, P iECF is the satellite-earth vector in the WGS84 coordinate system; M ECF2ECI is the transformation matrix from the WGS84 coordinate system to the J2000.0 geocentric equatorial inertial coordinate system at time t i , M orb2ECI is the transformation matrix from the satellite orbit coordinate system to the J2000.0 geocentric equatorial inertial coordinate system, M orb2body is the transformation matrix from the satellite orbit coordinate system to the satellite body coordinate system calculated according to the attitude rotation sequence "123"; Step S5.4: Calculate the angle between the satellite-ground vector and the Y-axis of the satellite's body frame b OZ b plane, and denote it as t i The angle between the satellite-ground vector and the Y-axis of the satellite's body frame at time t b OZ b plane is η i The calculation formula for η i is as follows: X b ＝[1,0,0] T Among them, it is defined that the angle between the satellite-ground vector and the X-axis of the satellite's body frame is positive when it is greater than 90°, and negative when it is less than 90°; b The angle between the satellite-ground vector and the X-axis of the satellite's body frame is positive when it is greater than 90°, and negative when it is less than 90°; Step S5.5: Calculate the angle between the satellite-ground vector and the Y-axis of the satellite body frame, and denote the angle between the satellite-ground vector and the Y-axis of the satellite body frame at time t b as λ b . The calculation formula for λ i is as follows: b i b i i ​​​​​ Y b ＝[0,1,0] T Alternatively, the implementation of step S5.4 is as follows: calculate the angle η between the satellite-ground vector and the Y b OZ b plane at each time point i ; X b ＝[1,0,0] T η i = |γ i - 90°|; where γ i is the angle between the satellite-ground vector and the X i axis at time t b axis.

7. The imaging attitude on-orbit planning method for a radar satellite to observe a moving target according to claim 1, characterized in that, The said Step S6 includes: If the current time is t k The satellite - ground vector and the satellite - body system Y b OZ b The included angle η between the planes k Satisfy η k ≥0, while for the previous two times t k-1 and t k-2 The satellite - ground vectors and the satellite - body system Y b OZ b The included angles η k-1 、η k-2 Both satisfy η k-1 <0 and η k-2 <0, then there exists an over - head time; Calculation method for the overtop moment t g is as follows: where t m represents the mean value of t k , t k-1 and t k-2 at three moments, and η m represents the mean value of the angle between the satellite-ground vector and the Y b OZ b plane at the corresponding three moments, and K1 is the time correction amount.

8. The imaging attitude on-orbit planning method for a radar satellite to observe a moving target according to claim 1, wherein The said Step S7 includes: Step S7.1: Using the satellite-ground distances and semi-major axes at three moments \(t\) k-2 , \(t\) k-1 and \(t\) k , calculate the satellite-ground distance and semi-major axis at the overpass moment. The formula for calculating the magnitude \(p\) g of the satellite-ground distance at the overpass moment is as follows: p g = p m + K2(t g - t m ) where p k-2 , p k-1 , and p k are the magnitudes of the space - to - ground distance vectors at times t k-2 , t k-1 , and t k respectively, p m represents the mean value of the magnitudes of the space - to - ground distance vectors at three times t k , t k-1 , and t k-2 , and K2 represents the distance correction amount; The semi-major axis a at the overtop moment g The calculation formula is as follows: a g = a m + K3(t g - t m ) where a k-2 , a k-1 and a k are the major semi-axes at times t k-2 , t k-1 and t k respectively, a m represents the mean value of the major semi-axes at the three times t k , t k-1 and t k-2 , and K3 represents the major semi-axis correction amount; Step S7.2: Calculate the ground distance from the sub-satellite point to the target at the overpass moment. The ground distance L from the sub-satellite point to the target at the overpass moment g is calculated as follows: Step S7.3: If the satellite-ground distance at the overpass moment is less than the given value, and the ground distance from the sub-satellite point of the satellite to the target is within the given range, it is considered that there is an imaging opportunity, and Step S8 is triggered; otherwise, it is considered that there is no imaging opportunity, and the calculation ends.

9. The imaging attitude on-orbit planning method for a radar satellite to observe a moving target according to claim 1, characterized in that, The said Step S8 includes: If the angle λ b between the satellite-ground vector and the Y-axis of the satellite's body frame at the overpass moment g is less than 90°, the radar satellite needs to use a right-looking attitude for imaging; when λ g is greater than 90°, the radar satellite needs to use a left-looking attitude for imaging. The calculation formula for λ g at the overpass moment is as follows: λ g = λ m + K4(t g - t m ) where λ k-2 , λ k-1 and λ k are the angles between the satellite - ground vector and the Y b axis of the satellite body frame at times t k-2 , t k-1 and t k respectively. λ m represents the average value of the angles between the satellite - ground vector and the Y b axis of the satellite body frame at three times t k , t k-1 and t k-2 , and K4 represents the angle correction amount.

10. An imaging attitude on-orbit planning system for a radar satellite to observe moving targets, characterized in that, Including: Module M1: Determine the initial parameters of the moving target and the orbit extrapolation duration dt; Module M2: Read the satellite orbit determination data at the moment of T0 + dt from the satellite bus, where T0 is the current on-board time; Module M3: Calculate the satellite's three-axis attitude angles; Module M4: Estimate the position vector of the target in the WGS84 coordinate system according to the target initial parameters; Module M5: Calculate the angle between the space-ground vector and the Y-axis of the satellite's body coordinate system b OZ b plane; Module M6: Determine whether there is an overpass moment based on the change in the included angle between the satellite-ground vector and the Y-axis of the satellite's body coordinate system b OZ b plane included angle Module M7: Calculate the satellite-ground distance at the overpass moment and the ground distance from the sub-satellite point to the target, and determine whether there is an imaging opportunity; Module M8: Calculate the angle between the satellite-ground vector and the Y-axis of the satellite's body frame at the over-the-top moment to determine the imaging attitude. b Axis to determine the imaging attitude.

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