An on-orbit control method for large-slant-view imaging of a micro SAR satellite

Abstract

An on-orbit control method for large-slant-view imaging of a micro SAR satellite is proposed. This method employs STK software for orbit prediction and target coverage simulation, selecting the target to be observed from the target library of the ground control system. Based on the predicted orbital root number and target position, the required slant angle for observation is calculated. A suitable slant angle is selected based on the pulse repetition frequency range achievable by the radar receiver, the azimuth ambiguity of the SAR image, and the application requirements of the scenario. The beamline vector of the observed target in the orbital coordinate system is obtained. The satellite attitude sequence is determined, and the ground slant angle, down-angle angle, satellite yaw angle, and SAR antenna electronic scanning angle are calculated based on the satellite-ground geometry of large-slant-view imaging. The ground control system generates SAR working parameter packages, satellite attitude maneuver parameter packages, and imaging mission command sequences, which are then uploaded to the satellite control system.

Description

Technical Field

[0001] This invention relates to an on-orbit control method for large-angle imaging of a micro SAR satellite, belonging to the field of overall design of micro SAR satellites. Background Technology

[0002] With the continuous development of spaceborne synthetic aperture radar (SAR) technology and the increasing demand for multi-angle imaging applications, the need for large-angle SAR imaging with early observation or back-view capabilities is becoming more and more urgent.

[0003] Large angle-of-sight imaging requires the azimuth beam to form a large angle with the flight direction (called the angle of view), which can be achieved through SAR antenna electronic scanning or satellite attitude maneuvering. Considering the application value in practical scenarios, the angle of view can usually reach tens of degrees. If only the SAR antenna electronic scanning method is used to achieve this, it will greatly increase the size of the SAR antenna and the scale of the TR components, thereby multiplying the weight and size of the satellite.

[0004] Therefore, how to effectively conduct large-angle on-orbit imaging of micro SAR satellites without changing the satellite's weight and size is the key problem that this invention aims to solve. Summary of the Invention

[0005] The technical problem solved by this invention is: in response to the problem that traditional large-angle imaging in the existing technology leads to a significant increase in the weight and size of SAR antennas and satellites, a method for on-orbit control of large-angle imaging of micro SAR satellites is proposed.

[0006] The present invention solves the above-mentioned technical problem through the following technical solution:

[0007] An on-orbit control method for large-slant-view imaging of a micro SAR satellite includes:

[0008] The orbital number of satellites within a preset time range is determined by orbital prediction, and the target to be observed is selected based on the satellite coverage area;

[0009] Calculate the satellite position and velocity parameters in the inertial coordinate system within a preset time range, and calculate the oblique angle required for satellite observation of the target within the current time period based on the target position of the target to be observed;

[0010] Based on the pulse repetition frequency range of the radar receiver, the azimuth ambiguity of the SAR image, and the requirements of the satellite imaging mission, the required satellite position and velocity parameters are selected, and the corresponding oblique angle is determined.

[0011] Construct the beamline vector of the target to be observed in the Earth-fixed coordinate system and transform it to the beamline vector in the orbital coordinate system;

[0012] Determine the satellite attitude sequence, calculate the ground oblique angle and downward angle based on the beamline vector in the orbital coordinate system, and calculate the satellite yaw angle and SAR antenna electronic scanning angle based on the satellite-ground geometry.

[0013] Based on the oblique angle and the SAR antenna electronic scanning angle, SAR working parameters are designed and SAR working parameter packages are generated; at the same time, satellite attitude maneuver parameter packages are generated and uploaded to the satellite together with the SAR working parameters.

[0014] According to the preset satellite attitude and radar operating parameters, the target to be observed is subjected to large oblique-view imaging, and the radar echo data, navigation data and ephemeris data are transmitted down to the ground data transmission station.

[0015] The target to be observed is selected from a known ground target database. After selecting the target, the target position P of the target to be observed is determined in the Earth-fixed coordinate system. tECEF The preset time range is within the period [-T0, T0].

[0016] Calculate the oblique angle θ required for satellite observation of the target during the current time period. sq The steps are as follows:

[0017] The position parameters of the satellite in the inertial coordinate system are calculated based on the six orbital roots as P. sECI The speed parameter is V sECI ;

[0018] Based on the satellite's position parameter P sECEF The speed parameter is V sECEF Construct the transformation matrix from the inertial coordinate system to the Earth-fixed coordinate system, and change the satellite position P in the inertial coordinate system. sECI and speed V sECI Transformation to Earth-Fixed Coordinate System for Satellite Position Parameter P sECEF and velocity parameter V sECEF ;

[0019] Calculate the target slant range R and Doppler center frequency f. DC The oblique angle required for satellite observation of the target within the current time period is calculated based on the obtained data.

[0020] The position parameter of the satellite in the inertial coordinate system is P. sECI The speed parameter is V sECI The calculation method is as follows:

[0021]

[0022]

[0023] In the formula, a is the semi-major axis of the orbit, e is the eccentricity, i is the orbital inclination, Ω is the right ascension of the ascending node, ω is the argument of perigee, u is the argument of latitude, and ω s v is the satellite's angular velocity. e This is the Earth's rotational angular velocity;

[0024] R s Distance of the satellite from the Earth's center:

[0025]

[0026] The rate of change of the satellite's distance from Earth:

[0027]

[0028] The satellite position parameter P sECEF and velocity parameter V sECEF The calculation method is as follows:

[0029]

[0030]

[0031] In the formula, ε GST For Greenwich Mean Time, η is the precession, nutation, and polar motion correction matrix.

[0032] The method for calculating the target slant distance is as follows:

[0033] R = |P tECEF -P sECEF |

[0034] The Doppler center frequency f DC The calculation method is as follows:

[0035] f DC =2 / (λR)×dot(V) sECEF ,P sECEF -P tECEF In the formula, λ is the radar wavelength, and dot represents the vector dot product;

[0036] The oblique angle θ required for satellite observation of the target during the current time period sq The calculation method is as follows:

[0037]

[0038] The method for constructing the beamline vector in the orbital coordinate system is as follows:

[0039] Construct the beamline vector α in the Earth-fixed coordinate system ECEF =P sECEF -P tECEF ;

[0040] Construct the transformation matrix from the Earth-fixed coordinate system to the orbital coordinate system;

[0041] Perform beamline vector transformation in orbital coordinate system:

[0042]

[0043] In the formula, α o This is the beamline vector in the orbital coordinate system.

[0044] The calculation methods for the ground oblique angle and downward angle are as follows:

[0045]

[0046]

[0047] In the formula, γ1, γ2, and γ3 are the three-axis projections of the beamline vector in the orbital coordinate system.

[0048] The satellite-to-ground geometry is determined based on the satellite's flight direction and the SAR antenna's installation method. After determining the satellite-to-ground geometry, the initial satellite yaw angle is determined as follows:

[0049]

[0050] The method for determining the electrical scanning angle of a SAR antenna is as follows:

[0051] cos(γ)=cos(θ sq cos(γ0)

[0052] γ0=acos(cos(γ) / cos(θ sq ))

[0053] θ = acos(cos(γ) / cos(θ) sq ))-ε roll

[0054] In the formula, ε roll It is the angle at which the satellite rotates around its roll axis when observing the target.

[0055] During large squint imaging, if the satellite adopts a two-dimensional yaw guidance mode, the preset satellite attitude is corrected, and the corrected yaw angle ε is determined. yaw and pitch angle ε pitch :

[0056]

[0057]

[0058] The advantages of this invention compared to the prior art are:

[0059] This invention provides an on-orbit control method for large-angle-view imaging of a micro SAR satellite. It is the first to propose an implementation method for large-angle-view imaging of SAR satellites that combines satellite attitude maneuvering and antenna electronic scanning. The large angle of view is achieved by attitude maneuvering with yaw and roll angles, which effectively reduces the deep coupling between range and azimuth directions and simplifies the complexity of ground imaging processing. By designing the beamline vector, the large angle of view can be effectively decomposed into satellite attitude control and SAR payload subsystems. The process is clear and easy to implement in engineering. Attached Figure Description

[0060] Figure 1 A flowchart of the on-orbit implementation method for large-angle imaging of a micro SAR satellite provided for the invention;

[0061] Figure 2 A schematic diagram of the geometric relationship for SAR satellite large squint imaging provided for the invention; Detailed Implementation

[0062] An on-orbit control method for large-slant-view imaging of a micro SAR satellite is proposed. This method employs STK software for orbit prediction and target coverage simulation, selecting the target to be observed from the target library of the ground control system. Based on the predicted orbital root number and target position, the required slant angle for observation is calculated. A suitable slant angle is selected based on the pulse repetition frequency range achievable by the radar receiver, the azimuth ambiguity of the SAR image, and the application requirements of the scenario. The beamline vector of the observed target in the orbital coordinate system is obtained. The satellite attitude sequence is determined, and the ground slant angle, down-angle angle, satellite yaw angle, and SAR antenna electronic scanning angle are calculated based on the satellite-ground geometry of large-slant-view imaging. The ground control system generates SAR working parameter packages, satellite attitude maneuver parameter packages, and imaging mission command sequences, which are then uploaded to the satellite control system.

[0063] The following description, in conjunction with the accompanying drawings and preferred embodiments, provides further details:

[0064] In the current embodiment, an on-orbit implementation method for large-squint-angle imaging using a micro SAR satellite is provided, such as... Figure 1 As shown, it includes the following steps:

[0065] Step S1: Based on the orbit determination results from the ground-based telemetry and control system, select the initial predicted time -T0, and use STK software to extrapolate the orbit, obtaining the six orbital elements of the satellite within the time period [-T0, T0]. Simulate the target coverage area based on the satellite's attitude maneuverability and the electronic scanning angle range of the SAR antenna. Select the target to be observed from the target database of the ground-based telemetry and control system, obtain the target's latitude and longitude, and convert it to the position coordinates P in the Earth-fixed coordinate system. tECEF ;

[0066] Step S2: Construct the transformation matrix from the Earth-fixed coordinate system to the inertial coordinate system, and convert the six satellite orbital roots in [-T0, T0] into the satellite position P in the Earth-fixed coordinate system. sECEF and speed V sECEF Calculate the target slant range R and Doppler center frequency f. DC and oblique angle θ sq ;

[0067] Step S3: Select the appropriate oblique angle and corresponding satellite position and velocity based on the pulse repetition frequency (PRF) range achievable by the radar receiver, the azimuth ambiguity of the SAR image, and the actual application requirements.

[0068] Step S4: Construct the beamline vector α in the Earth-fixed coordinate system ECEF The transformation matrix from the Earth-fixed coordinate system to the orbital coordinate system will transform the beamline vector α. ECEF Transform the orbital coordinate system α o

[0069] Step S5: The satellite attitude control subsystem employs a pitch-yaw-roll sequence to achieve the large oblique angle required for imaging. Based on this sequence, according to the beamline vector α in the orbital coordinate system... o Calculate the ground oblique angle And the downward viewing angle γ; then, the satellite yaw angle ε is calculated based on the star-ground geometry of large squint imaging. yaw and the SAR antenna electrical scanning angle θ;

[0070] Step S6: Based on the oblique angle θ selected in Step 4 sq Based on the SAR antenna electronic scanning angle θ calculated in step 5, parameters such as transmit bandwidth, sampling frequency, pulse width, start sampling time, number of sampling points, and duty cycle are designed to generate a SAR working parameter package; a satellite attitude maneuver parameter package is generated based on the satellite attitude rotation matrix δ obtained in step 5; the timing sequence of a series of satellite actions such as satellite attitude maneuvering, data recording and playback, radar echo transmission and reception is determined during the imaging mission, and an imaging mission command sequence is generated; the instruction is packaged according to the satellite remote control frame format and uploaded to the satellite telemetry and control system before the imaging mission.

[0071] Step S7: At the time of overhead pass, the satellite performs large oblique-view imaging of the ground target according to the pre-designed attitude and radar operating parameters, and transmits the radar echo data, navigation data and ephemeris data to the ground data transmission station.

[0072] Under the premise that the satellite weight and size remain unchanged, the specific process and parameter description for effectively carrying out large-slant-angle on-orbit imaging of a micro SAR satellite are as follows:

[0073] I. The calculation method for large oblique angles includes the following processing steps:

[0074] Step S2.1: Convert the six satellite orbital roots Orbit = [a; e; i; Ω; ω; u] within the range [-T0, T0] into the satellite position P in the inertial coordinate system. sECI and speed V sECI :

[0075]

[0076]

[0077] Where a is the semi-major axis of the orbit, e is the eccentricity, i is the orbital inclination, Ω is the right ascension of the ascending node, ω is the argument of perigee, and u is the argument of latitude. s Let ω be the satellite's angular velocity. e This is the Earth's rotational angular velocity.

[0078] R s Distance of the satellite from the Earth's center:

[0079]

[0080] The rate of change of the satellite's distance from Earth:

[0081]

[0082] Step S2.2: Construct the transformation matrix from the inertial coordinate system to the Earth-fixed coordinate system, and change the satellite position P in the inertial coordinate system. sECI and speed V sECI Transform to satellite position P in Earth-fixed coordinate system sECEF and speed V sECEF :

[0083]

[0084]

[0085] Where ε GST For Greenwich Mean Time, η is the precession, nutation, and polar motion correction matrix.

[0086] Step S2.3: Calculate the target slope distance R = |P tECEF -P sECEF | and the Doppler center frequency f DC :

[0087] f DC =2 / (λR)×dot(V) sECEF P sECEF -P tECEF )

[0088] Where λ is the radar wavelength, and dot represents the vector dot product.

[0089] Step S2.4: Based on the Doppler center frequency f DC and satellite velocity V sECEF Calculate the oblique angle θ sq :

[0090]

[0091] II. Calculation method of beamline vector in orbital coordinate system, such as Figure 2 As shown, the processing steps include the following:

[0092] Step S4.1: Construct the beamline vector (α) in the Earth-fixed coordinate system ECEF =P sECEF -Pt ECEF ;

[0093] Step S4.2: Construct the transformation matrix from the Earth-fixed coordinate system to the orbital coordinate system, and transform the beamline vector into the orbital coordinate system α. o :

[0094]

[0095] Wherein, γ1, γ2, and γ3 are the three-axis projections of the beamline vector in the orbital coordinate system.

[0096] III. Calculation method of SAR antenna electronic scanning angle and satellite attitude angle, including the following processing steps:

[0097] Step S5.1: According to the appendix Figure 2 Geometric relationships, calculating ground oblique angle The downward angle γ is:

[0098]

[0099]

[0100] Step S5.2: Based on the satellite's flight direction and the installation method of the SAR antenna, determine the satellite's initial yaw angle.

[0101] Step S5.3: According to the appendix Figure 2 From the geometric relationship, we can derive cos(γ)=cos(θ) sq )cos(γ0), and thus obtain the angle γ0 under the frontal side view γ0=acos(cos(γ) / cos(θ) sq Since the viewing angle under a frontal side view is composed of both satellite roll and SAR antenna electronic scanning, the SAR antenna electronic scanning angle θ = acos(γ) / cos(θ) is obtained.sq ))-ε roll ;

[0102] Step S5.4: If the satellite uses two-dimensional yaw guidance by default, the satellite attitude at the imaging time needs to be corrected to obtain the corrected yaw angle and pitch angle:

[0103]

[0104]

[0105] Step S5.5: The satellite attitude control subsystem adopts a pitch-yaw-roll transformation sequence. The transformation matrix from its orbital coordinate system to the satellite body coordinate system is as follows:

[0106]

[0107] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

[0108] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. An on-orbit control method for large-slant-view imaging of a micro SAR satellite, characterized in that... include: The orbital number of satellites within a preset time range is determined by orbital prediction, and the target to be observed is selected based on the satellite coverage area; Calculate the satellite position and velocity parameters in the inertial coordinate system within a preset time range, and calculate the oblique angle required for satellite observation of the target within the current time period based on the target position of the target to be observed; Based on the pulse repetition frequency range of the radar receiver, the azimuth ambiguity of the SAR image, and the requirements of the satellite imaging mission, the required satellite position and velocity parameters are selected, and the corresponding oblique angle is determined. Construct the beamline vector of the target to be observed in the Earth-fixed coordinate system and transform it to the beamline vector in the orbital coordinate system; Determine the satellite attitude sequence, calculate the ground oblique angle and downward angle based on the beamline vector in the orbital coordinate system, and calculate the satellite yaw angle and SAR antenna electronic scanning angle based on the satellite-ground geometry. Based on the oblique angle and the SAR antenna electronic scanning angle, SAR working parameters are designed and SAR working parameter packages are generated; at the same time, satellite attitude maneuver parameter packages are generated and uploaded to the satellite together with the SAR working parameters. According to the preset satellite attitude and radar operating parameters, the target to be observed is subjected to large oblique-view imaging, and the radar echo data, navigation data and ephemeris data are transmitted down to the ground data transmission station.

2. The on-orbit control method for large-slant-view imaging of a micro SAR satellite according to claim 1, characterized in that: The target to be observed is selected from a known ground target database. After selecting the target, the target position P of the target to be observed is determined in the Earth-fixed coordinate system. tECEF The preset time range is within the period [-T0, T0].

3. The on-orbit control method for large-slant-view imaging of a micro SAR satellite according to claim 2, characterized in that: Calculate the oblique angle θ required for satellite observation of the target during the current time period. sq The steps are as follows: The position parameters of the satellite in the inertial coordinate system are calculated based on the six orbital roots as P. sECI The speed parameter is V sECI ; Based on the satellite's position parameter P sECEF The speed parameter is V sECEF Construct the transformation matrix from the inertial coordinate system to the Earth-fixed coordinate system, and change the satellite position P in the inertial coordinate system. sECI and speed V sECI Transformation to Earth-Fixed Coordinate System for Satellite Position Parameter P sECEF and velocity parameter V sECEF ; Calculate the target slant range R and Doppler center frequency f. DC The oblique angle required for satellite observation of the target within the current time period is calculated based on the obtained data.

4. The on-orbit control method for large-slant-view imaging of a micro SAR satellite according to claim 3, characterized in that: The position parameter of the satellite in the inertial coordinate system is P. sECI The speed parameter is V sECI The calculation method is as follows: In the formula, a is the semi-major axis of the orbit, e is the eccentricity, i is the orbital inclination, Ω is the right ascension of the ascending node, ω is the argument of perigee, u is the argument of latitude, and ω s Let ω be the satellite's angular velocity. e This is the Earth's rotational angular velocity; R s Distance of the satellite from the Earth's center: The rate of change of the satellite's distance from Earth:

5. The on-orbit control method for large-slant-view imaging of a micro SAR satellite according to claim 4, characterized in that: The satellite position parameter P sECEF and velocity parameter V sECEF The calculation method is as follows: In the formula, ε GST For Greenwich Mean Time, η is the precession, nutation, and polar motion correction matrix.

6. The on-orbit control method for large-slant-view imaging of a micro SAR satellite according to claim 5, characterized in that: The method for calculating the target slant distance is as follows: R=|P tECEF -P sECEF | The Doppler center frequency f DC The calculation method is as follows: f DC =2 / (λR)×dot(V) sECEF ,P sECEF -P tECEF In the formula, λ is the radar wavelength, and dot represents the vector dot product; The oblique angle θ required for satellite observation of the target during the current time period sq The calculation method is as follows:

7. The on-orbit control method for large-slant-view imaging of a micro SAR satellite according to claim 6, characterized in that: The method for constructing the beamline vector in the orbital coordinate system is as follows: Construct the beamline vector α in the Earth-fixed coordinate system ECEF =P sECEF -P tECEF ; Construct the transformation matrix from the Earth-fixed coordinate system to the orbital coordinate system; Perform beamline vector transformation in orbital coordinate system: In the formula, α o This is the beamline vector in the orbital coordinate system.

8. The on-orbit control method for large-slant-view imaging of a micro SAR satellite according to claim 7, characterized in that: The calculation methods for the ground oblique angle and downward angle are as follows: In the formula, γ1, γ2, and γ3 are the three-axis projections of the beamline vector in the orbital coordinate system.

9. The on-orbit control method for large-slant-view imaging of a micro SAR satellite according to claim 8, characterized in that: The satellite-to-ground geometry is determined based on the satellite's flight direction and the SAR antenna's installation method. After determining the satellite-to-ground geometry, the initial satellite yaw angle is determined as follows: The method for determining the electrical scanning angle of a SAR antenna is as follows: cos(γ)=cos(θ sq )cos(γ0) γ0=acos(cos(γ) / cos(θ) sq )) θ=acos(cos(γ) / cos(θ) sq ))-e roll In the formula, ε roll It is the angle at which the satellite rotates around its roll axis when observing the target.

10. The on-orbit control method for large-slant-view imaging of a micro SAR satellite according to claim 9, characterized in that: During large squint imaging, if the satellite adopts a two-dimensional yaw guidance mode, the preset satellite attitude is corrected, and the corrected yaw angle ε is determined. yaw and pitch angle ε pitch :

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