Laser ranging test window selection method and system for lunar satellite

Abstract

The present invention provides a method and system for selecting a laser ranging test window for a lunar satellite, and relates to the technical field of laser ranging for lunar satellites, including: step S1: establishing a high-precision lunar satellite dynamics model; step S2: establishing a laser ranging test constraint model; step S3: calculating the laser ranging test observation window according to the high-precision lunar satellite dynamics model and the laser ranging test constraint model; step S4: calculating the laser echo rate according to the ranging system, satellite and environmental parameters; step S5: selecting a ground station with reference to the weather forecast value; step S6: selecting the final observation window according to the laser echo rate and the ground station. The present invention can improve the success rate of the lunar satellite laser ranging test.

Description

Technical Field

[0001] The present invention relates to the technical field of laser ranging of a lunar satellite, and in particular to a method and system for selecting a laser ranging test window of a lunar satellite. Background Art

[0002] Lunar laser ranging can achieve centimeter-level accuracy and is currently the most accurate means of measuring the distance between the Earth and the Moon. It is widely used to study lunar orbits, geophysics, verify general relativity, monitor the dynamics of the Earth-Moon system, and support deep space exploration and space navigation. Applying satellite laser ranging technology to lunar satellite orbit determination can improve the current hundred-meter-level orbit determination accuracy to the meter level. In laser ranging, the number of echo photons is inversely proportional to the fourth power of the distance; under the same conditions, the number of echo photons obtained when performing laser ranging on a lunar satellite is about 1 / 10000 of that of a geosynchronous orbit satellite, so laser ranging on a lunar satellite is much more difficult than conventional SLR. Therefore, the success rate of lunar satellite laser ranging experiments is extremely low.

[0003] The invention patent with publication number CN102313533A discloses a method for error analysis of on-orbit detection data of a lunar laser altimeter, including: dividing the massive lunar elevation data measured by the laser altimeter into regions according to latitude; searching for repeated elevation measurement point sets in each divided region; eliminating gross errors, calculating residuals and standard deviations for the searched repeated measurement point sets; comparing the elevation data processing results of the same latitude zones in the north and south latitudes of the moon, and analyzing the error distribution characteristics. Summary of the invention

[0004] In view of the defects in the prior art, the present invention provides a method and system for selecting a laser ranging test window for a lunar satellite.

[0005] According to a method and system for selecting a laser ranging test window for a lunar satellite provided by the present invention, the scheme is as follows: In a first aspect, a method for selecting a laser ranging test window for a lunar satellite is provided, the method comprising: Step S1: Establish a high-precision lunar satellite dynamics model; Step S2: Establishing a laser ranging test constraint model; Step S3: calculating the laser ranging test observation window according to the high-precision lunar satellite dynamics model and the laser ranging test constraint model; Step S4: Calculate the laser echo rate according to the ranging system, satellite and environmental parameters; Step S5: Using the weather forecast value as a reference, select a ground station; Step S6: Select the final observation window according to the laser echo rate and the ground station.

[0006] Preferably, step S1 comprises: for a lunar satellite, the coordinate system selects the epoch moon-centered inertial coordinate system, and the gravitational forces of the sun, the moon, the earth and other celestial bodies on the lunar satellite, the lunar solid tidal perturbation, the lunar physical libration, the solar radiation pressure, the jet unloading and the high-precision ephemeris factors are considered, and the dynamic model of the lunar satellite is as follows:

[0007] The above formula can be abbreviated as:

[0008] in, for The differential of is the state vector of the state model; They are the position and velocity of the lunar satellite in the X, Y, and Z directions respectively; is the system nonlinear continuous state transfer function of the state model; represents the system noise; represents the vector from the center of the moon to the satellite; Represents the vector from the center of the Earth to the satellite; heliocentric-to-satellite vector; are the gravitational constants of the Sun, Moon, and Earth respectively; is the vector from the heliocenter to the satellite; is the vector from the center of the moon to the center of the earth in the geocentric coordinate system; is the vector from the center of the moon to the center of the sun; is the coordinate of the moon's position in the solar mass center coordinate system; is the coordinate of the earth's position in the geocentric coordinate system; is the coordinate of the sun's position in the sun's mass center coordinate system; are the system noise respectively.

[0009] Preferably, the step S2 includes: setting laser ranging test constraint conditions, wherein the constraint conditions specifically include: Set the thresholds for the angle between the sun and the corner reflector axis, the sun altitude angle, the satellite altitude angle, and the earth-moon-sun angle; The satellite in the large elliptical frozen orbit around the moon remains unchanged in the inertial system. When the satellite and the earth are on opposite sides of the moon, the moon's occlusion must be considered. The observation time every night must be more than one hour, and the observation time should be avoided during the rainy season.

[0010] Preferably, step S4 comprises: Step S4.1: Obtaining parameters of the ranging system and the corner reflector; Step S4.2: Calculate the relative positions of the satellite and the laser station; Step S4.3: Calculate the equivalent divergence angle of laser reflection; Step S4.4: Calculate the two-way atmospheric transmittance according to the satellite altitude angle; Step S4.5: Calculate the attenuation factors related to cirrus clouds, atmospheric jitter, turbulence, telescope tracking accuracy, and telescope pointing accuracy; Step S4.6: After obtaining all the above parameter values, the ranging echo rate is calculated according to the laser echo rate formula.

[0011] Preferably, the step S4.3 comprises: calculating the satellite aberration according to the relative speed between the satellite and the laser station, and the aberration calculation formula is as follows:

[0012] in, is the satellite's aberration angle, is the speed of the satellite relative to the station, is the speed of light, is the velocity direction of the station The angle between the satellite and the direction of sight; The angular distribution and energy density of the far field of the corner reflector are measured by diffraction test, and then the optical scattering cross section (OCS) value of the reflector to be tested is quantitatively measured by comparison with the standard part. The equivalent divergence angle of laser reflection is calculated based on the aberration and optical scattering cross section OCS value. The expression is as follows:

[0013] in, is the optical scattering cross section (OCS) value of the target; is the optical reflectivity of the laser reflector, which indicates the proportion of energy radiated out after the target intercepts the laser; is the effective reflection area of ​​the laser reflector; is the target gain coefficient, is the target backscatter solid angle; is the equivalent divergence angle of laser reflection.

[0014] Preferably, the step S4.6 comprises: The formulas for laser echo photon number and echo rate are as follows:

[0015] The formula for the probability of receiving k echo photons by a single pulse laser is as follows:

[0016] The echo rate calculates the probability of a single pulse laser obtaining one or more photons. The echo rate is expressed by the following formula:

[0017] in, is the theoretical echo photon number of a single pulse; is the laser single pulse energy; is Planck's constant; is the speed of light; is the laser wavelength; and are the transmitting optical system efficiency and the receiving optical system efficiency respectively; is the two-way atmospheric transmittance; and are the effective reflection cross-sectional area of ​​the reflector and the effective receiving area of ​​the telescope respectively; is the ranging distance; and are the emission divergence angle and the reflection divergence angle respectively; is the reflectivity of the reflector; is the receiving detector efficiency; is the attenuation factor; is the echo rate; is the number of echo photons (k=1, 2, 3, ...); is the factorial of k; is the base of natural logarithms.

[0018] In a second aspect, a laser ranging test window selection system for a lunar satellite is provided, the system comprising: Model M1: Establish a high-precision lunar satellite dynamics model; Model M2: Establishing the laser ranging test constraint model; Model M3: Calculate the laser ranging test observation window based on the high-precision lunar satellite dynamics model and the laser ranging test constraint model; Model M4: Calculate the laser echo rate based on the ranging system, satellite and environmental parameters; Model M5: Ground station selection based on weather forecast values; Model M6: Select the final observation window based on the laser echo rate and ground station.

[0019] Preferably, the module M1 includes: for a lunar satellite, the coordinate system selects the epoch moon-centered inertial coordinate system, and considers the gravitational forces of the sun, moon, earth and other celestial bodies on the lunar satellite, the lunar solid tidal perturbation, the lunar physical libration, solar light pressure, jet unloading and high-precision ephemeris factors. The dynamic model of the lunar satellite is as follows:

[0020] The above formula can be abbreviated as:

[0021] in, for The differential of is the state vector of the state model; They are the position and velocity of the lunar satellite in the X, Y, and Z directions respectively; is the system nonlinear continuous state transfer function of the state model; represents the system noise; represents the vector from the center of the moon to the satellite; Represents the vector from the center of the Earth to the satellite; heliocentric-to-satellite vector; are the gravitational constants of the Sun, Moon, and Earth respectively; is the vector from the heliocenter to the satellite; is the vector from the center of the moon to the center of the earth in the geocentric coordinate system; is the vector from the center of the moon to the center of the sun; is the coordinate of the moon's position in the solar mass center coordinate system; is the coordinate of the earth's position in the geocentric coordinate system; is the coordinate of the sun's position in the sun's mass center coordinate system; are the system noise respectively.

[0022] Preferably, the module M2 includes: setting laser ranging test constraint conditions, wherein the constraint conditions specifically include: Set the thresholds for the angle between the sun and the corner reflector axis, the sun altitude angle, the satellite altitude angle, and the earth-moon-sun angle; The satellite in the large elliptical frozen orbit around the moon remains unchanged in the inertial system. When the satellite and the earth are on opposite sides of the moon, the moon's occlusion must be considered. The observation time every night must be more than one hour, and the observation time should be avoided during the rainy season.

[0023] Preferably, the module M4 comprises: Module M4.1: Obtaining the parameters of the ranging system and corner reflector; Module M4.2: Calculate the relative positions of satellites and laser stations; Module M4.3: Calculate the equivalent divergence angle of laser reflection; Module M4.4: Calculate two-way atmospheric transmittance based on satellite altitude angle; Module M4.5: Calculation of attenuation factors related to cirrus clouds, atmospheric jitter, turbulence, telescope tracking accuracy, and telescope pointing accuracy; Module M4.6: After obtaining all the above parameter values, the ranging echo rate is calculated according to the laser echo rate formula; The module M4.3 includes: calculating the satellite aberration according to the relative speed between the satellite and the laser station, and the aberration calculation formula is as follows:

[0024] in, is the satellite's aberration angle, is the speed of the satellite relative to the station, is the speed of light, is the velocity direction of the station The angle between the satellite and the direction of sight; The angular distribution and energy density of the far field of the corner reflector are measured by diffraction test, and then the optical scattering cross section (OCS) value of the reflector to be tested is quantitatively measured by comparison with the standard part. The equivalent divergence angle of laser reflection is calculated based on the aberration and optical scattering cross section OCS value. The expression is as follows:

[0025] in, is the optical scattering cross section (OCS) value of the target; is the optical reflectivity of the laser reflector, which indicates the proportion of energy radiated out after the target intercepts the laser; is the effective reflection area of ​​the laser reflector; is the target gain coefficient, is the target backscatter solid angle; is the equivalent divergence angle of laser reflection; The module M4.6 includes: The formulas for laser echo photon number and echo rate are as follows:

[0026] The formula for the probability of receiving k echo photons by a single pulse laser is as follows:

[0027] The echo rate calculates the probability of a single pulse laser obtaining one or more photons. The echo rate is expressed by the following formula:

[0028] in, is the number of single pulse echo photons; is the laser single pulse energy; is Planck's constant; is the speed of light; is the laser wavelength; and are the transmitting optical system efficiency and the receiving optical system efficiency respectively; is the two-way atmospheric transmittance; and are the effective reflection cross-sectional area of ​​the reflector and the effective receiving area of ​​the telescope respectively; is the ranging distance; and are the emission divergence angle and the reflection divergence angle respectively; is the reflectivity of the reflector; is the receiving detector efficiency; is the attenuation factor; is the echo rate; is the number of echo photons (k=1, 2, 3, ...); is the factorial of k; is the base of natural logarithms.

[0029] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a reference for the appropriate time to carry out laser ranging tests by jointly calculating the satellite laser test observation window and the laser echo rate, thereby effectively improving the success rate of the lunar satellite laser ranging test.

[0030] Other beneficial effects of the present invention will be explained in the specific implementation manner through the introduction of specific technical features and technical solutions. Through the introduction of these technical features and technical solutions, those skilled in the art should be able to understand the beneficial technical effects brought about by the technical features and technical solutions. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings: Figure 1 It is the overall flow chart of the present invention; Figure 2 This is a flow chart of the laser ranging echo rate calculation process of the present invention. DETAILED DESCRIPTION

[0032] The present invention is 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 are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0033] The embodiment of the present invention provides a method for selecting a laser ranging test window for a lunar satellite. Based on satellite orbit parameters, laser station ranging system conditions, environmental parameters, etc., the observation time window and the echo rate of the ranging test are calculated to select a suitable observation time, thereby improving the success rate of the lunar satellite laser ranging test. Figure 1 As shown, the method includes: Step S1: Establish a high-precision lunar satellite dynamics model.

[0034] For lunar satellites, the coordinate system is the lunar-centered inertial coordinate system of the epoch (J2000.0), and the gravitational forces of the sun, moon, earth and other celestial bodies on the lunar satellite, the lunar solid tidal perturbation, the lunar physical libration, solar radiation pressure, jet unloading and high-precision ephemeris are considered. The dynamic model of the lunar satellite is as follows:

[0035] The above formula can be abbreviated as:

[0036] in, for The differential of is the state vector of the state model; They are the position and velocity of the lunar satellite in the X, Y, and Z directions respectively; is the system nonlinear continuous state transfer function of the state model; represents the system noise; represents the vector from the center of the moon to the satellite; Represents the vector from the center of the Earth to the satellite; heliocentric-to-satellite vector; are the gravitational constants of the Sun, Moon, and Earth respectively; is the vector from the heliocenter to the satellite; is the vector from the center of the moon to the center of the earth in the geocentric coordinate system; is the vector from the center of the moon to the center of the sun; is the coordinate of the moon's position in the solar mass center coordinate system; is the coordinate of the earth's position in the geocentric coordinate system; is the coordinate of the sun's position in the sun's mass center coordinate system; are the system noise respectively.

[0037] Step S2: Establishing a laser ranging test constraint model.

[0038] This step sets the laser ranging test constraint conditions, and the typical values ​​of the constraint conditions specifically include: 1) When the corner reflector is working, it should be protected from direct sunlight. Considering the existence of the sunshade, the angle between the sunlight and the axial direction of the corner reflector should be set to be greater than 36°.

[0039] 2) The laser station should carry out observations on a clear, cloudless night, and take into account the influence of factors such as atmospheric refraction, and set the solar altitude angle to less than -5°.

[0040] 3) In order to reduce the propagation length of the laser in the atmosphere, the satellite altitude angle is set to be greater than 30°.

[0041] 4) In order to reduce the impact of lunar background noise on laser ranging, the Earth-Moon-Sun angle is set to be greater than 40°.

[0042] 5) The satellite in a large elliptical frozen orbit around the moon remains unchanged in the inertial system. When the satellite and the earth are on opposite sides of the moon, the moon's obstruction must be considered.

[0043] 6) The observation time every night must be greater than one hour to allow for the accumulation of laser ranging echo signals.

[0044] 7) Observation time should avoid the rainy season.

[0045] Step S3: According to the constraints of step S2, the laser test observation window is calculated by combining the satellite orbit information and the laser station position information.

[0046] According to the above position information, the parameters in step S2 are calculated, and arc segments where the angle between the sun and the corner reflector axis is less than 36°, the sun altitude angle is greater than -5°, the satellite altitude angle is less than 30°, the earth-moon-sun angle is less than 40°, and the duration is less than 1 hour are eliminated, and the remaining arc segments are the observation windows; Step S4: Calculate the laser echo rate according to the ranging system, satellite and environmental parameters.

[0047] The formulas for laser echo photon number and echo rate are as follows:

[0048] The formula for the probability of receiving k echo photons by a single pulse laser is as follows:

[0049] The echo rate calculates the probability of a single pulse laser obtaining one or more photons. The echo rate is expressed by the following formula:

[0050] in, is the number of single pulse echo photons; is the laser single pulse energy; is Planck's constant; is the speed of light; is the laser wavelength; and are the transmitting optical system efficiency and the receiving optical system efficiency respectively; is the two-way atmospheric transmittance; and are the effective reflection cross-sectional area of ​​the reflector and the effective receiving area of ​​the telescope respectively; is the ranging distance; and are the emission divergence angle and the reflection divergence angle respectively; is the reflectivity of the reflector; is the receiving detector efficiency; is the attenuation factor; is the echo rate; is the number of echo photons (k=1, 2, 3, ...); is the factorial of k; is the base of natural logarithms.

[0051] Reference Figure 2 As shown, calculating the lunar satellite laser ranging echo rate includes the following steps: Step S4.1: Obtaining parameters of the ranging system and the corner reflector; Including the echo rate formula , , , , , , , , parameter; Step S4.2: Calculate the state vector of the satellite at any time t according to the satellite dynamics equation in step S1 , the position of the laser station at any time t can be read from the ITRF framework file , the relative position speed of the satellite and the laser station is .

[0052] Step S4.3: Calculate the equivalent divergence angle of laser reflection; calculate the satellite aberration according to the relative speed between the satellite and the laser station. The aberration calculation formula is as follows:

[0053] in, is the satellite's aberration angle, is the speed of the satellite relative to the station, is the speed of light, is the velocity direction of the station The angle between the satellite and the direction of sight; The angular distribution and energy density of the far field of the corner reflector are measured by diffraction test, and the optical cross section (OCS) value of the reflector to be tested is quantitatively measured by comparison with the standard part. The equivalent divergence angle of laser reflection is calculated based on the aberration and optical scattering cross section OCS value. The expression is as follows:

[0054] in, is the optical scattering cross section (OCS) value of the target; is the optical reflectivity of the laser reflector, which indicates the proportion of energy radiated out after the target intercepts the laser; is the effective reflection area of ​​the laser reflector; is the target gain coefficient, is the target backscatter solid angle; is the equivalent divergence angle (full angle) of laser reflection.

[0055] Step S4.4: Calculate the two-way atmospheric transmittance based on the satellite altitude angle. When observing on a clear and cloudless night, the two-way atmospheric transmittance is generally between 0.81 and 0.9.

[0056] Step S4.5: Calculate the attenuation factor related to cirrus, atmospheric jitter, turbulence, telescope tracking accuracy, and telescope pointing accuracy. In this embodiment, the attenuation factor related to cirrus, atmospheric jitter, turbulence, telescope tracking accuracy, and telescope pointing accuracy is 0.05 to 0.5.

[0057] Step S4.6: After obtaining all the above parameter values, the ranging echo rate is calculated according to the laser echo rate formula.

[0058] Step S5: Select ground stations with reference to weather forecast values. That is, select ground stations for the test with reference to weather forecast values ​​of the test stations 1 to 2 days before the test.

[0059] Step S6: According to the laser echo rate calculated above, an observation window with a higher success rate is selected from the observation windows that meet the constraint conditions, and the typical echo rate threshold can be set to 1%.

[0060] The present invention also provides a laser ranging test window selection system for a lunar satellite, which can be implemented by executing the process steps of the laser ranging test window selection method for a lunar satellite, that is, those skilled in the art can understand the laser ranging test window selection method for a lunar satellite as a preferred implementation of the laser ranging test window selection system for a lunar satellite. The system specifically includes the following contents: Module M1: Establish a high-precision lunar satellite dynamics model.

[0061] For lunar satellites, the coordinate system is the lunar-centered inertial coordinate system of the epoch (J2000.0), and the gravitational forces of the sun, moon, earth and other celestial bodies on the lunar satellite, the lunar solid tidal perturbation, the lunar physical libration, solar radiation pressure, jet unloading and high-precision ephemeris are considered. The dynamic model of the lunar satellite is as follows:

[0062] The above formula can be abbreviated as:

[0063] in, for The differential of is the state vector of the state model; They are the position and velocity of the lunar satellite in the X, Y, and Z directions respectively; is the system nonlinear continuous state transfer function of the state model; represents the system noise; represents the vector from the center of the moon to the satellite; Represents the vector from the center of the Earth to the satellite; heliocentric-to-satellite vector; are the gravitational constants of the Sun, Moon, and Earth respectively; is the vector from the heliocenter to the satellite; is the vector from the center of the moon to the center of the earth in the geocentric coordinate system; is the vector from the center of the moon to the center of the sun; is the coordinate of the moon's position in the solar mass center coordinate system; is the coordinate of the earth's position in the geocentric coordinate system; is the coordinate of the sun's position in the sun's mass center coordinate system; are the system noise respectively.

[0064] Module M2: Establish a laser ranging test constraint model.

[0065] This module sets the laser ranging test constraints, which specifically include: 1) When the corner reflector is working, it should be protected from direct sunlight. Considering the existence of the sunshade, the angle between the sunlight and the axial direction of the corner reflector should be set to be greater than 36°.

[0066] 2) The laser station should carry out observations on a clear, cloudless night, and take into account the influence of factors such as atmospheric refraction, and set the solar altitude angle to less than -5°.

[0067] 3) In order to reduce the propagation length of the laser in the atmosphere, the satellite altitude angle is set to less than 30°.

[0068] 4) In order to reduce the impact of lunar background noise on laser ranging, the Earth-Moon-Sun angle is set to be greater than 40°.

[0069] 5) The satellite in a large elliptical frozen orbit around the moon remains unchanged in the inertial system. When the satellite and the earth are on opposite sides of the moon, the moon's obstruction must be considered.

[0070] 6) The observation time every night must be greater than one hour to allow for the accumulation of laser ranging echo signals.

[0071] 7) Observation time should avoid the rainy season.

[0072] Module M3: According to the constraints of module M2, the laser test observation window is calculated by combining the satellite orbit information and the laser station position information.

[0073] Module M4: Calculates the laser echo rate based on the ranging system, satellite and environmental parameters.

[0074] The formulas for laser echo photon number and echo rate are as follows:

[0075] The formula for the probability of receiving k echo photons by a single pulse laser is as follows:

[0076] The echo rate calculates the probability of a single pulse laser obtaining one or more photons. The echo rate is expressed by the following formula:

[0077] in, is the number of single pulse echo photons; is the laser single pulse energy; is Planck's constant; is the speed of light; is the laser wavelength; and are the transmitting optical system efficiency and the receiving optical system efficiency respectively; is the two-way atmospheric transmittance; and are the effective reflection cross-sectional area of ​​the reflector and the effective receiving area of ​​the telescope respectively; is the ranging distance; and are the emission divergence angle and the reflection divergence angle respectively; is the reflectivity of the reflector; is the receiving detector efficiency; is the attenuation factor; is the echo rate; is the number of echo photons (k=1, 2, 3, ...); is the factorial of k; is the base of natural logarithms.

[0078] Reference Figure 2 As shown, the calculation of the lunar satellite laser ranging echo rate includes: Module M4.1: Obtaining the parameters of the ranging system and corner reflector; Module M4.2: Calculate the relative positions of the satellite and the laser station based on the ephemeris and the satellite kinematic equations.

[0079] Module M4.3: Calculate the equivalent divergence angle of laser reflection; calculate the satellite aberration according to the relative speed between the satellite and the laser station. The aberration calculation formula is as follows:

[0080] in, is the satellite's aberration angle, is the speed of the satellite relative to the station, is the speed of light, is the velocity direction of the station The angle between the satellite and the direction of sight; The angular distribution and energy density of the far field of the corner reflector are measured by diffraction test, and the optical cross section (OCS) value of the reflector to be tested is quantitatively measured by comparison with the standard part. The equivalent divergence angle of laser reflection is calculated based on the aberration and optical scattering cross section OCS value. The expression is as follows:

[0081] in, is the optical scattering cross section (OCS) value of the target; is the optical reflectivity of the laser reflector, which indicates the proportion of energy radiated out after the target intercepts the laser; is the effective reflection area of ​​the laser reflector; is the target gain coefficient, is the target backscatter solid angle; is the equivalent divergence angle (full angle) of laser reflection.

[0082] Module M4.4: Calculate the two-way atmospheric transmittance based on the satellite altitude angle. When observing on a clear and cloudless night, the two-way atmospheric transmittance is generally between 0.81 and 0.9.

[0083] Module M4.5: Calculate the attenuation factors related to cirrus, atmospheric jitter, turbulence, telescope tracking accuracy, and telescope pointing accuracy. In this embodiment, the attenuation factors related to cirrus, atmospheric jitter, turbulence, telescope tracking accuracy, and telescope pointing accuracy are 0.05 to 0.5.

[0084] Module M4.6: After obtaining all the above parameter values, the ranging echo rate is calculated according to the laser echo rate formula.

[0085] Module M5: Select ground stations based on weather forecast values. That is, select ground stations for the test based on weather forecast values ​​1 to 2 days before the test.

[0086] Module M6: According to the laser echo rate calculated above, an observation window with a higher success rate is selected from the observation windows that meet the constraint conditions.

[0087] The embodiment of the present invention provides a method and system for selecting a laser ranging test window for a lunar satellite, which improves the success rate of the laser ranging test for the lunar satellite by calculating and analyzing the laser ranging echo window and echo rate of the lunar satellite.

[0088] Those skilled in the art know that, in addition to realizing the system and its various devices, modules, and units provided by the present invention in a purely computer-readable program code, it is entirely possible to realize the same functions 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 as a hardware component, and the devices, modules, and units included therein for realizing various functions can also be regarded as structures within the hardware component; the devices, modules, and units for realizing various functions can also be regarded as both software modules for realizing the method and structures within the hardware component.

[0089] The above describes the specific embodiments of the present invention. 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. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A method for selecting a laser ranging test window for a lunar satellite, characterized in that: include: Step S1: Establish a high-precision lunar satellite dynamics model; Step S2: Establishing a laser ranging test constraint model; Step S3: calculating the laser ranging test observation window according to the high-precision lunar satellite dynamics model and the laser ranging test constraint model; Step S4: Calculate the laser echo rate according to the ranging system, satellite and environmental parameters; Step S5: Using the weather forecast value as a reference, select a ground station; Step S6: Select the final observation window according to the laser echo rate and the ground station.

2. The method for selecting a laser ranging test window for a lunar satellite according to claim 1, characterized in that: The step S1 includes: for a lunar satellite, the coordinate system selects the epoch moon-centered inertial coordinate system, and considers the gravitational forces of the sun, the moon, the earth and other celestial bodies on the lunar satellite, the lunar solid tidal perturbation, the lunar physical libration, the solar radiation pressure, the jet unloading and the high-precision ephemeris factors. The dynamic model of the lunar satellite is as follows: The above formula can be abbreviated as: in, for The differential of is the state vector of the state model; They are the position and velocity of the lunar satellite in the X, Y, and Z directions respectively; is the system nonlinear continuous state transfer function of the state model; represents the system noise; represents the vector from the center of the moon to the satellite; Represents the vector from the center of the Earth to the satellite; heliocentric-to-satellite vector; are the gravitational constants of the Sun, Moon, and Earth respectively; is the vector from the heliocenter to the satellite; is the vector from the center of the moon to the center of the earth in the geocentric coordinate system; is the vector from the center of the moon to the center of the sun; is the coordinate of the moon's position in the solar mass center coordinate system; is the coordinate of the earth's position in the geocentric coordinate system; is the coordinate of the sun's position in the sun's mass center coordinate system; are the system noise respectively.

3. The method for selecting a laser ranging test window for a lunar satellite according to claim 1, characterized in that: The step S2 includes: setting laser ranging test constraint conditions, wherein the constraint conditions specifically include: Set the thresholds for the angle between the sun and the corner reflector axis, the sun altitude angle, the satellite altitude angle, and the earth-moon-sun angle; The satellite in the large elliptical frozen orbit around the moon remains unchanged in the inertial system. When the satellite and the earth are on opposite sides of the moon, the moon's occlusion must be considered. The observation time every night must be more than one hour, and the observation time should be avoided during the rainy season.

4. The method for selecting a laser ranging test window for a lunar satellite according to claim 1, characterized in that: The step S4 comprises: Step S4.1: Obtaining parameters of the ranging system and the corner reflector; Step S4.2: Calculate the relative positions of the satellite and the laser station; Step S4.3: Calculate the equivalent divergence angle of laser reflection; Step S4.4: Calculate the two-way atmospheric transmittance according to the satellite altitude angle; Step S4.5: Calculate the attenuation factors related to cirrus clouds, atmospheric jitter, turbulence, telescope tracking accuracy, and telescope pointing accuracy; Step S4.6: After obtaining all the above parameter values, the ranging echo rate is calculated according to the laser echo rate formula.

5. The method for selecting a laser ranging test window for a lunar satellite according to claim 4, characterized in that: The step S4.3 comprises: calculating the satellite aberration according to the relative speed between the satellite and the laser station, and the aberration calculation formula is as follows: in, is the satellite's aberration angle, is the speed of the satellite relative to the station, is the speed of light, is the velocity direction of the station The angle between the satellite and the direction of sight; The angular distribution and energy density of the far field of the corner reflector are measured by diffraction test, and then the optical scattering cross section (OCS) value of the reflector to be tested is quantitatively measured by comparison with the standard part. The equivalent divergence angle of laser reflection is calculated based on the aberration and optical scattering cross section OCS value. The expression is as follows: in, is the optical scattering cross section (OCS) value of the target; is the optical reflectivity of the laser reflector, which indicates the proportion of energy radiated out after the target intercepts the laser; is the effective reflection area of ​​the laser reflector; is the target gain coefficient, is the target backscatter solid angle; is the equivalent divergence angle of laser reflection.

6. The method for selecting a laser ranging test window for a lunar satellite according to claim 4, characterized in that: The step S4.6 comprises: The formulas for laser echo photon number and echo rate are as follows: The formula for the probability of receiving k echo photons by a single pulse laser is as follows: The echo rate calculates the probability of a single pulse laser obtaining one or more photons. The echo rate is expressed by the following formula: in, is the number of single pulse echo photons; is the laser single pulse energy; is Planck's constant; is the speed of light; is the laser wavelength; and are the transmitting optical system efficiency and the receiving optical system efficiency respectively; is the two-way atmospheric transmittance; and are the effective reflection cross-sectional area of ​​the reflector and the effective receiving area of ​​the telescope respectively; is the ranging distance; and are the emission divergence angle and the reflection divergence angle respectively; is the reflectivity of the reflector; is the receiving detector efficiency; is the attenuation factor; is the echo rate; is the number of echo photons (k=1, 2, 3, ...); is the factorial of k; is the base of natural logarithms.

7. A laser ranging test window selection system for a lunar satellite, characterized in that: include: Model M1: Establish a high-precision lunar satellite dynamics model; Model M2: Establishing the laser ranging test constraint model; Model M3: Calculate the laser ranging test observation window based on the high-precision lunar satellite dynamics model and the laser ranging test constraint model; Model M4: Calculate the laser echo rate based on the ranging system, satellite and environmental parameters; Model M5: Ground station selection based on weather forecast values; Model M6: Select the final observation window based on the laser echo rate and ground station.

8. The laser ranging test window selection system for a lunar satellite according to claim 6, characterized in that: The module M1 includes: for the lunar satellite, the coordinate system selects the epoch moon-centered inertial coordinate system, taking into account the gravitational forces of the sun, the moon, the earth and other celestial bodies on the lunar satellite, the lunar solid tidal perturbation, the lunar physical libration, the solar radiation pressure, the jet unloading and the high-precision ephemeris factors, the lunar satellite dynamics model is as follows: The above formula can be abbreviated as: in, for The differential of is the state vector of the state model; They are the position and velocity of the lunar satellite in the X, Y, and Z directions respectively; is the system nonlinear continuous state transfer function of the state model; represents the system noise; represents the vector from the center of the moon to the satellite; Represents the vector from the center of the Earth to the satellite; heliocentric-to-satellite vector; are the gravitational constants of the Sun, Moon, and Earth respectively; is the vector from the heliocenter to the satellite; is the vector from the center of the moon to the center of the earth in the geocentric coordinate system; is the vector from the center of the moon to the center of the sun; is the coordinate of the moon's position in the solar mass center coordinate system; is the coordinate of the earth's position in the geocentric coordinate system; is the coordinate of the sun's position in the sun's mass center coordinate system; are the system noise respectively.

9. The laser ranging test window selection system for a lunar satellite according to claim 6, characterized in that: The module M2 includes: setting laser ranging test constraint conditions, and the constraint conditions specifically include: Set the thresholds for the angle between the sun and the corner reflector axis, the sun altitude angle, the satellite altitude angle, and the earth-moon-sun angle; The satellite in the large elliptical frozen orbit around the moon remains unchanged in the inertial system. When the satellite and the earth are on opposite sides of the moon, the moon's occlusion must be considered. The observation time every night must be more than one hour, and the observation time should be avoided during the rainy season.

10. The laser ranging test window selection system for a lunar satellite according to claim 6, characterized in that: The module M4 comprises: Module M4.1: Obtaining the parameters of the ranging system and corner reflector; Module M4.2: Calculate the relative positions of satellites and laser stations; Module M4.3: Calculate the equivalent divergence angle of laser reflection; Module M4.4: Calculate two-way atmospheric transmittance based on satellite altitude angle; Module M4.5: Calculation of attenuation factors related to cirrus clouds, atmospheric jitter, turbulence, telescope tracking accuracy, and telescope pointing accuracy; Module M4.6: After obtaining all the above parameter values, the ranging echo rate is calculated according to the laser echo rate formula; The module M4.3 includes: calculating the satellite aberration according to the relative speed between the satellite and the laser station, and the aberration calculation formula is as follows: in, is the satellite's aberration angle, is the speed of the satellite relative to the station, is the speed of light, is the velocity direction of the station The angle between the satellite and the direction of sight; The angular distribution and energy density of the far field of the corner reflector are measured by diffraction test, and then the optical scattering cross section (OCS) value of the reflector to be tested is quantitatively measured by comparison with the standard part. The equivalent divergence angle of laser reflection is calculated based on the aberration and optical scattering cross section OCS value. The expression is as follows: in, is the optical scattering cross section (OCS) value of the target; is the optical reflectivity of the laser reflector, which indicates the proportion of energy radiated out after the target intercepts the laser; is the effective reflection area of ​​the laser reflector; is the target gain coefficient, is the target backscatter solid angle; is the equivalent divergence angle of laser reflection; The module M4.6 includes: The formulas for laser echo photon number and echo rate are as follows: The formula for the probability of receiving k echo photons by a single pulse laser is as follows: The echo rate calculates the probability of a single pulse laser obtaining one or more photons. The echo rate is expressed by the following formula: in, is the number of single pulse echo photons; is the laser single pulse energy; is Planck's constant; is the speed of light; is the laser wavelength; and are the transmitting optical system efficiency and the receiving optical system efficiency respectively; is the two-way atmospheric transmittance; and are the effective reflection cross-sectional area of ​​the reflector and the effective receiving area of ​​the telescope respectively; is the ranging distance; and are the emission divergence angle and the reflection divergence angle respectively; is the reflectivity of the reflector; is the receiving detector efficiency; is the attenuation factor; is the echo rate; is the number of echo photons (k=1, 2, 3, ...); is the factorial of k; is the base of natural logarithms.

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