SST gravitational field measurement system and method based on inspection mass spacing measurement

Abstract

The invention belongs to the technical field of satellite gravitational field measurement, and particularly discloses an SST gravitational field measurement system and method based on inspection mass spacing measurement. The system is applied to two satellite platforms on a target orbit, and comprises a control unit, two laser interference measurement systems and two quality inspection units, wherein one laser interference measurement system and one inspection quality unit are correspondingly arranged on one satellite platform; on two gravitational field measurement satellites of a low satellite tracking satellite, laser interference is utilized to directly measure the distance and the variation rate between the inspection masses installed on the two satellites, and the measurement of the global gravitational field is realized. According to the invention, the space-between-satellite measurement and the non-conservative force measurement are integrated, the unification of the space-between-satellite measurement coordinate reference and the non-conservative force measurement coordinate reference is realized, the disturbance effect introduced by the conversion of two sets of independent coordinate systems and the change of a coordinate frame in the existing scheme is reduced, and the measurement sensitivity and confidence level are higher.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of satellite gravity field measurement, and more particularly relates to an SST gravity field measurement system and method based on test mass distance measurement. BACKGROUND

[0002] The earth's gravity field is a vector field formed by the combined action of the internal mass distribution of the earth and its rotation, which is affected by uneven distribution of matter inside the earth, as well as modulation of various factors such as mountain undulation on the earth's surface, ocean depth changes, centrifugal force generated by the earth's rotation, and solid earth deformation. High-precision measurement of the earth's gravity field not only has important significance for understanding the internal structure and dynamics evolution of the earth, but also plays a key role in many application fields such as global water resource management, ice cap mass change monitoring, sea level rise assessment, and natural disaster prediction. Currently, the earth's gravity field measurement mainly includes ground gravimeter measurement, aviation and marine gravity measurement, and satellite-based gravity field inversion methods. Among them, satellite gravity measurement has become the mainstream method for current gravity field research due to its outstanding advantages such as wide coverage, strong periodicity, and global unified measurement.

[0003] Traditional satellite gravity measurement tasks mainly use a double-satellite formation configuration to measure the relative distance change between satellites through microwave links, thereby inverting the redistribution of the earth's mass in space and time. However, the traditional measurement method is easily limited by non-conservative disturbances of the satellite platform itself, such as residual gas resistance, thermal radiation pressure, etc. These disturbance factors will introduce additional noise and system errors, resulting in low precision of the final gravity field measurement.

[0004] Therefore, how to better measure the earth's gravity field has become a technical problem to be solved in the industry. SUMMARY

[0005] In view of the defects of the prior art, the purpose of the present application is to better measure the earth's gravity field, and to solve the problem of low precision of gravity field measurement in the prior art.

[0006] To achieve the above purpose, in a first aspect, the present application provides an SST gravity field measurement system based on test mass distance measurement, which is applied to two satellite platforms on a target orbit, comprising: a control unit, two laser interferometry systems, and two test mass units; wherein one laser interferometry system and one test mass unit are arranged on one satellite platform; each laser interferometry system is connected to the control unit; The two laser interferometry systems are used to establish an inter-satellite laser link between the two satellite platforms. The control unit is configured to measure distance change information between test masses in the two test mass units by using the two laser interferometry systems, and to inverse the gravity field disturbance information based on the measured distance change information.

[0007] Optionally, the laser interferometry system comprises a laser light source, a laser emission and receiving light path, an interference optical platform, a photoelectric detector, and a phase measurement unit; the light inlet of the test mass unit is located on a target transmission light path of the laser emission and receiving light path. The laser emission and receiving light path is configured to transmit laser output by the laser light source to the test mass surface of the opposite satellite platform through the inter-satellite laser link to generate first reflected light, so that the reference laser component reserved by the interference optical platform of the opposite satellite platform is superimposed with the first reflected light to form a first heterodyne interference signal, and the first interference phase information corresponding to the first heterodyne interference signal is determined. The laser emission and receiving light path is also configured to transmit laser output by the laser light source of the opposite satellite platform received through the inter-satellite laser link to the local test mass surface to generate second reflected light, and transmit the second reflected light to the interference optical platform. The interference optical platform is configured to superimpose the locally reserved reference laser component with the second reflected light to form a second heterodyne interference signal, so that the second heterodyne interference signal is converted into corresponding electrical signal by the photoelectric detector and then transmitted to the phase measurement unit. The phase measurement unit is configured to determine the second interference phase information corresponding to the second heterodyne interference signal based on the electrical signal.

[0008] Optionally, the laser emission and receiving light path comprises a turning mirror, a beam splitter, and a beam expander. The turning mirror is located on the light outlet side of the laser light source, the beam splitter is located on the reflected light path of the turning mirror, the beam expander is located on the reflected light path of the beam splitter, the interference optical platform is located on the first transmission light path of the beam splitter, and the light inlet of the test mass unit is located on the second transmission light path of the beam splitter; the first transmission light path is collinear with the reflected light path of the turning mirror, and perpendicular to the second transmission light path; and the second transmission light path is the target transmission light path of the laser emission and receiving light path.

[0009] Optionally, the phase measurement unit in each laser interferometry system is connected with the control unit. The control unit is configured to acquire the first interference phase information and the second interference phase information, and to perform time series difference processing according to the first interference phase information and the second interference phase information to determine the distance change information between the two test masses.

[0010] Optionally, the test mass unit comprises a shell, the test mass, a controller, and a plurality of electrostatic control plates arranged around the test mass; the test mass, the controller, and each of the electrostatic control plates are arranged in the shell; and each of the electrostatic control plates is connected to the controller. The controller is configured to control the plurality of electrostatic control plates to generate electrostatic force to control the suspension of the test mass. The shell of the test mass unit on the side facing the spectroscope is provided with an entrance of the test mass unit; the electrostatic control plate of the test mass unit on the side facing the spectroscope is provided with an opening; the opening is coaxially arranged with the entrance, and the size of the opening is not less than the size of the entrance.

[0011] Optionally, the test mass unit further comprises an inertial sensing unit, which is connected to the controller. The inertial sensing unit is configured to measure the motion acceleration information of the test mass relative to the local satellite platform. The controller is further configured to control the plurality of electrostatic control plates to generate electrostatic force based on the motion acceleration information to control the pose of the suspended test mass.

[0012] Optionally, the satellite platform comprises a micro-thrust module, an attitude control unit, and a data processing unit; the micro-thrust module and the attitude control system are respectively connected to the data processing unit; and the data processing unit is connected to the control unit. The data processing unit is configured to generate control instructions based on the acquired orbit attitude information of the local satellite platform. The attitude control unit is configured to adjust the orbit attitude of the satellite platform in response to the control instructions from the data processing unit, so as to make the local laser interferometric measurement system and the opposite laser interferometric measurement system laser-aimed, and establish the inter-satellite laser link between the two satellite platforms. The micro-thrust module is configured to adjust the orbit attitude of the satellite platform in response to the control instructions from the data processing unit, so as to suppress external disturbances. The data processing unit is further configured to control the two laser interferometric measurement systems to perform laser interferometric measurement on the test masses in the two test mass units in response to the control instructions from the control unit.

[0013] In a second aspect, the present application provides a measurement method applied to the SST gravity field measurement system as described in any one of the preceding aspects, comprising: controlling orbit attitudes of the two satellite platforms for laser alignment of the two laser interferometry systems to establish an inter-satellite laser link between the two satellite platforms; measuring distance change information between test masses in the two test mass units by the two laser interferometry systems; inverting gravity field disturbance information based on the measured distance change information.

[0014] Optionally, the two satellite platforms are a master satellite platform and a slave satellite platform; and the measuring distance change information between test masses in the two test mass units by the two laser interferometry systems comprises: transmitting laser output by a laser source in the master satellite platform to a test mass surface of the slave satellite platform through the inter-satellite laser link to generate first reflected light, so that a reference laser component reserved by an interferometric optical platform of the slave satellite platform interferes with and superimposes on the first reflected light to form a first heterodyne interference signal, and first interference phase information corresponding to the first heterodyne interference signal is obtained; transmitting laser output by a laser source in the slave satellite platform to a test mass surface of the master satellite platform through the inter-satellite laser link to generate second reflected light, so that a reference laser component reserved by an interferometric optical platform of the master satellite platform interferes with and superimposes on the second reflected light to form a second heterodyne interference signal, and second interference phase information corresponding to the second heterodyne interference signal is obtained; obtaining the first interference phase information and the second interference phase information, and performing time series difference processing according to the first interference phase information and the second interference phase information to determine distance change information between the two test masses.

[0015] Overall, compared with the prior art, the above technical solutions conceived by the present application have the following beneficial effects: The present application provides an SST gravity field measurement system and method based on test mass distance measurement. By introducing a test mass unit arranged inside a satellite platform as an inertial reference, and combining a high-precision laser interferometry distance measurement method, the inter-satellite distance measurement and non-conservative force measurement are integrated into one design, and a "test mass-test mass" inter-satellite distance measurement path is constructed. The unity of the inter-satellite distance measurement and the non-conservative force measurement coordinate reference can be achieved, so that the measurement error introduced by the non-conservative force can be suppressed from the source, the measurement accuracy of the gravity field measurement system is significantly improved, and the anti-disturbance ability and long-term stability of the measurement system are also improved. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is a structural schematic diagram of an SST gravity field measurement system based on test mass distance measurement provided by an embodiment of the present application; Figure 2 This is a schematic diagram of the structure of the laser interferometry system provided in the embodiments of this application; Figure 3 This is a schematic diagram of the structure of the inspection quality unit provided in the embodiments of this application; Figure 4 This is a flowchart illustrating the measurement method of the SST gravity field measurement system provided in this application embodiment. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0018] The terms "first" and "second," etc., used in the specification and claims of this application are used to distinguish different objects, not to describe a specific order of the objects. For example, "first interference phase information" and "second interference phase information," etc., are used to distinguish different interference phase information, not to describe a specific order of the interference phase information.

[0019] In the embodiments of this application, the terms "exemplary" or "for example" are used to indicate that something is an example, illustration, or description. Any embodiment or design that is described as "exemplary" or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design. Specifically, the use of the terms "exemplary" or "for example" is intended to present the relevant concepts in a specific manner.

[0020] The embodiments of this application are described below with reference to the accompanying drawings.

[0021] Figure 1 This is a schematic diagram of the SST gravity field measurement system based on the measurement of the mass gap provided in this application embodiment. The system is applied to two satellite platforms 2 in the target orbit, as shown below. Figure 1 As shown, the system may include: Control unit 1, two laser interferometry systems 21 and two quality inspection units 22; In this system, a laser interferometry system 21 and a quality inspection unit 22 are each deployed on a satellite platform 2; each laser interferometry system 21 is connected to the control unit 1. Two laser interferometry systems 21 are used to establish an inter-satellite laser link between the two satellite platforms 2; The control unit 1 is used to measure the distance change information between the inspection masses in the two inspection quality units 22 using two laser interferometry systems 21, and to retrieve the gravitational field disturbance information based on the measured distance change information.

[0022] Specifically, the two satellite platforms described in this application embodiment are deployed in low Earth or medium-high Earth orbit. They can be divided into a master satellite platform and a slave satellite platform, which form a synchronous formation flight configuration. Satellite tracking satellite (SST) technology is used to achieve long-term, continuous, and global coverage measurements of the Earth's gravitational field.

[0023] It should be noted that the connection between the units / systems described in the embodiments of this application is an electrical connection, which can be a direct circuit connection or a signal transmission through a communication protocol.

[0024] In the embodiments of this application, a laser interferometry system and an inspection quality unit are each deployed on a satellite platform. That is, each satellite platform has a laser interferometry system and an inspection quality unit. The two laser interferometry systems, under the control of the control unit, establish a stable and collimated inter-satellite laser link between the two satellite platforms to achieve dynamic measurement of the relative distance changes between subsequent inspection qualities, capturing the inter-satellite relative motion caused by the inhomogeneity of the Earth's gravitational field.

[0025] It should be noted that the control unit can be located on the ground control console or directly on the satellite platform, etc. This application does not make any specific restrictions on this.

[0026] In the embodiments of this application, two inspection quality units are respectively set inside the corresponding satellite platform. The inspection quality is set inside the inspection quality unit, which can provide a stable inertial reference for the satellite platform and can be directly coupled with the laser interference optical path provided by the corresponding laser interferometry system to achieve high-sensitivity distance measurement between "inspection quality and inspection quality", so as to significantly reduce the impact of non-conservative interference force on the accuracy of interferometry.

[0027] Furthermore, in the embodiments of this application, the coupling method between the inspection quality and the laser interferometry system includes: adjusting the optical path and structural layout within the laser interferometry system so that the measurement path of the laser interferometry system traverses the location region of the inspection quality, making the inspection quality a reference endpoint for inter-satellite link ranging. Compared to traditional methods that only measure the distance between the outer shells of satellites, the system in the embodiments of this application can essentially transform inter-satellite interferometry into a measurement between inertial reference points, thus effectively avoiding the errors and modeling complexity caused by the intermediate reference frame conversion involved in traditional methods.

[0028] Understandably, during system operation, the laser interferometry system performs high-precision measurements of the relative displacement between "inspection masses." Combined with existing non-conservative perturbation modeling, attitude and orbit calculation, and phase demodulation algorithms, it can accurately extract information on inter-satellite distance variations caused by changes in the Earth's gravitational field from the interferometric data. Based on this, using a conventional orbital dynamics inversion model, the measured distance variation information between the inspection masses within the two satellite platforms can be inverted into gravitational field perturbation information, thereby enabling the construction of an Earth gravitational field model with high spatial resolution and temporal dynamics.

[0029] It should be noted that existing low-low satellite tracking gravity measurement systems generally adopt a "satellite spacing measurement + independent non-conservative force compensation" approach. This involves measuring satellite spacing using microwaves or lasers while simultaneously relying on accelerometers to measure the effects of non-conservative forces. However, this method suffers from the problem that the satellite spacing measurement and non-conservative force compensation fall on different reference points. The results must rely on the on-orbit stability of the spacecraft and payload assembly structure to be guaranteed, making it susceptible to limitations imposed by platform disturbances and baseline inconsistencies, thus reducing the confidence level of the measurements.

[0030] In this embodiment, the inspection quality is directly introduced into the laser interferometric link as an inertial reference, realizing the integrated measurement of "inertial reference + laser interferometric ranging". By utilizing the synergistic effect between the inertial reference's perception of non-conservative force disturbances and the internal drag-free control's mechanism for canceling non-conservative forces, it is possible not only to ensure that the inter-satellite spacing and non-conservative force compensation are carried out under the same reference system, but also to significantly reduce the errors caused by structural inconsistencies and asynchronous disturbance sources. This enables high-confidence and high-precision measurement of inter-satellite spacing and its rate of change, providing innovative technical support for next-generation satellite Earth gravity field measurement.

[0031] The SST gravity field measurement system based on inspection mass spacing measurement in this application embodiment introduces inspection mass units deployed inside the satellite platform as inertial references and combines them with high-precision laser interferometric ranging to integrate inter-satellite spacing measurement and non-conservative force measurement into a single design. This constructs an "inspection mass-inspection mass" inter-satellite distance measurement path, which can unify the coordinate references for inter-satellite spacing measurement and non-conservative force measurement. This can suppress measurement errors introduced by non-conservative forces from the source, significantly improve the measurement accuracy of the gravity field measurement system, and also enhance the measurement system's anti-disturbance capability and long-term stability.

[0032] Figure 2 This is a schematic diagram of the structure of the laser interferometry system provided in the embodiments of this application, as shown below. Figure 2As shown in the embodiments of this application, the laser interferometric measurement system 21 may specifically include a laser source 211, a laser emitting and receiving optical path 212, an interferometric optical platform 213, a photodetector 214, and a phase measurement unit 215; the light inlet of the inspection quality unit 22 is located on the target transmission optical path of the laser emitting and receiving optical path 212. The laser transmitting and receiving optical path 212 is used to transmit the laser output from the laser source 211 to the inspection quality surface of the peer satellite platform through the inter-satellite laser link to generate the first reflected light, so that the reference laser component retained by the interferometric optical platform of the peer satellite platform can be superimposed with the first reflected light to form the first heterodyne interference signal, and the first interference phase information corresponding to the first heterodyne interference signal can be determined. The laser transmitting and receiving optical path 212 is also used to transmit the laser light received from the laser source of the other satellite platform through the inter-satellite laser link to the local inspection quality surface to generate a second reflected light, and to transmit the second reflected light to the interference optical platform 213. The interferometric optical platform 213 is used to interfere and superimpose the locally retained reference laser component with the second reflected light to form a second heterodyne interference signal, so that the second heterodyne interference signal is converted into a corresponding electrical signal by the photodetector 214 and then transmitted to the phase measurement unit. The phase measurement unit 215 is used to determine the second interference phase information corresponding to the second heterodyne interference signal based on the electrical signal.

[0033] Specifically, in the embodiments of this application, the laser interferometry system set on each satellite platform can be composed of a laser source, a laser emitting and receiving optical path, an interferometric optical platform, a photodetector, and a phase measurement unit arranged sequentially according to a preset optical path. The laser source is specifically a laser used to provide a high-coherence, low-frequency noise reference light source, which can generate laser output with stable frequency, low phase noise, and narrow linewidth, supporting single-frequency or frequency-modulated interferometry modes.

[0034] In the embodiments of this application, the laser emitting and receiving optical path can transmit the laser output from the laser source to the counterpart satellite platform through the inter-satellite laser link. On the other hand, the laser output from the laser source can be transmitted to the local interferometric optical platform through the guidance of the local laser emitting and receiving optical path and retained as a reference laser component.

[0035] At the other end, the laser light transmitted through the laser emission and reception optical path of the satellite platform is transmitted to the inspection quality surface within its inspection quality unit, thereby generating a first reflected light. This reflected light can then return along the original optical path and be transmitted to the interferometric optical platform. Furthermore, through the processing of the laser source, laser emission and reception optical path, and interferometric optical platform of the satellite platform, the interferometric optical platform pre-reserves a corresponding reference laser component. Therefore, after the first reflected light is transmitted to the interferometric optical platform, it can interfere and superimpose with the reference laser component retained by the interferometric optical platform to form a first heterodyne interference signal. Further, through processing by the photodetector and phase measurement unit at the other end, phase information is extracted from the first heterodyne interference signal, and the first interference phase information corresponding to the first heterodyne interference signal can be output.

[0036] Here, heterodyne interference signal refers to the frequency difference signal generated after the measured signal and the reference signal interfere with each other using the heterodyne method.

[0037] Similarly, the local laser transmitting and receiving optical path can also be used to receive laser light output from the laser source of the remote satellite platform via an inter-satellite laser link, and transmit it to the inspection quality surface within the local inspection quality through a pre-designed special optical path structure, thereby generating a second reflected light. This reflected light can then return along the original optical path and be transmitted to the local interferometric optical platform. Here, the interferometric optical platform can specifically be an optical imaging system.

[0038] Furthermore, the local optical imaging system can interfere and superimpose the locally retained reference laser component with the second reflected light to form an interference fringe pattern signal, i.e., a second heterodyne interference signal. This interference signal is then projected onto a photodetector via the imaging system, converted into a corresponding electrical signal, and transmitted to the phase measurement unit. Finally, the phase measurement unit extracts the phase change of the interference fringes based on this electrical signal, thereby outputting the second interference phase information corresponding to the second heterodyne interference signal. In this way, the interferometric measurement of the distance between the inspection masses of the two-end laser interferometry system can be completed.

[0039] The system in this embodiment constructs a highly stable laser interferometric measurement link by introducing a pre-designed laser emission and reception optical path, an interferometric optical platform, a photodetector, and a phase measurement unit. This allows the laser interferometric measurement beam to accurately pass through the optical cavity region of the test quality through a specially designed collimation and pointing structure, achieving highly stable coupling with its fixed reflective surface or equivalent optical element. This configuration not only ensures good optical path consistency of the interference signal but also improves the sensitivity to small drifts in the test quality, thereby providing more direct and clear data support for the extraction of inter-satellite inertial point displacement.

[0040] Based on the above embodiments, as an optional embodiment, the phase measurement unit in each laser interferometry system is connected to the control unit; The control unit is used to acquire the first interference phase information and the second interference phase information, and to perform time series differential processing based on the first interference phase information and the second interference phase information to determine the distance change information between the two inspection qualities.

[0041] Specifically, in the embodiments of this application, the phase measurement unit in each laser interferometry system is connected to the control unit. The control unit can acquire the interference phase information output by each phase measurement unit. Then, the continuously acquired phase data can be arranged in chronological order to form a time series. Subsequently, differential operations are performed on adjacent phase data in the time series to obtain the phase change. This phase change is proportional to the change in distance between the two ends, thereby determining the distance change information between the two test masses.

[0042] The system in this application embodiment obtains the interference phase information measured by the two laser interferometry systems through the control unit and performs time series differential processing on it, which can effectively eliminate the influence of initial phase and phase drift and improve the accuracy of distance change calculation between the inspection quality of the satellite platform.

[0043] It should be noted that the core of low-low satellite tracking gravity field measurement lies in the high-precision acquisition of inter-satellite distances. The detection sensitivity of traditional measurement methods has long been limited by the wavelength limitation of traditional microwave ranging methods, making it difficult to achieve sub-nanometer level measurement.

[0044] The system of this application embodiment, by utilizing the high sensitivity characteristics of short-wavelength lasers and introducing the aforementioned highly stable laser interferometry link between satellites, combined with a low-noise optical platform and phase measurement technology, can significantly improve the resolution of inter-satellite distance and relative displacement.

[0045] Compared with existing technologies, the interferometric measurement method provided in this application can not only break through the sensitivity bottleneck of microwave ranging, but also achieve more accurate capture of changes in the Earth's gravity field through high-precision phase calculation of the interferometric signal. This improves the spatial resolution and reliability of low-low satellite gravity detection as a whole, and provides a technical foundation for the establishment of a high-precision Earth gravity field model.

[0046] Continue to refer to Figure 2 Based on the above embodiments, as an optional embodiment, the laser emitting and receiving optical path 212 includes a rotating mirror 2121, a beam splitter 2122, and a beam expander 2123; The rotating mirror 2121 is located on the output port side of the laser source 211, the beam splitter 2122 is located on the reflected light path of the rotating mirror 2121, the beam expander 2123 is located on the reflected light path of the beam splitter 2122, the interference optical platform 213 is located on the first transmission light path of the beam splitter 2122, and the light inlet of the inspection quality unit 22 is located on the second transmission light path of the beam splitter 2122. The first transmission light path is collinear with the reflected light path of the rotating mirror 2121 and perpendicular to the second transmission light path. The second transmission light path of the beam splitter 2122 is the target transmission light path of the laser emission and reception light path 212.

[0047] Specifically, in the embodiments of this application, the laser emitting and receiving optical path may include a rotating mirror, a beam splitter, and a beam expander. The rotating mirror may specifically be an adjustable-angle reflector. Figure 2 As shown, the rotating mirror is located on the output side of the laser source and is used to guide the laser beam emitted from the laser source to the beam splitter via reflection. The beam is split into a reference beam and a measurement beam by the beam splitter. The reference beam is transmitted to the interferometric optical platform for retention through the first transmission path of the beam splitter. Through reflection by the beam splitter, the measurement beam can have its exit direction adjusted by the rotating mirror and is finally emitted after passing through the beam expander, precisely pointing towards the distant satellite. After being transmitted via the inter-satellite laser link, the measurement beam interferes with the reference beam on the remote satellite platform.

[0048] Simultaneously, the measurement light from the other end is transmitted via the inter-satellite laser link, passes through a local beam expander and beam splitter, and then forms a transmitted beam through the second transmission path of the beam splitter, which enters the light inlet of the inspection quality unit. The transmitted beam is transmitted to the inspection quality surface for reflection, and the reflected light returns to the beam splitter along the original optical path. It is then reflected by the beam splitter and transmitted to the optical interference platform, where it interferes with the reference light retained by the optical interference platform.

[0049] Furthermore, in the specific implementation process, the interference signal is projected to the photodetector through the optical interference platform, and finally the phase change of the interference fringes is extracted by the phase measurement unit, thereby obtaining the dynamic change of the one-dimensional relative displacement between the inspection masses of the satellite platform.

[0050] The system in this application embodiment constructs a laser emission and reception optical path by introducing a rotating mirror, a beam splitter, and a beam expander. The optical path structure is simple and efficient. At the same time, the introduced beam expander can improve the spatial coherence of inter-satellite laser propagation and reduce the diffraction effect.

[0051] Figure 3 This is a schematic diagram of the structure of the inspection quality unit provided in the embodiments of this application, as shown below. Figure 3As shown in the embodiment of this application, the inspection quality unit 22 includes a housing 224, an inspection quality unit 221, a controller 222, and a plurality of electrostatic control plates 223 (partially labeled in the figure) disposed around the inspection quality unit 221; the inspection quality unit 221, the controller 222, and each electrostatic control plate 223 are all disposed inside the housing 224; the plurality of electrostatic control plates 223 are all connected to the controller 222; The controller 222 is used to control the suspension of the inspection quality 221 by controlling multiple electrostatic control plates 223 to generate electrostatic force. The outer wall of the housing 224 of the inspection quality unit 22 facing the beam splitter 2122 is provided with the light inlet 10 of the inspection quality unit 22; the electrostatic control plate of the inspection quality unit facing the beam splitter is provided with the opening 20; the opening 20 is coaxially arranged with the light inlet 10, and the size of the opening 20 is not smaller than the size of the light inlet 10.

[0052] Specifically, in the embodiments of this application, the inspection quality unit mainly includes an inspection quality unit, electrostatic control plates, and a controller, with each electrostatic control plate connected to the controller. Under the control of the controller, the inspection quality unit can achieve triaxial electrostatic levitation and disturbance suppression through the surrounding electrostatic control plates.

[0053] In the embodiments of this application, the outer wall of the housing facing the beam splitter of the inspection quality unit is provided with an inlet for the inspection quality unit. The inlet for the inspection quality unit is located on the second transmission optical path of the beam splitter. Simultaneously, an opening is provided on the electrostatic control plate facing the beam splitter of the inspection quality unit, and this opening is required to be coaxial with the inlet for the light, and the size of the opening is not smaller than the size of the inlet for the light. This ensures that the measurement laser transmitted from the beam splitter can be fully and accurately transmitted to the surface of the inspection quality for reflection. Therefore, according to the aforementioned integrated measurement method of "inertial reference + laser interferometric ranging," the reflected light returns to the laser interferometric measurement system along the second transmission optical path of the beam splitter and interferes with the reference light, realizing the absolute displacement measurement between the inspection qualities of the two satellite platforms.

[0054] The shape of the light inlet of the inspection quality unit and the opening on the electrostatic control plate can be designed to be the same, such as a square hole, a round hole, etc. This application does not make specific limitations on this.

[0055] The system in this application embodiment, on the one hand, can effectively isolate non-conservative force disturbances such as solar radiation pressure and residual atmospheric drag by introducing an electrostatically driven suspended inspection mass unit structure; on the other hand, by adjusting the optical path and structural layout between the inspection mass unit and the laser interferometry system, the laser interferometry path passes through the inspection mass location area, thereby making the inspection mass a reference endpoint for inter-satellite link ranging, and constructing a laser interferometry ranging link directly connecting the two inspection masses, which is beneficial to achieving high-precision, low-disturbance measurement of the relative motion between satellites.

[0056] Continue to refer to Figure 3 In the embodiments of this application, the quality inspection unit 22 further includes an inertial sensing unit 225, which is connected to the controller 222. The inertial sensing unit 225 is used to measure the motion acceleration information of the inspection mass 221 relative to the local satellite platform; The controller 222 is also used to control multiple electrostatic control plates 223 to generate electrostatic force based on motion acceleration information in order to perform pose control on the suspended inspection quality 221.

[0057] The system in this embodiment of the application introduces an inertial sensing unit to measure the inertial information of the inspection mass relative to the satellite platform in real time. Combined with the suspension control of the electrostatic control plate, the posture of the inspection mass can be adjusted from different degrees of freedom, and the relative motion state of the inspection mass with respect to the satellite platform can be precisely controlled. This can achieve sub-micron level attitude control and improve the accuracy of the inspection mass unit as an inertial reference.

[0058] Based on the above embodiments, as an optional embodiment, the satellite platform includes a micro-thrust module, an attitude control unit, and a data processing unit; the micro-thrust module and the attitude control system are respectively connected to the data processing unit; the data processing unit is connected to the control unit; The data processing unit is used to generate control commands based on the acquired orbital attitude information of the local satellite platform; The attitude control unit is used to respond to control commands sent by the data processing unit to adjust the orbital attitude of the satellite platform so that the local laser interferometry system and the remote laser interferometry system can perform laser alignment and establish an inter-satellite laser link between the two satellite platforms. The micro-thrust module is used to adjust the orbital attitude of the satellite platform in response to control commands sent by the data processing unit, so as to suppress external disturbances; The data processing unit is also used to respond to control commands sent by the control unit and control the two laser interferometry systems to perform laser interferometry measurements on the inspection quality within the two inspection quality units.

[0059] Specifically, in this embodiment, the satellite platform mainly includes a micro-thrust module, an attitude control unit, and a data processing unit. The data processing unit is responsible for acquiring, caching, and managing interferometric measurement data, control commands, and telemetry information, and performs some preprocessing tasks. Based on the acquired orbital attitude information of the local satellite platform, it can generate control commands to adjust the satellite platform's orbital attitude.

[0060] In this embodiment, the attitude control unit may specifically include a star sensor, gyroscope, magnetic torque generator, or reaction wheel to ensure platform attitude stability and laser link alignment capability. In practice, the attitude control unit can respond to control commands from the data processing unit and adjust the satellite platform's orbital attitude under the control of the data processing unit. This enables the local laser interferometry system to align with the remote laser interferometry system, establishing an inter-satellite laser link between the two satellite platforms, facilitating subsequent quality checks and laser interferometric ranging.

[0061] In this embodiment, the micro-thrust module can specifically adopt cold gas propulsion, electric field propulsion, or ion propulsion to achieve high-precision orbit and attitude adjustment of the platform. It can respond to control commands sent by the data processing unit and adjust the orbit and attitude of the satellite platform under its control to suppress external environmental disturbances during the measurement process.

[0062] In this embodiment of the application, when the gravity field measurement begins, the control unit can send a control command to the data processing unit. In response to the control command, the data processing unit controls the laser interferometry system to perform laser interferometry with the counterpart laser interferometry system to obtain interferometric measurement data of laser interferometric ranging between the inspection quality.

[0063] The system in this application embodiment introduces a micro-thrust module, an attitude control unit, and a data processing unit to assist in the precise adjustment of the orbital attitude of its own satellite platform during the gravity field measurement process, thereby effectively ensuring the stable execution of the laser interferometric ranging process between the two satellite platforms for quality inspection.

[0064] The measurement method of the SST gravity field measurement system based on the measurement of inspection mass spacing provided in this application is described below. The measurement method described below can be referred to in correspondence with the execution process of the SST gravity field measurement system based on the measurement of inspection mass spacing described above.

[0065] Figure 4 This is a flowchart illustrating the measurement method of the SST gravity field measurement system provided in this application embodiment. This method can be applied to any of the aforementioned SST gravity field measurement systems, such as... Figure 4 As shown, the measurement method specifically includes: Step S1: Control the orbital attitude of the two satellite platforms so that the two laser interferometry systems can perform laser alignment and establish an inter-satellite laser link between the two satellite platforms. Step S2: Use two laser interferometry systems to measure the distance change information between the inspection quality units within the two inspection quality units; Step S3: Invert the gravitational field disturbance information based on the measured distance change information.

[0066] It is understood that the specific implementation methods and steps described above can be found in the detailed description of the functional implementation of each unit / module in the aforementioned SST gravity field measurement system.

[0067] It should be understood that the above method can be applied to the system in the above embodiments. The implementation principle and technical effect of the above method are similar to those described in the above measurement system. The implementation process of the method can refer to the corresponding working process in the above measurement system, which will not be repeated here.

[0068] The measurement method of the SST gravity field measurement system in this application introduces a verification mass unit deployed inside the satellite platform as an inertial reference, and combines it with high-precision laser interferometric ranging to integrate inter-satellite distance measurement and non-conservative force measurement into a single design. This constructs a "verification mass-verification mass" inter-satellite distance measurement path, which can unify the coordinate references for inter-satellite distance measurement and non-conservative force measurement. This can suppress measurement errors introduced by non-conservative forces from the source, significantly improve the measurement accuracy of the gravity field measurement system, and also enhance the measurement system's anti-disturbance capability and long-term stability.

[0069] Based on the above embodiments, as an optional embodiment, two satellite platforms are designated as a master satellite platform and a slave satellite platform; two laser interferometry systems are used to measure the distance change information between the inspection qualities within the two inspection quality units, including: The laser output from the laser source in the main satellite platform is transmitted to the inspection quality surface of the slave satellite platform through the inter-satellite laser link to generate the first reflected light. The reference laser component retained by the interferometric optical platform of the slave satellite platform is then superimposed with the first reflected light to form the first heterodyne interference signal, thereby obtaining the first interference phase information corresponding to the first heterodyne interference signal. The laser output from the laser source in the satellite platform is transmitted to the inspection quality surface of the main satellite platform through the inter-satellite laser link to generate a second reflected light. The reference laser component retained by the interference optical platform of the main satellite platform interferes and superimposes with the second reflected light to form a second heterodyne interference signal, thereby obtaining the second interference phase information corresponding to the second heterodyne interference signal. First interference phase information and second interference phase information are acquired, and time series difference processing is performed based on the first interference phase information and second interference phase information to determine the distance change information between the two test qualities.

[0070] Specifically, in the embodiments of this application, the two satellite platforms can be divided into a master satellite platform and a slave satellite platform, each equipped with a laser interferometry system and a test quality unit, forming a stable inter-satellite interferometry link. The laser interferometry system may include a laser source, a laser emission and reception optical path, an interferometric optical platform, a photodetector, and a phase measurement unit. The measurement principle of the distance change information between the two test qualities is as follows: First, the control unit issues control commands to activate the laser interferometry system on the master satellite platform. The master laser emitted from the laser source on the master satellite platform is collimated via the laser emission and reception optical paths and propagates along the inter-satellite laser link, entering the laser interferometry system on the slave satellite platform. It then illuminates the center of the reflective surface used for quality inspection on the slave satellite, generating a first reflected light. This reflected light returns along the original optical path to the interferometric optical platform of the slave satellite platform, where it interferes with and superimposes with the reference laser component retained within it to form a first heterodyne interference signal. This signal is converted into an electrical signal by a photodetector and input to the phase measurement unit to extract the first interference phase information. Through heterodyne phase-locked loop technology, precise locking of the laser phase between the master and slave satellites is achieved, thereby ensuring high consistency of optical frequency and phase between the two satellites.

[0071] Based on this, the measurement laser from the satellite platform enters the main satellite optical platform along the reverse inter-satellite laser link, and illuminates the center of the quality-checking reflective surface on the main satellite platform in the same manner as described above, generating a second emitted light. This reflected light returns to the interferometric optical platform within the laser interferometry system of the main satellite platform, where it interferes and superimposes with its internal reference light to form a second heterodyne interference signal. After the phase is extracted by the photoelectric detection and phase measurement unit, the interference phase data at the main satellite end is obtained, thus obtaining the second interference phase information corresponding to the second heterodyne interference signal.

[0072] Furthermore, in the embodiments of this application, by extracting the phase of the heterodyne interferometric beat frequency signals at both ends of the master and slave satellite platforms, the control unit can obtain the first interference phase information and the second interference phase information, and perform time-series differential processing on the first and second interference phase information. The system can accurately invert the relative displacement change between the test masses of the master and slave satellite platforms, and achieve high-precision measurement of the distance change between the two test masses. This measurement result corresponds to the small orbital changes between satellites caused by the Earth's gravitational field, thereby providing basic observations for the inversion of the gravitational field.

[0073] The satellite tracking gravity field measurement method based on direct measurement of the distance between test masses provided in this application can not only effectively improve the resolution and reliability of the global gravity field model, but also be widely applicable to the study of major scientific issues of the Earth system such as polar ice evolution and sea level change, and has broad engineering application prospects and scientific research value.

[0074] Based on the methods in the above embodiments, this application provides a computer-readable storage medium storing a computer program that, when run on a processor, causes the processor to execute the methods in the above embodiments.

[0075] Based on the methods in the above embodiments, this application provides a computer program product that, when run on a processor, causes the processor to execute the methods in the above embodiments.

[0076] It is understood that the processor in the embodiments of this application can be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, transistor logic devices, hardware components, or any combination thereof. A general-purpose processor can be a microprocessor or any conventional processor.

[0077] The method steps in this application embodiment can be implemented in hardware or by a processor executing software instructions. The software instructions can consist of corresponding software modules, which can be stored in random access memory (RAM), flash memory, read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), registers, hard disks, portable hard disks, CD-ROMs, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor, enabling the processor to read information from and write information to the storage medium. Of course, the storage medium can also be a component of the processor. The processor and the storage medium can reside in an ASIC.

[0078] In the above embodiments, implementation can be achieved entirely or partially through software, hardware, firmware, or any combination thereof. When implemented using software, it can be implemented entirely or partially as a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the processes or functions described in the embodiments of this application are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted through the computer-readable storage medium. The computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, fiber optic, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that integrates one or more available media. The available medium can be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape), an optical medium (e.g., DVD), or a semiconductor medium (e.g., solid-state disk (SSD)).

[0079] It is understood that the various numerical designations used in the embodiments of this application are merely for the convenience of description and are not intended to limit the scope of the embodiments of this application.

[0080] It should be understood that expressions such as “comprising” and “may include” used in this application indicate the existence of the disclosed functions, operations, or constituent elements, and do not limit one or more additional functions, operations, and constituent elements. In this application, terms such as “comprising” and / or “having” are to be interpreted as indicating a particular characteristic, number, operation, constituent element, component, or combination thereof, but not to exclude the existence or possibility of adding one or more other characteristics, numbers, operations, constituent elements, components, or combinations thereof.

[0081] Furthermore, in the embodiments of this application, the mathematical concept of "perpendicular" is used. This limitation is relative to the current technological level, rather than an absolutely strict definition in a mathematical sense. Slight deviations are allowed, and approximations of perpendicularity are acceptable. For example, "A is perpendicular to B" means that A and B are perpendicular or approximately perpendicular.

[0082] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A SST gravity field measurement system based on the measurement of the quality of the separation of the tests, applied to two satellite platforms in the orbit of the target, characterized in that, The application relates to a satellite laser interferometry system. The satellite laser interferometry system comprises a control unit, two laser interferometry systems and two test mass units. One of the laser interferometry systems and one of the test mass units are arranged on one satellite platform, and each laser interferometry system is connected to the control unit. The two laser interferometry systems are used to establish an intersatellite laser link between two satellite platforms. The control unit is used to measure distance change information between test masses in the two test mass units by using the two laser interferometry systems, and to inversely calculate gravity field disturbance information based on the measured distance change information.

2. The SST gravity field measurement system of claim 1, wherein, The laser interferometry system comprises a laser light source, a laser emission and receiving light path, an interference optical platform, a photoelectric detector and a phase measurement unit. An entrance of the test mass unit is located on a target transmission light path of the laser emission and receiving light path. The laser emission and receiving light path is used to transmit laser output by the laser light source to a test mass surface of a satellite platform at the other end through the intersatellite laser link to generate first reflected light. The first reflected light is used to form a first heterodyne interference signal by interference superposition of a reference laser component reserved by an interference optical platform of the satellite platform at the other end and the first reflected light, and to determine first interference phase information corresponding to the first heterodyne interference signal. The laser emission and receiving light path is also used to transmit laser received from the satellite platform at the other end through the intersatellite laser link to a test mass surface of the local satellite platform to generate second reflected light, and to transmit the second reflected light to the interference optical platform.

3. The SST gravity field measurement system of claim 2, wherein, The interference optical platform is used to form a second heterodyne interference signal by interference superposition of a reference laser component reserved locally and the second reflected light. The second heterodyne interference signal is used to be converted into corresponding electrical signals by the photoelectric detector, and then transmitted to the phase measurement unit.

4. The SST gravity field measurement system of claim 2, wherein, The phase measurement unit is used to determine second interference phase information corresponding to the second heterodyne interference signal based on the electrical signals. The laser emission and receiving light path comprises a turning mirror, a beam splitter and a beam expander. The turning mirror is located on a light outlet side of the laser light source. The beam splitter is located on a reflected light path of the turning mirror. The beam expander is located on a reflected light path of the beam splitter. The interference optical platform is located on a first transmission light path of the beam splitter. An entrance of the test mass unit is located on a second transmission light path of the beam splitter. The first transmission light path is collinear with the reflected light path of the turning mirror, and perpendicular to the second transmission light path. The second transmission light path is a target transmission light path of the laser emission and receiving light path. The phase measurement unit in each laser interferometry system is connected to the control unit. The control unit is used to acquire the first interference phase information and the second interference phase information, and to perform time sequence difference processing according to the first interference phase information and the second interference phase information to determine distance change information between the two test masses.

5. The SST gravity field measurement system of claim 3, wherein, The test mass unit comprises a shell, the test mass, a controller and a plurality of electrostatic control plates arranged around the test mass; the test mass, the controller and each of the electrostatic control plates are arranged in the shell; the plurality of electrostatic control plates are connected with the controller; The controller is configured to control the plurality of electrostatic control plates to generate electrostatic force, and to control the suspension of the test mass; An entrance of the test mass unit is arranged on an outer wall of the shell facing the spectroscope; An opening is arranged on the electrostatic control plate of the test mass unit facing the spectroscope; the opening is coaxially arranged with the entrance, and the size of the opening is not less than that of the entrance.

6. The SST gravity field measurement system of claim 5, wherein, The test mass unit further comprises an inertial sensing unit connected with the controller; The inertial sensing unit is configured to measure the motion acceleration information of the test mass relative to the local satellite platform; The controller is further configured to control the plurality of electrostatic control plates to generate electrostatic force based on the motion acceleration information, so as to control the pose of the suspended test mass.

7. The SST gravity field measurement system of any one of claims 1-6, wherein, The satellite platform comprises a micro-thrust module, an attitude control unit and a data processing unit; the micro-thrust module and the attitude control system are connected with the data processing unit respectively; the data processing unit is connected with the control unit; The data processing unit is configured to generate control instructions based on the acquired orbit attitude information of the local satellite platform; The attitude control unit is configured to adjust the orbit attitude of the satellite platform in response to the control instructions from the data processing unit, so as to perform laser alignment between the local laser interferometric measurement system and the opposite laser interferometric measurement system, and to establish the inter-satellite laser link between the two satellite platforms; The micro-thrust module is configured to adjust the orbit attitude of the satellite platform in response to the control instructions from the data processing unit, so as to suppress external disturbance; The data processing unit is further configured to control the two laser interferometric measurement systems to perform laser interferometric measurement on the test masses in the two test mass units in response to the control instructions from the control unit.

8. A method of measurement applied to the SST gravity field measurement system according to any one of claims 1 to 7, characterized in that, Comprise: controlling the orbit attitude of the two satellite platforms for laser alignment by the two laser interferometric measurement systems, and establishing the inter-satellite laser link between the two satellite platforms; measuring the distance change information between the test masses in the two test mass units by the two laser interferometric measurement systems; inverting the gravity field disturbance information based on the measured distance change information.

9. The measurement method according to claim 8, characterized in that, The two satellite platforms are a master satellite platform and a slave satellite platform; The measuring the distance change information between the test masses in the two test mass units by the two laser interferometric measurement systems comprises: The laser output by the laser light source in the master satellite platform is transmitted to the test mass surface of the slave satellite platform through the inter-satellite laser link to generate first reflected light, so that the reference laser component reserved by the interferometric optical platform of the slave satellite platform and the first reflected light are superimposed to form a first heterodyne interference signal, and first interference phase information corresponding to the first heterodyne interference signal is obtained; The laser output by the laser light source in the slave satellite platform is transmitted to the test mass surface of the master satellite platform through the inter-satellite laser link to generate second reflected light, so that the reference laser component reserved by the interferometric optical platform of the master satellite platform and the second reflected light are superimposed to form a second heterodyne interference signal, and second interference phase information corresponding to the second heterodyne interference signal is obtained; The first interference phase information and the second interference phase information are obtained, and time series difference processing is performed according to the first interference phase information and the second interference phase information to determine the distance change information between the two test masses.

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