Formation satellite inter-satellite pointing index evaluation method

Abstract

The application relates to a formation satellite inter-satellite pointing index evaluation method applied to the field of formation satellites with inter-satellite pointing requirements, and solves the problem of accurate evaluation of double-satellite inter-satellite pointing indexes. The ground simulation task is in an equal-step simulation task by changing a simulation system time module; the simulation data obtained when asynchronous device simulation verification is carried out is consistent by using an external system to perform external synchronization on the ground simulation equipment; the simulation task is continuous by processing external interruption through ground simulation task division; and the ground simulation data with consistent time marks are obtained by changing the ground simulation equipment, so that the actual pointing angle calculation is carried out.

Description

Technical Field

[0001] This invention relates to a method for evaluating inter-satellite inter-pointing indices of formation satellites, applicable to the field of formation satellites with inter-satellite pointing requirements. Background Technology

[0002] For two-satellite formations with inter-satellite pointing requirements, maintaining relative pointing is a critical indicator affecting mission success. To accurately evaluate the inter-satellite pointing indicators, factors such as strict synchronization of ground simulation time for both satellites and strict synchronization of ground simulation time for a single satellite need to be considered. Existing subsystem ground simulation equipment lacks the capability to verify and evaluate these indicators. The following three problems exist in the pointing control indicators and pointing verification process of the inter-satellite pointing system for formation satellites:

[0003] First, the satellite and ground use asynchronous clocks, and the orbital information between the satellite and ground is not strictly consistent, which leads to errors in attitude angle.

[0004] Secondly, traditional simulation systems require two satellites to be simulated simultaneously for inter-satellite pointing control and performance verification. Since the simulation process is not physically related, the data obtained is asynchronous, resulting in significant errors in the evaluation of inter-satellite pointing performance.

[0005] Third, traditional simulation verification systems generate orbital data during the verification process, resulting in a large amount of data required to calculate the actual inter-satellite pointing angle, leading to low processing efficiency. Summary of the Invention

[0006] The technical problem to be solved by this invention is to overcome the shortcomings of the prior art and solve the problem of accurate evaluation of the pointing index between two stars.

[0007] The objective of this invention is achieved through the following technical solutions:

[0008] A method for evaluating inter-satellite cross-reference indices of satellite formations includes:

[0009] Two independent ground simulation systems were used to conduct simulation tests and verification.

[0010] Taking a single set as an example, the data stream of a single simulation device includes:

[0011] A) The ground simulation system acquires control signals from the actuators in real time;

[0012] B) The ground dynamics model of the ground simulation system updates the satellite's attitude information in real time based on the control variables;

[0013] C) The ground simulation system updates orbital information, satellite position vectors in the J2000 inertial coordinate system, and other information based on the Earth model;

[0014] D) Calculate the data corresponding to the on-board sensors under the new attitude;

[0015] E) The ground simulation system drives the signal excitation based on the sensor data and uploads the data of each sensor to the on-board control computer;

[0016] F) After collecting sensor data, the onboard control computer outputs the next control quantity and the actual pointing angle according to the control algorithm;

[0017] G) Repeat the above steps to complete the closed-loop test of the entire control subsystem;

[0018] After the two simulation systems conducted simulation experiments, the host computer software read the orbital information from the database and used the orbital information to calculate the theoretical pointing angle between the two stars.

[0019] The inter-satellite pointing accuracy is evaluated by comparing the theoretical pointing angles and actual pointing angles of the binary stars.

[0020] Preferably, time synchronization of the ground simulation system includes:

[0021] The clock module of the ground simulation system uses an external FPGA counter to time 10ms (adjustable) to trigger the simulation task, providing the external interrupt required for the scheduling of the simulation task for attitude and orbit simulation calculations.

[0022] The clock module of the ground simulation system receives external synchronization pulses and their corresponding time stamps.

[0023] Preferably, the clock module of the ground simulation system includes:

[0024] Monitor task execution time;

[0025] The task completion time is categorized into different cases.

[0026] The ground simulation system's time module is compatible with the verification of the control subsystem and the integration of the entire satellite into the GNSS subsystem for time synchronization.

[0027] Preferably, the attitude and orbit simulation module of the ground simulation system completes the simulation modeling of satellite attitude and orbit;

[0028] The attitude and orbit simulation module performs attitude simulation and orbit extrapolation calculations based on the onboard output, generating the required satellite position vector in the J2000 inertial coordinate system.

[0029] Preferably, during ground verification, unified time-stamped data can be obtained through asynchronous simulation verification experiments.

[0030] Preferably, the evaluation method further includes:

[0031] The host computer software can query orbital data at the same time scale, align and process the data to calculate the actual pointing angle;

[0032] The host computer software can compare the actual pointing angle with the satellite pointing angle, evaluate the satellite pointing control, and accurately quantify the satellite pointing accuracy.

[0033] Compared with the prior art, the present invention has the following advantages:

[0034] (1) The method of the present invention has the characteristics of independent verification and does not affect normal ground simulation verification. It uses semi-physical simulation test data to verify the inter-finite control, achieving the advantages of objectivity and accuracy.

[0035] (2) The method of the present invention can be used to asynchronously verify the inter-satellite pointing control function and control indicators.

[0036] (3) The method of the present invention uses automatic evaluation of inter-satellite pointing accuracy, which can efficiently complete the system evaluation.

[0037] (4) The method of the present invention achieves the simulation task of the ground simulation task being in the same step size by changing the time module of the simulation system; achieves the consistency of the simulation data obtained when the asynchronous device is simulated and verified by using an external system to externally synchronize the ground simulation equipment; handles external interruptions by dividing the ground simulation task to ensure the continuity of the simulation task; obtains ground simulation data with consistent time scale by changing the ground simulation equipment, and then calculates the actual pointing angle. Attached Figure Description

[0038] Figure 1 This is a simplified simulation verification diagram of the method of the present invention;

[0039] Figure 2 A timing diagram for control cycle calibration is introduced into the ground simulation system of the method of this invention;

[0040] Figure 3 A GNSS second pulse timing diagram is introduced into the ground simulation system of the method of this invention;

[0041] Figure 4 This is a specific implementation process for evaluating the inter-star pointing index of binary stars in the constellation according to the method of the present invention. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0043] A method for evaluating inter-satellite cross-reference indices of satellite formations includes:

[0044] Two independent ground simulation systems were used to conduct simulation tests and verification.

[0045] Taking a single system as an example, the data stream of a single ground simulation system includes:

[0046] A) The ground simulation system acquires control signals from the actuators in real time;

[0047] B) The ground dynamics module of the ground simulation system updates the satellite's attitude information in real time based on the control variables;

[0048] C) The ground simulation system updates orbital information, satellite position vectors in the J2000 inertial coordinate system, and other information based on the Earth model;

[0049] D) Calculate the data corresponding to the on-board sensors under the new attitude;

[0050] E) The ground simulation system drives the signal excitation based on the sensor data and uploads the data of each sensor to the on-board control computer;

[0051] F) After collecting sensor data, the onboard control computer outputs the next control quantity and the actual pointing angle according to the control algorithm;

[0052] G) Repeat the above steps to complete the closed-loop test of the entire control subsystem;

[0053] After the two ground simulation systems conducted simulation tests, the host computer software read the orbit information from the database and used the orbit information to calculate the theoretical pointing angle between the two stars.

[0054] The inter-satellite pointing accuracy is evaluated by comparing the theoretical pointing angles and actual pointing angles of the binary stars.

[0055] In the above-mentioned evaluation method for inter-satellite cross-reference index of formation satellites, the traditional ground simulation system operation cycle is task-triggered, with a low time task level. The cycle triggering is constrained by the running time of previous tasks, so the simulation step size (10ms) is uneven. In order to facilitate the alignment of orbit data of the two-satellite simulation system, the simulation step size (10ms) of the two ground simulation systems is strictly controlled within the standard 10ms. The time module of the ground simulation verification system is modified by hardware, changing from system task triggering to external FPGA counter timing 10ms to trigger the simulation task operation. In this way, the simulation step size of the two ground simulation systems is 10ms, which facilitates data alignment.

[0056] Ground simulation tests are usually conducted using two sets of ground simulation equipment, or one set of ground simulation equipment is used to conduct simulation tests of two satellites at different times. However, the two sets of ground simulation equipment are subject to clock drift and are not physically connected. To ensure that the data of the two ground simulation systems are at the same time scale, they need to be externally synchronized using the same time source.

[0057] Generally, satellite formations offer high pointing accuracy, and introducing GNSS second pulses for time synchronization also ensures high accuracy. GNSS time is based on a whole second plus a fractional second. When introducing time synchronization, it's necessary to consider that the fractional second value of each second pulse is different. After introducing GNSS system time synchronization into the satellite control system, the time of the synchronized simulation system becomes misaligned. To achieve time alignment, ground simulation system synchronization is performed in 10ms increments.

[0058] Every second, the GNSS subsystem sends a second pulse signal to the central control unit of the satellite control subsystem, and simultaneously sends the second pulse to the ground simulation system. After receiving the second pulse signal, the central control unit sends the time information to the time module of the ground simulation system via serial port. Since the time synchronization introduced by the GNSS second pulse involves both whole second and fractional second values, the following processing is performed for the GNSS second pulse time synchronization introduced in the whole-satellite AIT test:

[0059] When the ground simulation system receives the GNSS second pulse signal for the first time, it does not perform synchronization but only time synchronization. The ground simulation system's time module records the current control time t0. When the next GNSS second pulse signal arrives, the ground simulation system's time module's satellite time t1 is set to the previous satellite time t0+1 recorded by the simulation equipment's system time module. When the control satellite time arrives, the time difference Δt1 between the current cycle's time module t1 and the control satellite time T is calculated. When the next second pulse arrives, the ground simulation system's time module's satellite time t2 is set to the previous satellite time t1+1+Δt1 recorded by the ground simulation equipment's system time module. This process is repeated to complete the satellite-ground time unification. For the specific time synchronization procedure, see [link to procedure]. Figure 2 .

[0060] Because the received control satellite time T contains a fractional second value ΔT, in order to ensure synchronization, the timing is checked and processed on the ground simulation system as follows:

[0061] 1) Set the task completion time base a = 6ms for the simulation step size (10ms) of the ground simulation system;

[0062] 2) When the second pulse arrives, the satellite time of the ground simulation system is ΔT. The satellite time of the ground simulation system is t_1 in seconds, which is the simulation step size. For example, if the satellite time of the ground simulation system is 105ms, then t_1 is 5ms. The actual running time of the ground simulation system task is t_2.

[0063] 3) When the second pulse arrives, the simulation task running time is t_2>a, that is, the simulation task has finished running. Then the time is recorded and the simulation is synchronized in t_m=(T+10-t_1)ms, that is, the synchronization is completed in the whole 10ms of this simulation cycle.

[0064] 4) When the second pulse arrives, the running time of the simulation task is t₂<a, that is, the simulation task is not completed, the time is recorded and simulation synchronization is performed at tₙ=(T+20-t₁)ms, that is, the synchronization is completed at the exact 10ms of the next simulation cycle;

[0065] 5) Synchronization and time calibration are performed in each GNSS time calibration cycle to ensure the time synchronization of ground simulation data.

[0066] If the ground simulation test does not use the on-board GNSS for time calibration, the internal time information of the control subsystem computer can also be used for synchronization and time calibration.

[0067] The control tasks of the on-board control computer of the control subsystem have a strict time management mechanism. The task running time is managed by time slice division. The on-board control cycle is used as the synchronization pulse signal of the ground simulation system to perform external synchronization time calibration on the ground simulation system. The separated on-board control cycle is used as the time calibration reference of the ground simulation system, which not only ensures the unification of the time of the ground simulation system and the satellite time system, but also ensures that the two sets of simulation systems are consistent in time even if triggered by clocks of different sources.

[0068] The on-board control computer sends a synchronization pulse signal to the clock module of the ground simulation system through the ground detection point every control cycle (default 500ms). The synchronization pulse signal is of the same source and strictly aligned with the periodic signal of the on-board control computer. When the on-board control computer sends out the synchronization pulse signal, it sends the on-board time corresponding to the synchronization pulse signal to the clock module of the ground simulation system in the manner of a communication serial port. At this time, the clock module receives the synchronization pulse signal and its corresponding time stamp (i.e., the on-board time). The clock module will take the received synchronization pulse signal as the trigger source, take this moment as the starting point, and the ground simulation system outputs attitude and orbit simulation tasks at a step size of every 10ms. By analogy, the clock module will be calibrated once every control cycle (500ms) to ensure that the on-board time is consistent with the ground time.

[0069] When the synchronization pulse signal is sent out, considering the clock drift problem of different clocks of the on-board and ground simulation systems, the operation of the ground simulation task is affected by the synchronization pulse interrupt, and the synchronization pulse and task operation are processed as follows:

[0070] 1) Through monitoring the ground simulation task, the maximum running time of the simulation task does not exceed 6ms. Therefore, the task completion time reference a=6ms is set for the simulation step size (10ms) of the ground simulation system, and t is the actual completion time of each task of the ground simulation system. When t>a, it is considered that the simulation task of this cycle is completed, and when t<a, it is considered that the simulation task of this cycle is not completed;

[0071] 2) The ground simulation system starts running from the first simulation task. The on-board control signal sends a synchronization pulse signal to the first simulation task and the 51st simulation task. If the synchronization pulse signal arrives in the 51st cycle of the ground simulation system, that is, the 51st cycle of the ground simulation system task is completed, then the new task scheduling and simulation task synchronization will start based on the current synchronization pulse signal.

[0072] 3) If the synchronization pulse signal arrives in the 51st cycle of the simulation equipment, that is, the ground simulation system task in the 51st cycle has not been completed, then no synchronization will be performed, only time updates will be performed, and the simulation cycle task count will be based on the current synchronization pulse time.

[0073] 4) When the next synchronization pulse signal arrives, continue to determine whether synchronization is achieved based on whether the ground simulation system's task has been completed; see the synchronization timing diagram. Figure 3 .

[0074] This design timing supports the separate verification of the control subsystem using the same simulation equipment and different simulation equipment.

[0075] After the simulation task is completed, data processing is performed using host computer software. The processing method is as follows:

[0076] Taking a simulation device as an example, the satellite is simulated and verified at different times. The host computer selects the start time in the ground simulation system, queries the orbital data in the ground simulation system, and compares and aligns the orbital position information of the two satellites according to the time-scaled information (satellite time information) in the ground simulation system to obtain a set of J2000 inertial coordinate system satellite position vector data r with consistent time scale (for both satellites). pv [3], r pv [3] Includes satellite three-axis position vector information, with the X-axis position vector information being r pv [0], the Y-axis position vector information is r pv [1], the z-axis position vector information is r pv [2] The formula for calculating the position vector is as follows:

[0077]

[0078] Where satOrbitT_x is the position of the target star along the X-axis in the J2000 inertial coordinate system, satOrbitC.x is the position of the local star along the X-axis in the J2000 inertial coordinate system, satOrbitT_y is the position of the target star along the Y-axis in the J2000 inertial coordinate system, satOrbitC.y is the position of the local star along the Y-axis in the J2000 inertial coordinate system, satOrbitT_z is the position of the target star along the Z-axis in the J2000 inertial coordinate system, and satOrbitC.z is the position of the local star along the Z-axis in the J2000 inertial coordinate system.

[0079] The relative position r in the orbital system is calculated using the transformation relationship. pvo [3], r pvo [3] Includes satellite three-axis position vector information, with the X-axis position vector information being r pvo [0], the Y-axis position vector information is r pvo [1], the Z-axis position vector information is r pvo [2] The formula for calculating the relative position is as follows:

[0080] r pvo [3] = A o r pv [3] (2)

[0081]

[0082] Where A o This is the transformation matrix from the J2000 inertial coordinate system to the orbital system.

[0083] By relative position r in the orbital system pvo [3] The relative pitch axis angle θ can be calculated using a formula. T and relative yaw axis angle

[0084]

[0085] The host computer software can be installed on any computer. The simulation evaluation steps are as follows:

[0086] 1) Set the initial simulation parameters using the host computer software;

[0087] 2) After setting, the single-satellite on-board control computer will start synchronously to separate the satellites and run the ground simulation system, forming a closed loop between the satellite and the ground.

[0088] 3) After the simulation starts, perform simulation calculations of the single satellite's attitude and orbit, and input the simulation data into the database;

[0089] 4) After completing the closed-loop simulation of the two stars, the host computer software retrieves the orbital data for calculating the theoretical angle of the inter-star pointing between the two stars, and completes the evaluation of the inter-star pointing index between the two stars in the constellation.

[0090] Figure 1 This is a simplified simulation verification diagram of the method of the present invention; the specific data flow during the entire simulation verification process is as follows: Figure 4 .

[0091] The contents not described in detail in this specification are common knowledge to those skilled in the art.

[0092] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

Claims

1. A method for evaluating inter-satellite cross-reference indices of satellite formations, characterized in that, comprising: two independent ground simulation systems respectively perform simulation test verification work; for each set of the ground simulation systems, the operations include: A) the ground simulation system collects control signals of the actuator in real time; B) the ground simulation system updates the attitude information of the satellite in real time according to the control quantity; C) the ground simulation system updates orbit information and the satellite position vector in the J2000 inertial coordinate system according to the Earth model; D) the ground simulation system calculates data corresponding to the on-board sensor under the new attitude; E) the data of the on-board sensor from the ground simulation system is uploaded to the on-board control computer; F) after collecting the sensor data, the on-board control computer outputs the next-step control quantity and the actual pointing angle according to the control algorithm; after the two sets of ground simulation systems respectively complete the simulation tests, the upper computer software reads the orbit information, and performs calculation of the theoretical inter-satellite pointing angle of the two satellites based on the orbit information; the inter-satellite pointing accuracy is evaluated by comparing the theoretical pointing angle and the actual pointing angle of the two satellites; When using the GNSS second pulse as the time reference, the ground simulation system does not perform synchronization but only time adjustment after receiving the GNSS second pulse signal for the first time. The time module of the ground simulation system records the current control time. When the next GNSS second pulse signal arrives, set the satellite time module of the ground simulation system. Record the star time for the last simulation equipment system time module. And calculate the time module for this cycle when the control satellite time arrives. Time difference with control star time T When the next second pulse arrives, the satellite time module of the ground simulation system will be activated. Record the satellite time for the last time the ground simulation equipment system time module recorded the satellite time. This process is repeated to achieve unified space-to-ground time.

2. The method for evaluating inter-satellite cross-reference indices of formation satellites according to claim 1, characterized in that, the simulation step size of each ground simulation system does not exceed a preset duration.

3. The method for evaluating inter-satellite cross-reference indices of formation satellites according to claim 1, characterized in that, The two sets of ground simulation systems use the same time source for external synchronization.

4. The method for evaluating inter-satellite cross-reference indices of formation satellites according to claim 1, characterized in that, Because the received control satellite time T contains a microsecond value. To ensure synchronization, timing is assessed and processed on the ground simulation system as follows: 1) setting a task completion time reference a for the simulation step size of the ground simulation system; 2) When the second pulse arrives, the satellite time microsecond of the ground simulation system is... The microsecond value of the satellite time in the ground simulation system, expressed in seconds with the simulation step size, is t_1, and the actual running time of the ground simulation system task is t_2. 3) When the second pulse arrives, the simulation task has run for t_2 > a, meaning the simulation task has finished. Record the time and set it at t_m = +10-t_1 is used for simulation synchronization; 4) when the second pulse arrives, if the running time of the simulation task is t_2 < a, that is, the simulation task is not completed, the time is recorded and simulation synchronization is performed at t_n = T + 20 - t_1; 5) synchronization and time calibration are performed in each GNSS time calibration period to ensure the time synchronization of ground simulation data.

5. The method for evaluating the mutual pointing index between formation flying satellites according to claim 1, characterized in that: The host computer selects the start time in the ground simulation system, queries the orbital data in the ground simulation system, and compares and aligns the orbital position information of the two satellites according to the time-scale information in the ground simulation system to obtain a set of J2000 inertial coordinate system satellite position vector data with consistent time-scales. ; The relative position in the orbital system is calculated by transforming the relationship. ; Includes satellite three-axis position vector information, with the X-axis position vector information being... The Y-axis position vector information is The Z-axis position vector information is ; By relative position in the orbital system The relative pointing pitch angle can be calculated using the following formula. and relative pointing yaw angle : 。 6. The method for evaluating inter-satellite cross-reference indices of formation satellites according to claim 5, characterized in that, Satellite position vector data Includes satellite three-axis position vector information, with the X-axis position vector information being... The Y-axis position vector information is The z-axis position vector information is The formula for calculating the position vector is as follows: （1） in The position of the target star along the X-axis in the J2000 inertial coordinate system. This represents the position of the local star along the X-axis in the J2000 inertial coordinate system, where... The position of the target star along the Y-axis in the J2000 inertial coordinate system. This represents the position of the local star along the Y-axis in the J2000 inertial coordinate system, where... The target star's position along the Z-axis in the J2000 inertial coordinate system. This indicates the position of this star along the Z-axis in the J2000 inertial coordinate system.

7. The method for evaluating inter-satellite cross-reference indices of formation satellites according to claim 5, characterized in that, Relative position in orbital system Includes satellite three-axis position vector information, with the X-axis position vector information being... The Y-axis position vector information is The Z-axis position vector information is The formula for calculating the relative position is as follows: （2） （3） in This is the transformation matrix from the J2000 inertial coordinate system to the orbital system.

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