GB/T 47584-2026On-orbit modal parameter measurement and identification method for large flexible structures of space stations (English PDF)

6.2 Sensors

6.2.1 Performance Requirements The sensor performance requirements are as follows:

a) The frequency response range covers the frequency range of the flexible structure under test. For the space station's solar panels, the sensor's frequency response... The range should cover

0 Hz to

b) The sampling frequency should generally be 5 to 10 times the upper limit of the vibration frequency to be measured of the flexible structure under test, preferably 10 times.

c) The signal-to-noise ratio of the measurement data should meet the accuracy requirements for modal parameter identification of the space station, and should preferably be greater than 10.

d) The sensor installed on the flexible structure being tested should be small in size and light in weight.

e) Measurement error over the entire temperature range in orbit. 1) The displacement sensor is better than 2 mm; 2) The accelerometer is better than 2×10^-3 m/s^2; 3) The angular velocity sensor is better than 1×10-3 °/s.

6.2.2 Layout Requirements Simulations were conducted to predict the dynamics of the large flexible structure under test on the space station, and the simulation results were used to guide the selection and placement of sensors. The sensor placement requirements are as follows:

a) The excitation response measurement data at the sensor measurement point should have a high signal-to-noise ratio, preferably greater than 10.

b) The number of sensor measurement points should be sufficient to meet the requirements for mode shape identification; generally, an optical camera is selected. The optical camera should be able to... Effective observation of the area/point to be measured in the flexible structure.

c) Meet the space station's installation constraints for measurement sensors.

6.3 Information Processing Unit The information processing unit has the following requirements.

a) Processor. Clock speed not less than 50 MHz, 64-bit clock/counter, continuous timing capability greater than 30 days, meeting high-speed data acquisition requirements; Requirements for storage, transmission, and clock synchronization.

b) Data storage. This includes the amount of data per frame from the measurement sensor, sampling frequency, acquisition duration of a single test, and data transmission after multiple tests. Related to parameters such as cycle time. The space station's on-orbit measurement and identification mission requires an effective storage capacity of no less than 58 GB, optical... The camera storage area should be no less than 56 GB, and the accelerometer storage area should be no less than 2 GB.

8.2 Incentive Requirements

8.2.1 Incentive Position Requirements Under active excitation, the excitation location should be selected to excite the main modes of the flexible structure and to ensure engineering feasibility.

8.2.2 Incentive Method Requirements Prioritize the use of attitude control and orbit control thrusters, control torque gyroscopes, and flexible structure drive mechanisms from the space station to control the measured flexibility. The structure implements active stimulation. When active stimulation is inconvenient, the space station's orbital control, attitude control, and docking maneuvers can be utilized. Passive incentives are implemented through actions such as striking.

8.2.3 Requirements for Active Excitation Signals The requirements for active excitation signals are as follows:

a) Fully stimulate the dynamic motion of the flexible structure under test; the signal-to-noise ratio of the excitation response measurement data should be greater than 10 to meet the requirements of the space station in orbit. Identify the minimum requirements for the intensity of the vibration response signal;

b) The mechanical load on the flexible structure of the space station caused by the excitation should not exceed the design constraints of the flexible structure, and the load generated at the root of the solar panels should be within acceptable limits. The acceleration is no greater than 0.01g and the torque is no greater than 350 N·m, which meets the safety constraints of the space station's solar array structure.

c) The maximum attitude angle does not exceed 30° and the maximum angular velocity does not exceed 0.3°/s, satisfying the attitude safety constraints of the space station;

d) The excitation torque of the control torque gyroscope is no greater than.200 N·m, which satisfies the output capability constraint of the active excitation actuator.

8.3 Data Acquisition Duration Requirements The effective duration of a single data acquisition, from the start of excitation to the end of identifiable measurement data, should meet the modal... The parameter identification accuracy requires a minimum duration for experimental data processing. This duration is determined through theoretical analysis and mathematical simulation.

8.4 On-orbit identification window requirements The time window requirements for on-orbit identification are as follows:

a) The lighting conditions of the track meet the imaging requirements of the optical camera;

b) The ambient temperature conditions meet the operating temperature requirements of each measuring sensor;

c) The measurement, control, and lighting conditions can meet the minimum time requirement for a single on-orbit identification test;

d) Meet the space station's constraints on energy and thermal control subsystems.

8.5 Predictive Prediction of Identification Accuracy Before Experiment Before the experiment, a simulation to predict the accuracy of the identification should be conducted, with the following requirements.

9.2 Proactive Motivation

9.2.1 Preparations before incentives The following are the preparation requirements before proactively motivating others.

a) The control subsystem should ensure the attitude stability of the space station and maintain the angular momentum of the control moment gyroscope group within a reasonable range. The space station is in an experimental attitude, and the large flexible structure under test is in the configuration to be tested. Various subsystems of the space station related to the on-orbit identification experiment... The system is functioning normally.

b) The proposed active excitation signal should be verified and confirmed by the mechanical safety constraints of the space station.

c) To address potential issues during the test, such as attitude angle deviations, attitude angular velocity deviations, and solar array root acceleration deviations. Contingency plan preparation.

9.2.2 Incentive Process The incentive process requires the following.

a) The selected excitation signal can be excited by excitation actuators such as thrusters, control torque gyroscopes, and flexible structure drive mechanisms. The excitation output and excitation signal should meet the actual capabilities of the selected actuator to ensure system safety. (b) Necessary measures should be taken to ensure that the entire incentive process is under control and should not jeopardize the safety of the space station.

9.2.3 Recovery after excitation After each on-orbit identification test data collection is completed, the control system should restore the space station's attitude angles and attitude angular velocities to the expected mission parameters. Within the specified requirements, ensure the safety of the space station's attitude.

9.2.4 Data Acquisition On-orbit identification test data acquisition includes the acquisition of excitation input and output data. The data acquisition period should include the excitation process and the excitation... Data collection of free response after the excitation ends.

9.2.5 Ground monitoring and processing Throughout the active stimulus identification test, ground control should closely monitor the on-orbit test status, promptly and accurately interpret the data, and detect any abnormalities or malfunctions. Address any issues promptly after they arise.

9.3 Passive Incentives The requirements for passive excitation process control are as follows:

a) Utilizing the impact of the space thermal environment, space station attitude and orbital maneuvers, docking impact of visiting spacecraft, fixed angle servoing of solar arrays, and large... On-orbit flexibility measurement and identification are performed based on the excitation effects generated by the conventional on-orbit motion of the flexible structure.

b) Before passive excitation begins, after confirming the sensor's normal operating status using telemetry data, prepare to start data acquisition until passive excitation begins. Data collection stops after the valid duration of a single identification cycle ends. All collected sensor data is completely transmitted to the ground. The identification and analysis were carried out on the surface.

9.4 Handling Abnormal Situations During active excitation, if the space station's attitude angle, angular velocity, or flexible structural mechanical load exceeds the safety threshold, or if excitation failure occurs... In the event of a malfunction in the flight mechanism or a serious failure in the attitude sensor, excitation should be terminated immediately, and the space station should be switched to safety protection mode as soon as possible to ensure the safety of the space station. Normal posture is safe.

10.2 Data Preprocessing

10.2.1 Time Synchronization Processing By aligning the time stamps of the sensor measurement data, time synchronization of the measurement data from each sensor is achieved. The synchronization error should be better than [specific value missing]. 20 ms, to meet the time synchronization accuracy requirements for on-orbit identification of the space station.

10.2.2 Other Data Preprocessing The raw sensor measurement data is preprocessed by filtering, removing outliers, detrending, and interpolation, as follows:

a) Data filtering. Implemented using digital filters. If a low-pass filter is used, the filter cutoff bandwidth should be greater than the target resolution. The highest frequency of the dominant mode, and less than half the data sampling frequency; if a bandpass filter is used, the filter passband width should cover The frequency range of the flexible modes is to be identified.

b) Outlier data removal. This is determined by comparing the variation between the current value and neighboring values. When the absolute value of the variation exceeds three times the sensor measurement... When measuring mean squared error, the current value can be treated as an outlier and removed, and then supplemented by interpolation.

c) Data detrending. Remove constant biases and linear biases present in the measurement data.

d) Data interpolation. Outliers or missing values in the measurement data can be filled in using polynomial interpolation.

10.3 Identification Method

10.3.1 General Requirements Using the input and output data of the flexible structure's vibration, or only using the output data, to identify the structure's modal parameters is generally possible. Modal parameter identification was performed using two types of identification methods. frequency domain analysis and time domain analysis. This method is suitable for identifying the time-varying modal characteristics of flexible structures. In cases of nonlinearity, appropriate identification methods should be adopted based on the specific characteristics. For flexible structures that can be described by linear time-invariant models, the Fast Fourier Transform (FFT) method and the characteristic system implementation method are preferred. (ERA) to conduct modal parameter identification.

10.3.2 Fast Fourier Transform (FFT) Method The modal frequencies can be identified using the Fast Fourier Transform method, as follows:

a) Obtain the discrete spectrum corresponding to the processed discrete sampling signal sequence of the flexible measurement based on the Fast Fourier Transform. For the amplitude-frequency curve of the discrete spectrum, the frequency point corresponding to the peak value of the amplitude-frequency curve where the amplitude is significantly greater than the noise floor is selected as the flexible structure. The initial selected mode frequencies;

b) The final confirmation of the initially selected modal frequencies should take into account the dynamic characteristics of the object being identified, the sensor response characteristics, the test environment, and other factors. A reasonable judgment.

10.3.3 Feature System Implementation Method (ERA) The displacement, acceleration, and angular velocity measurement curves at various measuring points caused by the modal motion of the large flexible structure are all... It can reflect the vibration frequency of each mode and its damping attenuation characteristics. The characteristic system realization method (ERA) is used to identify the natural frequencies, modal damping, and mode shapes of the modes, as follows:

a) Using the preprocessed displacement measurement data, acceleration measurement data, and angular velocity measurement data, construct the corresponding... The Hankel matrices H(0) and H(1) are given in formulas (1) and (2).

11 Evaluation of the effectiveness of identification results The effectiveness of on-orbit identification results can be evaluated by the prediction accuracy based on the identification model or the effect of third-party applications.

a) Validity of modal parameter identification results theta (including natural frequencies, modal damping, and mode shapes) based on the prediction accuracy of the identification model. The evaluation criteria are as follows:

b) Third-party application effect evaluation. By applying the identification results to specific applications such as dynamic model correction and control parameter optimization, and evaluating... The effectiveness of the identification results is evaluated based on the results achieved by the application. The on-orbit test modal identification results, which have been evaluated and confirmed, can serve as the basis for subsequent design optimization.