On-Orbit Measurement and Analysis of the Micro-vibration in a Remote-Sensing Satellite
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With the improvement of the image resolution produced by remote-sensing satellites, the cameras onboard are increasingly sensitive to the micro-vibration caused by the moving parts of the satellite buses. The disturbance measurement in ground tests is often with low confidence, since the dynamic characteristics of the moving parts as well as the satellite structure are strongly influenced by many environmental factors which are quite different in space, such as atmosphere pressure, air damping or acoustic transmission. Therefore, on-orbit micro-vibration measurement is an important way to learn the characteristics of the disturbing source and the micro-vibration transmission along with the satellite structure in vacuum and weightless environment. In the present study, the on-orbit micro-vibration measurement system onboard a remote-sensing satellite is introduced. The measured data are analysed in three aspects of background noise level, disturbance source characteristics, and satellite structure transmission characteristics. From the measured data, it is found that local vibration caused by control moment gyro (CMG) and momentum wheels have the highest level, while the vibration transmitted to the payload is mainly caused by CMG and two-axis antenna. The response at the payload interface is much lower than the disturbance source interface, which means that the vibration level is attenuated largely by the satellite structure.
KeywordsRemote-sensing satellite Micro-vibration On-orbit measurement Data analysis
Micro-vibration induced by the moving parts onboard spacecraft may affect the pointing stability and imaging quality of sensitive payload. With the improvement of the image resolution produced by remote-sensing satellites, the cameras onboard are increasingly sensitive to the micro-vibration caused by the moving parts of the satellite bus. Attenuation of micro-vibration became a necessary progress to ensure the image resolution [1, 2]. Nevertheless, evaluation of the satellite bus micro-vibration is the foundation for micro-vibration attenuation and improvement of image quality.
Evaluation of micro-vibration through mechanical analysing or ground test has run into many difficulties. Application of FEM in micro-vibration analyse is limited due to large error in middle-high frequency band, with difficulty in describing the structure uncertainty induced by micro-deformation and lacking evidence for structure parameters with micro-deformation, etc. [3, 4]. The ground test needs to make up for the test error resulting from different environments between ground and onboard: different boundary conditions, different mounting status of flexible accessories, structure dynamic bias induced by gravity, air damping, etc.
Evaluating the micro-vibration level at the spacecraft structure using on-orbit micro-vibration measurement unit (OMMU) is the most direct and accurate way. NASA has measured the on-orbit micro-vibration for many times from 1970s, along with the development of OMMU such as SAMS-II  and AMAMS . PAX developed by ESA were mounted on several satellites to measure the on orbit micro-vibration, and perform SPOT-4 to compare micro-vibration on earth with on orbit . There are several satellites launched with OMMU and the micro-vibration level in orbit was measured in China as well since 2011 [8, 9].
On-orbit micro-vibration measurement scheme is presented in this paper; the test data were analysed from three aspects: background noise, moving part properties, transfer characteristics of satellite structure.
2 OMMU Hardware Configuration
Data acquisition parameters
3 × 3
2.1 Transducer Allocation
Location of the micro-vibration transducers
Measure point number
Measure point location
+ Y solar array SADA holder mounting point
Service cabin top plate − Y − Z CMG mounting point
Service cabin top plate − Y + Z momentum wheel mounting point
Camera 1 bottom plate + Z near mounting point
Camera 2 side plate − Y + Z near mounting point
Antenna assembly mounting point
2.2 Measurement Cases
On-orbit measurement cases
CMG, momentum wheel, SADA, antenna working stable, camera I imaging
Camera 2 imaging, only antenna, momentum wheel and SADA work at same time
3 Data Analysis
3.1 Background Noise
3.2 Moving Part Excitation Properties
3.2.1 CMG Excitation Property
According to CMG disturbance analysis and ground tests, the rotation speed is 6000 r/min, which means the relative frequency is 100 Hz. There would be harmonic disturbance due to bearing defects at 0.6 times of the relative frequency. So the disturbance of CMG mainly composed of 60 Hz, 100 Hz, and their frequency multiplication . The frequency components tested on-orbit were similar to ground test and analysis result.
From the spectrum of CMG disturbance tested on-orbit, it can be found that the amplitude at the rotation frequency is higher than other peaks. The natural frequency of the CMG structure is 110 Hz, which indicates that the disturbance near this frequency band would be amplified. Disturbance in the high-frequency band can be attenuated by isolation, caused by structural flexibility or be amplified by coupling effect with the high-order modes. Because of the limitation of the measurement system, current data cannot cover the disturbance above 250 Hz, which is more sensitive to optical imaging payload. Therefore, it is necessary to carry on wide-band measurement.
3.2.2 Double Axis Antenna Assembly Excitation Property
3.2.3 Momentum Wheel Excitation Property
3.2.4 SADA Excitation Property
Background noise was relatively small when all the moving parts were shut down; thus, the moving part excitations were the main disturbance.
Disturbance of CMG and momentum wheel was relatively large.
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