Micro-vibration Disturbances Research Articles

A Method for micro-vibration test analysis of small satellites with laser loading

Based on the parameters of the structure configuration and equipment layout of a small laser satellite in the design stage, the in-orbit micro-vibration simulation analysis of the satellite is carried out by finite element method, which mainly includes [1-2]: 1) modal analysis obtaining the main vibration frequency and modal shape of the satellite in orbit; 2) micro-vibration analysis of the satellite in orbit with the micro-vibration disturbance of the moment gyroscope as the excitation condition. Through the in-orbit micro-vibration simulation analysis of the satellite, we can obtain the vibration transmission relationship from the moment gyroscope to the laser communication load and the micro-vibration state of the laser communication load.

Modeling and analysis of the influence caused by micro-vibration on satellite attitude control system

A closed-loop integrated model including micro-vibration disturbance, dynamic characteristics of satellite, optical system of star sensor and attitude control algorithm is established. The control torque error caused by additional disturbance torque and the star sensor imaging error caused by structural resonance is fully integrated analyzed, which are firstly presented into the attitude control system (ACS). Steady-state and transient response analyses are completed to evaluate the impact of such two errors on performances of (ACS). Steady-state response results show that the effect of control torque error appears in lower frequency band with a peak of 6.784E-8″ at 53 Hz, while influence of star sensor imaging error on attitude determination mainly concentrates in high frequency band with maximum response of 0.4101″ at 315 Hz. Transient response results show that the two errors will not significantly affect control indicators such as rise time, overshoot and peak time. The results indicate that the influence of star sensor imaging error is non-negligible for satellite ACS which required milli-arc-second attitude control accuracy. According to the analytical results, traditional analysis only on payload optical axis cannot reveal the whole impact of micro vibration on LOS error, the two errors of micro-vibration introduced to ACS in this work must be considered for the development of spacecraft with 0.1″ pointing accuracy.

Microvibration simulation of reaction wheel ball bearings

Microvibrations on board satellites are a well-known problem affecting their pointing accuracy by inducing oscillations to the line-of-sight. Fast rotating devices, such as reaction wheel assemblies (RWAs) are a major cause of these onboard mechanical disturbances. Imbalances in the flywheel, as well as imperfections in the ball-bearing components yield low-amplitude vibrations that are transmitted to the satellite structure, adversely affecting the performance of sensitive onboard instruments. This research focuses on the RWA’s ball bearing microvibration frequency and amplitude characterization. This is achieved by introducing specific geometry imperfections on the ball bearing rotating elements. In addition, variables such as the ball bearing preload, the number of balls and their dimensions are altered to understand how the bearing microvibration changes in order to minimize it. Finally, available physical microvibration test data is used to compare and cross-correlate the microvibration waterfall plots obtained from the transient FEA of the parametrized bearing models introduced herein. This work provides a better understanding of the relation between the main structural ball bearing parameters and the microvibration disturbances emitted by the RWA to minimize its mechanical noise.

A Reliable Anti-Interference Temperature Sensor Based on a Four-Hole Microstructure Optical Fiber Mach–Zehnder Interferometer

In this paper, an in-line Mach-Zehnder interferometer (ILMZI)-based temperature sensor of a sandwich-like composite structure was proposed and experimentally demonstrated. Using simple cleaving and splicing operations, ILMZI was formed by compactly sandwiching a section of four-hole microstructure optical fiber (FHMF) of ultra-short length between two segments of multi-mode fibers and single-mode fibers in turn. Thanks to the large thermo-optic coefficient difference between the silica and air modes in FHMF, the sensor achieves a comparable sensitivity of 67.29 pm/°C over a wide dynamic range of 20.8-100.4 °C. Because the sensing area length is only a few hundred microns, the long-term stability and anti-interference of the sensor is greatly enhanced. In addition, the large airhole design confines the propagation mode in silica medium by total internal reflection, reducing the interaction between the liquid sample and the sensing element, making the sensor inert to the ambient refractive index. The maximum response deviation of the sensor under micro-vibration disturbances is 3.51×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> nm/°C, and the maximum cross-sensitivity under strain disturbances is only 0.0018 °C/με. The proposed sensor is excellent in performance, easy in fabrication, simple in structure and low in cost, which can be expected to be used in practical temperature sensing applications without any additional packaging.

Research on isolation method of spacecraft reaction wheels using electromagnetic shunt damping

The spacecraft flywheel system is widely used in various space missions due to its cleanliness, high reliability and high control accuracy, such as spacecraft attitude control and large-angle turning maneuvers. However, current research agrees that the high-speed rotating flywheel system is one of the main sources of micro-vibration disturbances on spacecraft. In view of the variable speed characteristics of the flywheel, this paper proposes a new vibration isolation system based on Stewart vibration isolation platform and electromagnetic shunt damping (EMSD). Attempts to connect three circuits of pure resistance circuit, resistance-inductance circuit and resistance-inductance-capacitor circuit to the new vibration isolation system in order to improve the isolation performance. Through theoretical analysis and numerical simulation, the effect of circuit parameters on isolation performance of each circuit are studied. The results show that EMSD can significantly reduce the disturbance input of the flywheel, and frequency modulation can be achieved through the conversion circuit to avoid resonance.

Millimetron microvibration analysis at low frequency range

This paper presents the results of Millimetron microvibration analysis at low frequencies. Millimetron telescope structure behavior was studied in order to predict its central mirror response from microvibration disturbance caused by mechanical cryocoolers. The results contain the most significant values of acceleration which appeared on the mirror surface as well as rotational deflections which affect the telescope optical axis stability. To make it possible the microvibration analysis technique was derived from the theoretical aspects and other researches results. This technique was adapted to Millimetron microvibration analysis using its finite-element model and taking into account several assumptions which were also discussed at this paper.

Performance Enhancement of Spaceborne Cooler Passive Launch and On-Orbit Vibration Isolation System

A spaceborne cryogenic cooler induces undesirable microvibration disturbances during its on-orbit operation, which is one of the main sources that degrades the image quality of submeter-level high-resolution observation satellites. Several types of vibration isolation systems based on passive approaches have been developed for reducing the microvibration of the cooler. A coil-spring-type passive vibration isolation system developed in a previous study has shown excellent performance in both launch vibration and on-orbit microvibration isolation. To improve the capability of the conventional cooler isolator, including the position sensitivity and launch vibration reduction, we propose a new version of a dual coil-spring-type passive vibration isolator system. The effectiveness of the newly proposed design was validated through a microjitter measurement test, position sensitivity test, and qualification-level launch vibration test of the isolator.

Managing the microvibration impact on satellite performances

Due to the increasing needs on the performance of satellites, in particular optical satellites, microvibrations have become more and more important over the last years.Microvibrations affect a large number of satellites for both Earth observation and space observation missions. Further, microvibrations are also a concern for other missions with sensitive instruments like Fourier spectrometers, high-precision accelerometers or reference oscillators.In classical fields like structural dynamic engineering, management approaches have been established and implemented in all space projects. This paper presents a corresponding approach for the area of microvibrations. Focus is on the definition of all key elements needed to establish a microvibration control approach. This includes the establishment of microvibration budgets and associated summation rules. A systematic way for microvibration disturbance minimization is presented and rules for the application are defined. Specific emphasis is given to the definition of microvibration interface requirements and the associated control process.The concepts provided in this paper have been verified by tests performed in the frame of various satellite programs and studies. Tests related to the superposition of different noise sources are presented in here.

Microvibration isolation by adaptive feedforward control with asymmetric hysteresis compensation

Abstract This paper proposes an improved adaptive filtered-x normalized least-mean-square (FxNLMS) algorithm to achieve active microvibration isolation. Physically, microvibration disturbance is attenuated by a custom-developed magnetostrictive-actuated device. Whereas, magnetostrictive materials characterize hysteresis. Particularly, when the amplitude of the input current is large, the hysteresis loop describes strong asymmetry and nonlinearity. To avoid this phenomenon, in some studies, the actuators are limited to move over a small range, and thus the potential range of the isolated microvibration is restrictive. Then Jiles-Atherton model and Bouc-Wen model are utilized to compensate hysteresis, however these models are non-analytical with certain approximation. In order to compensate hysteresis more accurately, Preisach model, a popular operator-based model, is presented. However, due to the double integrals in this model, the hysteresis identification and inversion process is complicated. Therefore, we reduce hysteresis based on a modified Prandtl-Ishlinskii (PI) model which is more simple but effective. This model utilizes the polynomial operators to describe hysteresis asymmetry and nonlinearity. The inverse hysteresis is then applied to compensate the magnetostrictive-induced hysteresis and to alleviate microvibration combining with the conventional FxNLMS algorithm. An experimental setup is fabricated and some experimental investigations are conducted. Experimental results show that the improved FxNLMS algorithm enhances the performance of microvibration isolation effectively—in the presence of single-tone (4 Hz at amplitude of 250 μm) and double tone (2 Hz mixed with 6 Hz at amplitude of 250 μm) excited microvibration, the isolation ratios of the improved FxNLMS controller are 20.79 dB and 15.32 dB respectively, while those of the conventional FxNLMS controller are 13.83 dB and 10.65 dB respectively.

Numerical Feasibility Study for a Spaceborne Cooler Dual-function Energy Harvesting System

Spaceborne cryocoolers produce undesirable micro-vibration disturbances during their on-orbit operation, which are a primary source of image-quality degradation for high-resolution observation satellites. Therefore, to comply with the strict mission requirement of high-quality image acquisition, micro-vibration disturbances induced by cooler operation have always been subjected to an isolation objective. However, in this study, we focused on the applicability of energy harvesting technology to generate electrical energy from micro-vibration energy of the cooler and investigated the feasibility of utilizing harvested energy as a power source to operate low-power-consumption devices such as micro-electromechanical system (MEMS) devices. A tuned mass damper (TMD)-type electromagnetic energy harvester combined with a conventional passive vibration isolator was proposed to achieve this objective. The system performs the dual functions of electrical energy generation and micro-vibration isolation. The effectiveness of the strategy was evaluated through numerical simulations.

Modeling and analysis of a viscoelastic micro-vibration isolation and mitigation platform for spacecraft

A new viscoelastic micro-vibration isolation and mitigation platform is proposed to reduce disturbances generated by flywheels on board spacecraft. Firstly, property tests on the high-damping viscoelastic material used in the micro-vibration isolation and mitigation element are conducted. Experimental results show that the developed viscoelastic material has better energy dissipation capability under micro-vibration conditions. A mathematic model is employed to describe the dynamic properties of the high-damping viscoelastic material and is used to model the isolation and mitigation element. Secondly, a viscoelastic micro-vibration isolation and mitigation platform, which consists of four elements, is proposed and the analytical model of the coupled system that consists of the platform with flywheel is established. Finally, the isolation and mitigation performances of this micro-vibration isolation and mitigation platform are analyzed and discussed. The results show that the isolation and mitigation platform can effectively reduce the micro-vibration disturbances induced by the flywheel.

Innovative viscoelastic material selection strategy based on dma and mini-shaker tests for spacecraft applications

With the increase of payload sensitivity (such as high precision optics for sub-metric imager), micro-vibration disturbances generated by spinning actuators, if not controlled, may affect on-board instruments and may worsen the quality of pictures taken by an Earth observation imager. For the last two decades, viscoelastic materials have been gradually used in isolators designed for space applications. Their attractiveness comes from their ability to act as a second order low pass filter to minimise micro-vibration forces. In this study, an innovative viscoelastic material pre-selection process has been developed to assess the mechanical and thermal properties of viscoelastic isolators during early design stages. In order to characterise the viscoelastic isolators, tests have been performed at viscoelastic material level (material characterisation) and at viscoelastic isolator level (isolator characterisation). A qualitative correlation has been established between the master curves (material characterisation) and the transmissibility curves (isolator characterisation) which leads to a possible prediction of expected isolation performances of a viscoelastic material during early design stages.

블레이드 기어를 적용한 2축 짐발 구동 안테나의 미소진동 절연성능

ABSTRACT A 2-axis gimbal-type X-band antenna has been widely used to effectively transmit the high reso-lution image data from the observation satellite to the desired ground station. However, a dis-continuous stepper motor activation for rotating the pointing mechanism in azimuth and elevation di-rections induces undesirable micro-vibration disturbances which can result in the image quality degra-dation of a high-resolution observation satellite. To enhance the image quality of the observation sat-ellite, attenuating the micro-vibration induced by an activation of the stepper motor for rotational movements of the antenna is important task. In this study, we proposed a low-rotational-stiffness blade gear applied to the output shaft of the stepper motor to obtain the micro-vibration isolation performance. The design of the blade gear was performed through the structure analysis such that this gear is satisfied with the margin of safety rule under the derived torque budget. In addition, the micro-vibration isolation performance of the blade gear was verified through the micro-vibration measurement test using the dedicated micro-vibration measurement device proposed in this study.

소형 위성 영상안정화를 위한 능동형 광학 보정장치 설계

This paper describes the design of the active optical compensation movements(at focal plane, secondary mirror) for the image stabilization of a small satellite camera. The movements can correct optical misalignment on-line and directly compensate vibration disturbances in the focal plane. Since the devices are installed inside the space camera, it has an remarkable advantage to deal with the structural deformation of a space camera effectively. In this paper, the requirements of the active optical compensation movements for 1m GSD small satellite camera have been analyzed. Based on the established requirements, the design of the active compensation movements have been conducted. The designed active optical compensation system can control 5 axes movements independently to compensate micro-vibration disturbances in the focal plane and to refocus the optical misaligned satellite camera.

Receptivity of plane Poiseuille flow to local micro-vibration disturbance on wall

The receptivity of plane Poiseuille flow to local single-period micro-vibration disturbances with different phases at the top and bottom walls was investigated through direct numerical simulation of three-dimensional incompressible Navier-Stokes equations. Results show that the disturbance presents a symmetrical distribution in the spanwise direction when the micro-vibration on the wall ends, and the initial disturbance velocities and spatial distribution of the disturbance structure are different at the top and bottom walls. The disturbance's velocity, amplitude, and high- and low-speed streaks increase with time, and the amplitude of streamwise disturbance velocity is larger than those of spanwise and vertical disturbance velocities. However, no significant Tollmien-Schlichting wave was found in the flow field. The number of disturbance vortex cores gradually increases with the disturbance area. High-speed disturbance fluid concentrates near the wall and its normal velocity largely points to the wall, while low-speed disturbance fluid largely deviates from the wall. Furthermore, the streamwise velocity profiles near the top and bottom walls both become plump because of the existence of the disturbances, and the streamwise velocity profiles show a trend of evolving into turbulent velocity profiles. The shear stress near the wall increases significantly. The local micro-vibration disturbance on the wall in plane Poiseuille flow can induce the development of a structure similar to turbulent spots.

SMA 메쉬 와셔를 적용한 우주용 냉각기 수동형 진동절연기의 궤도 미소진동 절연성능 검증

Pulse tube-type spaceborne cryocooler is widely used to cool down the infrared sensor of observation satellites. However, such cryocooler also generates micro-vibration which is the one of main sources to seriously affect the image quality during its on-orbit operation. Therefore, to comply with the mission requirement of high resolution observation satellite, additional technical efforts have been required. In this study, we proposed a spaceborne cryocooler passive vibration isolator using SMA mesh washer, which guarantees the structural safety of both the micro-vibration disturbance source and itself under harsh launch vibration loads without an additional holding mechanism and the micro-vibration isolation performance on orbit environment. To verify the micro-vibration isolation performance of the proposed vibration isolator, we performed the micro-vibration isolation measurement test using the dedicated micro-vibration measurement device proposed in this study.

Performance evaluation of spaceborne cryocooler micro-vibration isolation system employing pseudoelastic SMA mesh washer

A spaceborne cryocooler produces undesirable micro-vibration disturbances during its on-orbit operation, which is one of the main sources of degradation of the image quality of high-resolution observation satellites. Therefore, to comply with the strict mission requirement for the acquisition of high-quality images, micro-vibration disturbances induced by cryocooler operation need to be isolated. In this study, we proposed a spaceborne cryocooler micro-vibration isolator that employs a pseudoelastic shape memory alloy (SMA) mesh washer, which guarantees vibration isolation performance in a severe launch vibration environment while effectively isolating the micro-vibrations from the cryocooler on-orbit. Basic characteristics of the cryocooler assembly integrated with the proposed isolators were measured through static tests and free vibration tests. The effectiveness of the isolator design was demonstrated by the micro-vibration measurement tests under qualification temperature limits.

Micro-vibration model and parameter estimation method of a reaction wheel assembly

Abstract Reaction wheel assemblies (RWAs) are a source of disturbance in satellites, and they are regarded as the largest jitter contributor in optical payloads. In order to ensure a stringent jitter requirement, the wheel disturbance effects on spacecraft should be predicted precisely prior to launch through analytical or experimental approaches. For this purpose, the wheel disturbance should be identified and modeled accurately. In the present study, a micro-vibration model of the RWA is introduced through coupling an analytical wheel model and an empirical disturbance model; furthermore, a parameter estimation process of the coupled model from the micro-vibration disturbance data is proposed. In order to verify the modeling and estimation techniques, a micro-vibration model of a numerical RWA is established and its estimation error is validated. Then, the micro-vibration model is extended to consider an axial disturbance and a measurement offset effect. Finally, the micro-vibration model is applied to a commercial RWA and the model parameters are extracted from the disturbance test data of the RWA using the parameter estimation process. The analytical and experimental results demonstrate that the proposed micro-vibration model and parameter estimation process are effective in the dynamic disturbance modeling of RWAs.

Parameter Identification of Reaction Wheel Disturbance Model Based WLS-SVR Method

In order to predict the micro-vibration disturbance of reaction wheel, an improved experience model has been provided, which expresses the effect of the reaction wheels natural frequencies being the dominating factor in amplifying the disturbance. WLS-SVR algorithm is applied to identify the parameters of this model. The robust characteristic of this algorithm promises the global optimal estimation can be achieved. Experiment has been set up to measure the disturbance of the reaction wheel. Data achieved from the experiment are used to get the parameters of model and verify the identification results of WLS-SVR algorithm. The results show the improved model describes the properties of disturbance more precisely and the WLS-SVR algorithm can achieve accurately identification results.

스텝핑 모터 특성에 따른 2축 짐발 안테나 시스템의 미소진동 측정 시험

A 2-axis gimbal system is one of main disturbance sources affecting image jitter response of a satellite. The gimbal system comprises azimuth stage and elevation stage, and these pointing mechanism can be rotated by stepping motors about its azimuth and elevation axes simultaneously. Because of the complex and coupled dynamic motion of the gimbal system, its moment of inertia and structural modes can be changed according to the system configuration, and thus the gimbal system generates complicated and non-linear disturbance characteristics. In order to improve the jitter response of a spacecraft, it is an indispensable process to reduce the micro-vibration disturbance level of the antenna system. In the present research, a 2-axis gimbal system was manufactured and then its micro-vibration test was performed in terms of two types of stepping motors(2-phase and 5-phase). The test results show that the disturbance level of the gimbal system can be reduced by replacing the 2-phase stepping motor with the 5-phase one, and the average disturbance attenuation ratio is 56 % in peak level and 48 % in standard deviation level. The experimental results confirm that it is an efficient jitter reduction method to adopt a high-phase stepping motor.