Flywheel Jitter Modeling And Isolation Research Of Optical Remote Sensing Satellite

When the optical remote sensing satellite is working in-orbit,high-precise and stable attitude are highly required to realize the image process of desired area.However,flywheel—the attitude control components that are applied for guaranteeing the accuracy of attitude control of the whole satellite,cannot avoid microstructural errors during manufacturing,such as static,dynamic unbalances,bearing unbalances and so on.These unbalances would introduce unexpected,low-amplitude,broadband disturbing forces and torques.These disturbing forces and torques will affect the pointing-stability accuracy of the whole satellite and relative-position accuracy of the sensitive optical components,even worse,bring in distortion,degradation and blurry.To guarantee the designed in-orbit imaging indicators,researches on flywheel disturbances become very important.Based on a sub-meter satellite of ‘Jilin-01' satellite constellation,this paper carries out a series of researches on modeling of flywheel disturbances,analysis of affection brought up by flywheel disturbances,on-ground experimental jitter techniques and isolation schemes for on-board flywheel jitter problems in depth.Firstly,this paper performs deep researches on disturbing nature of flywheel.As for the angular contact bearing couple-assembling situation in flywheel,by applying the basic principles of rotor dynamics,Hertz contact theories and structural dynamic equations of bear,functional relations of disturbing amplitudes and frequencies whose variables are wheel speed,assembly stiffness and damping are promoted.Experimental tests are then completed for the disturbances,with the test data,fittings are carried out on the key parameters,and the numerical models of flywheels are constructed.Secondly,by applying integrated modeling method,the analytical model which integrates the Finite Element(FE)model of whole satellite,the optical model and control model is obtained.With this model,theoretical calculations are completed on the image motions that are caused by the flywheel at variable speeds.Combining with statistical moment method and based on the imaging principles of Time Delay and Integration Charge Coupled Devices(TDI CCD),a calculation method that transfers frequency-domain image motion induced by flywheel into average MTF is carried out.By applying the calculation method,the MTF caused by flywheel is preliminarily predicted.The analytical results indicate that the satellite is risking exceed jitter at certain wheel speeds.A high-fidelity testbed which can be applied for precise image motion measurement is designed and constructed.On the testbed,not only check tests are finished on the analytical results,but also researches on coupling characteristics between control strategy and each flywheel are carried out.According to the test results,the correctness and error characteristics of the integrated modeling method are understood and the conjecture about image motion caused by controlled flywheels equaling to linear superposition of image motions caused by each stable-working flywheel is verified.Based on the conjecture,average MTF calculations are carried out when the flywheels are controlled working in orbit.Besides,with the precise test data,a new jitter modeling method named empirical modeling method is promoted.By comparison of the integrated modeling method and empirical modeling method,the advantages and disadvantages as well as applicative occasions of each method are analyzed.The average MTF predictions that caused by flywheel disturbances of in-orbit working situations indicate that the satellite is risking jitter affection at certain wheel speed combinations and the flywheel along Y axis is the sensitive flywheel,isolation are quite necessary on it.According to vibration system with single degree of freedom,this paper analyzes the isolation principles of flywheel and camera isolations.Brief isolation mountings are carried out on the flywheel and camera.Integrated modeling analysis as well as experimental test is completed on different isolation schemes.By isolation efficiency analysis of each isolation scheme,the final decision is made on the isolator choice.Reasonability checks are finally completed on the isolation scheme.The check results indicate that the isolation is effective within all kinds of requirements.