Research On Pod Improvement Of Navigation Satellites Augmented By On-board Accelerometer

Due to the affection of various perturbations,the orbit of artifical satellite is not the ideal Keplerian orbit.The perturbation can be divided into two parts:conservative force and non-conservative force.Solar radiation pressure is the largest non-conservative force suffered by the navigation satellite.However,It is difficult to model it accurately due to various factors,which directly affects the quality and performance of the Global Navigation Satellite System.What’s more,there is not a SRP model suit for all GNSS systems.And high-precision navigation satellite orbit information is the premise and foundation of various GNSS applications.The satellite-borne accelerometer to sense the non-conservative forces directly is of practical significance for improving the service performance of navigation satellites.In recent years,a large number of low-orbit satellites launched have equipped with spaceborne GPS receivers to provide precise orbit information.Compared with low-orbit satellite dynamics and reduced dynamic orbits,precise kinematic orbits only use GPS geometric distance observations to achieve precise orbit determination of LEO satellites,and do not contain a priori gravity field and force model information.However,the precision kinematic orbit will inevitably involve the problem of fixed ambiguity,which leads to the correlation between the epochs of the solution of the orbit;and the velocity and acceleration information cannot be directly solved.The dynamic method and reduced dynamic method are more or less affected by the a priori gravity field and the mechanical model,which attribute to that the precise orbits will contain the a priori gravity field information including the efficiency.If it is applied to the pure satellite gravity field determination procedure,it will cause"pollution"in the final POD.The GPS phase direct differential method does not require a fixed ambiguity,which weakens the influence of the correlation between orbit epochs,respect to the kinematic orbit difference method and provides high-precision velocity and acceleration information for Gravity Field Model Determination.The main research contents are as follows:(1)the main modeling methods of SRP have been summarized and studied,and the research background of three types of modeling methods,and introduced the specific model details of three types of SRP models have been elaborated.The advantages and disadvantages of the analytical model,the empirical model and the semi-analytical/semi-empirical model,as well as the applicable conditions have been described.(2)The mathematical model of satellite precise orbit dynamics method has been introduced in detail,the main force model,motion equation and observation equation are given,and the solution of the variational equation have been mainly investigated.(3)Using the L1B data of GRACE Follow-On from DOY 305 to 314 in 2018,CODE precise ephemeris and 5 s clock corrections,the results have shown that when the length of the differentiator was set to 9 points,the 3D velocity rms of satellite C and D are up to 0.2276 mm/s and 0.2384 mm/s(differentiator interval=60 s);the acceleration 3D rms of satellite C and D is Respectively up to 4.1μm/s~2and 4.5μm/s~2(differentiator interval=90 s)compared to the precise reduced-dynamic orbits provided by JPL.(4)The basic parameters and characteristics of the accelerometer currently loaded on the artificial satellite have been introduced,and the performance requirements of the spaceborne accelerometer required on the navigation satellite,mainly including the measurement range and resolution have also been discussed.Based on accelerometers with five different accuracies from A to E,the satellite IGS precision ephemeris and known tracking station positions have been used to simulate GPS satellite precise orbit determination.The results show that the on-board accelerometer directly measures the non-conservative will help precision orbit determination of GNSS system.As the accuracy of the accelerometer improves,the calibrated accelerometer parameters gradually approach the"true value"and the error decreases.The accelerometer-augmented GNSS POD accuracy in schemes C～D is equivalent to using the ECOM 9parameter model,and the Accelerometers whose accuracy are better than 1×10"m/s~#are suitable for POD of GNSS.Moreover,the navigation satellites based on spaceborne accelerometer have some advantages in inversion of low-order gravity field coefficients,which verifies the correctness and effectiveness of spaceborne accelerometer in enhancing navigation satellites’service performance.