The physical investigations on the accuracy improvement to the measurement of the Earth's gravity field recovery are carried out based on the next-generation Pendulum-A/B out-of-plane twin-satellite formation in this paper. Firstly,the Earth's gravity field complete up to degree and order 100 is, respectively, recovered by the collinear and pendulum satellite formations using the orbital parameters of the satellite and the matching accuracies of key payloads from the twin GRACE satellites. The research results show that the accuracy of the Earth's gravity field model from the Pendulum-A/B satellite formation is about two times higher than from the collinear satellite formation, and the further improvement of the determination accuracy of the Earth's gravity field model is feasible by the next-generation Pendulum-A/B out-of-plane twin-satellite formation. Secondly, the Earth's gravity field from Pendulum-A/B complete up to degree and order 100 is accurately recovered based on the orbital parameters of the satellite(e.g., an orbital altitude of 400 km, an intersatellite range of 100 km, an orbital inclination of 89?and an orbital eccentricity of 0.001), the matching accuracies of spaceborne instruments(e.g. 10-6m in the intersatellite range, 10-3m in the orbital position, 10-6m/s in orbital velocity, and10-11m/s2 in non-conservative force), an observation time of 30 days and a sampling interval of 10 s. The measurement accuracy of the Earth's gravity field from the next-generation Pendulum-A/B out-of-plane twin-satellite formation is full of promise for being improved by about 10 times compared with that from the current GRACE satellite formation. Finally,the physical requirements for the next-generation Pendulum-A/B out-of-plane twin-satellite formation are analyzed, and it is proposed that the satellite orbital altitude be preferably designed to be close to 400±50 km and the matching precision of key sensors from the Pendulum-A/B mission be about one order of magnitude higher than from the GRACE program.
The characteristics of the geopotential coefficient J2 in different periods are analyzed using satellite laser ranging data spanning the last 27 years.The satellites used in the analysis are Lageos1 and Lageos2.The variations in J2 are obtained by determining the dynamic orbit.The results show that there are strong seasonal and long-term variations.For different data spans,the seasonal variations agree well in terms of both amplitude and phase.Using all the data,the amplitude and phase of the annual term are 2.5 10-10 and 127°,respectively,while the amplitude and phase of the semiannual term are 0.94 10-10 and 213°,respectively.In the case of long-term variation,the secular variation in J2(J2) is-2.2 10-11 a-1 from 1984 to 2010.J2 differs for the different periods because of interannual variations,such as the "1998 anomaly".Another anomaly may have taken place during 2007-2010.Although the cause of the anomaly is unknown,it is an important observational constraint on the shape of the Earth.
The precision of Earth's gravitational field from GRACE up to degree and order 120 was studied for different inter-satellite ranges using the improved energy conservation principle.Our simulated result shows that:For long wavelength(L≤20)at degree 20,the cumulative geoid-height error gradually decreased with increasing range,from 0.052 cm for 110 km to 1.156 times and 1.209 times as large for 220 km and 330 km,respectively.For medium-wavelength(100≤L≤120)at degree 120,the cumulative geoid-height error decreased from 13.052 cm for 110 km,to 1.327 times and 1.970 times as large for the ranges of 220 km and 330 km,respectively;By adopting an optimal range of 220±50 km,we can suppress considerably the loss of precision in the measurement of the Earth's long-wavelength and medium-wavelength gravitational field.
With the successful launch and official commissioning of China's first dynamic ocean environment satellite Haiyang-2(HY-2),China's capabilities for oceanic environment monitoring and oceanic resource detecting have been further improved and enhanced.Precise tracking and orbit determination are not only key technical concerns in the ocean dynamic environment satellite project but also necessary conditions for carrying out related oceanic science research using observational data obtained using spaceborne instruments including radar altimeter.In this study,the current available status of international satellite laser ranging(SLR) monitoring on HY-2 was introduced.Six-months of SLR data from HY-2 were processed to obtain precise satellite orbit information using the dynamic orbit determination method.We carried out a detailed assessment of the SLR orbit accuracy by internal evaluation,comparisons with the orbit derived by the French Doppler orbitography and radio-positioning integrated by satellite(DORIS) system,and station-satellite distance validation.These assessments indicate that the three-dimensional orbital accuracy of HY-2 is about 12.5 cm,and the radial accuracy is better than 3 cm.It provides a good example of the application of international SLR monitoring and precise orbit determination in China's earth observation satellite project.
