Determination of Precise Orbits and Gravity Models Using Simulated ROCSAT-3/COSMIC Tracking Data

• Main Authors: Yi-Shan Lee, 李宜珊
• Other Authors: Cheinway Hwang
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/3h999a

碩士 === 國立交通大學 === 土木工程系所 === 92 === In this study, a ’two-step’ approach is used to compute precise orbits and estimate parameters of satellite perturbing forces. The approach is based on satellite equations of motion (EOM) and parameter estimation theory. The perturbing forces under consideration are the earth’s non-sphericity, air-drag, solar radiation and empirical accelerations. Programs for precise orbit and gravity determinations in this work are coded in Fortran 90. In the experiments, the EGM96 geopotential model is regarded as the true field, and the OSU91A geopotential model as the initial field in the parameter estimations. In terms of the accuracy of the recovered geopotential coefficients, the results from the simulations show that: (1) in a degree-5 solution with one day of tracking data the RMS relative error (RRE) is 5×10-7, (2) in a degree-5 solution with three days of tracking data the RRE is 3×10-7, (3) in a degree-10 solution with one day of tracking data, the RRE is 1.5×10-5, and (4) in a degree-10 solution with three days of tracking data the RRE is 6.6×10-6. To assess the accuracy of the computed satellite orbits, we experimented with two different orbital inclinations. The cases with a 90°-inclination are to validate the computer programs, and the results show that: (1) in a degree-5 solution with three days of tracking data the RMS orbit error (ROE) is 0.16 cm, (2) in a degree-10 with one day of tracking data the ROE is 0.55cm. The cases with a 72°-inclination are for the ROCSAT3/COSMIC mission, and the results show that: (1) in a degree-5 solution with one day of tracking data the ROE is 2 cm, (2) in a degree-5 solution with three days of tracking data the ROE is 9 cm, (3) in a degree-10 solution with one day of tracking data the ROE is 1.9 m, and (4) in a degree-10 solution with three days of tracking data the ROE is 2.1 m. Future work will be to improve the accuracy and precision of the computer package in precise orbit and gravity determinations.