一號、二號三號衛星利用GPS作軌道測定之誤差研究

Abstract

本計畫將全球GPS追蹤站資料發展一誤差函數以為GPS差分修正用。此誤差函數考慮到GPS時錶誤差，星曆誤差及電離層誤差，可用以修正中華一、二號GPS L1 導航解所求得之軌道。修正後之軌道可用一解析式（自線性軌道理論推得）再予以平滑及改善。在台灣附近，將用較密的亞洲GPS追蹤站資料求得一特殊誤差函數，且利用軌道短弧代表式修正一、二號GPS定軌結果。此差分修正法預期可將一、二號GPS定軌誤差降至5公尺或更小。三號衛星則將用幾何法以三號原始的GPS資料（相位及碼）進行定軌，預期可達一公尺的軌道精度。此幾何法將應用到一顆與三號衛星相同的衛星上。改善後的一、二號軌道將以台灣兩追蹤站提供的距離變化率及角度資料評估。

In this project, we will develop a global GPS error function for differential correction using data from a global GPS tracking network. The error function accounts for the GPS clock error, ephemeris error and ionospheric error, and will be used to correct for the ROCSAT-1/2 orbits determined with the GPS L1 navigational solution. An analytical orbit representation, based on the linear orbit theory, is then used to approximate the corrected orbit for a further orbit improvement and smoothing. Over Taiwan, a dense GPS network in Asia will be used to develop a special error function, which, together with a short-arc representation of an orbital pass, will significantly improve the accuracy of orbit around Taiwan. The ROCSAT-3 orbit will be determined by a geometric method using the raw GPS data (phases and codes) of ROCSAT-3. This method will be applied to a satellite mission similar to the ROCSAT-3 mission. The improved orbits of ROCSAT-1/2 will be evaluated using the range rates and angle data obtained at two tracking stations of Taiwan.