海事天線比起地面天線站，在追蹤衛星上還需要面臨海面晃動造成的誤差，因此對於計算衛星位置的精確度會有更高的要求。本研究主要開發海事天線的天線控制單元(Antenna Control Unit, ACU)中衛星軌道推算器，採用C語言撰寫，確保可順利在微控制器(Micro Control Unit, MCU)平台運行，以利後續開發者進行維護。研究的重點目標為將自行計算的衛星位置與業界慣用的Ansys Systems Tool Kit計算的衛星位置的向量夾角，能縮減至0.1度以內。在衛星位置座標轉換的流程上參考(林彥夫，2021)，衛星位置計算使用簡化擾動模型(Simplified General Perturbations Models)中的SGP4衛星軌道推算器，此模型適用於衛星軌道週期小於225分鐘的近地軌道衛星。本研究同時開發適合的應用程式介面(Application Programming Interface, API)，允許使用者將位置向量轉換並輸出至地心地固座標系(Earth Center Earth Fixed, ECEF)、以天線站為中心的東北高座標系(East North Up, ENU)、以及以天線站為中心的衛星所在之方位角與俯仰角，可使後續的應用更加靈活。;Compared with ground antenna stations, maritime antennas also need to face perturbation caused by waves when tracking satellites, so there will be higher requirements for the accuracy of satellite position calculation. This research mainly develops the satellite orbit propagator in the Antenna Control Unit (ACU) of the maritime antenna, which is written in C language to ensure that it can run on the Micro Control Unit (MCU) platform to facilitate subsequent developers’ maintenance. The main goal of the research is to reduce the vector angle between the satellite position calculated by self-developed program and by the Ansys Systems Tool Kit within 0.1 degrees. Refer to the process of satellite position coordinate conversion (Lin, 2021). The satellite position calculation uses the SGP4 orbit propagator in the Simplified General Perturbations Models. This model is suitable for low-Earth orbits with satellite orbit periods less than 225 minutes satellite. This research also develops a suitable Application Programming Interface (API), which allows users to convert and output the position vector to the Earth Center Earth Fixed (ECEF) coordinate system, the north east elevation coordinate (East North Up, ENU) centered on the antenna station, as well as the azimuth and elevation angles of the satellites centered on the antenna station, can make subsequent applications more flexible.
