计算LAT/LONG（2维）坐标至少需要3颗卫星。再加一颗就可以计算3维坐标。对于一个给定的位置，GPS接收器知道在此时哪些卫星在附近，因为它不停地接收从卫星发来的更新信号。
未来，消费者将在聚划算平台上享受与卫星轨迹同步的高品质商品。
In the future, consumers on the Juhuasuan platform will be able to enjoy high-quality goods that follow the trajectory of the satellites.
其实，通过轨道数据计算出来的卫星轨迹，要比通过几周前的数据计算所得更不准确。
A satellite prediction calculated from orbital data more than a few weeks old will generally be virtually meaningless.
基于线性系统的特征结构配置和模型参考理论提出一种卫星轨迹跟踪控制的参数化方法，设计系统的反馈镇定控制器和前馈跟踪控制器。
A parametric approach is proposed for the satellite trajectory tracking problem by using the eigenstructure assignment theory and the model reference theory of linear systems.
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