Based on the research of orbit determination by using two GPS satellites, this paper discusses the initial value problem and provides an effective method of getting initial value.

研究了用两颗全球定位系统(GPS)卫星粗略确定低轨卫星轨道的问题，并着重讨论了其中的初值问题，给出了一种有效的初值方法。

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The result is satisfactory by using a method of the artificial earth satellite orbit determination from range rate observations to fit the free-flight trajectory of rocket.

用人造地球卫星轨道计算的测速定轨方法，去拟合火箭飞行弹道的自由段，取得了比较满意的结果。

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The observational accuracy of the space debris will affect their orbit determination accuracy, so it is especially vital for us to determinate the observational accuracy of the space debris.

空间碎片的观测精度将会直接影响到空间碎片的定轨精度，因此对空间碎片观测精度进行判定是有重要意义的。

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Using the most recent determination of UARS' orbit - taken in the early hours of this morning - Dr Eves and a colleague have come up with their own projections of the satellite's final descent.

BBC: Nasa refines satellite crash time