It has been recognized since the early days of interplanetary spaceflight that accurate navigation requires taking into account changes in the Earth’s rotation. In the 1960s, tracking anomalies during the Ranger VII and VIII lunar missions were traced to errors in the Earth orientation parameters. As a result, Earth orientation calibration methods were improved to support the Mariner IV and V planetary missions. Today, accurate Earth orientation parameters are used to track and navigate every interplanetary spaceflight mission. The approach taken at JPL (Jet Propulsion Laboratory) to provide the interplanetary spacecraft tracking and navigation teams with the UT1 and polar motion parameters that they need is based upon the use of a Kalman filter to combine past measurements of these parameters and predict their future evolution. A model was then used to provide the nutation/precession components of the Earth’s orientation. As a result, variations caused by the free core nutation were not taken into account. But for the highest accuracy, these variations must be considered. So JPL recently developed an approach based upon the use of a Kalman filter and smoother to provide smoothed and predicted celestial pole offsets (CPOs) to the interplanetary spacecraft tracking and navigation teams. The approach used at JPL to do this and an evaluation of the accuracy of the predicted CPOs is given here. For assessing the quality of JPL’s nutation predictions, we compare the time series of dX, dY provided by JPL with the predictions obtained from the IERS Rapid Service/Prediction Centre. Our results confirmed that the approach recently developed by JPL can be used for the successful nutation prediction. In particular, we show that after 90 days of prediction, the estimated errors are 43% lower for dX and 33% lower for dY than in the case of the official IERS products, and an average improvement is 19% and 22% for dX and dY, respectively.

中文翻译：

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使用卡尔曼滤波器和平滑器平滑和预测天极偏移

早在行星际航天飞行的早期就已经认识到，精确导航需要考虑地球自转的变化。在 1960 年代，Ranger VII 和 VIII 月球任务期间的跟踪异常被追溯到地球方向参数的错误。因此，地球方向校准方法得到改进，以支持水手 IV 和 V 行星任务。今天，准确的地球方向参数被用于跟踪和导航每一次行星际太空飞行任务。JPL（喷气推进实验室）为行星际航天器跟踪和导航团队提供他们所需的 UT1 和极地运动参数所采用的方法是基于使用卡尔曼滤波器将这些参数的过去测量值结合起来并预测它们的未来演变. 然后使用一个模型来提供地球方向的章动/进动分量。因此，没有考虑自由核心章动引起的变化。但是为了获得最高的准确度，必须考虑这些变化。因此，JPL 最近开发了一种基于使用卡尔曼滤波器和平滑器的方法，为行星际航天器跟踪和导航团队提供平滑和预测的天极偏移 (CPO)。此处给出了 JPL 用于执行此操作的方法以及对预测 CPO 准确性的评估。为了评估 JPL 章动预测的质量，我们将 JPL 提供的 dX、dY 时间序列与从 IERS 快速服务/预测中心获得的预测进行比较。我们的结果证实，JPL 最近开发的方法可用于成功的章动预测。特别是，我们表明，经过 90 天的预测，dX 的估计误差比官方 IERS 产品低 43% 和 dY 低 33%，dX 和 dX 的平均改进分别为 19% 和 22%。分别为 dY。