基于地基-星基联合测量的深空探测转移轨道确定及星上自主导航方法研究

Orbit determination for the deep space transfer orbit is different from the orbit around the Earth/Moon/Mars, the regime offers little dynamics constraints thus requiring an extensive amount of time and tracking data in order to attain a solution. Chinese Lunar missions were performed primarily through the Earth-based mesasurements, such as ranging/doppler, which offer the line-of-sight information of the spacecraft (S/C), as well as △DOR, which determine the angular spacecraft position. Learning from the experience of other countries, one technology can be used which is the S/C-based optical data taken by the onboard camera. In this proposal, considering interplanetary orbital characteristics, we propose to develop an interplanetary navigation orbit determination software using various measurements. For this purpose, we should establish dynamics models and measurement models. Further more, analysis is planed to be taken combing the ranging/doppler data , VLBI data and optical data to increase the accuracy of the interplanetary orbit determination. Moreover, the automation of interplanetary spacecraft is becoming increasingly desirable to meet various mission requirements. This proposal will develop the onboard orbit determination software.Since the onboard processors speed is slow, we limit the force modeling and use the Kalman filter formation. The results of this proposal can be applied to the developments in Chinese deep space exploration and achieve a certain significance.

深空探测转移轨道构型较差，随着探测器距离地球越来越遥远，定轨所需弧长越长，地基测量精度变差且观测几何单一，最终导致定轨精度变差。目前我国深空探测测量手段仅局限于地基观测，借鉴国际上常用做法，可以加入星基光学观测，通过观测探测器附近天体以提供不同于地基测量的观测几何，更有利于轨道确定工作。本项目以深空探测转移轨道定轨软件研发为主，针对转移段轨道特征，选择合适的动力学模型，并对地基、星基多种测量模型精确建模，结合地面测距/测速、VLBI干涉测量、星基光学观测等多种手段，对深空探测转移轨道定轨技术以及定轨精度进行研究。此外，考虑到深空探测器自主导航的灵活性，本项目还将进行星上自主定轨软件的研发。受到星上存储空间以计算效率的限制，星上自主定轨软件研制相比较地面软件在定轨方法，动力学模型建模，积分器等方面都有着不同的要求。本项目的研究成果可以为我国未来的深空探测作为研究参考。

本项目以深空探测转移轨道定轨软件研发为主，针对转移段轨道特征，选择合适的动力学模型，并对地基、星基多种测量模型精确建模，结合地面测距/测速、VLBI干涉测量、星基光学观测、星载GNSS测量等多种手段，进行实时和事后定轨算法研究和定轨软件研制，并对定轨精度进行分析研究。计算分析表明，地基数据单独定轨策略下，转移轨道定轨精度与探测器地心距相关，当有星基光学观测数据加入后，可以显著提高定轨精度，针对国内测控站的可见弧段，设计组合导航定轨算法，确定组合导航方案。分析地面无线电导航精度等因素对组合导航精度的影响，进行数学仿真验证。对多种地火转移轨道长弧和短弧定轨结果表明：器地组合导航定轨精度相比较仅使用地面无线电导航可提高约一个量级。对我国CE-5T1探测器搭载的高灵敏度接收机首次在地月/月地转移轨道段获取的实测GNSS数据进行定轨分析，定轨预报精度可以达到109m，联合GNSS和地基测量数据可以进一步提高到47m，优于地基多站定轨预报精度（位置误差369m）。针对典型探月任务各轨道段开展仿真分析，对于地月转移轨道段各次中途修正前，利用GNSS测量数据定轨预报位置精度优于400m；对于环月轨道变轨前，定轨预报位置精度优于60m；对于动力下降段轨迹确定精度优于100m；对于月面工作段，定位精度可以达到50m；均可满足我国月球探测任务定轨预报精度要求。尤其是在地月转移段和环月段单圈定轨预报情况下，利用GNSS数据的精度优于地基测量数据。CE-5T1探测器实测数据滤波结果表明，对于地月/月地转移段和环月段，测量数据噪声稳定时，该算法滤波估计与精密定轨（事后批处理）结果精度相当。转移轨道段GNSS数据和环月段地基测量数据滤波后位置偏差分别可以达到130m和30m。