| 其他摘要 | Low earth orbit (LEO) satellites play an indispensable role in a series of scientific research and engineering applications such as remote sensing, navigation and communication. Precise position information is the premise and foundation to complete the above tasks. Since global positioning system (GPS) was successfully applied to the precise orbit determination (POD) of TOPEX satellite, the POD of LEO satellite using spaceborne GNSS receiver has been deeply studied and widely used. The orbit determination accuracy based on reduced dynamic and kinematic technology has reached the centimeter level. Compared with a single large spacecraft, formation satellites can improve the flexibility of mission implementation, reduce risk and cost, and shorten the mission cycle. Synthetic aperture radar (SAR) interferometry and earth gravity field recovery put forward high requirements for the relative position information of formation satellites. The relative orbit determination accuracy of formation satellites based on GPS has reached millimeter level.With the completion of BeiDou global satellite navigation system (BDS-3) and Galileo system, the POD of LEO satellites based on BDS-3 and Galileo systems data has become a hotspot. Based on the foundation of achievements, this paper has explored the theory and method of absolute and relative orbit determination of LEO satellites, including LEO satellite attitude modeling, in-flight calibration of receiver antenna phase center variation (PCV), and precise orbit determination based on BDS-3, to further improve the POD accuracy. The main researches are summarized as follows:1. A satellite attitude determination method based on dual GNSS antennas is proposed to improve the orbit determination accuracy in the case of missing or unavailable attitude information. Satellite attitude is necessary to connect the satellite body fixed frame and inertial system. High-precision modeling of non-conservative forces such as atmospheric drag and solar radiation pressure also require the precise satellite attitude. In the absence of attitude information, a satellite attitude estimation method based on dual GNSS antennas is proposed. The data collected by Sentinel-6a spaceborne GNSS and GNSS-RO POD antennas is used for precise orbit determination. The satellite attitude is estimated based on the POD results and the baseline information between antennas. Results show that the attitude modeling accuracy is better than 0.25 degrees, the dual-antenna based orbit consistency is improved from the decimeter level when using the nominal attitude to the millimeter level, and the SLR residuals reduced from 30mm to 10mm, which validate the attitude determination method based on dual GNSS antennas and provides a feasible way to derive the satellite attitude when the measured data is not available.2. Single receiver ambiguity resolution of GPS/Galileo is studied to improve the orbit determination accuracy of LEO satellites. In the process of POD, due to the hardware biases of GNSS satellite and receiver, the carrier phase ambiguity is a float number. The GNSS observation specific bias (OSB) product is used to fix the carrier phase ambiguity, and finally POD based on integer ambiguity is realized. Multiple orbit determination modes including GPS-only, Galileo-only and GPS/Galileo combined POD are carried out using the on-board GPS and Galileo data of Sentinel-6a. Results show that the ambiguity fixing rate is better than 96%, the consistency of GPS-only and Galileo-only orbits with GPS/Galileo combined orbit are better than 5mm, and the root mean squares (RMS) of SLR residuals is less than 10mm. Fixing the ambiguity to integer improves the POD accuracy of LEO satellites and makes a foundation for precise data processing in the LEO-based earth observation missions.3. Relative orbit determination of LEO formation satellites based on single receiver ambiguity resolution and double difference ambiguity resolution are studied. A baseline accuracy evaluation method of triple-satellite formation based on closure error is proposed. In-flight PCV calibration of spaceborne GNSS antenna is carried out with the residual approach to improve the absolute and relative orbit determination accuracy. Results show that the radial orbit accuracy of GRACE-FO satellite with fixed ambiguity is better than 6mm, and the relative orbit accuracy with single receiver ambiguity resolution and double difference ambiguity resolution is better than 1.8 and 0.9mm respectively, which achieves the sub-millimeter level for formation satellites. The baseline accuracy evaluation method for triple-satellite formation based on closure error is proposed. Results show that the relative orbit determination accuracy of swarm-A/C formation is better than 1.9mm, and the accuracy of swarm-A/B and swarm-B/C formation is better than 3.5mm. The main reason for the lower accuracy is that the swarm-B satellite flies in a different orbital plane and is far away from the swarm-A and C satellites. Precise relative orbit determination of millimeter level is achieved, which breaks through the limitation of the distance between formation satellites. It is significant for the on orbit mission implementation and task expansion of formation satellites such as SAR.4. Absolute and relative POD of LEO formation satellites based on the BDS-3 B1C and B2a signals is studied. The BDS-only, GPS-only and BDS/GPS combined POD is carried out using the on-board data of the RSW satellites. The antenna PCOs related to the BDS-3 and GPS systems are estimated to improve the POD accuracy. The performance of BDS-3 B1C and B2a signals is analyzed with the tracking satellites, code multipath, residuals and POD accuracy. Results show that the ranging accuracy of BDS-3 new signal is significantly improved, the accuracy of B1C is better than that of GPS L1 C/A, and the accuracy of B2a is comparable with GPS L5. Compared with the orbits derived with BDS/GPS combined solutions, the absolute orbit determination consistency of BDS-only solution is better than 15mm (1D). The radial consistency of BDS-only relative orbit determination is better than 8mm, and the cross-track and along-track orbit consistency is 4–5mm, which is comparable to the results of GPS-only result. The excellent service performance of BDS-3 is validated and the capability of BDS-3 to fully support the independent and autonomous operation of LEO satellites is verified.5. The joint POD method of BDS-3 and LEO satellites is studied to improve the orbit determination accuracy of GNSS satellite with regional stations. Taking LEO satellite as a monitoring station, the joint orbit determination observation equation is constructed. The BDS-3 satellite orbit is determined with combined data collected by LEO satellite and ground stations. Two cases of stations are used in the POD: 6 stations around China (regional stations) and 30 stations around the world (global stations) are used with RSW satellite for joint orbit determination. In the case of regional stations, the BDS-3 orbit determination accuracy is improved by 55% with combining the data of RSW satellite; In the case of global stations, an improvement of 3%–13% for BDS-3 POD accuracy is observed. In both cases, the POD accuracy of RSW satellite is better than 45mm. When BDS-3 and GPS satellite orbits are determined together, the orbit accuracy of LEO satellite can be further improved. The combined orbit determination of GNSS and LEO satellites with regional ground stations provides an effective way to determine the precise orbits of GNSS satellites and improves the performance of satellite navigation system under special circumstances. |
修改评论