Lue Chen

High Precision Determining and Predicting of Earth Orientation Parameters for Supporting Spacecraft Navigation

Earth Orientation Parameters (EOP) are essential for spacecraft navigation missions, such as deep space navigation and GNSS navigation mission, directly affecting navigation accuracy of spacecraft. First, this paper introduces the theories of EOP determination based on VLBI and EOP prediction in Beijing Aerospace Control Center (BACC), with some new data processing methods and strategies. The systems of EOP determination and prediction in BACC, consisting of VieVS and EOPS software (EOPS), could provide daily products of EOP determination and prediction. Then, The EOP determination products in BACC are compared with the products of International Earth Rotation and Reference Systems Service (IERS) and International GNSS Service (IGS). The EOP prediction products in BACC are compared with the products of IERS, United States Naval Observatory, (USNO) and EOP_PCC. The determination standard deviation of Earth polar motion x-component (PMX) is lower than 0.2 mas, Earth polar motion y-component (PMY) is lower than 0.3 mas, UT1-UTC is lower than 0.02 ms, and the determination accuracy is at the same level of the products of IERS and IGS. Meanwhile, the short-term prediction error of PMX/PMY/UT1-UTC is a little lower than EOP_PCC, and is at the same level of IERS and USNO. These compared results show that EOP products in BACC with high precision could effectively meet the requirement of spacecraft navigation mission. Finally, EOP prediction products in BACC were successfully applied on China’s first reentry return flight test mission to support spacecraft’s navigation.

Earth Polar Motion Parameters High Accuracy Differential Prediction

This paper proposes a method of Earth polar motion parameters prediction by dual differential least-squares (LS) and autoregressive (AR) model. Firstly, polar motion parameters are processed by dual differential method, the stationarity of polar motion parameters is improved. Then, LS+AR method is utilized to analyze the dual differential polar motion parameters to obtain the preliminary prediction results. Finally, the preliminary prediction results are processed by inverse dual differential method to obtain high accuracy polar motion prediction results. The prediction results are compared with EOP prediction comparison campaign (EOP_PCC) results, it shows that the short-term polar motion parameters prediction error is at the same level of EOP_PCC. The one day prediction accuracy of PMX is at the level of 0.25 mas, PMY is 0.2 mas, they are better than EOP_PCC one day polar motion prediction accuracy.

Monitoring CE’3 Rover Movement Using Same-Beam Interferometry with China’s Deep Space Network

China’s Deep Space Network (DSN) was deployed in 2013, a high-accuracy interferometric tracking observable was successfully used for orbit determination in the CE’3 project. This chapter presents the results of the rover’s status monitoring by earth-based same-beam interferometry (SBI) measurement. Phase delay with a biased offset is induced to identify the rover’s movement status, which could be up to three orders of magnitude better than conventional group delay. Based on the tracking data within China’s DSN, the status of the rover including going ahead, turning over, and changing signal can be successfully identified with a higher resolution. Combined with baseline length within China’s DSN, the movement of the rover in the order of centimeters can be identified, which testifies the effectiveness of this technique and algorithm.

Performance of DOR measurement in China CE’2 navigation

Very Long Baseline Interferometry (VLBI) has been successfully used in many deep space exploration projects over the past decades. Because it does not lose sensitivity to spacecraft declination when the spacecraft is near earth’s equatorial plane, as is the case for Doppler tracking. Differential One-way Ranging (DOR) can improve the accuracy of delay through wide spanned bandwidth. In this paper, performance of DOR experiment is analyzed, accuracy of results can satisfy China CE’2 navigation.

Lunar Satellite Orbit Measurement Based on Visual/Radio Fusion

A set of new orbit Measurement method was proposed based on the integration of high-resolution lunar surface imaging and ground-based radio measurement. Through the method, the advantage of stable tracking by radio measurements and the advantage of short-range measurement by onboard camera are expect to be fully integrated. The basic idea of the method is as following. First, combined with orbit constraints of a lunar high resolution imaging satellite, relying on optical imaging information and available reference images on the lunar surface, and based on the visual related theory of multi-view geometry and photogrammetry, the accurate location information of the satellite platform in a moment was calculated. Then, the location information was fused reasonably with satellite speed, range and angle by ground radio measurements. Thereby, a more flexible lunar orbiter orbit determination method than the existing methods was established. Currently, based on real data of “Chang’E II” satellite, visual/radio fusion-based orbit determination model were studied. Transfer relationship of the position and attitude between the satellite and imaging points on lunar surface was derived. Typical aspects of information fusion-based orbit determination were analyzed. Preliminary experimental results verify the feasibility of the proposed method. After parameter calibration, the partial positioning accuracy of “Chang’E II” is better than 100 m, variance limits at 30 m.

Processing Method and Verification of Local Correlation for Spacecraft DOR Signals

Differential One-way Ranging (DOR) is an interferometry method to obtain high precision delay in deep space exploration. Two stations track the same spacecraft to obtain high precision deep space spacecraft’s angle information. The process of DOR signal local correlation processing shows as follows, the model of DOR local signal is firstly constructed, then this model is used to do local correlation processing with the received spacecraft’s radio signal, to obtain high precision delay. Compared with the traditional DOR method, DOR local correlation processing method can be more effective in low SNR conditions to get correct measurement information. Firstly, prior delay model is calculated by orbit prediction, and the spacecraft’s emission frequency is calculated through effective frequency evaluation method, then the prior delay model and emission frequency are used to construct the DOR local model signal, then correlation phase is extracted by cross-correlation processing, finally, DOR group delay is calculated. This paper introduces the mathematical model of DOR local correlation processing in detail, and especially analyzes the technical difficulty in DOR local correlation processing. Based on the theoretical analysis, the algorithm of DOR local correlation processing is executed, and this method is verified by simulation, with the simulation measurement precision is about 0.1 ns, this verifies the effectiveness of DOR local correlation processing, and provides an effective technology for precise spacecraft orbit measurement.

High Accuracy Algorithm of Airborne Interferometric Synthetic Aperture Radar

Interferometric Synthetic Aperture Radar is one of the most important technologies for topographic mapping. The DEM quality of airborne InSAR system depends on both system hardware performance and data processing methods. To derive large scale topographic and thematic maps up to scale 1:50000 and 1:10000, the whole data processing methods were presented. The methods included SAR imaging, interferometric processing and cartographic processing. Special methods were induced to resolve the problems encountered in project applications. Results using X-band airborne InSAR system data showed validity of the algorithm.

The Algorithm of VLBI Wide-Band Correlation and CE-2 Broadband Signal Processing

In this paper, firstly, we discuss the specific processing algorithm of wide-band VLBI signal，which can be used in astronomy and geodesy. We focus on the theory, algorithm, result and by simulation we verified it. When the Chang’E Ⅱ on its orbit, we organize a short baseline interferometer experiment and get correlation fringe successfully, meanwhile, we compare the result with the data of precise theoretical orbit. It proves that the system is successful, and the algorithm is useful and correct.