A new precise orbit determination (POD) strategy based on the combination of satellite laser ranging (SLR) and C-band transfer ranging for geostationary satellites (GEO) is presented. Two approaches to calibrate ranging biases of the C-band ranging system are proposed, namely the two tracking system co-location comparison and the combined POD method, with calibration accuracies estimated to be 0.5 ns and 1 ns respectively. Using data from a C-band tracking network in China, POD experiments indicate that meter-level POD accuracy is achievable for GEO. Root-mean-square (RMS) of the post-fit C-band ranging data is about 0.205 m. The radial component errors of POD are evaluated with SLR data from a station in Beijing, with residual RMS of 0.133 m. Orbital overlapping experiments show the total orbit error is a few meters. Computations of SLR residuals also suggest that for 2-hour prediction, the predicted radial error is about 0.373 m.

Precise orbit determination for geostationary satellites with multiple tracking techniques

Chang’E-3 landed on the east of Sinus Iridum area on December 14, 2013, performing China’s first successful soft landing on the lunar surface. We present the results on precision orbit determination and positioning of the lander and the rover. We describe the data, modeling, and methods used to achieve position knowledge over the period December 2–21, 2014. In addition to the radiometric X-band range and Doppler tracking data, delta differential one-way ranging data are also used in the calculation, which show that they strongly improve the accuracy of the orbit reconstruction. Total position overlap differences are about 20 and 30 m for the 100 km × 100 km and 100 km× 15 km lunar orbit, respectively, increased by ~50 % with respect to CE-2 and at the same level as other lunar spacecrafts of recent era such as SELENE and lunar reconnaissance orbiter (LRO). The position error of the soft landing trajectory is less than 100 m. A kinematic statistical method is applied to determine the position of the lander and relative position of the rover with respect to the lander. The position difference of the lander is better than 50 m compared to LRO photograph result. Compared with the delta very long baseline interferometry (VLBI) group delay between the lander and the rover, the delta VLBI phase delay can improve the relative position of the rover from ~1,000 to ~1 m.

Orbit determination of Chang’E-3 and positioning of the lander and the rover

Orbit Determination of Chang'e-3 and Positioning of the Lander and the Rover

There will be 70~90 navigation satellites operating at the same time when Glonass and Galileo reach full operation capability. As a result, the number of visible satellites can reach 30. Thus the positioning accuracy will be improved greatly. However, so many satellite measurements may burden the receiverpsilas processing element when to use them to find a solution and to do integrity monitoring. Satellite selection can decrease the number of measurements and as a result can shorten the computing time. ldquoDoes satellite selection be still needed for multi-constellation?rdquo At first, this paper analyses the amount of calculation of least square estimation techniques to calculate user position with different number of measurements. The results show that reducing the number of measurements can cut the amount of calculation greatly. Then the relationship between GDOP and the volume of polyhedron formed by the ends of unit user-to-satellite vectors is analyzed. We found that the relationship when the number of satellites is more than 4 is different with that when the number of satellites equals 4. Therefore the relationship when the number of satellites is more than 4 is researched in detail and a fast satellite selection method is proposed. The main idea is selecting a subset whose geometry is most similar to the optimal subset among all the visible satellites. The simulation tests prove that the fast satellite selection method can reduce the number of required subsets to look up the optimal geometry greatly and the increased GDOP is relatively small. Meanwhile, this method can not only be applicable for multi-constellation, but also for single constellation.

Satellite selection for multi-constellation

In this paper, a novel method for selecting a navigation satellite subset for a global positioning system (GPS) based on a genetic algorithm is presented. This approach is based on minimizing the factors in the geometric dilution of precision (GDOP) using a modified genetic algorithm (MGA) with an elite conservation strategy, adaptive selection, adaptive mutation, and a hybrid genetic algorithm that can select a subset of the satellites represented by specific numbers in the interval (4 ∼ n) while maintaining position accuracy. A comprehensive simulation demonstrates that the MGA-based satellite selection method effectively selects the correct number of optimal satellite subsets using receiver autonomous integrity monitoring (RAIM) or fault detection and exclusion (FDE). This method is more adaptable and flexible for GPS receivers, particularly for those used in handset equipment and mobile phones.

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A Novel Method for Optimum Global Positioning System Satellite Selection Based on a Modified Genetic Algorithm.

Selection of GPS satellites for the optimum geometry

Both of the oceanographic research by using altimetry and the application of InSAR of ERS-2 satellite need the precise ephemerides of the satellite. In this note, the ERS-2 orbit is precisely determined by using SLR and PRARE observations to take advantage of the high accuracy of SLR and the widespread data coverage of PRARE. Based on the software system SODS-VCE established by us, the ERS-2 orbits in 1997 are calculated. The evaluation from tracking data fits, endpoint consistency of orbital arcs and comparison with independent orbit implies an orbit accuracy of 5–6 cm in radial component which can satisfy the requirement of being better than 10 cm in oceanographic research by altimetry, being less than 20 cm in cross-track component which can meet the requirement of InSAR. In orbit computation, the method of variance component estimation is employed to weight the SLR, PRARE range and Doppler measurements properly. The results indicate that the application of the method can improve the computation accuracy efficiently.

Huang Cheng

Papers

Selection of GPS satellites for the optimum geometry

Precision ERS-2 orbit determination combining multiple tracking techniques

Orbit determination of satellite “Tance 1” with VLBI data

On the singular points of the Abelian integral transformation in the GPS/LEO occultation technique†⋆

Measuring and modeling the solubility of carbon dioxide in protic ionic liquids