A More Reliable Orbit Initialization Method for LEO Precise Orbit Determination Using GNSS

Precise orbit determination (POD) using GNSS has been rapidly developed and is the mainstream technology for the navigation of low Earth orbit (LEO) satellites. The initialization of orbit parameters is a key prerequisite for LEO POD processing. For a LEO satellite equipped with a GNSS receiver, sufficient discrete kinematic positions can be obtained easily by processing space-borne GNSS data, and its orbit parameters can thus be estimated directly in iterative manner. This method of direct iterative estimation is called as the direct approach, which is generally considered highly reliable, but in practical applications it has risk of failure. Stability analyses demonstrate that the direct approach is sensitive to oversized errors in the starting velocity vector at the reference time, which may lead to large errors in design matrix because the reference orbit may be significantly distorted, and eventually cause the divergence of the orbit parameter estimation. In view of this, a more reliable method, termed the progressive approach, is presented in this paper. Instead of estimating the orbit parameters directly, it first fits the discrete kinematic positions to a reference ephemeris in the form of the GNSS broadcast ephemeris, which construct a reference orbit that is smooth and close to the true orbit. Based on the reference orbit, the starting orbit parameters are computed in sufficient accuracy, and then the final orbit parameters are estimated with a high accuracy by using discrete kinematic positions as measurements. The stability analyses show that the design matrix errors are reduced in the progressive approach, which would assure more robust orbit parameter estimation than the direct estimation approach. Various orbit initialization experiments are performed on the KOMPSAT-5 and FY3C satellites. The results have fully verified the high reliability of the proposed progressive approach.

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Calculation of temporally high-resolution scaling factors for the thermospheric density from SLR observations

10.5194/egusphere-egu2020-15238 ◽

2020 ◽

Author(s):

Lea Zeitler ◽

Michael Schmidt ◽

Mathis Bloßfeld ◽

Sergei Rudenko

Keyword(s):

Parameter Estimation ◽

Orbit Determination ◽

Precise Orbit Determination ◽

Joint Estimation ◽

Model Parameters ◽

Gravitational Acceleration ◽

Scaling Factors ◽

Precise Orbit ◽

Swarm Satellites ◽

Leo Satellites

The motion of a satellite depends on gravitational and non-gravitational accelerations. A major problem in precise orbit determination (POD) of low-Earth orbiting (LEO) satellites is modelling the thermospheric drag. It is the largest non-gravitational acceleration acting on satellites with altitudes lower than 1000 km and decelerates them. In case of the Swarm satellites with an altitude of around 460 km not considering the drag within a POD would cause an error of around 3 meters per revolution in the along-track direction.In this study, we present results of DGFI-TUM in the context of the project TIPOD (Development of High-Precision Thermosphere Models for Improving Precise Orbit Determination of Low-Earth-Orbiting Satellites) funded by DFG in the frame of the SPP 1788 &#8216;Dynamic Earth&#8217;. One aim of this project is the computation of scaling factors for the thermospheric density from different satellite observation techniques, such as SLR, DORIS, GNSS or accelerometry. For a joint estimation of thermospheric model parameters the spatial, temporal and spectral content of the different scaling factors have to be analysed and interpreted. For example, accelerometer measurements along the satellite orbit provide scaling factors as point values. In this study we derive scaling factors from SLR measurements which could be interpreted as quasi-point values. For the POD of LEO satellites, DGFI-TUM&#8217;s software package DOGS (DGFI-TUM Orbit and Geodetic parameter estimation Software) is used. It is characterized by the ability to process observations of different space geodetic techniques and to combine their linear parameter estimation systems within a joint Gauss-Markov model. Here, we estimate scaling factors for the thermospheric density with a time resolution much higher than in our previous studies. Therefore, we use information of short passages from selected spherical satellites above SLR ground stations. Different temporal resolutions for the scaling factors varying from 6 hours down to 5 minutes will be tested and discussed in terms of reliability.

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Precise Orbit Determination of Combined GNSS and LEO Constellations with Regional Ground Stations

Proceedings of the 30th International Technical Meeting of The Satellite Division of the Institute of Navigation (ION GNSS+ 2017) ◽

10.33012/2017.15329 ◽

2017 ◽

Author(s):

Bofeng Li ◽

Liangwei Nie ◽

Haibo Ge ◽

Maorong Ge ◽

Ling Yang

Keyword(s):

Orbit Determination ◽

Precise Orbit Determination ◽

Precise Orbit

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General relativistic effects acting on the orbits of Galileo satellites

Celestial Mechanics and Dynamical Astronomy ◽

10.1007/s10569-021-10014-y ◽

2021 ◽

Vol 133 (4) ◽

Author(s):

K. Sośnica ◽

G. Bury ◽

R. Zajdel ◽

K. Kazmierski ◽

J. Ventura-Traveset ◽

...

Keyword(s):

General Relativity ◽

Orbit Determination ◽

Final Height ◽

Precise Orbit Determination ◽

Satellite System ◽

De Sitter ◽

Circular Orbits ◽

Precise Orbit ◽

Artificial Earth Satellites ◽

Artificial Earth

AbstractThe first pair of satellites belonging to the European Global Navigation Satellite System (GNSS)—Galileo—has been accidentally launched into highly eccentric, instead of circular, orbits. The final height of these two satellites varies between 17,180 and 26,020 km, making these satellites very suitable for the verification of the effects emerging from general relativity. We employ the post-Newtonian parameterization (PPN) for describing the perturbations acting on Keplerian orbit parameters of artificial Earth satellites caused by the Schwarzschild, Lense–Thirring, and de Sitter general relativity effects. The values emerging from PPN numerical simulations are compared with the approximations based on the Gaussian perturbations for the temporal variations of the Keplerian elements of Galileo satellites in nominal, near-circular orbits, as well as in the highly elliptical orbits. We discuss what kinds of perturbations are detectable using the current accuracy of precise orbit determination of artificial Earth satellites, including the expected secular and periodic variations, as well as the constant offsets of Keplerian parameters. We found that not only secular but also periodic variations of orbit parameters caused by general relativity effects exceed the value of 1 cm within 24 h; thus, they should be fully detectable using the current GNSS precise orbit determination methods. Many of the 1-PPN effects are detectable using the Galileo satellite system, but the Lense–Thirring effect is not.

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A Second-Order Time-Difference Position Constrained Reduced-Dynamic Technique for the Precise Orbit Determination of LEOs Using GPS

Remote Sensing ◽

10.3390/rs13153033 ◽

2021 ◽

Vol 13 (15) ◽

pp. 3033

Author(s):

Hui Wei ◽

Jiancheng Li ◽

Xinyu Xu ◽

Shoujian Zhang ◽

Kaifa Kuang

Keyword(s):

Orbit Determination ◽

Dynamic Models ◽

Precise Orbit Determination ◽

Second Order ◽

Time Difference ◽

Error Sources ◽

Precise Orbit ◽

Unmodeled Dynamic ◽

Reduced Dynamic

In this paper, we propose a new reduced-dynamic (RD) method by introducing the second-order time-difference position (STP) as additional pseudo-observations (named the RD_STP method) for the precise orbit determination (POD) of low Earth orbiters (LEOs) from GPS observations. Theoretical and numerical analyses show that the accuracies of integrating the STPs of LEOs at 30 s intervals are better than 0.01 m when the forces (<10−5 ms−2) acting on the LEOs are ignored. Therefore, only using the Earth’s gravity model is good enough for the proposed RD_STP method. All unmodeled dynamic models (e.g., luni-solar gravitation, tide forces) are treated as the error sources of the STP pseudo-observation. In addition, there are no pseudo-stochastic orbit parameters to be estimated in the RD_STP method. Finally, we use the RD_STP method to process 15 days of GPS data from the GOCE mission. The results show that the accuracy of the RD_STP solution is more accurate and smoother than the kinematic solution in nearly polar and equatorial regions, and consistent with the RD solution. The 3D RMS of the differences between the RD_STP and RD solutions is 1.93 cm for 1 s sampling. This indicates that the proposed method has a performance comparable to the RD method, and could be an alternative for the POD of LEOs.

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