Precise Orbit Determination Processing Research Articles

Measuring the Orbit Drift of Near-Earth Asteroids by the Yarkovsky Effect

The Yarkovsky effect causes the semimajor axis drift of near-Earth asteroids. The drift can be detected by a precise orbit determination process. Using the proposed algorithm, 2233 out of 27,078 near-Earth asteroids are chosen as the initial candidates. Out of these initial candidates, 769 have a measurable Yarkovsky effect with a signal-to-noise ratio (S/N) larger than 1, and 166 have a measurable Yarkovsky effect with an S/N larger than 3. The ratio between retrograde and prograde near-Earth asteroids is plotted with respect to their size. An average ratio of 2 is found for asteroids with an absolute magnitude between 14 and 21. The measurement work is carried out based on orbit determination software developed by the authors that considers a high-precision dynamical model.

On simulation of precise orbit determination of HY-2 with centimeter precision based on satellite-borne GPS technique

The HY-2 satellite carrying a satellite-borne GPS receiver is the first Chinese radar altimeter satellite, whose radial orbit determination precision must reach the centimeter level. Now HY-2 is in the test phase so that the observations are not openly released. In order to study the precise orbit determination precision and procedure for HY-2 based on the satellite-borne GPS technique, the satellite-borne GPS data are simulated in this paper. The HY-2 satellite-borne GPS antenna can receive at least seven GPS satellites each epoch, which can validate the GPS receiver and antenna design. What’s more, the precise orbit determination processing flow is given and precise orbit determination experiments are conducted using the HY-2-borne GPS data with both the reduced-dynamic method and the kinematic geometry method. With the 1 and 3 mm phase data random errors, the radial orbit determination precision can achieve the centimeter level using these two methods and the kinematic orbit accuracy is slightly lower than that of the reduced-dynamic orbit. The earth gravity field model is an important factor which seriously affects the precise orbit determination of altimeter satellites. The reduced-dynamic orbit determination experiments are made with different earth gravity field models, such as EIGEN2, EGM96, TEG4, and GEMT3. Using a large number of high precision satellite-borne GPS data, the HY-2 precise orbit determination can reach the centimeter level with commonly used earth gravity field models up to above 50 degrees and orders.

Orbit Determination and Prediction of the International Space Station

The International Space Station is equipped with Global Positioning System receivers that provide real-time position information at the 10m accuracy level. In preparation of the Atomic Clock Ensemble in Space experiment, measurements from Russian and American receivers have been used to assess the navigation accuracy that can be achieved through postprocessing of navigation solutions and raw data in a precise orbit determination process. In addition, the capability to accurately forecast the space station orbit for operation of microwave and laser terminals has been studied. It is shown that the orbit can be reconstructed with a 1 m position accuracy and a 1 mm/s velocity accuracy even from single-frequency Global Positioning System measurements. For the test period in mid 2006, short arc orbit predictions with a median error of 20 and 70 m could be obtained over forecast intervals of 6 and 12 h, respectively. The navigation accuracy obtained is compatible with the mission requirements for the relativistic correction of the atomic clocks and the quick look clock performance monitoring.

Parameter sensitivity of TOPIX orbit and derived mean sea level to DORIS stations coordinates

When determining precise orbits from altimetric satellites, the choice of the terrestrial reference frame is a key issue but still an open scientific topic. The terrestrial reference frame realization choice in the precise orbit determination processing will usually lead to systematic effects coming from the adoption of translations, scale factor and rotations but also others effects more difficult to assess, coming from a possible erroneous choice of a station coordinate. The goal of this paper is to try to characterize the effect of an erroneous individual station coordinate in vertical and horizontal components on the satellite orbit determination (characterization of the error, order of magnitude, consequences assessment of the on derived oceanographic products). Simulations have been realized at Institut Géographique National using the GIPSY/OASIS software from actual TOPEX DORIS data. These studies show that the stations whose latitude are close to the orbit inclination have the largest effect on the orbit error. These simulations will also help us to better estimate the required accuracy of a new tracking station. Additionally the study has been extended to try to predict the future uncertainty in the mean sea level determination in the 2000–2010 period derived for the present accuracy of the ITRF97 coordinates and velocities. Present uncertainties in the ITRF97 realization will create systematic errors in the TOPEX derived mean sea level at the 1 mm level in 2010.

Improved modelling of surface forces in the orbit determination of ERS and ENVISAT

Precise orbit determination of the European remote sensing satellites ERS-2 and ENVISAT, a prerequisite for the processing of their altimeter data, requires highly accurate force models. Inaccuracies in the modelling of non-gravitational forces, caused by interaction of photons, molecules, and atoms with the spacecraft surfaces, form a major error source. A highly detailed new non-gravitational force modelling package named ANGARA was implemented and tested for ERS-2 and ENVISAT. The resulting orbits for ERS-2 were compared with those from an existing box-wing panel model and a simple constant-area model. In addition, the effects on orbit accuracy of three thermospheric density models (DTM94, MSIS-86, and NRLMSISE-00) and a horizontal wind model (HWM-93) were evaluated. Force model parameters, estimated from tracking data during the precise orbit determination process, absorb most of the differences between the considered models. At the same time, an analysis of these parameters, and orbit determination runs with a limited parameterization, can give important clues about modelling accuracy. Atmospheric density is the dominant error source at high solar activity, degrading the radial orbit accuracy. Radiation pressure forces, for which uncertainties in material properties are the largest error source, play an equally important role at low solar activity.