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1
Content available remote Comparison of Selected Geopotential Models in Terms of the GOCE Orbit Determination Using Simulated GPS Observations
Bobojć A.
Acta Geophysica
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2016
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Vol. 64, no. 6
2761--2780
EN
This work contains a comparative study of the performance of six geopotential models in an orbit estimation process of the satellite of the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) mission. For testing, such models as ULUX_CHAMP2013S, ITG-GRACE 2010S, EIGEN-51C, EIGEN5S, EGM2008, EGM96, were adopted. Different sets of pseudo-range simulations along reference GOCE satellite orbital arcs were obtained using real orbits of the Global Positioning System satellites. These sets were the basic observation data used in the adjustment. The centimeter-accuracy Precise Science Orbit (PSO) for the GOCE satellite provided by the European Space Agency (ESA) was adopted as the GOCE reference orbit. Comparing various variants of the orbital solutions, the relative accuracy of geopotential models in an orbital aspect is determined. Full geopotential models were used in the adjustment process. The solutions were also determined taking into account truncated geopotential models. In such case, an accuracy of the solutions was slightly enhanced. Different arc lengths were taken for the computation.
2
Content available remote Application of Gravity Gradients in the Process of GOCE Orbit Determination
Bobojć A.
Acta Geophysica
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2016
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Vol. 64, no. 2
521--540
EN
The possibility of improving the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) mission satellite orbit using gravity gradient observations was investigated. The orbit improvement is performed by a dedicated software package, called the Orbital Computation System (OCS), which is based on the classical least squares method. The corrections to the initial satellite state vector components are estimated in an iterative process, using dynamic models describing gravitational perturbations. An important component implemented in the OCS package is the 8th order Cowell numerical integration procedure, which directly generates the satellite orbit. Taking into account the real and simulated GOCE gravity gradients, different variants of the solution of the orbit improvement process were obtained. The improved orbits were compared to the GOCE reference orbits (Precise Science Orbits for the GOCE satellite provided by the European Space Agency) using the root mean squares (RMS) of the differences between the satellite positions in these orbits. The comparison between the improved orbits and the reference orbits was performed with respect to the inertial reference frame (IRF) at J2000.0 epoch. The RMS values for the solutions based on the real gravity gradient measurements are at a level of hundreds of kilometers and more. This means that orbit improvement using the real gravity gradients is ineffective. However, all solutions using simulated gravity gradients have RMS values below the threshold determined by the RMS values for the computed orbits (without the improvement). The most promising results were achieved when short orbital arcs with lengths up to tens of minutes were improved. For these short arcs, the RMS values reach the level of centimeters, which is close to the accuracy of the Precise Science Orbit for the GOCE satellite. Additional research has provided requirements for efficient orbit improvement in terms of the accuracy and spectral content of the measured gravity gradients.
3
Content available remote GOCE satellite orbit in the aspect of selected gravitational perturbations
Bobojć A., Drożyner A.
Acta Geophysica
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2011
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Vol. 59, no. 2
428-452
EN
In this work, the GOCE satellite orbit is described in the aspect of perturbations in the Keplerian osculating elements. The perturbations come from the Earth and ocean tides, the gravitation of the Moon, the gravitation of the Sun, the gravitation of planets and Pluto, and the relativity effects. These perturbations are computed for the 30-day interval with a sampling of 2 min. To obtain the simulated orbit, the Cowell numerical integration method of 8th order is used. The first part of the work contains the root mean square (RMS) values of aforementioned perturbations due to the specified forces. The perturbations were compared taking into account their RMS characteristics. Perturbations in elements of the GOCE osculating orbit are also presented on the plots for successive epochs of the 30-day interval. Changes of the obtained perturbations were described and their characteristic periodic components were distinguished.
4
Content available remote Selected Accelerations and Orbital Elements of the GOCE Satellite in the Time Domain
Bobojć A.
Technical Sciences / University of Warmia and Mazury in Olsztyn
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2009
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nr 12
104-117
EN
The work contains the results of the GOCE satellite orbit simulation. The GOCE satellite orbit was presented in the aspect of the temporary changes in selected accelerations and in selected keplerian elements. The satellite accelerations due to: the geopotential, the Earth tides and the ocean tides (the radial component for both), the gravitation of the Moon and the gravitation of the Sun, were presented in function of time. The showed changes in orbital elements include the semi-major axis, eccentricity, inclination, argument of perigee and right ascension of ascending node. For the orbit determination the Cowell numerical integration method of the eighth order was used. The geopotential was described by means of the EGM96 model. The mentioned temporary changes in the selected accelerations and orbital elements were described. Most of them contain the characteristic periodic components, which are close to the satellite orbital period, the Earth's rotation period and the Moon's synodic period.
PL
Praca zawiera wyniki symulacji orbity satelity GOCE. Orbitę satelity GOCE przedstawiono w aspekcie zmian czasowych wybranych przyśpieszeń i elementów keplerowskich. Przyśpieszenia satelity spowodowane przez: geopotencjał, pływy skorupy, pływy oceaniczne (składowa radialna dla obu), grawitację Słońca i grawitację Księżyca, przedstawiono w funkcji czasu. Pokazane zmiany w elementach orbity obejmują półoś wielką, mimośród, nachylenie, argument perygeum i rektascensję węzła wstępującego. Do wyznaczenia orbity użyto całkowania numerycznego metodą Cowella ósmego rzędu. Geopotencjał opisano modelem EGM96. Opisano wspomniane zmiany czasowe wybranych przyśpieszeń i elementów orbity. Większość z nich zawiera charakterystyczne składowe okresowe, które są zbliżone do okresu orbitalnego satelity, okresu rotacji Ziemi oraz okresu synodycznego Księżyca.
5
Content available remote Spectral analysis of the selected accelerations and orbital elements for the GOCE satellite orbit
Bobojć A.
Artificial Satellites : Journal of Planetary Geodesy
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2008
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Vol. 43, No. 3
109--127
EN
The work contains the results of research of the simulated GOCE satellite orbit. For the 30-day orbit determination the Cowell numerical integration of the eighth order was used and the geopotential was described by means of the EGM96 model. The selected accelerations and the Keplerian elements were computed along this orbit. These accelerations included the satellite accelerations due to: the geopotential, the Earth tides and the ocean tides (the radial component for both), the gravitation of the Moon, the gravitation of the Sun, the gravitation of the Venus and the relativity effects. The computed accelerations and Keplerian elements were treated as the input data for the DFT algorithm (Discrete Fourier Transform) to determine their spectral characteristics, i.e. the amplitude power spectral densities (PSD). Additionally, the averages and standard deviations were obtained for the aforementioned accelerations and Keplerian elements. The numerous periodic components were identified. The characteristic resonances with the satellite orbital period, with the Earth’s rotation period and with the Moon’s synodic period were described.
6
Content available remote Determination of the GOCE satellite orbit sensitivity under the influence of perturbing forces
Bobojć A., Drożyner A.
Artificial Satellites : Journal of Planetary Geodesy
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2007
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Vol. 42, No. 2
121--128
EN
The work contains the results of research into the simulated orbit of the GOCE satellite. Satellite accelerations due to atmospheric drag, the gravitation of the Moon, the gravitation of the Sun, the gravitation of the planets, the Earth tides, the ocean tides, the solar radiation pressure, the reflected solar radiation pressure and the relativity effects were computed. Besides the reference orbit (i.e. the orbit as close as possible to the GOCE planned orbit), the various variants of the satellite orbit (called the modified reference orbits – with different motion models) were obtained. The motion models contained the forces determining the satellite motion. For the orbital computations, the Cowell numerical integration of the eighth order was used. The geopotential was described by means of the EGM96 model. In order to obtain the influence of the aforementioned forces on the GOCE orbit, the percentage contributions of the accelerations due to these forces in the sum of all accelerations were computed. The maximum values of the mentioned accelerations were computed for the GOCE orbit variant with the motion model containing all given above forces. These values were compared with the measurement error of the linear accelerations by the GOCE satellite control system. The comparison between the reference orbit and the computed variants of the orbit was performed. In order to perform this comparison, the distances between the satellite position in the reference orbit and the satellite position in the given modified reference orbit (i.e. in a given orbit variant) were determined. These distances were compared with the total error of the GOCE satellite position determination. The orbital arc lengths, for which the selected forces can be neglected in the satellite motion model, were determined from this comparison. For these orbital arc lengths, the distance between the satellite position in the reference orbit and the satellite position in the given modified reference orbit is less or equal to the total error of the GOCE satellite position determination.
7
Content available remote Badania gradiometryczne w kontekście misji kosmicznej GOCE
Bobojć A., Drożyner A.
Geodezja / Akademia Górniczo-Hutnicza im. Stanisława Staszica w Krakowie
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2001
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T. 7, z. 2
151-158
PL
W najbliższych latach należy oczekiwać realizacji, przez Europejską Agencję Kosmiczną, misji kosmicznej Gravity Field and Steady-State Ocean Circulation Mission (GOCE). Satelita GOCE będzie wyposażony między innymi w elektrostatyczny gradiometr. W niniejszej pracy przeanalizowano możliwości wykorzystania obserwacji gradiometrycznych do wyznaczania orbity satelity. Przeprowadzone symulacje pozwalają określić optymalną długość łuku orbitalnego, preferowaną strategię pomiarową oraz oczekiwane dokładności wyznaczenia pozycji satelity. Wskazuje się także na perspektywy dalszych badań symulacyjnych gradiometrii satelitarnej w powiązaniu z planowaną misją GOCE
EN
The launch of the first satellite with the gradiometer on the board is planned between 2004 and 2005 year. This satellite will realize the Gravity Field and Steady-State Ocean Circulation Mission (GOCE). The presented work contains the theoretical aspects and simulation research of the satellite orbit determination by means of the Satellite Gravity Gradiometry observations. The process of the satellite orbit determination includes the estimation of the initial dynamic state vector corrections using the leas squares method. The performed simulations allow to obtain an optimal orbital arc, preferred measurement strategy and accuracy of the satellite position determination. The planned mission GOCE is the main reason for performing the future simulation investigations of the Satellite Gravity Gradiometry
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