Satellite Orbit and Ephemeris Determination using Inter Satellite Links

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Orbit ComputationInter Satellite Links() t m − m tm = D0⋅Eq. 4.2-59The mass flow can be also be a (commanded) function of time. However, most of thechemical propulsion systems have a fixed mass flow.Page 38R. Wolf
Inter Satellite LinksOrbit Computation4.3 Force Model ErrorsA given force model will only be accurate to a certain degree. This lead to a divergence of thepredicted trajectory, and the actual one. On the other hand, if computational recourses arerare, the orbit arc is short or the required accuracy is not that demanding, it is necessary toassess the impact of simplifying the force model. This section deals with the impact of theseforce model simplifications, as well as force model errors on the orbit prediction error.4.3.1 Earth's GravityAs shown in chapter 4.2.1, the impact of the higher order spherical harmonics of the earth'sgravity field decreases with orbit altitude. Neglecting higher order terms will therefore lead toprediction errors, but depending on orbit altitude. Another error source is the imperfection ofthe harmonic coefficients. To assess the impact of neglecting higher order terms, as well as animperfect gravity model, a reference trajectory has been computed using the full JGM-3,being a state of the art gravity model. Degree and order of the model has been decreasedsuccessively and the resulting trajectory has been compared to the reference orbit.Furthermore the reference trajectory has been compared to orbits computed with other fullgravity models. The following gravity models have been compared:Gravity ModelJGM-3 (ReferenceModel)Maximum Degree xOrder70 x 70JGM-2 70 x 70GEM-T3 50 x 50GRIM4-S4 66 x 66Table 4-4 Assessed Gravity ModelsAll these models have been derived by satellite measurements. To show the impact of theorbit altitude, different reference orbit have been computed:• a low earth orbit (LEO) with 1250 km orbit altitude• a GPS like orbit (MEO) with 20200 km orbit altitude• a geostationary orbit (GEO) with approximately 36 000 km orbit altitudeThe following figure indicates the prediction errors if a 1250 km LEO is predicted using onlya 15 x 15 gravity model. The errors shows a periodic behaviour reflecting the orbital period ofR. Wolf Page 39
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Satellite Orbit and EphemerisDeterm
Page 3 and 4: Inter Satellite LinksAbstractGlobal
Page 5 and 6: Inter Satellite LinksTable of Conte
Page 7 and 8: Inter Satellite Links6.2.2 IGSO WAL
Page 9 and 10: Inter Satellite LinksList of Figure
Page 11 and 12: Inter Satellite LinksFigure 6-38 Tr
Page 13 and 14: Inter Satellite LinksList of Tables
Page 15 and 16: Inter Satellite LinksJ2Earths Oblat
Page 17 and 18: Inter Satellite LinksIntroduction1
Page 19 and 20: Inter Satellite LinksIntroductionGE
Page 21 and 22: Inter Satellite LinksISL Observatio
Page 23 and 24: Inter Satellite LinksState Estimati
Page 26 and 27: State EstimationInter Satellite Lin
Page 36 and 37: Orbit ComputationInter Satellite Li
Page 86 and 87: Software DescriptionInter Satellite
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Software DescriptionInter Satellite
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Software DescriptionInter Satellite
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Simulations and ResultsInter Satell
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Satellite Orbit and Ephemeris Determination using Inter Satellite Links

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