Satellite Orbit and Ephemeris Determination using Inter Satellite Links
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Satellite Orbit and Ephemeris Determination using Inter Satellite Links

Satellite Orbit and Ephemeris Determination using Inter Satellite Links Satellite Orbit and Ephemeris Determination using Inter Satellite Links

athene.bibl.unibw.muenchen.de
from athene.bibl.unibw.muenchen.de More from this publisher
11.07.2015 Views

Simulations and ResultsInter Satellite Links1.41.21.0URE [m]0.80.60.40.20.02450997.2 2450997.4 2450997.6 2450997.8 2450998.0Julian Date [Days]Figure 6-41 Ageing of Ephemeris MEO, raw estimate ground only 12 states 1 hourEach bar represent the URE of one set of parameters valid for one hour. The satelliteephemeris are degrading fast with time and exceed the 1 meter level after approximately 15hours.In the next example, the same determined satellite orbit is used, but now the last 6 hours ofposition estimates are used to derived a smoothed initial position for the propagation process.This is achieved by feeding a least squares estimator with the positions an estimating the"true" position at the initial epoch. The follwong figure shows the orbit error evolution, if thissmoothed position is now propagated.Page 140R. Wolf

Inter Satellite LinksSimulations and ResultsRadial Error [cm] 1998 07 02 14:35 - 1998 07 04 02:3510.0-10.00[h]5 10 15 20 25 30 35Along Track Error [cm] 1998 07 02 14:35 - 1998 07 04 02:3579.0-79.00[h]5 10 15 20 25 30 35Cross T rack Error [cm] 1998 07 02 14:35 - 1998 07 04 02:355.0-5.00[h]5 10 15 20 25 30 35Figure 6-42 MEO propagation error with 6 hour smoothingThe along track error also shows a secular error tendency, but much smaller than that of thepropagated raw estimate. If the same broadcast model is fit over this propagated orbit, theURE remain below 30 cm even nearly up to 24 hours, as can be seen in the following picture.R. Wolf Page 141

Simulations <strong>and</strong> Results<strong>Inter</strong> <strong>Satellite</strong> <strong>Links</strong>1.41.21.0URE [m]0.80.60.40.20.02450997.2 2450997.4 2450997.6 2450997.8 2450998.0Julian Date [Days]Figure 6-41 Ageing of <strong>Ephemeris</strong> MEO, raw estimate ground only 12 states 1 hourEach bar represent the URE of one set of parameters valid for one hour. The satelliteephemeris are degrading fast with time <strong>and</strong> exceed the 1 meter level after approximately 15hours.In the next example, the same determined satellite orbit is used, but now the last 6 hours ofposition estimates are used to derived a smoothed initial position for the propagation process.This is achieved by feeding a least squares estimator with the positions an estimating the"true" position at the initial epoch. The follwong figure shows the orbit error evolution, if thissmoothed position is now propagated.Page 140R. Wolf

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