Satellite Orbit and Ephemeris Determination using Inter Satellite Links

More documents

Recommendations

Info

Autonomous Onboard ProcessingInter Satellite LinksNow, what this all to do with autonomous onboard processing? The measures 1. / 2. and 3. forone satellite could easily be provided by each satellites onboard processor! Imagine thefollowing: presumed, measurements are taken onboard the satellite. The onboard processoruses these observations to update the error estimates of position, velocity and clock. Theseerrors can directly be used as correction to the ephemeris derived satellite position andtherefore be immediately transmitted to the user. Data latency: negligible, especially ifcompared to a conventional ground based system! This seems should be in fact a sufficientmotivation to take the effort with respect to space craft complexity and cost of implementing aonboard processing “facility”.7.2 Implementation Aspects of Onboard ProcessingThe software for an autonomous onboard processor has to satisfy some requirementdepending on the tasks to be performed. The complete chain from the raw measurements tointeger ephemeris information for the navigation user requires the software to providefollowing functionalities:• conversion of raw measurements to ranges and range rate observables• detection and isolation of outlying measurements• orbit propagation using a precise force model• estimation of orbit and clock errors from measurements• a possibility to reset the state estimator if desired or necessary• coordinate conversion from a terrestrial reference frame to ECI-J2000• accept upload of celestial body ephemeris, earth rotation parameters ...• adjusting the broadcast message to a period of predicted position vectors.• detection and computation of required orbit manoeuvres to maintain desired orbitproperties.• orbit propagation using the broadcast message• detection and isolation of abnormal clock drift or orbit degradation• integrity check on the ephemeris and clock parameter message delivered to the user• accept new upload from ground for reference trajectory data• consistency check of own computed dataNot all tasks have the same performance requirements. The used CPU should be fast enoughto allow at least one duty cycle per second for the integrity processing. Orbit prediction forexample can be performed with slower update rates. Integrity checks of ephemeris and clockparameters have to be performed once per second.The measurements can be ground links, as well as inter satellite links. These are especiallyvaluable to check integrity of the satellite ephemeris.Page 154R. Wolf
Inter Satellite LinksAutonomous Onboard Processing7.2.1 Complexity of Orbit Prediction and Estimation AlgorithmsAccording to estimations made during the AUNAP project, the computational load for themodel using a 4 x 4 earth model requires about 5 – 10 percent of today available spacequalified CPU's if performing one duty cycle per second. Also, in the DIODE experiment, a15 x 15 gravity model has successfully been used in an onboard processor. The followingfigure shows a block diagram of the precise orbit estimation process.Figure 7-1 Block Diagram of Orbit DeterminationThe orbit integrator is needed twice, as non linear state predictor in the state estimationprocess and after determination of an accurate satellite state vector, for orbit propagation. Anadditional orbit propagator based on the broadcast ephemeris model is also needed.The following table contains an estimation of the algorithmic complexity of an orbitestimation process (precise estimation). These numbers have been investigated during theGerman AUNAP project.All Routines,one DutyCycle11 States8 Obs.GP 4 x 411 States8 Obs.GP 15 x 1511 States8 Obs.GP 70 x 70Add /SubtractMul / Div math. Func. Loops /Cond.InstructionsAssignments15409 19015 826 6216 1261433537 27611 10022 7888 25814554653 1058323 235878 45288 316874Table 7-1 Estimated Algorithmic Complexity of Orbit Estimation Process(AUNAP 1996)R. Wolf Page 155
Page 1 and 2:
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 28 and 29:
Page 30 and 31:
Page 32 and 33:
Page 34 and 35:
Page 36 and 37:
Orbit ComputationInter Satellite Li
Page 38 and 39:
Page 40 and 41:
Page 42 and 43:
Page 44 and 45:
Page 46 and 47:
Page 48 and 49:
Page 50 and 51:
Page 52 and 53:
Page 54 and 55:
Page 56 and 57:
Page 58 and 59:
Page 60 and 61:
Page 62 and 63:
Page 64 and 65:
Page 66 and 67:
Page 68 and 69:
Page 70 and 71:
Page 72 and 73:
Page 74 and 75:
Page 76 and 77:
Page 78 and 79:
Page 80 and 81:
Page 82 and 83:
Page 84 and 85:
Page 86 and 87:
Software DescriptionInter Satellite
Page 88 and 89:
Page 90 and 91:
Page 92 and 93:
Page 94 and 95:
Page 96 and 97:
Page 98 and 99:
Page 100 and 101:
Page 102 and 103:
Page 104 and 105:
Page 106 and 107:
Page 108 and 109:
Simulations and ResultsInter Satell
Page 110 and 111:
Page 112 and 113:
Page 114 and 115:
Page 116 and 117:
Page 118 and 119:
Page 120 and 121: Simulations and ResultsInter Satell
Page 168 and 169: Autonomous Onboard ProcessingInter
Page 206 and 207: ReferencesInter Satellite Linksinte
Page 208 and 209: ReferencesInter Satellite Linkshalf
Page 210: ReferencesInter Satellite LinksSan
show all

Satellite Orbit and Ephemeris Determination using Inter Satellite Links

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?