GPS Solutions

, Volume 12, Issue 3, pp 187–198 | Cite as

Precision real-time navigation of LEO satellites using global positioning system measurements

  • Oliver Montenbruck
  • Pere Ramos-Bosch
Original Article


Continued advancements in remote sensing technology along with a trend towards highly autonomous spacecraft provide a strong motivation for accurate real-time navigation of satellites in low Earth orbit (LEO). Global Navigation Satellite System (GNSS) sensors nowadays enable a continuous tracking and provide low-noise radiometric measurements onboard a user spacecraft. Following the deactivation of Selective Availability a representative real-time positioning accuracy of 10 m is presently achieved by spaceborne global positioning system (GPS) receivers on LEO satellites. This accuracy can notably be improved by use of dynamic orbit determination techniques. Besides a filtering of measurement noise and other short-term errors, these techniques enable the processing of ambiguous measurements such as carrier phase or code-carrier combinations. In this paper a reference algorithm for real-time onboard orbit determination is described and tested with GPS measurements from various ongoing space missions covering an altitude range of 400–800 km. A trade-off between modeling effort and achievable accuracy is performed, which takes into account the limitations of available onboard processors and the restricted upload capabilities. Furthermore, the benefits of different measurements types and the available real-time ephemeris products are assessed. Using GPS broadcast ephemerides a real-time position accuracy of about 0.5 m (3D rms) is feasible with dual-frequency carrier phase measurements. Slightly inferior results (0.6–1 m) are achieved with single-frequency code-carrier combinations or dual-frequency code. For further performance improvements the use of more accurate real-time GPS ephemeris products is mandatory. By way of example, it is shown that the TDRSS Augmentation Service for Satellites (TASS) offers the potential for 0.1–0.2 m real-time navigation accuracies onboard LEO satellites.


Real-time navigation Orbit determination GPS LEO satellites 



PRB acknowledges a fellowship from the Departament d’Universitats, Recerca i Societat de la Informacio de la Generalitat de Catalunya, and from the European Social Fund, and wishes to thank its financial support. The present study makes use of GPS measurements from the CHAMP, GRACE, TerraSAR-X, ICEsat, SAC-C, and MetOp missions that have been made available by the GeoForschungsZentrum (GFZ), Potsdam, the Jet Propulsion Laboratory (JPL), Pasadena, the Center for Space Research, University of Texas at Austin (UT/CSR), the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT), Darmstadt, the European Space Agency (ESA/ESTEC), Noordwijk. GPS orbit and clock solutions have been obtained from the Center for Orbit Determination in Europe (CODE), which is part of the International GNSS Service (IGS; Beutler et al. 1999). Real-time generated GPS ephemerides have been provided by InfoTerra under license of JPL. The support of all institutions has been vital for this work and is gratefully acknowledged.


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Copyright information

© Springer-Verlag 2007

Authors and Affiliations

  1. 1.German Space Operations CenterDeutsches Zentrum für Luft- und RaumfahrtWeßlingGermany
  2. 2.Research Group of Astronomy and GeomaticsTechnical University of CataloniaBarcelonaSpain

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