Publications related to the GRACE Missions (no abstracts)

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Toward Robust GNSS Real–Time Orbit Determination for Microsatellites Using Factor Graph Optimization

Hou, Cong, Jin, Xiaojun, Yang, Xiaopeng, and Xiao, Tong, 2025. Toward Robust GNSS Real–Time Orbit Determination for Microsatellites Using Factor Graph Optimization. Remote Sensing, 17(7):1125, doi:10.3390/rs17071125.

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@ARTICLE{2025RemS...17.1125H,
       author = {{Hou}, Cong and {Jin}, Xiaojun and {Yang}, Xiaopeng and {Xiao}, Tong},
        title = "{Toward Robust GNSS Real-Time Orbit Determination for Microsatellites Using Factor Graph Optimization}",
      journal = {Remote Sensing},
     keywords = {microsatellite, real-time orbit determination, GNSS, factor graph optimization, sliding window},
         year = 2025,
        month = mar,
       volume = {17},
       number = {7},
          eid = {1125},
        pages = {1125},
     abstract = "{Extended Kalman Filter (EKF) is extensively employed in Global
        Navigation Satellite System (GNSS)-based real-time orbit
        determination (RTOD) for microsatellites due to its low
        complexity. However, the performance of EKF-RTOD is markedly
        degraded when the microsatellite deviates from a stable Earth-
        pointing attitude and employs a low-cost receiver. Factor graph
        optimization (FGO), which addresses nonlinear problems through
        multiple iterations and re-linearization, has demonstrated
        superior accuracy and robustness compared to EKF in challenging
        environments such as urban canyons. In this study, we introduce
        a novel FGO-based RTOD (FGO-RTOD) approach, which integrates
        state transfer factors to establish temporal connections between
        state nodes across multiple epochs. Real-time processing is
        achieved through a sliding window mechanism combined with
        marginalization. This paper evaluates the performance of the
        proposed algorithm in a regular scenario using data from GRACE-
        FO-A, which maintains the Earth-pointing attitude and employs a
        high-performance receiver. The positioning results of GRACE-FO-A
        indicate that FGO-RTOD marginally outperforms EKF-RTOD in
        accuracy. Furthermore, the performance of FGO-RTOD is assessed
        in challenging scenarios using simulation data and on-orbit data
        from Tianping-2B microsatellite, which is not in an Earth-
        pointing attitude and employs a low-cost receiver. The
        simulation results reveal that FGO-RTOD reduces the Root Mean
        Square (RMS) of positioning error by 79.0\% relative to EKF-RTOD
        and exhibits significantly enhanced smoothing. In the
        Tianping-2B experiments, FGO-RTOD reduces the RMS of carrier-
        phase ionosphere-free combination residuals from 2 cm to 1 cm
        relative to EKF-RTOD, alongside a substantial improvement in the
        ratio of valid observations. These findings underscore the
        effectiveness of FGO-RTOD in managing outlier measurements in
        challenging scenarios.}",
          doi = {10.3390/rs17071125},
       adsurl = {https://ui.adsabs.harvard.edu/abs/2025RemS...17.1125H},
      adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}

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