Abstract
As the first in-orbit formation satellites equipped with a Laser Ranging Interferometer (LRI) instrument, Gravity Recovery and Climate Experiment Follow-on (GRACE-FO) satellites are designed to evaluate the effective ability of the new LRI ranging system applied to satellite-to-satellite tracking. To evaluate the application of LRI in GRACE-FO, a relative kinematic orbit determination scheme for formation satellites integrating Kalman filters and GPS/LRI is proposed. The observation equation is constructed by combining LRI and spaceborne GPS data, and the intersatellite baselines of GRACE-FO formation satellites are calculated with Kalman filters. The combination of GPS and LRI techniques can limit the influence of GPS observation errors and improve the stability of orbit determination of the GRACE-FO satellites formation. The linearization of the GPS/LRI observation model and the process of the GPS/LRI relative kinematic orbit determination are provided. Relative kinematic orbit determination is verified by actual GPS/LRI data of GRACE-FO-A and GRACE-FO-B satellites. The quality of relative kinematic orbit determination is evaluated by reference orbit check and K-Band Ranging (KBR) check. The result of the reference orbit check indicates that the accuracy of GRACE-FO relative kinematic orbit determination along X, Y, and Z (components of the baseline vector) directions is better than 2.9 cm. Compared with the relative kinematic orbit determination by GPS only, GPS/LRI improves the accuracy of the relative kinematic orbit determination by approximately 1cm along with X, Y and Z directions, and by about 1.8 cm in 3D directions. The overall accuracy of relative kinematic orbit determination is improved by 25.9%. The result of the KBR check indicates that the accuracy of the intersatellite baseline determination is about +/−10.7 mm.
Highlights
Introduction iationsGravity Recovery and Climate Experiment Follow-on (GRACE-FO) is regarded as a new mission of gravity formation satellites launched jointly by the National Aeronautics and Space Administration (NASA) and Helmholtz-Centre Potsdam, German Research Centre for Geosciences (GFZ), with a design life of 5 years
The precise ephemeris, satellite clock offsets and Earth rotation parameter files are provided by the Center for Orbit Determination in Europe (CODE), and broadcast ephemeris are provided by the International GNSS Service (IGS)
Z direction, the accuracy of GPS/Laser Ranging Interferometer (LRI) relative kinematic orbit determination is improved by 15.2 mm, and the accuracy along the Z direction reaches 21.9 mm, with an accuracy increase of 41.0%; along the 3D direction, the accuracy of GPS/LRI relative kinematic orbit determination is improved by 17.5 mm, and the accuracy along the 3D direction reaches
Summary
LEO satellites’ orbit determination generally takes pseudo range and carrier phase of GPS as the main observed values. The pseudo range and carrier phase observation models are as follows:. ∇ N s0 ,s = N s − N s0 r,IF r,IF s ,s s ,s where ∇ Lr,IF and ∇ Pr,IF are single-difference observed values of the carrier phase and pseudo range. R0 ,r,IF = ∇ Nr,IF − ∇ Nr0 ,IF s ,s s ,s s ,s where double-difference observed values of ∆∇ Pr00,r,IF , ∆∇ Lr00 ,r,IF and ∆∇ Nr00,r,IF are doubledifference pseudo range, carrier phase and ambiguity, respectively. (i = 0 · · · n)) and the mean value (N LRI ) is calculated, and epochs with a difference greater than a threshold are marked as outliers This threshold is defined as follows: NLRI,0. After the observation equation is linearized, a Kalman filter process can be used for iterative processing
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