Two-antenna orbit solution of FORMOSAT
Two-antenna orbit solution of FORMOSAT-3/
Tzu-Pang Tseng and Cheng-Yuang Huang
GPS Science and Application Research Center, National Central University, Taiwan
1. FORMOSAT-3/COSMIC mission consists of six microsatellites, named FM1-FM6.
2. Each satellite is equipped with four antennas connected to one GPS receiver. Two signalpatch antennas for precise orbit determination (POD) are mounted on the upper part of
the satellite body and the other two antennas for radio occultation (GPS-RO) research
are mounted on the bottom part.
Different numbers of GPS observations in two
the POD antennas
There are 24 channels in the COSMIC GPS receiver. 12 channels are allocated to two
POD antennas and the others to two occultation antennas. Of these 12 channels in the
POD purpose, 9 channels are allocated to the default POD antenna and the others to the
non-default POD antenna. Precise Orbit Determination (POD)
• Reduced-dynamic orbit determination (DOD)
6 Keplerian parameters
9 solar radiation pressure parameters
240 empirical parameters
Epoch-wise receiver clocks
• Kinematic orbit determination (KOD)
– Epoch-wise 3-dimension coordinates
– Epoch-wise receiver clocks
Internal orbit accuracy
Accuracy of the orbit derived from oneantenna orbit solution (one-AOS)
Internal orbit accuracy
Two-antenna orbit solution (two-AOS)
Orbit derived from two-AOS One-AOS vs. two-AOS (1)
Fig: Sky plots of phase residuals for FM4 on DOY 300, 2009 using (a) POD-X with one-AOS, (b) POD+X with oneAOS, (c) POD-X with two-AOS and (d) POD+X with two-AOS, and the sky plots for (e) GRACE-A (DOY 365,
2008) and (f) GRACE-B (DOY 365, 2008) One-AOS vs. two-AOS (2) Table : Daily STD values (in cm) of phase residuals for POD-X and POD+X
antennas of FM4 based on the one-AOS and two-AOS One-AOS vs. two-AOS (3) Fig : Differences between one-AOS and two-AOS in (a) position and (b) velocity for
FM4 (DOY 300-307, 2009) One-AOS vs. two-AOS (4) Table : Daily STDs of differences in position and velocity for FM4 between the
one-AOS and two-AOS
• We determines the orbit of F3/C using GPS data from the two POD
antennas in order to strengthen the GPS geometry.
• In general, the observation residuals are minimized in the GPS-based orbit
determination using the least-squares parameter estimation. As such, the
few-mm degradation and improvement in POD-X and POD+X,
respectively, are shown when the two-AOS is used.
• Since F7/C2 will also equips with two POD antennas, this study can serve
as a reference for POD of F3/C when GPS data from two antennas is used.
We will provide the two-antenna orbit product for users in Taiwan RO
Process System (TROPS).
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