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IAA Transactions, No. 8, ``Celestial Mechanics'', 2002
Station coordinates from observations of DORIS
system TOPEX/Poseidon satellite
M. V. Vasiliev, E. I. Yagudina
Institute of Applied Astronomy, St. Petersburg, Russia
The satellite system DORIS (Doppler Orbitography and Radiopositioning In­
tegrated by Satellites System) is the effective means of space geodesy and geody­
namics. The system designs mainly for monitoring station coordinates (beacons)
and investigating the coefficients of the gravity field of the Earth. Along with
SLR, GPS observations of DORIS system are used also for EOP parameters de­
termination. The main teams for measurements process are NASA, GSFC (USA)
and CNES (France). The main software for DORIS measurements process are
GEODYN developed by JPL and GYPSY [1]. In IAA RAS the software is devel­
oped in the frame of ERA system [2] as alternative software for precision orbit
determination and monitoring of positions of the observational stations (beacons).
For testing the new software the T/P satellite observations have been taken from
website: ftp://cddisa.gsfc.nasa.gov/anonymous.
The first results of the processing by ERA system of Doppler observations
of the satellite system DORIS T/P are presented. The short arc orbit technique
has been used for the process of Doppler observations and the first values of the
determination of the station coordinates are presented. The three days sessions
have been used for the results received. The results are shown to be in a good
agreement with the results of other authors.
Now ERA system contains special software for calculation the motion of arti­
ficial satellites but it has to be changed and adopted for satellites with complex
shape and at low orbits (800--1300 km) similarly to satellites of DORIS system.
For this purpose it is necessary to change the radiation pressure model, and to
take into account the thermal emission of satellite. One also cannot consider the
satellite as cannonball any more and neglect its rotation, and so on . At present
for the force model of satellite DORIS system for example as T/P we take into
account all necessary forces mentioned in publications of IERS report 2000 [3].
Nowadays almost all features of the model are realized in frame of ERA system,
according to demands of IERS Standards, but for T/P satellite with very complex
shape and altitude control special software of taking into account the shape and
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radiation pressure as well as atmospheric drag must be developed [4]. Model of
density variation now is almost adopted for ERA. The solar geomagnetic indexes
are collected for ERA table.
For receiving the different parameters the Kalman filter procedure was devel­
oped too. Kalman filter is realized in ERA system. It is shown that in the case
of Kalman filter the representation of observations is by two times better than
in the case received by polynomial approximation of clock error. The application
of stochastic approach permitted to receive rather small residuals increasing the
reliability of parameters under consideration.
At present for processing the Doppler satellite observations the short arc orbit
technique is used very often. The general requirements of dynamical model satel­
lite motion are rather modest as compared with the case of big arcs processing. At
each 6 hours interval during the every one day we determined 6 coordinates and
velocities of satellite, two parameters of light pressure and 5 power polynomial
coefficients of clock behaviour at every passage above the station. The coordi­
nates of all stations have been determined at three daily intervals. In this way we
processed three days. The results of the determination of the station coordinates
are presented in the paper in table as the residuals after fitting . The uncertainties
of the corrections to the station coordinates are no more than \Sigma3 cm, that is ade­
quate to all processing of other authors. Further, after introducing in the satellite
model new forces (atmospheric drag, light pressure with taking into account the
shape of satellite) we are going to process the observations using full model. The
processing of observations at long intervals (1 month and more) using full model
can give us all parameters of EOP and gravity field coefficients.
References
1. Tapley B. D., Ries J. C. et al. ``Precision orbit determination for
TOPEX/Poseidon''. J. of Geophysical research, 1994, 99, No. C12, 24383--
24404.
2. Krasinsky G. A., Vasilyev M. V. ERA: knowledge base for ephemeris and
dynamical astronomy. In: Proceedings of IAU Colloquium 165, Poland, 1996,
239.
3. IERS Conventions 2000 (in press).
4. Antreasian P. G., Rosborought G. W. Prediction of Radiant Forces on the
Topex/Poseidon Spacecraft, Journal of Spacecraft and Rockets, 1992, 29,
81--90.
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