Possible Modification of Geopotential Co-efficients
to Improve Propagation Accuracy of Polar orbit

H.Dosho
DOSHO.HIROHIKO@TKJV01.NNET.NASDA.GO.JP
NASDA

Abstract:
The Japanese Marine Observation Satellite-1 (MOS-1), was launched
from the NASDA Tanegashima Space Center on February 19, 1987, and
has been operated in a sun-synchronous orbit with a recurrent
period of 17 days.

After completing of the 8 years mission operation, the semi-major
axis of the orbit was slightly shortened in order to change into
a recurrent period of 18 days.  After gathering the tracking data
for the following two months, the satellite was re-orbited using
all the remaining fuel and the satellite operations were
terminated on November 29, 1995.

From the early stage of its operation, we noticed the along-the-
track prediction error having periods of 8.5 days and 17 days and
had reported the phenomenon and the evaluation results of the
resonant terms of the geopotential model GEM10B in 1989**.

The same study was carried out again based on the above-mentioned
orbit data.  Following the estimation of the high order resonance
terms of the Goddard Earth Model 10B (GEM1OB) from MOS-lls new
orbit, was the modification of its specific terms for optimizing
the model to the orbit of MOS-1.  Following these procedures were
the evaluation of GEM10B and GEMT3.

The evaluation method is to compare the position error which
comes from geopotential model difference at each overlapping
period of the observation data, which are used for successive
orbit determination.  This particular method assumes that the
orbit errors caused by systematic errors may cancel out each
other, as it employs the differences obtained from the orbits
that are determined time after time.  Such presumption may serve
to display that a position deviation is caused only by gravity
model difference.

The study demonstrated the method's validity of estimation
concerning geopotential terms, with regard to improvement of
propagation accuracy for a specific polar orbit.

** Gravity model comparison by MOS-1 tracking data, T.Tajima, at
al., Intl.  Symposium of Space Dynamics, Toulouse, November 1989.