IEEE - Aerospace and Electronic Systems - February 2022 - 8

Comparison of Atmospheric Mass Density Models Using a New Data Source: COSMIC Satellite Ephemerides
Figure 1.
COSMIC satellite information [25]. (a) Illustration ofCOSMIC satellites. (b) Geometry of the COSMIC satellite.
atmospheric density do not skew the results. However,
the data sources used to compare model predictions
against are generally the same data used in the construction
of the latest model. This gives an unfavorable bias
toward the newer model being introduced.
In general, the performance of these empirical AMD
models has been evaluated using the following three different
methods:
1) comparison with total density estimates derived from
other in situ measurements/data [13],[15],[16], e.g.,
the thruster activation data in the Gravity Field and
Steady-State Ocean Circulation Explorer (GOCE)
mission [17] and accelerometer data in the Challenging
Minisatellite Payload (CHAMP), The Gravity
Recovery and Climate Experiment (GRACE), and
SWARM missions [17]-[21];
2) assessment in the orbit prediction (OP) process [11],
[13];
3) comparison with physical models [22], e.g.,TIEGCM.
In
the literature, three state-of-the-art empirical models
are mainly assessed: MSISE00, JB2008, and DTM2013.
In this work, a new testing model is also developed by
incorporating a range of ion contributions to the total
mass density. The performance of these models for a
higher orbit of approximately 800 km altitude in the LEO
region will be investigated. Specifically, these models are
compared using the predictions from orbit propagation
software to quantify model accuracy by determining the
deviation from the ephemerides of the Constellation
Observing System for Meteorology, Ionosphere, and Climate
(COSMIC) satellites [23]. These ephemerides have
not been used in any existing model (as far as the authors
can tell) and provide an unbiased way to test model accuracy
of existing AMD models. More importantly, the
COSMIC orbit has not been assimilated into any
8
aforementioned empirical AMD models, hence, can generate
unbiased assessment results for these models.
The rest of this article is organised as follows. The COSMIC
mission is briefly introduced in Section " Data Source "
with geometric information of the satellites and precise orbit
and attitude profiles. Section " Orbit Propagator " revisits the
classical orbit dynamics and elaborates the formulation for
surface force modeling ofaerodynamical drag and SRP. Four
AMD models, MSIS90/00, JB2008, and DTM2013, are
revisited in Section " Atmospheric Mass Density Models "
with focus on their principles, solar drivers and other working
conditions. A new testing model is introduced in Section
" New Testing Model. " Section " Data Retrieval and Space
Weather Conditions " introduces how the COSMIC data are
retrieved and weather conditions for the data periods. Section
" ComparisonMethodology and Results " delineates the comparison
methodology and OP results are presented and analyzed.
The conclusion of this article is drawn in Section
" Conclusion. "
DATA SOURCE
COSMIC is a joint U.S.-Taiwan space program to provide
high-quality radio occultation profiles for meteorologic,
ionospheric, climatological, and space weather
research [23]. The constellation consists of six identical
satellites and the first one was launched into space in 2006.
Currently only four ofthem are fully operational, in a circular
orbit with an altitude of approximately 800 km and an
inclination of 72. The COSMIC satellites are shown in
Figure 1(a). The precise ephemerides ofthese satellites can
be retrieved from the COSMIC Data Analysis and Archive
Center (CDAAC) at https://cdaac-www.cosmic.ucar.edu.
These ephemerides are calculated in the precise orbit determination
process using the spaceborne GPS observations
[24]. It is reported an orbit accuracy of 2 cm to 3 cm
was achieved using both the kinematic and dynamic
approaches. Attitude state of the satellites and their solar
IEEE A&E SYSTEMS MAGAZINE
FEBRUARY 2022

https://cdaac-www.cosmic.ucar.edu

IEEE - Aerospace and Electronic Systems - February 2022

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