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EXECUTIVE SUMMARY
OF THE
MicroCosm® POD SOFTWARE SYSTEM
CAPABILITIES
The MicroCosm® POD state-of-the-art precision orbit and geodetic
parameter determination software system substantially improves upon and
fully implements the NASA GEODYN II, version 8609, precision orbit and
geodetic parameter determination software system.
The capabilities of MicroCosm® POD include:
Numerical integration of satellite equations of motion for orbit
prediction, Orbit state vector estimation, Determination of parameters used to model atmospheric drag, direct
solar radiation and Y-bias effects on the satellite orbit, Determination of measurement and time tag biases, tropospheric
refraction scale parameters, and station and satellite clock
polynomials, Determination of gravitational coefficients, Determination of tracking station coordinates, Modeling and estimation of polar motion and Earth
rotation, Modeling and estimation of solid Earth and ocean tides, Modeling of tectonic plate motion, Modeling of ocean loading effects on tracking station
locations, Modeling of point-mass Lunar, Solar and planetary
gravitation, Modeling of Earth precession and nutation, Processing of satellite tracking data for the determination
of the above parameters, and Simultaneous processing of multiple satellites per data arc and
multiple data arcs per job.
MicroCosm® POD uses Cowell's method for numerical integration of the
satellite equations of motion and the variational equations for the
force model parameters which are to be adjusted.
Cowell's method as implemented in MicroCosm® POD uses
predictor-corrector formulas for the equations of motion and corrector
formulas for the variational equations. Optional orders and time step
sizes may be selected for the integration process.
Since measurements are unlikely to occur coincidentally with the
integration steps, MicroCosm® POD uses an interpolation scheme for
computing the instantaneous satellite position, velocity and adjusted
force model partial derivatives. This interpolation scheme is a
variation of the integration corrector formulas and thus maintains the
same level of accuracy as the integrator.
All of the measurements modeled by MicroCosm® POD have geometric
relationships to the instantaneous satellite position and/or velocity.
Consequently, MicroCosm® POD uses these relationships to calculate
estimated values of the measurements based on the set of parameters
describing the motion of the satellite and the locations of the tracking
stations.
Since variations in any of these parameters will result in differences
between the observed and the calculated values of the measurements used,
dynamical relationships can be obtained which will allow the estimation
of these parameters. These relationships are simply the partial
derivatives of the measurements with respect to the parameter set to be
adjusted.
The set of measurements modeled by MicroCosm® POD include:
Topocentric right ascension and declination of the
satellite, Laser, radar and GNSS range (including single, double and triple
differences), Range rates or Dopplers (including single and double
differences), Radar altimeter range, East and north direction cosines, X and Y angles of the satellite relative to the tracking
station, Azimuth and elevation angles of the satellite relative to the
tracking station.
In addition to these instrument measurements, MicroCosm® POD will
also accept as data, instantaneous Earth-fixed Cartesian or inertial
Cartesian or Keplerian spacecraft ephemerides.
The data recorded at tracking stations contains certain known
systematic errors which can be removed and thus eliminated from the
estimation process. The systematic error corrections performed by
MicroCosm® POD are:
Conversion of all measurement times to ephemeris time
(ET), Correction of measurement times for electromagnetic propagation
delays, Precession and nutation of optical measurements to true of date
inertial coordinates, Modeling of annual aberration, diurnal aberration and parallactic
refraction effects on optical data, Corrections to range measurements for transponder delay, ranging
ambiguities and carrier phase cycle slips, Corrections for offsets of antennas and reflectors from the
spacecraft center of mass, Antenna axis displacement corrections to range and range rate
data measured from X/Y and hour angle/declination mounts, and Tropospheric refraction propagation delay and bending
effects.
Bayesian least squares estimation is used by MicroCosm® POD for
parameter determination. The batch mode of estimation is used and
iteration is performed both to facilitate automatic data editing and
because of the non-linearity of the orbit determination problem. Because
Bayesian estimation is used, MicroCosm® POD requires the input of
a priori estimates and uncertainties for all parameters to be
determined in the solution.
A partitioned solution of the normal equations is performed by
MicroCosm® POD. This permits the separation of parameters into a
global set and an arc set thus allowing the processing of more than one
arc at a time. MicroCosm® POD has also been designed to permit the
simultaneous inclusion in a single arc of over 100 satellites. This
capability permits the modeling and estimation of entire GNSS
constellations of satellites.
MicroCosm® POD Lite is a subset of the
MicroCosm® POD Software which does not include the
MicroCosm® FixClock program or the
MicroCosm® GDF program. Also missing from the
MicroCosm® POD Lite are several minor programs which
are used for the processing of GNSS observations.
MicroCosm® POD Lite is available only as a set of
executable programs. Those who purchase a license to use
MicroCosm® POD Lite Executables and who are current in
"Upgrade Maintenance to MicroCosm® POD Lite Executables"
may upgrade to
MicroCosm® POD Executables by purchasing a license to use
MicroCosm® GNSS Prep Executables.
- Eclipse - Detect eclipse events,
- FormSP3 - Put trajectory in GNSS SP3 format,
- NavMsg - Convert SP3 to RINEX Navigation,
- Orb_Diff - Difference trajectory files,
- Res_Edit - Eliminate edited residuals,
- Sim_Soft - Simulate GNSS, laser or radar data,
- Site_Evo - Tectonic & tide displacements, and
- SLR - Satellite Laser Ranging data reformatting.
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