HGS-1 Rescue
Year 2000
MicroCosm® and GNSS
MicroCosm® GNSS Prep
Timing Comparisons
Operating Environment
Other Information
Support Programs
Sign In
Pricing Information
Contact VMSI



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.


MicroCosm® POD Capabilities


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.


Integration and Interpolation


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.


Measurement Modeling


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.


Data Processing


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.


Statistical Estimation


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


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.


Additional Cost MicroCosm® Support Programs

  • 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.

Back to MicroCosm® Home Page