Orbit predictions

Laser ranging stations require satellite orbit information in order to point their instrument to the correct location and acquire returns from the retroreflectors. Mission operations groups generate these predicted future orbits from calculated ranging data orbits. Predicted orbit files typically contain orbit information for multiple days. Predictions are primarily available in daily files sorted by year and satellite; predictions for lower orbiting satellites, however, are often transmitted several times per day. The Consolidated Prediction Format (CPF) is now used operationally for satellite predictions within the ILRS; CPF provides orbit data that accurately predict positions and ranges for a large variety of targets in tables of X , Y , and Z positions, which can be interpolated for accurate predictions. SLR stations download these prediction files and coordinate tracking schedules for satellite acquisition.

Satellite prediction files are archived on the CDDIS by year and satellite. In addition, stations can retrieve the latest predicted orbit file for all laser tracked satellites in a single subdirectory.

The starting directory for these files in the is:

ftp://cddis.gsfc.nasa.gov/slr/cpf_predicts/

Append the following directory and file names to the starting directory:

YYYY/SATNAME/SATNAME_cpf_YYMMDD_###V.CEN

as described in the table below.

Code Meaning
SATNAMESatellite Name
YYYY 4-digit year
YY2-digit year
MM2-digit month
DD 2-digit day
### ephemeris version number
V version within the day
CEN mission group generating the prediction