the poniting screen.
If the calculation distinguish from the 170h prediction value an invalid I11 Alarm will be
displayed.
8.7.2 Two Line Elements Prediction (TLE)
The analytical propagation of a satellite was originally released in the 1980 and 1986 in the
spacetrack papers (SPACETRACK REPORT NO. 3). A detailed discussion of the theory and
history may be found in the 2006 aiaa paper by Vallado, Crawford, Hujsak, and Kelso. David
Vallado release based on these documents the calculation code in different programming
languages. This code are used with small improvements in the sat-nms ACU to calculate the
satellite position.
The calculation based on the given algorithm and the two line parameters are very simple:
Calculate from the TLE-Data the satellite position for the particular time of interest.
Calculate from the satellite's prediction position and the earth station's known position the
geometric pointing angles.
Finally theses pointing angles are corrected for the effects of atmospheric refraction.
The data have to be entered in the menu 'Orbital Data' in the Section TLE Elements. There are
99 datasets possible. To activate a dataset it must be set in the Tracking Parameter menu in the
Section Prediction Parameters TLE Ephemerides. To follow a satellite with the chosen dataset,
the Tracking Mode have to be set to 'TLE'.
Remark:
The parameter 'max. prediction age' will limit the execution time of the prediction Tracking.
After the limit is reached the antenna will stop the execution and an alarm will be displayed in
the pointing screen.
If the calculation failed an invalid TLE Alarm will be displayed.
The polarization prediction is defined to follow the polarization changes during the tracking
caused by the movement of the satellite. These Method is only be effective for geosynchronous
satellites in inclined operation. It is assumed that the satellite owners are attempting to hold
nominal longitude and a near circular orbit.
To calculate the polarization adjustment it will be necessary to solve the following terms:
Pol Offset abs: This is a linear absolutely offset defined by the satellite operator. The value
is defined as offset against the theoretical calculated polarization value. Most satellite
polarization offsets are around 0?? but nearly all Eutelsat satellites have a polarization
offsets of 3.535??.
Pol Offset look: This is an offset caused by the different look angles over time to the
satellite, if the satellite moves on an inclined geosynchronous circular orbit. This offset is a
sinusoidal movement based on the sidereal time with a time offset. The amplitude can be
calculated from the nominal Orbit position and the inclination. The time offset can be
calculated from the tracking data look angles and dynamic.
Pol Offset incl: This is an offset caused by the flight path. During the equator crosses of
the satellite this value will be + or ?? the inclination depending on the direction of the cross.
At the highest and lowest point this value will be zero. This offset is also a sinusoidal
(C) 2022, SatService GmbH
www.satnms.com
ACU2-19V2-UM-2209 Page 97/99
