8.8 Polarization Prediction

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 movement based on the sidereal time with a time offset. The amplitude is defined by the inclination. The time offset can be calculated from the tracking data look angles and dynamic.

The summary of these three terms will provided at least the polarization value.

As we see from above definition, it will necessary to have some additional information to initiate a polarization prediction. Therefore it will be necessary to provide the sat-nms ACU the following parameter in the ‘Tracking Parameter’ menu:

• Target orbit position: This Parameter should define the nominal Orbit position of the satellite. This value should be available from the satellite operator. Remark : In the Polarization prediction setting ‘ADAPTIVE’ this value will be recalculated after get a valid medium model, but only small changes are allowed per calculation cycle to the bases value (+/-0.5°). Therefore the start orbit position have to set within this range.
• Inclination: The actual inclination value of the satellite. This value should be also available from the satellite operator.Remark : In the Polarization prediction setting ‘ADAPTIVE’ this value will be recalculated after get a valid medium model, but only small changes are allowed per calculation cycle to the bases value (+/-0.5°). Therefore the start inclination have to set within this range.
• Satellite Pol offset: The linear polarization offset of the satellite. This value should be also available from the satellite operator or have to be measured.
• Since we need from the tracking also the dynamic of the satellite (movement up or down), the sat-nms ACU cannot start the polarization prediction immediately after setting the polarization prediction to ‘ON’ or ‘ADAPTIVE’, it need some tracking cycles to clearly identify the direction of movement (15min.). If the main tracking mode is ‘I11’ or ‘TLE’ the polarization prediction will start immediately because the movement of the satellite is already defined by the satellite ephemerides.