Memory space is very limited in the ACU-ODM. The file size is limited to 64 Kbytes, being
equivalent to about 12 days of AZ/EL data in 10 minutes intervals.
Memory Tracking is another tracking method which is based on step track unsing the recorded
antenna pointing as a backup if the beacon level drops too low for a successful steptrack. Unlike
Adaptive Tracking
which calculates a sinusodial model of the antenna movement, Memory
Tracking simply moves the antenna to the position it had one siderian day before, if a step track
attempt was not successful. Memory Tracking requires at least 24 hours of recorded tracking
data.
8.7 Prediction Tracking with Ephemeris Data
The Prediction Tracking move the antenna along a satellite position calculated from ephemeris
data. The sat-nms ACU recognizes the following data formats:
Keplerian elements : The ACU recognizes and parses keplerian elements in the NASA 2-
line format (TLE) . The two lines of element definition may be prepended by an additional
line with the satellite's name. A common source for Keplerian elements in this format is
www.celestrak.com
. The sat-nms ACU uses the NORAD SDP4 model to predict a satellite's
position from this type of data.
Intelsat elements : Intelsat publish ephemeris data (I11) for their communication satellites
at their web site but also other satellite operators deliver data in this format. The data format
and the mathematical model for this data is Intelsat proprietary and defined in the document
IESS412.
8.7.1 Intelsat eleven Parameter Prediction (I11)
The analytical propagation of a satellite in the eleven Parameter format was originally released
by Intelsat IESS412 document. The calculations which are used in the sat-nms ACU are based on
Review 3 of this document.
The calculation based on the given algorithm and the provided eleven parameters are very
simple:
Calculate from the I11-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.
To verify the satellite position calculation, there is also the satellite position after 170h available.
The sat-nms ACU use this parameter to verify the correct entry of the data.
The data have to be entered in the menu 'Orbital Data' in the Section I11 Elements. There are 99
datasets possible. To activate a dataset it must be set in the Tracking Parameter menu in the
Section Prediction Parameters I11 Ephemerides. To follow a satellite with the chosen dataset, the
Tracking Mode have to be set to 'I11'.
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
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