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.