TLE options

There are several options to build TLEs.

TLE building parameters

The parameters that will define how each TLE will be generated are the following ones:

• Position tolerance: it defines the precision on position obtained during the fitting process.
• Position Only: if this option is selected, the fitting iteration will only be done on positions and not velocity.
• Using BStar: with this option Bstar parameter will be taken into account
• Type of method: we may choose between two different methods
  • Differential method
  • Levenberg Marquardt method
• Maximum amount of iterations: this entry limits the amount of iteration during the fitting process.

All these parameters correspond to the PATRIUS TLE class. Thus, it is possible to get more information on it by reading the PATRIUS Wiki.

How to build TLEs

Then, it is possible to choose how TLE will be built:

Single TLE

Using this option, only one TLE will be computed. In that case, we will set:

• the required epoch for this TLE (mandatory after the initial orbit epoch … and before the 4th October 1957!).
• the amount of points in the ephemeris to fit the TLE.

A specific check box exists to know if maneuvers will be considered or not. This option is common to all the TLE build options. If the option is not selected, the TLE computation will not care about maneuvers even if some exist: in that case, the TLE precision will not be very good! On the contrary, if the option is selected, the ephemeris interval to take into account will be reduced to take into account only points before the first encountered maneuver.

Best single TLE

Only one TLE will be computed but a post process will be executed to search which amount of points in the ephemeris gives the best precision in semi-major axis. So, we will have to set the following parameters:

• the required epoch for this TLE as for the previous option.
• the maximum amount of points in the ephemeris to fit the TLE (so, the post process will compute TLE using 1 point to this amount of points). This amount of points will be eventually reduced if there is less points in the ephemeris
• the amount of points for comparison between points of the ephemeris and points computed thanks to this TLE.

Best dated TLEs

With this option, several TLEs will be computed for each epoch specified in the list below. So, we will have to set the following parameters:

• The maximum amount of points in the ephemeris to fit the TLE as in the previous option
• The minimum duration for updating a TLE (useful at the end of the ephemeris as when maneuvers are taken into account.
• The list of epochs.

Note that in case of several TLEs computation, if the “Maneuvers consideration” option is selected, the reduction of the amount of points as soon as a maneuver is detected will be done for each date.

Best periodic TLEs

It is almost the same kind of option as the dated one but rather than to specify a list of epochs, the user will specify an initial epoch and a recurrent period. The parameters to set will be:

• The maximum amount of points in the ephemeris to fit the TLE as in the previous option
• The minimum duration for updating a TLE as in the previous option.
• The initial epoch for the first TLE of the list.
• The period to update the TLE.