Methods

GENTLEMAN is working in two steps.

1. Propagation:

First it will propagate a trajectory thanks to PSIMU tool; all the possibilities linked to its use are available so, any kind of trajectories around the Earth are allowed (LEO, LEO, even reentry !). This trajectory will be stored in a SQlite data base with an output step defined by the user.

2. TLE building:

Once this trajectory has been computed, GENTLEMAN will generate one or several TLEs. The basic methods to build these TLEs are the ones proposed by PATRIUS (Differential or Levenberg Marquardt methods). But, GENTLEMAN adds a complementary functionality as it allows finding the best compromise on the amount of points to fit a TLE thanks to the propagated trajectory.

Let us give an example with a trajectory ephemeris (included in the SQlite file) composed of 50 output points.

• A first possibility is to fit a TLE by giving explicitly the amount of points to take into account: for example, the ten first ones.
• A second possibility is to leave GENTLEMAN to find this amount of points for such a fitting. To do it, GENTLEMAN will compute different TLEs using 1, then 2, then 3, then up to 50 points (or less if the user entered a maximum number). Considering each of these TLEs, GENTLEMAN will compute for each point of the trajectory (or less if the user entered another maximum number), the difference between the trajectory and the one propagated with the TLE as initial condition and the model linked to it (SGP4 for LEO and DeepSDP4 for LEO). GENTLEMAN will then select the TLE which will get the lowest value for the mean error in semi major axis.
• In case of maneuvers to take into account or if the user decided to compute several TLEs (for example one TLE by day), this process will be executed only in the interval between two TLEs (or one TLE and the next maneuver).