For optimum satellite tracking the software requires two things; good pointing across the whole sky (esp if you want to do high magnification imaging of ISS) and "real time" mount position coordinates. SkyTrack uses a closed loop for tracking, in one instance it calculates the current position of the satellite, the satellite's current angular velocity and queries where the point is currently pointing. It then uses the movexis command to determine a rate based on the satellite velocity and how much it needs to adjust to center the satellite in the FOV. The issue with some ASCOM drivers is that they may queue the mount's position, for example only querying its position once every second. For normal use this is quite adequate. For satellite tracking it becomes an issue, for example if the object is moving at 2 degrees/second and I query the mount for its position and the data is one second old, I now have random error of a whole 2 degrees.
You can use Skytrack three ways.
1) Connecting with the latest version of APCC Pro and ASCOM gives the best results. A model with APCC gives excellent pointing. Ray added some excellent features to APCC Pro that allows for "real time" (modelled) RA/Dec mount queries. In fact one command returns both values often in less than 15ms.
2) The next best method is connecting directly to the mount via a RS232 port (without ASCOM or APCC) using what I call in the software a legacy interface. This satisfies the "real time" mount position coordinates, however, pointing is less accurate without a model.
3) The least desirable method is connecting through the ASCOM driver only. There is not modelled pointing and the AP ASCOM driver queues the mount position every second or so. It will track, but it is not very smooth and it may be difficult to keep the object in the FOV depending on the size of the FOV.
The T+Epoch parameter is the age in days of the orbital elements in the downloaded TLE file. It is best to download a new file each evening before observing.