Adding new satellite to Gpredict
Although satellite community is usually very responsive when it comes to updating satellite information, when a new satellite gets launched it may take several days before its data becomes available in popular tracking software. If you want to start using a new "bird" as soon as it gets launched, it is easy to add it manually.
For Gpredict this is a 2-step process (note the instructions pertain to Gpredict 2.3-33, your menus may be different):
Launch providers will usually provide preliminary (pre-launch) TLEs. They are just an approximation and soon after launch will start getting out of date, but will get you started at least for the first few orbits.
One point worth noting is that these TLEs will tend to have a dummy Satellite Catalogue Number because the latter is only assigned once a satellite enters its orbit. Take note of the Satellite Catalogue Number used in your TLEs!.
Now that you've got the preliminary TLE data, save them into a file. In Gpredict select "Edit" -> "Update TLE data from local files" and select a directory you saved your file to. Note Gpredict will scan and try to import everything that looks like a file with TLE data. If you tend to have old TLEs saved in the same directory, you may prefer to create a temporary directory and save your file there.
If you get "New satellites: 1" (or, if you have previously imported this satellite, "Satellites updated: 1"), you can now track the new satellite.
While tracking satellites is nice, where tracking software really excels is Doppler correction. In recent Gpredict versions there is an option to pull this data from the SatNOGs database simply by running "Edit" -> "Update transponder data". However, for new satellites this information may not have been added yet (or may not be accurate).
If in Radio Control module you select the newly added satellite and see no transponders for it, you can also add it manually. In a folder ~/.config/Gpredict/trsp (on Linux/MacOS systems) create a file named after your Satellite Catalogue Number with .trsp extension, listing the satellite's transponders.
For example, for recently launched satellite XW-3, whose Satellite Catalogue Number is 50466, the file should be called 50466.trsp with the following contents (the format is pretty self-explanatory):
[Mode U - Telemetry] DOWN_LOW=435575000 MODE=CW BAUD=22 [Mode V/U - Transponder] UP_LOW=145855000 UP_HIGH=145885000 DOWN_LOW=435165000 DOWN_HIGH=435195000 MODE=USB INVERT=true [Mode U - GMSK4k8 AX.25 Telemetry] DOWN_LOW=435725000 MODE=GMSK BAUD=4800
If you now select the newly added satellite in your Radio Control module, you should be able to see the transponder data.