Orbitron uses TLE files for prediction like everyone else. There are options for sources of TLE's in the settings page.
Some of the options do not work, as some of the suppliers of TLEs have changed the formats and requirements.
Download: http://www.amsat.org/amsat/ftp/keps/current/nasabare.txt From: http://www.amsat.org/amsat-new/tools/keps.php under "Bare NASA (2-line) format elements for all satellites of interest to radio amateurs (updated 25 Jun, 2015)
Right click and save the txt file on your computer. The on Orbitron's main page on the right click LOAD TLE (near the time) and select the file.
You can get Orbitron to download some automatically, but many of the options no longer work. You should also synchronise your PC clock which is another option in the settings.