: This is the authoritative source for Two-Line Element (TLE) sets for all cataloged satellites. You can register for a free account at Space-Track to download custom satellite text files.
: Because satellite orbits decay or change, it is recommended to download a fresh version of these files every one to two weeks to maintain accuracy.
: Files with naming conventions like ndasat (often a contraction for "NASA data satellite") usually contain TLE data used to calculate the real-time position of satellites in the sky.