This is the format used by NASA to distribute satellite elements in their NASA Prediction Bulletin . The origin of the format is unknown. Tracking programs are generally unforgiving of anything that doesn't fit this format. Each number is in a specified fixed column.
Spaces are significant.
The last digit on each line is a mod-10 check digit, which is checked by the program. This is a very good set of checks, so this format is very safe, and robust. Line 1 Line 1 is a eleven-character name. Actually, there is some disagreement about how wide the name may be. Some programs allow 12 characters.