We will soon see TLE with Alpha-5 character in NORAD ID. Space-Track.org in operational satellites.
For the TLE row checksum, it is stated to be a modula-10 checksum, spacetrack:
The checksum is the sum of all characters in the data line, modulo 10. In this formula, the following non-numeric characters are assigned the indicated values:
Blanks, periods, letters, ‘+’ signs → 0
‘-’ signs → 1
I have not found a 100% clear definition (in my overthinking) on what to do with the alpha-5 characters. Orekit does, what I think is right, ignore the alpha-5 character as these are non-numeric and not listed in the bulleted exceptions, but one could perhaps argue that the value of these characters are numeric with values A=10, B=11 etc.
Do you have any clearer statements on this? Most examples I have seen online is using A character which is value 10 and thus not make a difference in final checksum. It will however take some time until the B series arrives
Greetz, and thanks for making the form up and running again!
I guess we should anticipate for ‘B’ = 11 as it is the more logical move forward and indeed is not a problem yet as this letter is not used (until someone decides to blow up some target in space just to show off).
There are many TLE on space-track with Alpha 5 NORAD beginning with T (=27 for alpha 5) which have check-sums treating the T as zero (mod 10). So I think you have enough evidence to evade the over-think.
Thanks @PeaDubYa for the information. You are right, we should just ignore alpha values in checksum then.
Now I am wondering the rationale for ‘T’ being already used.
I believe that Space Fence was allocated the range 270,000 to 339,999 for uncatalogued objects (T-Z). I can only guess they negotiated to get 70,000 numbers and worked up from the first one they were given, rather than down. A good job really because up in the Z range it’s a free-for-all with everyone borrowing numbers they have no right to!
