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GPS spacecraft are currently identified by their “Space Vehicle Number” (SVN) which now number 01 through 75. What will happen after 99 GPS satellites are launched? Is there any plan currently in place such as renumbering to 001 - 100+ or simply adding an extra digit?

This could happen soon enough due to 24+ satellites being launched by 2030 for the new GPSlll upgrade.

For those curious, I need to know in order to future proof some software...

Edit: While IGS and ANTEX files use a 3 digit SVN (or the equivalent of an SVN) these are related to the US government (and may do whatever they please?) all other places I have checked do not. Including:

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  • $\begingroup$ Is the SVN# used in the signals send by the satellite to the GPS receivers? Or is it used only in signals send to the satellites by GPS control stations on Earth? $\endgroup$
    – Uwe
    Dec 2, 2019 at 22:02
  • $\begingroup$ Excellent question, answering this would get to the bottom of the SVN's true current form. This indicates that the PRN code is transmitted by the satellite (in fact PRN stands for pseudo random noise). However I would not think the SVN is as the PRN is what matters for location determination. So JPL might make the conversion themselves (They use SVN over PRN due to it being a true ID number that can be used for decades with no confusion) $\endgroup$
    – johnDanger
    Dec 2, 2019 at 22:17
  • $\begingroup$ The satellite SVN# 37 was used for PRN# 07 , 01 and 24. So the SVN# might been used to address the satellite from ground control when changing the PRN#. $\endgroup$
    – Uwe
    Dec 2, 2019 at 22:47
  • $\begingroup$ Yes I would imagine the SVN is used solely by the ground segment, while the PRN is used to identify which component of the constellation each satellite is currently functioning as. Which would make it harder to determine the SVN's official form. Anyone know if the public has access to the upload signal data transmitted by the ground control stations? $\endgroup$
    – johnDanger
    Dec 2, 2019 at 23:08
  • $\begingroup$ This page suggests that the SVN is derived from the part of the P-code the satellite is transmitting, but as the P-code is cut up in 37 segments, an SVN > 37 wouldn't make sense. The page has no references unfortunately. $\endgroup$
    – Ludo
    Jul 30, 2020 at 10:10

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The numbering of 01-99 you refer to is the one used for the PRN of the satellites. The SVN is numbered using 3 digits in IGS files and is therefore not going to run out anytime soon. PRN's are often reassigned to different satellites, as this Wiki article shows. If you take a look at this ANTEX file you can see there are two identifiers, a double digit (e.g. G01) and a triple digit (G032). The G01 is the PRN and G032 is the SVN.

If you don't need to future proof your software for the case they launch another 925 GPS satellites I believe the triple digit SVN's should be fine for now.

As for the PRN, a 100 satellite constellation would be some serious overkill for GPS so I don't think they'll run out of PRN's anytime soon.

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  • $\begingroup$ I did note that ANTEX used a 3 digit code (plus a prefix), but I wondered if that was for compatibility with other numbering schemes (eg. GLONASS) rather than necessarily an indication that SVNs will be 3 digit, too. $\endgroup$
    – Starfish Prime
    Dec 2, 2019 at 14:58
  • $\begingroup$ Any other files that include SVN's? From what I've found, only ANTEX has SVN's in it. All other relevant IGS files just provide PRN no? $\endgroup$
    – Alexander Vandenberghe
    Dec 2, 2019 at 15:19
  • $\begingroup$ The GPS PRN# are limited to 37 therefore a 100 satellite constellation is impossible anyway. No more than 32 are used, the numbers 33 to 37 are reserved. $\endgroup$
    – Uwe
    Dec 2, 2019 at 18:12
  • $\begingroup$ The rest of that Wikipedia article, my data files (sourced from JPL, and the US coast guard navigation center all give the SVN's as two digit numbers. IGS is not a US government body and ANTEX seems like a unified system for all positioning system constellations? So probably their codes are not the official ones. I am concerned with the official government designations that would be used by other US government bodies. $\endgroup$
    – johnDanger
    Dec 2, 2019 at 18:34

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