GPS Rollover problems with Celestron Hand Controllers

Some GPS receivers may malfunction on or after 6 April 2019 due to the GPS Week Rollover.

This is a known issue caused by the way that GPS used to handle the week element of the navigation signal. GPS used a 10 bit field to encode the week number in each GPS time message. This means that a maximum of 1024 weeks could be handled. This period is called an epoch. At the end of each epoch, the receiver resets the week number to zero and starts counting again.

The current epoch started on 1 August 1999. The next GPS rollover is 6 April 2019 when the receiver will revert to week number zero and start counting up to 1023 again.

Celestron is indeed working on a firmware update for the hand control (HC) to address this issue.  If one contacts Celestron Tech Support you will receive their official response.  The current plan is that Celestron will create new firmware for the NexStar+ and StarSense HCs, run it through beta testing, and release it to the public in 4 to 6 weeks.  Also, they clarified that the GPS receivers used in their equipment since 2012 (not 2014 as I stated above) are NOT affected.   The current SkySync GPS module is okay, as are the CPCs manufactured since 2012.  We now know the older CPCs are affected.  I'm still verifying if the NexStar 8/9.25/11 GPS series and the older CN-16 GPS module are affected (they probably are).


In Celestron's official response, it also states that this will only be fixed via the NexStar+ and StarSense HCs.  Owners with older HCs (version 4 for CPCs manufactured prior to 2012, all of the HCs shipped with NexStar GPS scopes) are advised to:

  • purchase a NexStar+ HC (they are not doing this to sell HCs - it is just that updates of the older HCs are no longer provided due to technical issues)
  • purchase a new GPS module (SkySync is of course the suggested module, though I would recommend the much smaller and slightly cheaper StarGPS-NX - https://www.nexstars.../StarGPS-NX.htm), or
  • turn off GPS in the HC menu and manually enter the date/time.


For the older NexStar 8/9.25/11 GPS, many people have foregone use of the newer HCs as they do not offer the automated "North and Level" GPS Align routine.  That routine is only available on HCs version  1.6 and 2.2.  If these mounts are in fact affected by the week rollover and someone wants to use the older 1.6/2.2 HC on one of these scopes, I recommend opening the base, disconnecting the internal GPS and purchasing the StarGPS-NX I linked to above.  It can easily be mounted inside the right fork arm (the one with the HC recess) and then connected to the HC jack in that recess.  Then, use the HC plugged into one of the AUX jacks on top of the base.