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GPS-Enabled Scopes Display a Date 20 or 17 Years in the Past or Display a Date with a Year of "5" after GPS Link
Initially Posted 23 Apr 2019
Last updated 30 Aug 2019

GPS Week Rollover
On April 7, 2019, the Global Positioning System experienced its second "week rollover" event. The GPS system was originally designed using a 10-bit binary number as a counter to indicate the week of the current date transmitted from the satellites to the GPS receivers. 10 bits only provide 1024 possible values so every 1024 weeks (approximately 19.7 years) the system returns to its starting value of 0. At its base level, for most receivers that indicates a date in August 1999. Some GPS receivers are able to determine that a date in 1999 (or any date 19.7 years prior to today) is actually in the past and they will add 1024 to the week counter and thus return the correct date. Other GPS receivers are happy to tell us today is 19.7 years in the past.

Celestron's GPS Units
Celestron began offering GPS in its mounts in 2001 with the introduction of the NexStar 11 GPS. In 2002 it introduced its first add-on GPS unit, the CN-16. In 2005, the NexStar GPS series was replaced with the CPC series which also included an internal GPS receiver. In 2012 the CN-16 was replaced by the SkySync GPS module.

Throughout that time, Celestron used GPS receivers from a variety of manufacturers. Some of the receivers are affected by the week rollover and some are not. As of April 2019, the following are known to be affected {updated 20 May 2019}:

• CPC mounts manufactured up until sometime in 2012
• CN-16 modules
• NexStar 8/11 GPS mounts manufactured after sometime in late 2002, generally shipped with the version 2.2 hand control.  These mounts are actually reporting a date 17 years in the past. {added to this list 20 May 2019}
• NexStar 9.25 GPS mounts.  These mounts are actually reporting a date 17 years in the past. {added to this list 20 May 2019}

The following have thus far NOT been affected by the week rollover:

• NexStar 8/11 GPS mounts manufactured prior to late 2002, generally shipped with the version 1.6 (or original 1.2) hand control {this info updated 20 May 2019}
• CPC mounts manufactured after 2012 (exact date unknown)
• CPC Deluxe HD mounts
• SkySync GPS modules

The Fix
Beginning in April 2019, Celestron started working on a fix for this issue. By examining the date returned from the GPS receiver, the hand control can add 1024 weeks if necessary. This required a change to the firmware in the hand control. Celestron has released firmware for the NexStar version 4, NexStar+ and StarSense hand controls and is working on firmware for the StarSense hand control.  See the top of this page for updates and details.

If you are unable to update to a fixed version, it is possible to continue using one of the affected scopes by disabling GPS in the hand control menu and manually entering the date and time. On the NexStar+ and NexStar hand controls, press the MENU button, select Utilities, and you will find GPS on/off. On the StarSense hand control, press the MENU button, select Time and Location, and select Time/Location Source.  It is possible to turn GPS on, get a GPS link which will provide correct location and time, then turn it off and manually enter the date before proceeding with the alignment.

NOTE:  The NexStar version 1.6, 2.2 and 3.x hand controls are not upgradeable. Celestron only has the ability to fix this problem via the hand control. So, if you currently own an affected telescope with one of these older hand controls, you will either need to purchase a version 4 or NexStar+ hand control, use NexRemote or turn off GPS in the hand control menu and manually enter the date and time.

Copyright Michael Swanson     Contact the webmaster: swanson.michael@usa.net