NexStar Resource Site

line.gif (861 bytes)
Pop-Up Info Window
(close when finished)
line.gif (861 bytes)

line.gif (861 bytes)

Firmware Versions on the Advanced Series with GoTo

Non-English Hand Control Owners - read this.  The
information below is for English-version hand controls.

Celestron AS-GT scopes have two sets of processors. There are processors in the hand control (HC) and there are processors in the base of the scope in a section known as the motor control (MC). The MC firmware can be updated by the owner (read this). 

There have been three versions of hand control available for the AS-GT:

  • Hand control 3.03 and 3.04.  Hand controls prior to version 4 can NOT be updated.
  • Hand control version 4.X.  This hand control can be updated by the owner and was available for purchase from January 2006 through summer 2012.  Read this for info on purchasing the upgradeable hand control and this for step by step instructions on upgrading the firmware.
  • The NexStar+ hand control.  This hand control can be updated by the owner and is available for purchase since February 2012.  Read this for info on this new hand control and this for step by step instructions on upgrading the firmware.

For additional details about features on newer versions, check the Manuals section of this web site.

line.gif (861 bytes)
NexStar+ Hand Control

Celestron has posted an official document detailing all firmware versions for the NexStar+ hand control:
Check back periodically for updates.

line.gif (861 bytes)
Version 4 Hand Control
(firmware files are named GEM)

  • 4.21 - Fixed bugs related to tandem operation (OTA orientation), Meridian Mode and land objects.
  • 4.20 - Added "Custom Rate 9": the ability to set the maximum slew rate during a GoTo (requires motor control version 5.20 or higher).  Fixed a problem with a runaway slow slew if a GoTo is too near the meridian flip point.  No Response errors now give a "Press UNDO to continue" option.  For mounts with a GPS module in use, changed the messages displayed to clarify when the GPS was still attempting a link and when it was successful.  Fixed and error when syncing on stars in southern hemisphere via the RS-232 sync command (for example, from a planetarium program running on a laptop).
  • 4.19 - Adjust communication protocol to assist MCupdate.  Fixed an error in the GoTo RA-Dec menu item.  Hand Control now reports immediately if the are communication ("No Response") difficulties at start up.
  • 4.16 - Corrects alignment system errors for use in the Southern Hemisphere.  Fixed error when using SAO stars (selected from the STAR button) as alignment objects.
  • 4.15 - Introduced with the CGEM, this version includes several changes.  All-Star Polar Alignment (ability to perform polar alignment on any star, not just Polaris and Sigma Octanis) and tandem support (ability to turn the RA axis 90 degrees and mount multiple optical tubes side-by-side) are two new features.  The hand control now uses precession to calculate current coordinates rather than using static J2000 coordinates.  After polar alignment it is no longer necessary to repeat the star alignment.  User is now prompted automatically for the time during alignment if a GPS module is not in use.  Read the manual for the CGEM (found in the Manuals section of this web site) for details on how this all operates.  NOTE: This version is largely unusable in the Southern Hemisphere.
  • 4.13 - This version allows the motor control (MC) firmware to be upgraded via the port on the bottom of the hand control.
  • 4.12 - The most significant change in this version is variable brightness control for the display and buttons - values are from 0 (off) to 8 (full brightness).  There is also a fix that reduces (but does not eliminate) the chance that the display comes up blank the first time you power up, a problem much more prevalent in cold weather.  The fix on those occasions when it does still come up blank remains the same - turn off the power, wait a couple of seconds and turn on the power again.  The Version menu item has been changed - it now displays the mount model after displaying the HC and MC versions. 
  • 4.10 - The most significant change in this version is Sync and multiple mount calibration stars.  Sync is available both via the hand control and via PC software (TheSky, Starry Night, etc.).  This provides very accurate GoTo pointing in the area of the sky where the Sync is performed and it allows the PC software to match with the actual position the scope is pointed to.  Multiple mount calibration stars take the place of the previous use of one calibration star for determining cone error and the Dec switch/index mark offset resulting in much improved pointing accuracy.  Other new features:  a display of the polar alignment error, Solar System Align routine, the Sun is now available as a GoTo and alignment object, and "RA" and "Dec" are used in most places in the menus rather than "Alt" and "Azm".
  • 4.0 - The most significant new feature of this version is that it is user-upgradeable.  Other changes from previous versions are simply minor bug fixes.

line.gif (861 bytes)
Non-upgradeable Hand Control

  • 3.04 - The differences between this and 3.03 are unknown.
  • 3.03 - Original version on the AS-GT mount.

line.gif (861 bytes)
MC Versions

  • 5.20 - Support for "Custom Rate 9": the ability to set the maximum slew rate during a GoTo (requires hand control version 4.20 or higher).  The final GoTo approach is now faster and quieter.
  • 5.16 - Corrects problems in RA Limits (previously named Slew Limits) and improves precision of RA Limits to 1 degree (improved precision only available when using hand control version 4.16 or higher).
  • 5.14 - Corrects a potential problem with the cordwrap prevention feature.  Re-enables the RA Slew Limits.
  • 5.07 - An official version.  Minor changes - rate 1 is now 50% of sidereal while rate 2 is 100% of sidereal.  This makes manual guiding much easier.
  • 5.06 - First official version available for download from Celestron.  Improved anti-backlash, fixed runaway slews during normal use and when when autoguiding, general improvements to autoguiding, fixed occasional slow motion slews that never seem to reach their destination, improved sidereal tracking rate.
  • 5.04 - Original version on the AS-GT mount.

line.gif (861 bytes)
Determining Versions

Use the Version option on the Utility menu.

line.gif (861 bytes)

line.gif (861 bytes)
Michael Swanson
  Contact the webmaster: