The ATCS Controller

The hub of ATCS (Astrometric Telescope Control System) is the ATCS controller.  Astrometric's latest model is PrimeTCS-Ui.  PrimeTCS-Ui’s primary purpose is to control telescope motion using targeting algorithms to acquire and track celestial objects.  To physically achieve this, PrimeTCS-Ui is designed to control axial motors over a very large dynamic range thus enabling low-speed and smooth tracking while also providing high speed slew for object acquisition (i.e., GoTo).  Older ATCS controller models are detailed on our legacy products page and are upgradable to the latest functionality.

The Astrometric Telescope Control System (ATCS) provides sophisticated, yet easy to use control for all types of telescopes.

Visit our PrimeTCS-Ui Telescope Controller page for physical details on PrimeTCS-Ui.

Designed to control all types of telescopes

ATCS is designed to provide control for all types of equatorial or Alt/Az telescopes. ATCS performs the necessary coordinate translations between the mount’s arbitrarily oriented axes and the celestial sphere. Exact polar alignment is not necessary. ATCS implements a sophisticated “pointing model” which accepts celestial or horizontal coordinate targets, translates to telescope position, and positions the telescope accurately for both pointing and tracking.

  • Smooth and stable tracking.
  • Full GoTo capability from embedded object database, direct coordinate entry or attached 3rd party software.
  • Complete support of the ASCOM and Software Bisque X2 standards providing interface to popular planetarium software and other 3rd party software packages.
  • Dynamic “run time” corrections for mount errors, gear errors, telescope flexures and atmospheric refraction.
  • High speed slew and four user-selectable pan and slow-motion rates.
  • Full configurability for all types of telescopes equatorial or Alt/Az.
  • Flexible support for limits of motion including complete cable-wrap management and overlap of access at the meridian (for German mounts) or under the pole.
  • Supports either open-loop “motor only” operation or closed-loop encoder-based pointing and tracking to sub-arcsecond resolution.
  • Standard tracking rates along with continuously variable tracking rate for objects moving at non-sidereal rate.
  • Remote and unattended operation.
  • Time-tested reliability: Installed around the globe from the frigid arctic to the hot desert.
  • Stand-alone stability: Continuous operation regardless of PC vagaries.

Additional details on ATCS’ show-case features are included below.  Please visit our PrimeTCS-Ui controller page for more details on ATCS’ embodiment in our latest telescope controller product.

Maestro Software

Astrometric PC-based Interface

Maestro is our Windows-based user interface software for the Astrometric Telescope Control System (ATCS).  Maestro provides status and access to all ATCS settings and allows for complete ATCS operation.

3rd Party Software Support

Maestro exposes standards-based interfaces for 3rd party software to connect to ATCS providing control from one of the many commercial or shareware planetarium and other astronomy apps available today.


  • ASCOM: Maestro can simultaneously host multiple ASCOM compatible client software applications.
  • Software Bisque’s TheSky software. Maestro supports Bisque's X2 (for TheSkyX) interface standard.

These features provide a wide range of expanding options from “point and click” object selection and GoTo from planetarium software to fully robotic observatory systems using ATCS.

Astrometric's Maestro Software


Telescope Motor and Motion Control Features

The above plots show the pointing prior to, and after, setting up Dynamic Correction for use on a 0.8m equatorial telescope. Pointing accuracy averaged 105 arcseconds with no Dynamic Correction applied. Using Dynamic Correction, a 4.6 arcseconds solution is found.

Dynamic Correction:
Unparalleled Tracking and Pointing

ATCS is designed for controlling telescope mounts where accurate pointing and tracking are front-line requirements.  ATCS includes a feature called Dynamic Correction which corrects for different errors associated with pointing and tracking a telescope.  Dynamic Correction does not only adjust GoTo targets (like other non-integrated solutions); it actually continually (many times per second) adjusts telescope position to compensate for different errors.

Tracking errors resulting from atmospheric refraction, flexures and polar misalignment led to the need for variable-rate/two-axis tracking even for equatorial mounts.  Dynamic Correction continually adjusts the track rate, in both telescope axes, thereby compensating for these errors.

Flexible Limits of Motion

ATCS provides highly configurable soft and hard limits that control the “range of motion” for all types of telescope mounts.  RA/Az and Dec/Alt limit avoidance zones are configurable to accommodate diverse constraints of motion.  ATCS handles limit “overlap” or axial “wrap” at the meridian (for German mounts) and under the pole.  Limit overrides are provided to enable supervised motion outside of limits.

Stand-Alone Stability

The ATCS controller (e.g., PrimeTCS), together with its handpaddle, is a dedicated, compact and robust "stand-alone" controller that does not rely upon a PC to operate.  While most telescopes are used with a PC, the separation of ATCS from the PC assures that system reliability is not degraded by a potentially unstable PC or PC operating system.  ATCS will continue to function smoothly without stutter regardless of the behavior of an attached PC.

Axial Encoder Feedback

With optional high-resolution encoders installed on one or both telescope axes, ATCS becomes a "closed loop" controller and will very accurately position and track the telescope by directly and accurately measuring and referencing the angles of the actual telescope axes.  This removes all drive system errors (gears, bearings, rollers, pulleys/belts) and substantially improves upon the pointing and tracking provided through “open loop” control of motors only.

Eliminating Gear-Induced Tracking Errors

The adjacent graph shows the results for a 24” telescope that sports a high quality and large diameter RA worm gear (15” Byers Research series with 359 teeth).  The native periodic tracking error of this gear is about +/-3.5 arcsec which is very good for un-corrected tracking.  This gear also exhibits an often neglected 2nd order longer period track rate error that leads to track rate variation that is cyclical over the rotation of the gear.  Both of these errors are removed using axial encoders and ATCS’ axial encoder feedback feature.  The resulting measured tracking (better than 0.5 arcsec RMS) is shown by the bottom trace.

“The quality of the result speaks for itself.  The software is bug free and support is excellent”  Richard S Post, Post Observatory, Mayhill, NM

Support for Absolute Encoders

PrimeTCS-Ui interfaces to absolute encoders which provide ATCS with the capability of permanent alignment where no reference object or home position is needed to align at start-up.  PrimeTCS-Ui supports absolute encoders from Heidenhain, Renishaw and other vendors that use the EnDat, BiSS or SSI interfaces.



ATCS provides a hardware autoguider input that is industry standard.  Additionally, given Maestro’s ASCOM compliancy, 3rd party “software autoguider” solutions are available.

High Drives

The SwitchPro accessory provides high drive-strength signals which are high-current electronic outputs that can be assigned to a variety of functions.  For example, a High Drive output could be setup to toggle on/off and be connected to a telescope’s motorized dust cover.  Open/close of the dust cover is then available from Maestro, 3rd-party software or scripts.

Please contact us for more information

Field de-rotation for Alt/Az telescopes

When used with our RotatorProU product, ATCS provides field de-rotation and position-angle reset on GoTo.

Focus control from TCS

When used with our FocusProU product, ATCS' handpaddle can control focus position.


Clear and Complete Documentation

Astrometric provides clear, complete, and in-depth documentation along with excellent “Getting Started” guides to get your system operating quickly and trouble-free.

Functional Upgrades

Functional upgrades are continuously made available for ATCS.  New features and user’s suggestions/requests are regularly accommodated.  These functional upgrades generally involved synchronized upgrades to ATCS controller firmware and Maestro software.

As a customer of Astrometric Instruments, upgrades are available from our software upgrades page.

Support for Diverse Observatory "Use Models"

Our customers have a wide range of applications for our systems ranging from simply aiding visual observing, to astrophotography and all the way up to full control of remote and/or unattended telescopes.

Please visit our observatory use models page for further details.

Unparalleled Customer Support

We are renowned for providing quality customer support through many channels including:

Email (

Phone (9-5M-F USA/Eastern 508-836-3970)

Or our User’s Group at

For the Physical Details of the PrimeTCS-Ui Telescope Controller CLICK HERE