Telescope Control Software

ESO, the European Southern Observatory operates an astronomical observatory at Mount Paranal in Chile, where one of the world‘s biggest optical telescope arrays is located – the Very Large Telescope (VLT).

redlogix worked for ESO over many years to develop significant parts of the VLT control software. With these - still ongoing - projects redlogix has gained comprehensive know how with the design and development of telescope control systems, instrument control software and interferometer software, as well as adaptive optics and motion control hard- and software.

In general, for astronomy software we provide engineering services to develop custom control software, numeric algorithms, data flow or operator interfaces. Around the software we provide system engineering services.


Technologies Employed

  • VxWorks/Tornado
  • CCD-Cameras
  • UNIX (HP-UX, Solaris)
  • Transputer
  • RTAP
  • DIO A/D, D/A
  • OO-Design
  • Stepper- und DC-Motors
  • ANSI C/C++
  • VMEbus
  • Encoder
  • Fast Ethernet
  • FDDI


The Very Large Telescope

ESO operates one of the largest optical telescopes on top of the 2,635-meter high Paranal mountain in the Andes. The facility essentially consists of four identical telescopes with an aperture of 8.2 meters each plus three 1.8-meter mobile auxiliary telescopes and the VLT Survey Telescope, a 2.6-meter telescope for wide-field imaging. The relatively thin main mirrors are kept in shape by active optics, i.e. more than 150 axial and lateral actuators on the back and the sides actively adjust their shape during operation for optimum performance. Further, optical distortions, caused by atmospheric turbulence are corrected by adaptive optic systems, whereby redlogix has been involved in hard- and software of the MACAO system (see MACAO).

The facility is completed by a set of high-tech instrumentation, mounted at the various foci of each telescope, as shown below. These instruments are mainly developed by partner institute consortia of ESO and redlogix provides development services for the instrument control systems. In this way we are working for the GRAVITY instrument.

VLT Instrumentation

The individual telescopes can also be coupled with one another either in combined focus or in interferometry mode, the so-called VLT Interferometer (VLTI). When the final stage is completed, the system will have the resolving power of a single mirror with an aperture of 130 meters or total light-gathering power of a 16-meter mirror. redlogix also contributed and still contributes to the VLTI software (see VLTI).

Computer Systems

A distributed approach was chosen for the control and operation of the telescopes, domes and instrumentation, and the system architecture makes use of extensive networking. The control functions are distributed through a network of dedicated VMEbus systems, the so-called local control units. The VxWorks real-time operating system, as well as Linux run on the PowerPC CPUs.

The original UNIX workstations under Solaris and HP-UX, meanwhile replaced by Linux, are used for higher-level coordination as well as for user interfaces, archiving, remote access, etc.

Software Architecture

On top level, the VLT control system consists of several software packages, including the following:

  • CCS – Basic services
  • TCS – Telescope control
  • INS – Instrumentation software
  • ROS – Remote operation

redlogix Control Software

redlogix has been involved in the development of VLT software since 1996 and still is. Our activities have included design, implementation, testing and documentation of drivers and low level software,  infrastructural components and applications, both at the LCU level as well as at the workstation level. The VLT software components implemented by redlogix included the following:

  • Control of the telescope‘s main azimuth and elevation axes with a three-level control algorithm and a control frequency of 1000 Hz. Encoder readout and optimum characteristics for fast pointing, positioning and tracking.
  • Central interface of the TCS with other telescope subsystems, instrumentation and users. Parallel message routing with three instances taking into account authorization and exclusive access of the telescope.
  • Control of CCD cameras for technical and scientific applications. Extremely efficient transmission of images from camera heads and real-time pixel processing, as well as enhanced parallel operation of  individual process steps. For guiding purposes images were acquired at a frequency of 50 Hz and calibrated online with flat-field, dark frame and reference corrections.
  • Control of a system for atmospheric dispersion correction by movement of two linearly slidable prisms.
  • Coordination of telescope auto-guiding through evaluation of CCD images of a guide star and tracking correction.
  • Automatic pre-selection of guide stars through links to various star catalogs.
  • Numerical compensation of remaining mechanical inaccuracies after calibration and their consideration in telescope pointing and motion.
  • The controls for various dome systems, including air-conditioning, main doors and observation slit as well as synchronization of dome rotation and the retractable wind shields with the position and motion of the telescope.

Maintenance and Support

In extension to its development services, redlogix also provides support, since the VLT is in operation. This includes integration of new features, maintenance and troubleshooting, also on-site at Paranal.