The automated execution of scientific observations and engineering procedures at the Extremely Large Telescope (ELT) requires a standard tool: The Sequencer. For scientific observation, the Sequencer is responsible for controlling the telescope and its instruments to perform the observations. For engineering, it shall be used for commissioning and maintenance procedures. The ELT Sequencer allows building Directed Acyclic Graphs (DAG) representing tasks to be carried out. The generated graph defines every task needed (nodes), its order of execution, and its dependencies (edges). Python’s asyncio library is used to control and schedule the tasks derived from the DAG. It also allows for pseudo-parallelism between tasks. Despite being asyncio based, the Sequencer is task-agnostic, allowing standard python functions and coroutines to be executed as well. It is composed of various layers: Programmer’s API, execution kernel, command line tools and a GUI.
The concept of "Virtual Image Slicer" was developed and implemented at the Very Large Telescope (VLT). The Virtual Image Slicer consists in elongating the stars in a given direction by the use of the Active Optics of the telescope. Alignment of the major axis of the elongated star along the entrance slit of the spectrograph allows to increase the total signal collected in a single (polarimetric) spectrum by a factor of up to 100 or more relative to a perfectly shaped image for bright sources.
At Paranal Observatory in the YEPUN (UT4) telescope, two instruments are installed and equipped
with adaptive optics systems: an infrared spectro imager (CONICA) below the adaptive optics
module NAOS; and an integral field spectrograph (SINFONI). In the same telescope, the Laser
Guide Star Facility (LGSF) is installed to provide a reference star to the adaptive optics systems. The
LGSF is tuned to the sodium D2 line to use the resonance fluorescence of atomic sodium in the
mesospheric layer at an altitude of 90 Km.
The LGSF system has been fully operational for several years now. During this time, important
modifications have been made to the system to increase its availability, simplify its remote operation
and improve its performance.
In this contribution, we report on the latest upgrades in hardware as well as the software of the
system. Some upgrades like the exchange of the cooling system of the VERDI lasers, as well as the
exchange of motors in the PARSEC laser system, have been critical to improve the performance of
the system. We also describe the improvements in the maintenance and operation procedures and
operational constraints we have faced so far. Finally, we present and analyze the latest technical
performance achieved by the LGSF in operational conditions.
The Laser Guide Star Facility (LGSF) is installed on the UT4 (Yepun) telescope at Paranal Observatory in Chile. On the
same telescope, two instruments are equipped with adaptive optics: an infrared spectro imager (CONICA) below the
adaptive optics module NAOS; and an integral field spectrograph (SINFONI). The LGSF is tuned to the sodium D2 line
to generate an artificial reference star, for both CONICA and SINFONI.
Although the LGSF is a complex laser system, rather different from the other instruments at Paranal, it has been
designed to run remotely without any hand-on tuning for a period of one week. The LGSF system has now been in
operation for several months, in conjunction with the Aircraft camera Avoidance System (AAS).
In this article, we report on the technical performance achieved by the LGSF in operational conditions. We also provide
a summary of the technical problems and operational constraints we have faced so far. We present the current operations
and maintenance procedures implemented at Paranal.
We also present the evolution of the human resources needed to operate and maintain the LGSF operational from
commissioning to routine operations.
Finally, we discuss possible improvements to reduce the workload to maintain and operate the LGSF.
KEYWORDS: Telescopes, Control systems, Sensors, Digital signal processing, Standards development, Data modeling, Interferometers, Interferometry, Observatories, Astronomical telescopes
After having established routine science operations for four 8 m single dish telescopes and their first set of instruments at the Paranal Observatory, the next big engineering challenge for ESO has been the VLT Interferometer. Following an intense integration period at Paranal, first fringes were obtained in the course of last year, first with two smaller test siderostats and later with two 8 m VLT telescopes. Even though optical interferometry today may be considered more experimental than single telescope astronomy, we have aimed at developing a system with the same requirements on reliability and operability as for a single VLT telescope. The VLTI control system is responsible for controlling and co-ordinating all devices making up VLTI, where a telescope is just one out of many subsystems. Thus the pure size of the complete system increases the complexity and likelihood of failure. Secondly, some of the new subsystems introduced, in particular the delay lines and the associated fringe-tracking loop, have more demanding requirements in terms of control loop bandwidth, computing power and communication. We have developed an innovative generic multiprocessor controller within the VLT framework to address these requirements. Finally, we have decided to use the VLT science operation model, whereby the observation is driven by observation blocks with minimum human real-time interaction, which implies that VLTI is seen as one machine and not as a set of telescopes and other subsystems by the astronomical instrument. In this paper we describe the as-built architecture of the VLTI control and data flow system, emphasising how new techniques have been incorporated, while at the same time the investments in technology and know-how obtained during the VLT years have been protected. The result has been a faster development cycle, a robustness approaching that of VLT single dish telescopes and a "look and feel" identical to all other ESO observing facilities. We present operation, performance and development cost data to confirm this. Finally we discuss the plans for the coming years, when more and more subsystems will be added in order to explore the full potential of the VLTI.
POM, the `Pointing modeling module' of the VLT control system measures the pointing errors and derives a pointing model that is then applied within the tracking software of the telescope. The fit to the errors employs P.T. Wallace's TPOINT package, but POM is more that a wrapper for that software.
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