FORS (FOcal Reducer/low dispersion Spectrograph) is a multi-mode (imaging, polarimetry, long slit and multi-object spectroscopy) optical instrument mounted at the Cassegrain focus of one of the Unit Telescopes of ESO’s Very Large Telescope (VLT). Since FORS is a workhorse and quite unique instrument in Paranal, there is a strong need to upgrade it, both to address possible new scientific goals and to ensure regular instrument availability for the forthcoming years. The current instrument control software and electronics have been developed at the end of the ’90s, and several parts are becoming obsolete and do not follow the latest standards imposed by ESO for the VLT instruments. An initial collaboration has been setup between ESO and INAF – Astronomical Observatory of Trieste in 2018 for the feasibility study of the upgrade of the FORS control software and electronics with the latest VLT standard technologies (FORS-Up project). In the last years, however, ESO is developing new software and electronics control standards for the forthcoming ELT telescope with the aim to develop a full-fledged control system able to efficiently fight hardware obsolescence, offer modern software tools, lower costs, integration and maintenance efforts, and easy installation. This paper focuses on the FORS-Up control system based on the ELT Instrument Control Software Framework as presented at the FORS-Up Final Design Review in October 2021.
The first generation of ELT instruments includes an optical-infrared high resolution spectrograph, indicated as ELT-HIRES and recently christened ANDES (ArmazoNes high Dispersion Echelle Spectrograph). ANDES consists of three fibre-fed spectrographs (UBV, RIZ, YJH) providing a spectral resolution of ∼100,000 with a minimum simultaneous wavelength coverage of 0.4-1.8 µm with the goal of extending it to 0.35-2.4 µm with the addition of a K band spectrograph. It operates both in seeing- and diffraction-limited conditions and the fibre-feeding allows several, interchangeable observing modes including a single conjugated adaptive optics module and a small diffraction-limited integral field unit in the NIR. Its modularity will ensure that ANDES can be placed entirely on the ELT Nasmyth platform, if enough mass and volume is available, or partly in the Coudé room. ANDES has a wide range of groundbreaking science cases spanning nearly all areas of research in astrophysics and even fundamental physics. Among the top science cases there are the detection of biosignatures from exoplanet atmospheres, finding the fingerprints of the first generation of stars, tests on the stability of Nature’s fundamental couplings, and the direct detection of the cosmic acceleration. The ANDES project is carried forward by a large international consortium, composed of 35 Institutes from 13 countries, forming a team of more than 200 scientists and engineers which represent the majority of the scientific and technical expertise in the field among ESO member states.
FORS2 is a multi-mode (imaging, polarimetry, long slit and multi-object spectroscopy) optical instrument mounted on the Very Large Telescope (VLT) UT1 Cassegrain focus. It operates in the wavelength range of 330-1100 nm and, with the dismissed FORS1, is one of the most demanded instruments of the VLT in the astronomical community. After many years of operations (FORS1 was one of the first instruments installed at the VLT), an upgrade of the control system is absolutely required. Carried out by ESO and the Astronomical Observatory of Trieste, the upgrade will be applied to the decommissioned FORS1 instrument, that, when fully integrated, will replace FORS2 on the telescope. The upgrade will comprise the replacement of all the motors, the development of a new calibration unit, the adoption of a new ESO detector controller, and the design of a new control electronics based on Beckhoff PLC. Care will be given to the management of the motorized stages, about 50, avoiding MOS (Multi-Object Spectroscopy) slits and focal plane collision problems. The upgraded FORS will also be the first instrument to test the brand new ESO ELT instrument control framework, even if within the VLT environment. This paper will resume the design of FORS control electronics presented at the instrument Final Design Review. The new electronics layout, based on PLCs, and the motor’s control software management will be also described.
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