Major improvements to the SALT prime focus guidance system have been implemented over the last two years in the form of a new compact, modular and removable system with high optical efficiency. A double-probe positioning system allows both translation and rotation guidance, while optional beam-splitting allows closed-loop focus feedback to stabilise the focal plane. The features of this new system, its mechanical and optical performance and its control system architecture are presented.
To take full advantage of the upcoming era of LSST, time-domain astronomy, and proposals that span multiple semesters and may have hundreds of targets, it was decided to upgrade the software for the Southern African Large Telescope. At the heart of the upgrade were changes to the MySQL database. A new web-based API allows an automated submission of targets of opportunities. This API is also used by a React-based single page application for real time updates of time allocations. The software upgrade also includes extensible web pages for monitoring data quality.
After encountering difficulties in coordinating the compilation of the daily SALT software log between Sutherland and Cape Town, and struggling to identify the configuration of the telescope at a point in time, a new, automated system to record and consolidate the changes made to the telescope on a day-to-day basis has been developed. This has resulted in a reduction of administration overhead, more complete and timeous reporting of changes, and a daily report that is consistently formatted and contains easily searchable metadata.
A new guide probe, using a Pyramid WaveFront Sensor (PWFS), has been built for the guider port of the Robert Stobie Spectrograph (RSS) on the Southern African Large Telescope (SALT). The PWFS splits the light from a guide star into a double image of the star at the guider image plane. These two images move with respect to each other with changes in focus. Analysis of the movements in such two-star images allows for simultaneous tracking and focus adjustments while guiding. This paper describes the image processing software developed for the new guidance system. The PWFS is a custom made prism with a 9 degree prism apex angle. Incident light is split as it passes through the prism resulting in two images identical in shape, size and orientation resolving at the guider image plane. A point source, like a star, thus appears as a double image of the star at the image plane. These two images are affected identically with seeing fluctuations allowing one or both images to be used to calculate guidance offsets independently of the focus measurement. The separation of the two images correlates to the focus divergence from the ideal which is used to correct the telescope focus. The prism can be moved off to one side, such that the incident light is not split. In this configuration the guide probe provides guidance offsets without the focus adjustments for maximum sensitivity with dim guide. The software was developed using existing guider images to ensure that the algorithm could handle the image artefacts that are commonly encountered. To reduce processing time and the effects of anomalies the surrounding image is masked out leaving only the star. A centroiding algorithm is then applied to the star to estimate its location in the image. For PWFS double-star images, Zemax was used to model the effect of shifting focus on the light passing through the prism. From this a simulated data set was produced and the software expanded to detect the two stars and measure the separation. The software is capable of measuring star translational movements and double star separation reliability and accurately.
Following successful commissioning of the SALT Fiber Instrument Feed guidance system, the concept was developed further to re-design the guidance probe currently supporting observations with the Robert Stobie Spectrograph. Major advances of the new system include a compact, modular and line-replaceable design, high optical efficiency, a doubleprobe positioning system allowing both translation and rotation guidance corrections as well as closed-loop focus feedback.
The mechanical and optical designs, the control system architecture and performance aspects of the system are presented. The probe‘s integration with the greater telescope software control system is also discussed.
The efficient operation of a telescope requires awareness of its performance on a daily and long-term basis. This paper outlines the Fault Tracker, WebSAMMI and the Dashboard used by the Southern African Large Telescope (SALT) to achieve this aim. Faults are mostly logged automatically, but the Fault Tracker allows users to add and edit faults. The SALT Astronomer and SALT Operator record weather conditions and telescope usage with WebSAMMI. Various efficiency metrics are shown for different time periods on the Dashboard. A kiosk mode for displaying on a public screen is included. Possible applications for other telescopes are discussed.