The Southern African Large Telescope (SALT) is a 10-m class fixed-elevation telescope with a primary mirror composed of 91 spherically figured one metre segments. A prime focus tracker assembly carries the spherical aberration corrector (SAC) and two of SALT’s instruments, SALTICAM (the acquisition and imaging camera) and the multi-purpose Robert Stobie spectrograph (RSS). Included in the tracker payload is a fibre-instrument feed, that positions ~45m long fibre cables coupled to the spectrographs in thermal enclosures beneath the telescope. These are the High-Resolution Spectrograph (HRS) and NIRWALS (Near InfraRed Washburn Astronomical Laboratories Spectrograph). The other major undertaking is a custom-built laser frequency comb and precision radial velocity data pipeline for the HRS, due in 2025. A novel RSS slit-mask IFU was recently commissioned, adding optical IFU spectroscopy to SALT’s capabilities. Work is also underway to develop a new red channel to turn the RSS into a dual-beam spectrograph. A study done in 2021 investigated the feasibility of building deployable robotic arms equipped with mini SACs to take advantage of SALT’s huge uncorrected field of view. Lastly, a pre-study is now underway to explore options for replacing the SAC and prime focus payload on the tracker to improve telescope performance and make provision for future instrument development.
The facility instrument suite at the Southern African Large Telescope (SALT) is being extended into the near-infrared by the arrival of the SALT-NIR spectrograph in 2022. The SALT-NIR is fiber-fed via a set of integral field units that interfaces with the existing Fiber Instrument Feed. Extending the operational wavelength range of SALT from 320 - 900 nm to 320 - 1700 nm requires a number of changes to the physical and optical telescope subsystems and places new demands on its control and pointing software. We present the requirements, design and implementation of these updated systems.
The addition of multiple “mini-trackers” (MTs) to the Southern African Large Telescope (SALT) would create in effect several four-to-six-meter class telescopes that take advantage of the SALT 10-meter diameter primary mirror’s 35 degree diameter uncorrected field-of-view. These devices, with a 100 square degree patrol area, would provide valuable follow up capability for the large astronomical surveys either in operation (e.g. MeerKAT, eROSITA, Gaia), or expected to begin operations soon (e.g. LSST, SKA, Euclid). A feasibility study was conducted to evaluate the technical practicality associated with the design, fabrication, integration, and testing of a prototype MT for SALT. The study determined that the development of a mini-tracker was indeed feasible, and work has begun on the concept design phase of the project.
We present a low-resolution spectrograph design for the Southern African Large Telescope (SALT) primarily aimed at efficient identification spectroscopy of transients. The design extends the existing Robert-Stobie Spectrograph (RSS) by adding a new simultaneous red channel for wide visible wavelength coverage (360 nm to 900 nm). The design delivers R ~800 in the blue channel using the existing RSS optics and R ~2000 at a peak end-to-end instrument efficiency of 44% via the new red channel. We describe the instrument’s requirements, optical design and expected performance. Synergies with existing RSS functionality are explored that will allow dual-beam multi-object and future integral field unit spectroscopy.
A case study is presented to illustrate some of the performance and cost driving tradeoffs involved in the design and
tolerancing of optics and optomechanics, where simple lens barrels are concerned. A double Gauss lens was designed,
along with two variations of lens barrel designs for mounting the lenses. The two lens barrel designs are compared, and
one is selected for further analysis. Tolerance selection guidelines are given and discussed for the optics, as well as the
optomechanics. It is shown how the optomechanical tolerances (axial spacing, element decenter, and element tilt) are
derived from their primary parameters for the selected lens barrel design. Finally, Monte Carlo analysis is used, along
with the provided tolerancing guidelines, to determine reasonable tolerances in order to satisfy the optical performance
and yield requirements.
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