The Southern African Large Telescope (SALT) was completed in 2005 and began initial scientific operations in August
of that year. Built in just under 6 years and on budget, SALT has been a good example of a successfully managed
telescope project where systems engineering disciplines have been applied to good effect. This paper discusses the
experiences of completing and commissioning SALT and its first-light instruments and the early scientific operations.
Lessons learned in integrating the various telescope subsystems and implementation of the telescope control system are
presented. First Light was announced on 1 September 2005 following the installation of the last of the 91 mirror
segments and the commissioning of the UV-visible imager, SALTICAM. This was soon followed by the first scientific
observations and the beginning of the commissioning phase for the active optics system.
The Southern African Large Telescope (SALT) is a 10-m class telescope for optical/infrared astronomy based on the tilted Arecibo design first adopted by the Hobby Eberly Telescope. SALT is being constructed by a consortium consisting of 11 partners from six countries. SALT will enable a quantum leap in astronomical research capability in the African continent, where currently the largest telescope is a modest 1.9-m, dating to the 1940s. The SALT Project was approved in November 1999, the SALT project team started in January 2000, groundbreaking followed in September, the first mirror segment was installed in December 2002, and On-Sky Testing started in October 2003. SALT is due to start operations by 2005. The commissioning instrument has been developed by the South African Astronomical Observatory and the other first-light instrument is being developed by the University of Wisconsin-Madison. The major technical challenges in SALT are the alignment of the 91 identical spherical mirror segments, the position feedback of the prime focus tracker, and the dome seeing associated with large enclosures at a site with large daily thermal cycles. All of these issues were addressed thoroughly during the design phase, and first tests are showing very positive results in all these areas. This paper will summarize the international partnership in SALT and the management and organisation of the project and then address (1) the basic design, with emphasis on the technical challenges (2) the specified performance of SALT, (3) the progress and status of the project, including first light instruments.
The Southern African Large Telescope (SALT) is a little over 18 months away from completion (in early 2005). It is based on the innovative tilted-Arecibo optical analog, first pioneered by the Hobby-Eberly Telescope (HET). By the end of 2003, all major subsystems, including the verification instrument, will be in place and the commissioning of them begun. Tests of a 7-segment subset of the mirror array, including the Shack-Hartmann alignment instrument, the mirror actuators, capacitive edge sensors and active control system has recently started. The first engineering on-sky tests involving the complete light path, from object to detector, have begun. SALT's primary mirror consists of 91 identical segments mounted on a 9 point whiffle tree mount, using three actuators to control tip and tilt, and a foil-type capacitive edge sensor to detect mirror misalignment. These 480 relatively affordable sensors are permanently attached to the segment edges, and are capable of measuring all misalignment modes, including global radius of curvature. This sensing system, used together with a Shack-Hartman wavefront instrument at the center of curvature, controls the primary mirror array, and could be scaled to an array of the size envisaged for an ELT. SALT has developed some innovative designs improvement over the original HET concept. These include a more effective spherical aberration corrector (SAC), interferometric distance sensing and laser auto-collimation of the prime focus payload, the use of newly developed efficient and durable mirror coatings on the SAC optics, and the use of economical low expansion ceramics for the primary mirror segments. These innovative and cost effective solutions used on SALT have potential applications to ELT designs.
Although Systems Engineering has been widely applied to the defence industry, many other projects are unaware of its potential benefits when correctly applied, assuming that it is an expensive luxury. It seems that except in a few instances, telescope projects are no exception, prompting the writing of this paper. The authors postulate that classical Systems Engineering can and should be tailored, and then applied to telescope projects, leading to cost, schedule and technical benefits. This paper explores the essence of Systems Engineering and how it can be applied to any complex development project. The authors cite real-world Systems Engineering examples from the Southern African Large Telescope (SALT). The SALT project is the development and construction of a 10m-class telescope at the price of a 4m telescope. Although SALT resembles the groundbreaking Hobby-Eberly Telescope (HET) in Texas, the project team are attempting several challenging changes to the original design, requiring a focussed engineering approach and discernment in the definition of the telescope requirements. Following a tailored Systems Engineering approach on this project has already enhanced the quality of decisions made, improved the fidelity of contractual specifications for subsystems, and established criteria testing their performance.
Systems Engineering, as applied on SALT, is a structured development process, where requirements are formally defined before the award of subsystem developmental contracts. During this process conceptual design, modeling and prototyping are performed to ensure that the requirements were realistic and accurate. Design reviews are held where the designs are checked for compliance with the requirements. Supplier factory and on-site testing are followed by integrated telescope testing, to verify system performance against the specifications. Although the SALT project is still far from completion, the authors are confident that the present benefits from Systems Engineering on the project will be felt through telescope commissioning and testing.
The Southern African Large Telescope (SALT) is a 10-m class optical/IR segmented mirror telescope based on the groundbreaking, low cost, Hobby-Eberly Telescope (HET) design. Approval to construct and operate SALT, which will be the largest single optical telescope in the Southern Hemisphere, was given by the South African Government in November 1999, after sufficient guarantees of matching funding from international partners were secured. Facility construction started in January 2001, and SALT is due to start operations by December 2004. SALT will enable a quantum leap in astronomical research capability in Southern Africa, and indeed the continent, where currently the largest telescope is a modest 1.9-m, dating to the 1940s. A substantial amount of design work for SALT has been completed, sourced from multiple suppliers, with ~60% South African content. South African industry is well equipped to handle the construction of most of the telescope, the exceptions being the glass ceramic mirror blanks (from LZOS in Russia), the polishing and ion figuring of these (Eastman Kodak in the USA), and fabrication of the four-element spherical aberration corrector (SAGEM in France). This paper will present (1) the scientific requirements, (2) the specified performance of SALT, (3) the basic design, with emphasis on the innovative modifications to the HET design that enable significantly improved performance, (4) the progress and status of the project, currently in its construction phase, (5) the first generation instrument suite, (6) the management and organisation of the project and (7) the international partnership in SALT.
Segmented mirror telescopes take advantage of modular design to achieve large apertures at low cost. This paper describes the segment mount developed for the Southern African Large Telescope. The mount provides passive precision support for the optics, kinematic registration to the primary mirror truss, precision tip-tilt and piston adjustments, and interchangeability between segments and mounts. A trial production run of mounts is now in fabrication prior to full production of 91 units needed to populate the SALT primary.
SALT is a 10-m class telescope for optical/infrared astronomy to be sited at Sutherland, the observing state of the South African Astronomical Observatory. This telescope will be based on the principle of the Hobby-Eberly Telescope (HET) at McDonald Observatory, Texas. This cost-effective design is a tilted-Arecibo concept with a segmented spherical primary mirror of diameter 11 meters. The telescope has a fixed gravity vector but with full 360 degrees rotation in azimuth. A spherical aberration corrector mounted on a tracker beam at the prime focus enables a celestial object to be followed for 12 degrees across the sky. The SALT design enables over 70% of the sky to be accessed for about 20% of the cost of a conventional telescope of similar aperture. The telescope will be used primarily for spectroscopic studies of celestial objects with a light-weight low-dispersion imaging spectrograph mounted at the prime focus and other higher-dispersion instruments fiber-fed and mounted in an environmentally controlled basement. The concept design for SALT is presented with emphasis on the design changes between SALT and HET.