This paper will describe the progress of the SKA-1 Telescope during the period from Preliminary Design Review to Critical Design Review. In addition to this, it will provide information on the management of the project with respect to managing cost and scope whilst working within a fixed cost cap. The paper will consider the balance between the technical choices made with the risk of delivering a large, distributed observatory across several continents. In addition, it will consider the challenges of carrying this out whilst developing the organisation towards an Inter-Governmental Organisation. It will consider, briefly, the key management tools used and the lessons learned.
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.
While Systems Engineering appears to be widely applied on the very large telescopes, it is lacking in the development of many of the medium and small telescopes currently in progress. The latter projects rely heavily on the experience of the project team, verbal requirements and conjecture based on the successes and failures of other telescopes. Furthermore, it is considered an unaffordable luxury to "close-the-loop" by carefully analysing and documenting the requirements and then verifying the telescope's compliance with them.
In this paper the authors contend that a Systems Engineering approach is a keystone in the development of any telescope and that verification of the telescope's performance is not only an important management tool but also forms the basis upon which successful telescope operation can be built. The development of the Southern African Large Telescope (SALT) has followed such an approach and is now in the verification phase of its development.
Parts of the SALT verification process will be discussed in some detail to illustrate the suitability of this approach, including oversight by the telescope shareholders, recording of requirements and results, design verification and performance testing. Initial test results will be presented where appropriate.
The modern day computing power to cost ratio has allowed flexible yet complex mathematical models to be implemented in various arenas. A current example is the Southern African Large Telescope and the Hobby-Eberly Telescope, Arecibo-type large optical telescopes, which have a moving prime focus confined to a spherical surface. The complexity of the moving tracking mechanism, a stationary self-aligning mirror and the scales of the structures involved in such telescopes have led to the requirement of more flexible telescope mount models. In this way the combination of low cost and a requirement for flexibility has led to the design of new mathematical models for telescopes of this type.
A case in point is the Southern African Large Telescope, due to the specific design and calibration requirements during the design and commissioning of the telescope, an adaptable mathematical model is required. Such a model should have multiple easily accessible entry points and flexibility of conversion paths between the various coordinate systems involved. In this paper the authors present an overview of the special requirements for the Southern African Large Telescope and the eventual design and implementation of a mathematical model to cope with these requirements. Some of the topics that will be discussed include: tracking challenges on SALT; layering of complexity of the mathematical model; software design and access to mathematical parameters; analytical and statistical tools for model design; and design consistency between coordinate conversions.
The successful development of any complex control system requires a blend of good software management, an appropriate computer architecture and good software engineering. Due to the large number of controlled parts, high performance goals and required operational efficiency, the control systems for large telescopes are particularly challenging to develop and maintain.
In this paper the authors highlight some of the specific challenges that need to be met by control system developers to meet the requirements within a limited budget and schedule. They share some of the practices applied during the development of the Southern African Large Telescope (SALT) and describe specific aspects of the design that contribute to meeting these challenges. The topics discussed include: development methodology, defining the level of system integration, computer architecture, interface management, software standards, language selection, user interface design and personnel selection.
Time will reveal the full truth, but the authors believe that the significant progress achieved in commissioning SALT (now 6 months from telescope completion), can largely be attributed to the combined application of these practices and design concepts.
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.