VISTA is a survey telescope which will deliver 0.5 arc second images over a 2 degree diameter unvignetted field of view. The Telescope Work Package which includes both the Mount and M1 support system is being designed and built by VertexRSI. The Contract includes an extensive factory test programme after full assembly of the telescope systems. The main optical elements in projects this size are ordered early so that they are ready for integration with the telescope on site. This means that testing of the telescope with its optics in the factory environment is rarely possible. So to try and avoid problems during site integration, the scope and extent of hardware and control system factory testing is significant and should be suitably in-depth. This paper describes the metrology and testing carried out to date in the factory environment. In addition the axis control system was simulated using Matlab-Simulink models. The models were also used as the basis of software verification using hardware-in-the-loop tests in a model-based development process. This development process and subsequent factory testing is described in some detail, and covers the mount axes and the M1 support system. In conclusion this paper discusses the perceived usefulness of the extent of the factory testing employed and how this is expected to mesh with the process of telescope and optics integration on site.
The Cornell Caltech Atacama Telescope (CCAT) is a 25m far infrared telescope in the conceptual design phase. Its primary mirror is composed of a set of panels supported by a space truss. The primary and secondary mirror arrangement resembles the reflector and quadrapod arrangement seen in many radio telescopes, but with shallower primary mirror geometry. In addition, the optical layout calls for a close spacing between the tertiary mirror and the Nasmyth and bent Cassegrain instruments. The mount design is driven by the spacing of the optical elements, the presence of the Nasmyth and bent Cassegrain ports, and the size of the primary mirror truss. This paper examines the mechanical and control system design solutions provided in response to the challenges posed by the optical requirements. These solutions include tradeoffs in structure, drive, and control system design.
The 4.2 m Discovery Channel Telescope requirements create interesting challenges for the Mount mechanical and control system design. The wide field of view survey telescope incorporates two operational foci: prime focus and cassegrain, either one must be available during any night's observing. The mission for observing requires fast slewing / offsets between each exposure with fast settling times to maintain the mission requirements. The prime focus arrangement includes a dedicated camera on the spider assembly and the cassegrain configuration includes a secondary mirror at the spider assembly with a dedicated instrument located at the cassegrain focus. This requirement challenges the design team to incorporate a prime focus / secondary mirror flipping mechanism within the secondary spider. The configuration requires a substantial prime focus and cassegrain payload with long focal distances creating a large inertia on the altitude axis. These are a few of the interesting challenges that are presented in this paper along with the design, trade-offs of different solutions, and the recommended design for the telescope Mount.
VertexRSI completed the 4.2-meter Southern Astrophysical Research (SOAR) Telescope Mount in 2001. The Mount is now in assembly and test at the site in Chile. This paper will discuss the final mechanical design of the Mount and the implementation of the design requirements during fabrication, factory integration and testing. The final design includes detailed finite element structural analysis, 3-D design models, and precise machining requirements. These requirements were implemented in the fabrication using standard and novel machining approaches. Factory integration proved out the design and fabrication process. The connection of these items with the success of the testing is presented.
The success of giant telescopes is dependant not only in the optics design but also in the mechanics and electromechanics configurations. This paper addresses some of the key aspects of mechanical designs that impact this success. Areas investigated include methods for mitigating pointing errors caused by wind, thermal and gravity deflections; bearing and drive selection; and servo control issues. To reduce the cost of the telescope mount, it is hoped that conventional mechanical designs can be used to accomplish the high level of performance needed in the structure and drives area.
The telescope mount is an important component for the success of the Southern Observatory for Astronomical Research (SOAR) scientific mission. The SOAR telescope structure must have the best combination of extremely high structural stiffness, low torque bearings, sophisticated encoder pick-offs and smooth drive trains so that the servo system can achieve closed loop control in the sub-arc second regime. While challenging, these parameters are achievable. Once assembled, this mount will enable the telescope to have superior image viewing quality and large payload capacities. This paper will address the telescope mount structure, drive system performance, structural analysis and thermal design.