Research has been carried out on three major difficulties in designing efficient and economic telescopes with 8m f/1 lightweight mirrors. These problems are polishing f/1 aspherics, thermal distortion of borosilicate glass mirror and mirror seeing. Viable solutions to all three have been developed. Solving the fundamental problems allows future very large telescopes to use such mirrors as the basic elements in the design which will reduce the cost. Accurate mirror figure together with good pointing stability given by the short focal length will enable the telescope to form images as sharp as that permitted by nature on the ground. A new technology of polishing f/1 aspherics with a computer controlled stressed lap will give very accurate figure because the lap is changed accurately to adapt the desired figure. Design parameters and performance specifications for a 0.6m aluminum stressed lap for polishing a spun cast 1.8m f/1 borosilicate glass honeycomb mirror have been developed. These can be readily scaled up for polishing 8m f/1 mirrors. Stressed lap polishing also requires accurate material removal over the entire mirror surface. An optimization algorithm using the theory of material wear has been developed to search for the polishing strokes suited for uniform or other desired removal rates. Direct casting of lightweight mirrors requires that the glass be borosilicate. The figure distortion caused by the expansion of borosilicate glass requires the mirror be isothermal to less than 0.1°C for image degradation not to exceed 0.1 arcsecond. The problem of thermal interference by air and the environment has been investigated. A method of injecting well controlled air into the cells that forces the mirror to be isothermal to within 0.1°C has been discovered. Mirror seeing caused by temperature difference between the mirror and ambient air can degrade the telescope performance, but can be reduced by careful thermal design. A simple theoretical thermal model is used to select the glass thickness of a honeycomb structure mirror. Under air ventilation thermal control, the mirror responds to changing air temperature in less than an hour, reducing mirror seeing also to 0.1 arcsecond for telescopes at good seeing sites.

The construction of telescope systems with large apertures (≃10 meters) is currently being planned. These entire telescope systems should be optically tested in a double-pass configuration. The high cost of manufacturing optical flats large enough to test a large telescope has stimulated research on a new type of testing in which several smaller flats, or subapertures, are distributed over the telescope aperture. The problem is to combine the partial data obtained only over the subapertures in order to obtain the wavefront over the entire aperture. It was the purpose of this dissertation to prove experimentally that subaperture testing is feasible. The question of the necessity of phasing the subapertures relative to each other was specifically addressed in the experiment. A brief review is given of two algorithms utilizing Zernike polynomials. A third subaperture testing analysis algorithm, the Stuhlinger method, is developed in this work; this provides raw phase data over the entire aperture of the system under test. A statistical analysis of this algorithm is given. A 6 in. diameter array of seven subapertures was used in this small-scale test. Data were obtained with the array, a monolithic flat, and a mask simulating the array placed over the monolithic flat. The results of the experiment are in good agreement with control data measured with a Zygo interferometer. Data and analysis for the Stuhlinger method are also presented. Error analysis shows that Zernike coefficients derived using subaperture testing are 5 times less accurate than those derived using monolithic testing for the subaperture configuration used here. It is shown that knowledge of the subaperture tilts can produce accurate wavefront information with as few as 30 data points per subaperture, as compared with 750 data points per subaperture if tilts are unknown. In conclusion, subaperture testing indeed functions in the absence of subaperture phasing. Tilt information influences mostly the lower order Zernike coefficients; lack of such information may be compensated by the use of more data points. Algorithms yielding either Zernike coefficients or raw phase data were shown to function. (Abstract shortened with permission of author.)

Thesis (M.S.)--University of Hawaii at Manoa, 207. / Includes bibliographical references (leaves 82-84). / x, 84 leaves, bound ill. 29 cm

No description available.

No description available.

Submitted in fulfillment of the academic requirements for the Degree Master of Engineering: Electrical: Electronic Engineering, Durban University of Technology. Durban. South Africa, 2015. / A two element correlating radio telescope interferometer is the fundamental building block of modern radio telescope aperture synthesis arrays. Early radio telescopes consisted of a single antenna, usually a dish antenna. Larger and larger antennas were constructed in order to improve the resolution of the measurement of the direction and extent of radio frequency radiation coming from the sky. Telescope resolution is fundamentally limited by the ratio of the telescope aperture to the wavelength of the received radiation. For single element radio telescopes to approach the resolution of their optical telescope counterparts, they would need to be impractically large. Mathematical analysis of correlating two element radio telescope interferometers shows that very large aperture radio telescopes can be synthesized from a number of two element interferometers. An array of two element correlating radio telescope interferometers can be used to produce a synthesized aperture equal to the largest distance between two receiving antennas in the array. Telescope arrays thus enable very high resolution since the angular resolution of a telescope is proportional to the wavelength of the received signal divided by the aperture diameter. A spread of separation distances between antenna pairs is required to produce a complete image of the radiating sources in the field of view. Modern digital signal processing techniques can be used to provide cost effective performance and flexibility in two element correlating radio telescope interferometer design. The aim of this research project was to design and construct a two element correlating radio telescope interferometer using modern digital signal processing techniques and hardware. The relevant theory has been investigated together with suitable hardware and software platforms and tools used to produce such a system. The two element correlating radio telescope interferometer produced, will be used as a platform for further investigative research into its design, performance and application. The outcome of this research project was the successful completion of a working two element correlating radio telescope interferometer. The development process has been analysed and carefully documented. Some fringe measurements for a simple single frequency radiating point source have been taken and these measurements have been analysed according to theoretical expectation. Potential for further research, using the two element correlating radio telescope interferometer produced, has been identified and discussed.

Thesis (MTech (Design))--Cape Peninsula University of Technology, 2015. / Whether one is fascinated by the night sky as a child, or as a professional astronomer looking back to the beginning of time solving life’s big questions; at some point in our lives we have curiously looked up at the heavens above. The desire to explore the universe has lead us to constructing larger and more advanced telescopes, with the sole focus of observing deeper into the cosmos in an attempt to unravel its secrets. Like with most other technological advances, it has created advanced and technically complex control rooms. Based on a design ethnographic study this thesis will focus on the exploration of the effects of complex interfaces of a control room environment and its users, where one of the leading twenty first century telescopes of its kind, Southern Africa Largest Telescope (SALT), is studied. While the STS framework and policy debates concerning the rapid development and integration of complex human and non-human systems into larger systems become common practice. The design ethnographic study revealed that the operation of the SALT telescope and the research being conducted by the astronomers is clearly hindered by poor control room design. The study identified relationships between the framework and the empirical findings, which was used to frame a design pilot study to determine if further design intervention would have a positive impact on the interaction of a control room system. This project will consist of: a literature review, an ethnographic study and the analysis of the findings, design framing of a pilot study, a design pilot study, and an evaluation of the study. The results from the design pilot study clearly show that the application of a design intervention to a control room environment could potentially impact the space positively and reduced frustration, improve comfort, increased efficiency in the users work practices, and ultimately amplified productivity. Providing an appropriate starting point for the exploration of possible solutions for identified challenges experienced in complex control room environments, more importantly it contributed to narrowing the socio-technical gap, between the mechanical and research departments of a leading international optical telescope, SALT.

The design of the flexure mount recently submitted to NASA Ames for the structural support of the primary mirror of the Space Infrared Telescope Facility (SIRTF) is presented. The flexure system must passively accommodate the differential thermal contraction between the glass mirror and the aluminum structure of the telescope during cryogenic cooldown. Further, it must support the one meter diameter, 116 kilogram (258 pound) primary mirror during a severe launch to orbit. Procedures used to establish the required radial compliance using computer programs NASTRAN and FRINGE are discussed. The parametric design program developed to study early concepts is presented. Methods of combining modal responses resulting from a displacement response spectrum analysis are discussed, and a combination scheme called MRSS, Modified Root of Sum of Squares, is presented. Modal combination schemes using MRSS, SRSS, and ABS are compared to the results of a Modal Frequency Response analysis.

All future Extremely Large Telescopes (ELTs) will be segmented. However, as their size grows, they become increasingly sensitive to external disturbances, such as gravity, wind and temperature gradients and to internal vibration sources. Maintaining their optical quality will rely more and more on active control means. This thesis studies active optics of segmented primary mirrors, which aims at stabilizing the shape and ensuring the continuity of the surface formed by the segments in the face of external disturbances.<p><p>The modelling and the control strategy for active optics of segmented mirrors are examined. The model has a moderate size due to the separation of the quasi-static behavior of the mirror (primary response) from the dynamic response (secondary, or residual response). The control strategy considers explicitly the primary response of the telescope through a singular value controller. The control-structure interaction is addressed with the general robustness theory of multivariable feedback systems, where the secondary response is considered as uncertainty.<p><p>Scaling laws allowing the extrapolation of the results obtained with existing 10m telescopes to future ELTs and even future larger telescopes are addressed and the most relevant parameters are highlighted. The study is illustrated with a set of examples of increasing sizes, up to 200 segments. This numerical study confirms that scaling laws, originally developed with simple analytical models, can be used in confidence in the preliminary design of large segmented telescopes. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished