Space telescopes are required to be lightweight and small without compromising high optical performance. A Metallic mirror is one of the technologies that can meet launch conditions, the harsh space environment and achieve the optical requirements of an imaging payload and have been widely used from JWST to new space payloads. Flexible mounting pads are one of the geometrical designs within a metallic mirror that is a very critical part which mounts the mirror to the supporting structure. Flexible pads improve optical stability by reducing screw pressure from mounting and increase vibration endurance by creating more flexibility in the design. This study will use Finite Element Analysis to optimize the shape of flexible pads, examining the effects on mechanical and optical performance by varying geometric dimensions in a parametric study under multiple scenarios from manufacturing to operating in orbit. The results highlight the parameters that have the biggest impact on mechanical and optical performance in each scenario and describe the relation between the parameters that affect mechanical and optical performance that improve the understanding of the opto-mechanical design of metallic mirrors. Finally, the design will be optimized with multiple objectives to get the most optimal design based on all scenario’s conditions.
The parametric study could be analyzed with the sensitivity study, response surface, and optimization. The results show the parameters that have the most impact on performance and show its effect on performance in various conditions such as manufacturing load, grounded based stability with screw pressure, natural frequency, thermal load, and gravity release. The optimization process can lead to the improvement of the optical design. This study improves understanding of opto-mechanical design of the flexible pads in metallic mirrors, which can be applied to other metallic mirror designs.
The National Astronomical Research Institute of Thailand, together with the Institut d’Optique Graduate School and Centre de Researche Astrophysique de Lyon, has been developing the Evanescent Wave Coronagraph (EvWaCo) a new kind of Lyot coronagraph that uses a lens and prism placed in contact as its focal plane mask. By the principle of frustrated total internal reflection, EvWaCo enables an achromatic rejection and ability to collect the light from the star and the companion. An EvWaCo prototype equipped with adaptive optics will be installed at the Thai National Telescope as an on-sky demonstrator. This demonstrator will work on a 1.2 × 0.8 m2 elliptical sub-aperture of the Thai National Telescope to reach a raw contrast of 10−4 at 3λ/D over the wavelength range [600 nm, 900 nm]. The completed optical design contains all the essential light path channels in high contrast imaging fitted inside a 960 mm×960 mm optical breadboard, namely the guiding camera channel, companion channel, star channel, and wavefront sensing channel. We also show the results of the tolerancing and straylight analysis.
Achieving precise tolerances in the assembly of optical components is crucial for the performance of off-axis optical systems. This study focuses on the design and evaluation of assembly methods and mechanisms of an Offner spectrometer with the goal of demonstrating their capability to achieve tolerances within 40 microns. The methodology involves the development of assembly methods and mechanisms specifically tailored for off-axis optical systems. Representative models of optical components and custom adaptors were designed and manufactured to facilitate the assembly process. Procedures were devised for setting up, repositioning, and locking the representative models. The proposed methods and mechanisms were evaluated using measurements from a Coordinate Measuring Machine (CMM). The accumulated tolerance in each step of the assembly process was analyzed, ensuring that the overall performance met the desired specifications. The findings validate the effectiveness and reliability of the developed approach, offering valuable insights for the design and implementation of similar systems.
The Thai National Telescope (TNT) is the largest telescope in Southeast Asia with a primary mirror of 2.3-meter diameter located at altitude 2457 meters, Chiang Mai, Thailand. This telescope is equipped with two photometric cameras and a medium resolution spectrometer. The maximum instantaneous field of view (FOV) is circular of diameter equal to 15 arcminutes, provided by the camera called the “TNT Focal Reducer”. In this paper, we present the design and performance estimation of a prime focus camera for the TNT with the objective to reach a FOV equal to 1 degree. The TNT prime focus camera is specified to operate over the spectral domain 0.400-0.850 μm for spectral bands g’, r’ and i’ of the Sloan Digital Sky Survey (SDSS) photometric system. This camera is designed to reach a resolution better than 2 arcseconds, slightly above the seeing limit in median atmospheric conditions. The prime focus camera is planned to be installed at the secondary mirror (M2) and mounted on a hexapod manufactured by Physik Instrumente (PI) company. This hexapod will provide a positioning accuracy of ±2.5 μm of 3-axis translation. The orientation will be adjusted with an accuracy equal to ±1.03 arcseconds of rotation. The prime focus camera comprises five lenses made of S-FPL53, N-BAK2, SF1, BAF50 and SK3. This camera includes one aspherical concave surface of conic constant equal to -0.076 and the other surfaces are spherical. We have dedicated tolerance analysis to calculate the effects of manufacturing errors, alignment errors and stability on the operational performance. The results show that the operational angular resolutions over the full field of view should be better than 1.61 arcseconds. The results of the stray light analysis show that the ghost irradiance should be five orders of magnitude smaller than the image irradiance, assuming that the second lens of the camera and the detector window have an Anti-Reflective coating of reflectivity lower than 1%.
Over the past twenty years, a very high number of different space hyperspectral spectrometers have been designed, developed and launched. Recently, several new compact designs based on freeform optics have been proposed in the literature. We thus considered that it was interesting to make a survey of the already existing hyperspectral imagers and innovative freeform designs to identify the most promising solutions to increase the compactness and the performance. Some surveys on hyperspectral imagers have already been done in the past. For example, the survey by Herring et al, in 1993 which proposed some hyperspectral spectrometer concepts. However, these studies are now outdated and cannot be used to identify state of art concepts. The review proposed by Kumar et al., in 2015 presented the advantages to browse the different hyperspectral imager concepts but provided only superficial technical details that cannot be used to identify the specific designs that improve both the compactness and the image and spectral qualities. We thus decided to make a bibliographic survey to analyze the most recent designs of different space hyperspectral imagers with the objective to select the concepts that will provide the best compromise between the volume and the performance. We have categorized the different systems into four groups: prism based, Offner, Three Mirror Anastigmat (TMA) and Dyson spectrometers. We analyzed these different concepts and we identified and the advantages and the drawbacks. We concluded that the most interesting state-of-art designs are the Freeform Offner, double-pass TMA and Dyson spectrometers. These designs present the most interesting performance and combine with a compact volume. We thus established a preliminary trade-off that summarizes the advantages and the drawback of these concepts. This trade-off analysis could be used as a starting point for any future study aiming at designing compact hyperspectral imager. Finally, we present the progress of some important and recent technological developments related to the manufacturing of freeform and convex gratings.
The National Astronomical Research Institute of Thailand (NARIT) is currently developing a five lenses prime focus camera in order to enlarge the field of view of the 2.3 m Thai National Telescope to a one degree diameter circle. The instrument shall operate in the spectral bands B, V, R and I of the Johnson-Cousins photometric system with an angular resolution better than 2 arcsecond. In this paper, we describe the camera design, we estimate the theoretical performance in the V-band and we show that the theoretical angular resolution after tolerancing is better that 1.3 arcsecond. Then, we present the results of the stray light analysis and we show that the system is free of critical ghost images.
The observations of the solar system Jovian planets performed by ground-based medium size telescopes can provide an efficient support to the space missions by performing observations of the planet atmospheres. In particular, ground-based medium size telescopes are able to provide high resolution images close to the diffraction limit of giant planets while observing through the Earth atmosphere by using some Lucky Imaging processing. These observations of the Jovian planet atmospheres ideally require i) an instrument with a high angular resolution close to the diffraction limit and ii) a high contrast, especially for the low and medium spatial frequencies that corresponds to the turbulence areas inside the atmosphere clouds bands. We thus decided to design one telescope that shall provide diffraction limited images (without the contribution of the atmosphere) over a circular Field of View (FOV) of diameter equal to 2 arcminutes. This, over the photometric spectral band V, R and I of the Johnson-Cousin photometric. In this paper, we present the design and the performance of a Ritchey-Chretien telescope dedicated to solar system planet imagery with a linear central obscuration lower than 0.15 and an active system to correct the low frequency distortions of the wavefront before each observation. First, we describe the optical design, then we establish the image quality budget. Finally we show that the stray light signal induced by the moon light scattering is negligible during the observations of Jupiter.
The National Astronomical Research Institute of Thailand (NARIT) has developed since June 2014 an optical laboratory that comprises all the activities and facilities related to the research and development of new instruments in the following areas: telescope design, high dynamic and high resolution imaging systems and spectrographs. The facilities include ZEMAX and Solidwork software for design and simulation activities as well as an optical room with all the equipment required to develop optical setup with cutting-edge performance.
The current projects include: i) the development of a focal reducer for the 2.3 m Thai National Telescope (TNT), ii) the development of the Evanescent Wave Coronagraph dedicated to the high contrast observations of star close environment and iii) the development of low resolution spectrographs for the Thai National Telescope and for the 0.7 m telescopes of NARIT regional observatories. In each project, our activities start from the instrument optical and mechanical design to the simulation of the performance, the development of the prototype and finally to the final system integration, alignment and tests. Most of the mechanical parts are manufactured by using the facilities of NARIT precision mechanical workshop that includes a 3-axis Computer Numerical Control (CNC) to machine the mechanical structures and a Coordinate Measuring Machine (CMM) to verify the dimensions.
In this paper, we give an overview of the optical laboratory activities and of the associated facilities. We also describe the objective of the current projects, present the specifications and the design of the instruments and establish the status of development and we present our future plans.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.