The 2-m Ring Solar Telescope (RST) of the Yunnan Astronomical Observatory (YAO) is a new-generation solar telescope that will provide high-resolution solar observations. The RST is now under commissioning on the YAO campus. The secondary mirror of the RST is a 0.6-m diameter convex mirror that is supported by a hexapod system which is to provide precise and stable positioning and alignment of the secondary mirror. We present the development of the hexapod system, including its technical requirement, workspace, actuator and joint design. The classic Stewart type configuration is adopted for the hexapod design and the stepmotor-ballscrew concept for the actuator design. The one-part 2D flexure concept is used to manufacture the Hooke’s joints and also used for 3D rotary joint design. We also describe the performance tests of the hexapod system in laboratory. The hexapod is able to cover a sphere of sf7mm. The translational displacement resolution is down to 0.1μm and repeatability <0.1μm RMS, the rotational displacement resolution is down to 0.5 arcsec with repeatability <0.1 arcsec RMS. Besides, the hexapod exhibits high stiffness over 60Hz with a payload of 70kg.
We briefly report on the development of a 50 mm balloon-borne coronagraph and its recent ground experiment results made at the high altitude (4800 m above the sea level) site of Mt. Wumingshan in Daocheng, Sichuan of China. The main scientific purpose for developing this coronagraph is to investigate the morphology and dynamics of low-layer coronal structures before and during solar eruptions by observing at a float altitude of about 30 km from 1.08 Rsun to 1.5 Rsun at white light wavelength (centered at 550.0 nm, bandwidth 5 nm). The instrument is an internally occulted Lyot coronagraph developed by Yunnan Observatories in collaboration with Shangdong University (in Weihai) and Changchun Institute of Optics, Fine Mechanics and Physics. The coronagraph was designed with scattered light intensity level of better than 1×10-5 Isunin the inner field of view. A filter wheel system with linear polarizers and an sCMOS camera provided polarization and total brightness images of size 2048 x 2048 pixels. The first successful results were taken on February 27, 2021 in the Daocheng site. This coronagraph experiment obtained coronal images only showing obvious coronal structures very near limb. Furthermore, during the end of March and early April, after improving the polarizer filter system, higher-quality coronal images with pB coronal structures appeared in the full field of view were obtained in our ground-based experiments. Comparison between our results and the other coronal data in the world are discussed. The success of the 50 mm coronagraph in ground experiments is a milestone for us to develop the next-generation large-aperture coronagraph, as well as for future near space projects.
A so-called Semi-Active Support (SAS) system was proposed for the primary mirror of the YNAO 2-m Ring Solar Telescope (2-m RST of Yunnan Astronomical Observatory, China), whose primary mirror is distinctively figured in a ring with an outer diameter of 2.02 m and a ring width of 0.35 m. This paper reports the design and tests of the prototype of the pneumatic-based semi-active axial support system of the 2-m RST. The dummy mirror was a solid circular plate glass of 700 mm in diameter and 20 mm in thickness, which was support by nine Pneumatic Force Actuators (PFAs) organized in three groups, each group was regulated by one proportional regulating solenoid valve. Besides, three Displacement Actuators (DAs) were used to actively define the three Degrees Of Freedom (DOFs) of piston and tip/tilt of the dummy mirror. The pneumatic force actuators were to be actively pumped and regulated, meanwhile, the displacement actuators to actively define the primary’s position, according to the variation of the elevation pointing of the telescope. The PFA was build with a metal bellow as its cylinder, and a pressing load cell of 200 N capacity with 5 mN resolution was integrated on its output tip. The DA was a step-motor based design with a travel range of 4 mm and a theoretical resolution of 50 nm. Basic technical requirements for the PFAs and DAs were reviewed first. General consideration and configuration of the prototype was elaborated, followed by detailed designs and comprehensive tests of the either type standalone actuator. The prototype was finally tested on a systematic level as well. This prototype study has paved a reasonable way for critical design of the axial support system of the 2-m RST primary mirror.
A special 2-m Ring Solar Telescope (2-m RST) is to be built by YNAO-Yunnan Astronomical Observatory, Kunming, China. Its distinct primary mirror is distinctively shaped in a ring with an outer diameter of 2.02 m and a ring width of 0.35 m. Careful calculation and optimization of the mirror support pattern have been carried out first of all to define optimum blank parameters in view of performance balance of support design, fabrication and cost. This paper is to review the special consideration and optimization of the support design for the unique ring mirror. Schott zerodur is the prevailing candidate for the primary mirror blank. Diverse support patterns with various blank thicknesses have been discussed by extensive calculation of axial support pattern of the mirror. We reached an optimum design of 36 axial supports for a blank thickness of 0.15 m with surface error of ~5 nm RMS. Afterwards, lateral support scheme was figured out for the mirror with settled parameters. A classical push-and-pull scheme was used. Seeing the relative flexibility of the ring mirror, special consideration was taken to unusually set the acting direction of the support forces not in the mirror gravity plane, but along the gravity of the local virtual slices of the mirror blank. Nine couples of the lateral push-pull force are considered. When pointing to horizon, the mirror surface exhibits RMS error of ~5 nm with three additional small force couples used to compensate for the predominant astigmatism introduced by lateral supports. Finally, error estimation has been performed to evaluate the surface degradation with introduced errors in support force and support position, respectively, for both axial and lateral supports. Monte Carlo approach was applied using unit seeds for amplitude and position of support forces. The comprehensive optimization and calculation suggests the support systems design meet the technic requirements of the ring mirror of the 2-m RST.
Chinese Giant Solar Telescope (CGST) is the next generation infrared and optical solar telescope of China, which is proposed and pushed by the solar astronomy community of China and listed into the National Plans of Major Science and Technology Infrastructures. CGST is currently proposed to be an 8 meter Ring Solar Telescope (RST) with width of 1 meter, the hollow and symmetric structure of such an annular aperture facilitates the thermal control and high precision magnetic field measurement for a solar telescope. Adaptive optics (AO) is an indispensable tool of RST to obtain diffraction limited observations. How to realize AO involved wavefront sensing and correcting, and the degree of compensating in a narrow annular aperture is the primary problem of AO implementation of RST. Wavefront reconstruction involved problems of RST are first investigated and discussed in this paper using end to end simulation based on Shack-Hartmann wavefront sensing (SHWFS). The simulation results show that performance of zonal reconstruction with measurement noise no more than 0.05 arc sec can meets the requirement of RST for diffraction-limited imaging at wavelength of 1μm, which satisfies most science cases of RST in near infrared waveband.
Chinese Giant Solar Telescope, which has a 8m diameter segmented primary mirror, is a plan for the next generation ground-based large solar telescope in China. A major scientific requirement for this telescope is the high accuracy polarimetry. In this paper, the instrumental polarization of the main optics is analyzed by polarization modeling, which is caused by off-axial field of view, spider asymmetry, nonuniform segment gap and segment coating. The result shows that the net polarization is sensitive to the asymmetrical spider leg widening and the uniformity of the segment optical property. For meeting the accuracy requirement, the extinction ratio and retardence error for each segment should be less than 0.3% and 0.8 degree, respectively. Generally, the ring segmented primary mirror have advantage in controlling the instrumental polarization for large main optics.
Science goals of telescopes are the fundament data of integrated modeling of astronomical telescopes. The differences between science goals are sources of telescope’s diversities. Solar telescopes are a very special type in astronomical telescopes. Chinese Giant Solar Telescope1 (CGST) is currently designed to be an 8-meter Ring Interferometric Telescope (RIT). Even compare with the other solar telescopes, CGST is also an unusual telescope due to its ring aperture and distinctive science goals. As the initial data of integrated modeling of CGST, the main science cases determine the basic structure of the telescope as well as its working mode. This paper will discuss the importance of the primary science case in integrated modeling of CGST.
KEYWORDS: Mirrors, Telescopes, Solar telescopes, Sensors, Active optics, Control systems, Image segmentation, Finite element methods, Observatories, Segmented mirrors
The Chinese Giant Solar Telescope (CGST) is the next generation solar telescope of China with diameter of 8 meter. The unique feature of CGST is that its primary is a ring, which facilitates the polarization detection and thermal control. In its present design and development phase, two primary mirror patterns are considered. For one thing, the primary mirror is expected to construct with mosaic mirror with 24 trapezoidal (or petal) segments, for another thing, a monolithic mirror is also a candidate for its primary mirror. Both of them depend on active control technique to maintain the optical quality of the ring mirror. As a solar telescope, the working conditions of the CGST are quite different from those of the stellar telescopes. To avoid the image deterioration due to the mirror seeing and dome seeing, especially in the case of the concentration of flux in a solar telescope, large aperture solar projects prefer to adopt open telescopes and open domes. In this circumstance, higher wind loads act on the primary mirror directly, which will cause position errors and figure errors of the primary with matters worse than those of the current 10-meter stellar telescopes with dome protect. Therefore, it gives new challenges to the active control capability, telescope structure design, and wind shielding design. In this paper, the study progress of active control of CGST for its mosaic and monolithic mirror are presented, and the wind effects on such two primary mirrors are also investigated.
In order to detect the fine structures of solar magnetic field and dynamic field, an 8 meter solar telescope has been
proposed by Chinese solar community. Due to the advantages of ring structure in polarization detection and thermal
control, the current design of CGST (Chinese Giant Solar Telescope) is an 8 meter ring solar telescope. The spatial
resolution of CGST is equivalent to an 8 meter diameter telescope, and the light-gathering power equivalent to a 5 meter
full aperture telescope. The integrated simulation of optical system and imaging ability such as optical design, MCAO,
active maintenance of primary mirror were carried out in this paper. Mechanical system was analyzed by finite element
method too. The results of simulation and analysis showed that the current design could meet the demand of most science
cases not only in infrared band but also in near infrared band and even in visible band. CGST was proposed by all solar
observatories in Chinese Academy of Sciences and several overseas scientists. It is supported by CAS and NSFC
(National Natural Science Foundation of China) as a long term astronomical project.
By study of the classical testing techniques (such as Shack-Hartmann Wave-front Sensor) adopted in testing the
aberration of ground-based astronomical optical telescopes, we bring forward two testing methods on the foundation of
high-resolution image reconstruction technology. One is based on the averaged short-exposure OTF and the other is
based on the Speckle Interferometric OTF by Antoine Labeyrie. Researches made by J.Ohtsubo, F. Roddier, Richard
Barakat and J.-Y. ZHANG indicated that the SITF statistical results would be affected by the telescope optical
aberrations, which means the SITF statistical results is a function of optical system aberration and the atmospheric Fried
parameter (seeing). Telescope diffraction-limited information can be got through two statistics methods of abundant
speckle images: by the first method, we can extract the low frequency information such as the full width at half
maximum (FWHM) of the telescope PSF to estimate the optical quality; by the second method, we can get a more
precise description of the telescope PSF with high frequency information. We will apply the two testing methods to the
2.4m optical telescope of the GMG Observatory, in china to validate their repeatability and correctness and compare the
testing results with that of the Shack-Hartmann Wave-Front Sensor got. This part will be described in detail in our paper.
As one of the preliminary research projects of Chinese ELT, 30m RIT--Ring Interferometric Telescope are being
simulated and tentatively designed by Yunnan Astronomical Observatory, CAS. The simulations of 30m RIT are mainly
included as follows: PSF transform and the image quality at limited photons mode, active control mode of the primary
ring mirror, the phasing mode of 30m segmented ring mirror, the turbulent atmosphere and adaptive optics etc. This
paper also introduces some tentative design results of 30m RIT, such as the optical design, the conceptual design of the
enclosure. The astronomical experiments at seeing limited case and diffraction limited case are introduced in this paper
too. A ring aperture mask was put on the entrance pupil of a one meter telescope, real astronomical objects were
observed by this "ring telescope" and reconstructed by high resolution imaging techniques such as speckle masking,
iterative shift and add methods. The diffraction imaging ability and the full u-v coverage property of a ring aperture were
proved by these astronomical experiments.
KEYWORDS: Telescopes, Mirrors, Interferometry, Point spread functions, Modulation transfer functions, Stars, Synthetic apertures, Optical instrument design, Large telescopes, Imaging systems
For the demand of astronomical limitation observations, such as exploring extra-terrestrial planets, black hole accretion
disk and jet in the near-infrared and optical wave band, extremely large telescopes (optical and infrared) have become the
principal ground-based astronomical instrumentation. With the maturation of interferometric imaging theory, the
borderline between new generation ground-based extremely large telescope and interferometric array for aperture
synthesis imaging is increasingly going blurring and the only differences in their technical methods and characteristics
are also gradually disappearing. This report introduces some fruitful study results on the next generation ground-based
extremely large telescopes, especially the results about the PSF and MTF of the telescope system and the interferometric
imaging reconstruction arithmetic. The results not only can be used in the design of large interferometric array for
aperture synthesis imaging but also adaptable to the design of single aperture telescope. On the foundation of our results,
we bring forward a new concept ground-based extremely large telescope - 30m Ring Interferometric Telescope
(30mRIT). It has the direct imaging ability and resolution like single aperture telescope, and it also can image with high
resolution like the aperture synthesis imaging mode. The 30mRIT project is remarkably different from the conventional
ground-base telescopes and its pivotal techniques have got the support of CAS and China NSF.
KEYWORDS: Telescopes, Mirrors, Interferometry, Point spread functions, Modulation transfer functions, Stars, Synthetic apertures, Optical instrument design, Large telescopes, Imaging systems
For the demand of astronomical limitation observations, such as exploring extra-terrestrial planets, black hole accretion
disk and jet in the near-infrared and optical wave band, extremely large telescopes (optical and infrared) have become the
principal ground-based astronomical instrumentation. With the maturation of interferometric imaging theory, the
borderline between new generation ground-based extremely large telescope and interferometric array for aperture
synthesis imaging is increasingly going blurring and the only differences in their technical methods and characteristics
are also gradually disappearing. This report introduces some fruitful study results on the next generation ground-based
extremely large telescopes, especially the results about the PSF and MTF of the telescope system and the interferometric
imaging reconstruction arithmetic. The results not only can be used in the design of large interferometric array for
aperture synthesis imaging but also adaptable to the design of single aperture telescope. On the foundation of our results,
we bring forward a new concept ground-based extremely large telescope - 30m Ring Interferometric Telescope
(30mRIT). It has the direct imaging ability and resolution like single aperture telescope, and it also can image with high
resolution like the aperture synthesis imaging mode. The 30mRIT project is remarkably different from the conventional
ground-base telescopes and its pivotal techniques have got the support of CAS and China NSF.
We describe a solar seeing monitor used for the site testing for the 4 meter US Advanced Technology Solar Telescope and the 1 meter Yunnan Observatory Solar Telescope. It has two parts: a solar Differential Image Motion Monitor (S-DIMM) and a linear array of 6 solar scintillometers (SHABAR= SHAdow BAnd Ranger). The results obtained by both methods are compared on the basis of observations obtained in February 2002 at the Yunnan Observatory Fuxian Lake solar station. Analysis showed that these two ways of measuring the Fried parameter give consistent results. We confirm earlier observations that showed that the boundary layer seeing over lakes is strongly suppressed. The amount of this boundary layer seeing depends on the temperature difference between lake and air and on the wind velocity. We have also carried out seeing observation along a 9.15 km horizontal path across the lake. The Cn2 values derived from these is consistent with the solar observations. They confirm the dependence of Cn2 on the lake-to-air temperature difference. From the SHABAR we find a typical scale height for the boundary layer seeing of 20 meters and from inter-comparison of the S-DIMM and SHABAR observations we derive an outer scale of turbulence of about 50 meters.
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