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.
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.
Chinese Giant Solar Telescope (CGST) is the next generation ground-based solar telescope which was formally listed into the National Plans of Major Science and Technology Infrastructures. We have got series progresses of CGST in the recent years, from site testing to detailed designs. CGST is currently designed to be an 8m Ring Solar Telescope (RST). As an 8-meter solar telescope, the designing of CGST still faces some serious problems, although the ring structure is propitious to the thermo controlling and the high precision magnetic field measuring. The active control and the optical system of CGST are introduced. Then, simulations and the key calculations of the telescope, including the polarization analysis and the thermo calculation result are displayed. The present site testing methods and some results are introduced too. Finally, as the comparison in science and technology, the Chinese space solar telescope plans, such as the Deep Space Solar Observatory (DSO) and its progress are simply introduced.
KEYWORDS: Mirrors, Telescopes, Control systems, Solar telescopes, Control systems design, Actuators, Segmented mirrors, Sensing systems, Device simulation, Optical instrument design
The Chinese Giant Solar Telescope (CGST) is the China’s next generation solar telescope with an aperture of 8 m in
diameter. The unique feature of the CGST is its ring primary, which facilitates the polarization detection and thermal
control. The CGST is now in its design and development phase. A mosaic mirror with 24 trapezoidal segments is a
candidate for its primary mirror, which highly relies on a segment active control system to achieve competitive optical
quality of a monolithic mirror. The CGST is designed to operate in open-air observation mode, its active control system
thus faces new challenges. As the CGST has an aperture larger than that of current solar telescopes, and as the magnitude
of wind load in open air is greater than that of a stellar telescope with a similar aperture yet under the protection of a
dome and/or an enclosure. Furthermore, as a mosaic mirror, high precision real-time tip sensing is required to serve the
feedback of its control system. The accuracy depends on integration time (or working bandwidth) when an optical
metrology is adopted, which should match the bandwidth of the segment control system. In this paper, a dynamic
analysis of the segment control system of the CGST is presented. We demonstrate how the dynamic interaction between
the segment control system and the telescope structure impacts the telescope’s optical performance under wind
disturbances. The dynamic analysis helps to understand the bandwidth limit for the segment control system, and further
to clarify technical requirements for tip sensing implementation, telescope structure design and wind shielding design.
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.
KEYWORDS: Adaptive optics, Wavefront sensors, Solar telescopes, Observatories, Wavefronts, Digital signal processing, Mirrors, Telescopes, Multichannel imaging systems, Imaging systems
A low-order solar adaptive optics (AO) system, which consists of a fine tracking loop with a tip/tilt mirror and a
correlation tracker, and a high-order correction loop with a 37-element deformable mirror, a correlating Shack-Hartmann
wavefront sensor and a high-order wavefront correction controller, had been successfully developed and installed at 1-m
New Vacuum Solar Telescope of Full-shine Lake (also called Fuxian Lake) Solar Observatory. This system is an update
of the 37-element solar AO system designed for the 26-cm Solar Fine Structure Telescope at Yunnan Astronomical
Observatory in 2009. The arrangement of subapertures of the Shack-Hartmann wavefront sensor was changed from
square to hexagon to achieve better compensation performance. Moreover, the imaging channel of the updated system
was designed to observe the Sun at 710nm and 1555nm simultaneously. The AO system was integrated into the solar
telescope in 2011, and AO-corrected high resolution sunspots and granulation images were obtained. The observational
results show that the contrast and resolution of the solar images are improved evidently after the correction by the AO
system.
Chinese Giant Solar Telescope is the next generation ground based solar telescope of china. Due to the characteristics of ring aperture in polarization detection and thermal control, the current design of CGST is an 8 meter ring solar telescope. The simulation of science cases and the current observations from 1m class solar telescopes indicated the necessity of such a big aperture especially in infrared bands. 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. 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 visible band.
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.
In the last ten years, Chinese astronomers proposed two optical and near-infrared Extremely Large Telescope (ELT)
projects, one is 30m Chinese Future Giant Telescope (CFGT) the other is a 30m Ring Interferometric Telescope (RIT).
The current status in the development of these two projects and their key technology research and progress are described
in this paper. Both of the two plans are the preliminary projects of the National Astronomical Observatories (NAOC) of
the Chinese Academy of Sciences (CAS), and finance-supported from the NAOC. The National Science Foundation of
China (NSFC) also gives supports to key technology researches of the projects (such as, adaptive optics and
high-resolution imaging techniques). In the final part of this paper a brief description is given on the possibility of
international cooperation in the development of Chinese ELT. A review is also presented of other two ground-based
Extremely Large Projects (ELP), one is Five-hundred-Meter Aperture Spherical Radio Telescope (FAST), and the other
is a challenging PANDA (The Prydz bay, Amery ice shelf and Dome A Observatories) project in Antarctica.
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.
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