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Large-aperture space optical systems are important tools for observing our planet and conducting deep-space scientific research. More requirements have been put forward for large-aperture optical systems as the depth and breadth of related applications continue to increase. However, achieving the desired surface accuracy on lightweight materials for large-aperture mirror brings higher demands on relevant processing technologies, which increases the processing difficulty, cycle, and cost of large-aperture optical systems. Therefore, it is necessary to develop a new optical system technique with high tolerance for primary mirror machining errors to significantly reduce its machining accuracy requirements. This paper proposes a new optical system technique which introduces a small-aperture free-form surface into the large-aperture optical system’s post optical path. By combining the freeform correction and its misalignment on the system’s aberrations, the system’s wavefront can be adjusted to correct the wavefront distortion caused by the primary mirror’s machining errors. This reduced the machining accuracy requirements of the large-aperture primary mirror by about one order of magnitude, and high-quality imaging with a low-precision primary mirror is achieved.

The thermostressed state of one of the proposed telescope designs was analyzed by means of a finite element model using the ANSYS software package. It is shown that under normal thermal conditions, small temperature variations (within ±1°C) do not cause telescope malfunction. The range of possible temperature changes that result in the maximum permissible focus shifts and tilts of the axis of the secondary mirror relative to the primary mirror was determined.

The weight of the primary mirror increases as the aperture of ground-based telescopes increases, making it more challenging to maintain the positional stability and surface accuracy of the solid primary mirror. Consequently, a 2 m lightweight silicon carbide (SiC) mirror and an optimization method were proposed in this study. The relationship between the gravitational deformation of the mirror and its thickness and number of supports was derived based on force analysis of the mirror; the thickness of the mirror and the appropriate number of supports were obtained as initial parameters for optimization. The back structure of the mirror was designed in a lotus pattern to improve its rigidity. Numerous structural parameters were classified into major and non-major parameters based on the results of a sensitivity analysis. The non-major and major structural parameters were optimized using a Latin hypercube design method and a non-dominated sorting genetic algorithm, respectively. The optimized 2 m lightweight SiC mirror had a mass of 119 kg and an areal density of 38.7 kg/m2. The surface figure error root-mean-square (RMS) in the vertical state of the optical axis and the first modal resonance of the mirror assembly calculated using finite element analysis were 11.3 nm and 76.5 Hz, respectively. Modal tests of the mirror assembly were conducted using the hammering method, achieving a maximum relative frequency error of 7.4% compared with the simulation results. The optimized 2 m SiC mirror was over 50% lighter than traditional passive Zerodur mirrors of the same size.

Reflective optomechanical systems are widely used in fields such as space remote sensing due to their advantages of high resolution and no central obscuration. However, their performance is extremely sensitive to the alignment accuracy of key components (primary mirror, secondary mirror). To address the critical issues of precise positioning and high-reliability assembly of these components during the alignment process, this paper proposes a reliability-based adhesive bonding method based on threadless pre-stress. A threadless pre-stress assembly structure was designed, and through simulation experiments, it was verified that this method can achieve high-reliability adhesive assembly for optomechanical systems operating under conditions ranging from-20°C to 50°C.

The Wide Field Survey Telescope (WFST) is a dedicated photometric surveying facility being built jointly by University of Science and Technology of China (USTC) and the Purple Mountain Observatory (PMO). It is equipped with a 2.5-meter diameter primary mirror, an active optics system, and a mosaic CCD camera with 0.73 gigapixels on the primary focal plane for high-quality image capture over a 6.5-square-degree field of view. The installation of WFST near the summit of Saishiteng mountain in the Lenghu region is scheduled in summer of 2023, and the operation is planned to start three months later. WFST will scan the northern sky in four optical bands ( u, g, r and i ) at cadences from hourly/daily in the deep high-cadence survey (DHS) program, to semi-weekly in the wide field survey (WFS) program. During a photometric night, a nominal 30 s exposure in the WFS program will reach a depth of 22.27, 23.32, 22.84, and 22.31 (AB magnitudes) in these four bands, respectively, allowing for the detection of a tremendous amount of transients in the low- z universe and a systematic investigation of the variability of Galactic and extragalactic objects. In the DHS program, intranight 90 s exposures as deep as 23 ( u ) and 24 mag ( g ), in combination with target of opportunity follow-ups, will provide a unique opportunity to explore energetic transients in demand for high sensitivities, including the electromagnetic counterparts of gravitational wave events, supernovae within a few hours of their explosions, tidal disruption events and fast, luminous optical transients even beyond redshift of unity. In addition, the final 6-year co-added images, anticipated to reach g ≃ 25.8 mag in WFS or 1.5 mags deeper in DHS, will be of fundamental importance to general Galactic and extragalactic science. The highly uniform legacy surveys of WFST will serve as an indispensable complement to those of the Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST) that monitors the southern sky.

We present an overview of the National Science Foundation’s Daniel K. Inouye Solar Telescope (DKIST), its instruments, and support facilities. The 4 m aperture DKIST provides the highest-resolution observations of the Sun ever achieved. The large aperture of DKIST combined with state-of-the-art instrumentation provide the sensitivity to measure the vector magnetic field in the chromosphere and in the faint corona, i.e. for the first time with DKIST we will be able to measure and study the most important free-energy source in the outer solar atmosphere – the coronal magnetic field. Over its operational lifetime DKIST will advance our knowledge of fundamental astronomical processes, including highly dynamic solar eruptions that are at the source of space-weather events that impact our technological society. Design and construction of DKIST took over two decades. DKIST implements a fast (f/2), off-axis Gregorian optical design. The maximum available field-of-view is 5 arcmin. A complex thermal-control system was implemented in order to remove at prime focus the majority of the 13 kW collected by the primary mirror and to keep optical surfaces and structures at ambient temperature, thus avoiding self-induced local seeing. A high-order adaptive-optics system with 1600 actuators corrects atmospheric seeing enabling diffraction limited imaging and spectroscopy. Five instruments, four of which are polarimeters, provide powerful diagnostic capability over a broad wavelength range covering the visible, near-infrared, and mid-infrared spectrum. New polarization-calibration strategies were developed to achieve the stringent polarization accuracy requirement of 5×10 −4 . Instruments can be combined and operated simultaneously in order to obtain a maximum of observational information. Observing time on DKIST is allocated through an open, merit-based proposal process. DKIST will be operated primarily in “service mode” and is expected to on average produce 3 PB of raw data per year. A newly developed data center located at the NSO Headquarters in Boulder will initially serve fully calibrated data to the international users community. Higher-level data products, such as physical parameters obtained from inversions of spectro-polarimetric data will be added as resources allow.

In the field of modern large-scale telescope, primary mirror supporting system technology faces the difficulties of theoretically uniform output force request and bias compensation. Therefore, a novel position control system combining hydraulic system with servo motor system is introduced. The novel system ensures uniform output force on supporting points without complicating the mechanical structure. The structures of both primary mirror supporting system and novel position system are described. Then, the mathematical model of novel position control system is derived for controller selection. A proportional–derivative controller is adopted for simulations and experiments of step response and triangle path tracking. The results show that proportional–derivative controller guarantees the system with micrometer-level positioning ability. A modified proportional–derivative controller is utilized to promote system behavior with faster response overshoot. The novel position control system is then applied on primary mirror supporting system. Coupling effect is observed among actuator partitions, and relocation of virtual pivot supporting point is chosen as the decoupling measurement. The position keeping ability of the primary mirror supporting system is verified by rotating the mirror cell at a considerably high rate. The experiment results show that the decoupled system performs better with smaller bias and shorter recovery time.

The optical surface error of the space telescopes plays a decisive role in the image quality. As a key structural component supporting large-aperture optical payloads, the elastic response of the truss support structure under micro-vibration disturbances significantly affects wavefront quality. The paper focuses on a typical segmented primary mirror system and constructs a parameterized model of the truss support structure. The dynamic response of the structure under micro-vibration is systematically analyzed, and the resulting mirror surface deformation is reconstructed using Zernike polynomials. The results demonstrate that the structure exhibits highly localized dynamic responses at specific modal frequencies, which in turn induce optical aberrations, including low-order astigmatism and high-order coma. These findings demonstrate the high sensitivity of the truss structure to micro-vibration. The study elucidates the coupling relationship between structural dynamics and optical performance, providing theoretical support for structural optimization and vibration suppression in high-precision imaging systems.

Primary mirror (PM) supporting system design is one of the key components to the design of a telescope. This paper presents applications of extended multi-point supporting structures that are employed in ground based theodolites, 3 points positioning-9 points supporting system and 18 points supporting system. A number of theoretical studies have been performed using Finite Element Analysis (FEA) on each supporting system, in which the extended multi-point supporting system to 0.6-m and 1-m diameter primary mirror is particularly focused. Analyzing Zerodur major mirrors with a diameter to thickness ratio less than 7.3, deformation due to supporting gives an RMS value less than 6-nm which is 24% of the design requirement of 60-nm. Series of experiments have also been conducted using 4-D interferometer. The deformation due to supporting of major mirror has been predominantly suppressed mainly by deformation during the fabrication process. This indicates that the above supporting systems perform an excellent task under given conditions.

The integration of primary mirror (PM) and quaternary mirror (QM) has potential applications in on-axial four-mirror anastigmat space telescopes for low mass and compact structure. Aiming at fabricating silicon carbide (SiC) space mirrors by additive manufacturing, this paper presents the topology optimization method of a monolithic double-sided mirror with controlled surface errors. For optimization, the RMS deformation of PM under axial gravity is set as objective, and total weight is adopted as constraint. The evolution of surface figure errors (SFE) in topology optimization is explored for insights into optical performance. The relationships between SFE of the two optical surfaces are discussed, and the composite performances of mirror are evaluated with regard to polishing pressure load. A verification model is established by finite element method to evaluate the design results. Results show that by imposing an extrusion constraint and proper support boundary conditions, double-sided mirror with self-weight deformation superior to that of conventional isogrid mirror can be achieved. The surface errors of both PM and QM converge with similar trends in topology optimization, and the surface precision of QM is always better than that of PM. Thus, the precision of PM remains the major design concerns. Besides, the topology optimization only optimizes the aberrations with relatively high intensity. On the other hand, the mirror exhibits obvious print-through effect due to nonuniform rib distribution generated by topology optimization. A secondary optimization by adding cathedral ribs can alleviate this drawback with minor modifications to original design. Finally, a prototype is printed and machined to testify the feasibility of double-sided SiC mirror.