The optimization of the elevation rotation structure (ERS) is one of the critical problems in the design of a large submillimeter telescope (LST). Here, combining the super element model with topology optimization method and genetic algorithm (SEMTOMGA) is proposed for the ERS design of an LST. The SEMTOMGA has three key steps: (1) the super element model is applied to condensing all the degrees of freedom of the large structure elements, which needs no topology optimization, except for the connecting nodes and the objective structure elements; (2) the topology method is applied to optimizing the objective structure; (3) based on the optimization results of the second step, the further whole structure optimization with multiobjective genetic algorithm(GA) is performed. The SEMTOMGA, which exploits the complementary merits of the super element model, topology optimization method, and GA, solves the problem of the ERS design effectively. As an application, a 60-m submillimeter telescope is designed and optimized by SEMTOMGA. The results have shown that the SEMTOMGA not only obtains a lightweight design of the ERS but also has sufficient stiffness. Moreover, the performance of the whole structure has been improved, and the residual half-path length errors of the main reflector have declined from 263.7 to 135.6 μm, which is about half of the original 263.7 μm of the initial design.
HinOTORI is a China-Japan co-construction 50cm telescope with three-color (u', RC, and IC) simultaneous imager. The main purpose aims at identifying gravitational-wave electromagnetic counterpart and performing follow-up observation from ultraviolet to near-infrared band. The telescope locates at the Tibet plateau, China, with 5100 meters high altitude. The construction of the telescope has already finished, and now it is going on commissioning. In this paper we focus on the system and devices for remote control of multi-devices, including telescope, mount, dome, three cameras, Power Distribution Units (PDUs), sky monitor, and so on. We will also present system performance and site condition based on observations collected during commissioning.
The 60-meters submillimeter telescope is a large astronomical facility under proposed with the advantages of high sensitivity and large field of view, which mainly planned to observe the low temperature gas and dust in the universe. The aperture of primary reflector is 60 meters, and the requirement of surface error is 30μm rms which enables it to observe in the wavelength of 0.65mm to 3mm. In order to achieve the high accuracy requirements of telescope, the primary reflector is design to be composed of CFRP segments in one of the conceptual design schemes, similar to Large Millimeter Telescope (LMT). The natural limit of surface accuracy and pointing accuracy of telescope will be improved after the application of CFRP with the advantages of high specific stiffness and low thermal expansion, etc. This paper describes the initial development of a 3 meters prototype CFRP reflector segment, mainly including the design process of support truss and manufacture status of panel and truss.
The free-vibration modes of an annular mirror (FVMAM), derived from the thin plate theory and reflecting the intrinsic characteristics of the physical phenomenon of resonance, have been applied to compensate the aberrations of the active optics system. As an application example, the compensations of some low-order aberrations of the 2.5-m Wide-Field Survey Telescope with the FVMAM have been presented. In addition, a quantitative comparative study of the aberration corrections between the FVMAM and the annular Zernike polynomials has been carried out. The results have shown that the FVMAM are more effective to correct the aberrations.
One prototype carbon fiber-reinforced plastics (CFRP) panel for 5-m Dome A Terahertz Explorer antenna is replicated successfully in meeting the surface accuracy requirement of less than 10 μm rms by using resin-rich layer technology. By considering the unconventional thermal deformation behavior of a composite structure, a finite-element model (FEM) is produced to predict the thermal deformation behavior of the panel at low temperature. Effects of structural parameters on thermal deformation behavior of the panel are discussed and they are used in the design and in the structural optimization for minimizing surface thermal deformation error at low temperature. An experimental method based on high precision photogrammetry is used to measure the thermal deformation error of the prototype panel. The method has been used for updating the properties of the FEM so that the FEM becomes even more accurate. A prototype panel with high surface accuracy and high thermal stability has been manufactured recently based on the design parameters given by the updated FEM. Plans for improvements in structure design and molding process are also provided at the end of the paper.
KEYWORDS: Reflectors, Antennas, Actuators, Signal to noise ratio, Near field, Telescopes, Spatial resolution, Holography, Radio telescopes, Transmitters
We describe a method for the measurement and alignment of reflector surfaces of radio telescopes with high precision. The scheme is based on antenna gain measurements under a series of active surface perturbations in terms of a set of orthogonal basis functions. Both local and global basis functions can be employed, resulting in different spatial resolution and different requirements on signal-to-noise ratio. Both theoretical studies and numerical simulations are presented, and demonstration experiments on a 1.2-m submillimeter antenna are reported. Practical considerations, including the effects of antenna mispointing and near field operation, are also discussed.
The free-vibration modes of an annular mirror (FVMAM), reflecting the natural properties of the physical phenomenon of resonance, are proposed to represent the optical aberrations. A realistic dynamics model is presented to investigate the physical properties of an annular mirror on the natural frequencies of FVMAM. An explicit solution is derived from the analytic method based on the thin plate theory. Taking the primary mirror of the 2.5-m-wide field survey telescope as an example, the FVMAM is numerically calculated and studied. The results have shown that the mode shapes resemble the optical aberrations, and there is almost a one-to-one match between each free-vibration mode and each optical aberration. In addition, the results of the analytic method are validated by the finite-element method. The conclusions suggest that the results obtained by the two methods are in good agreement with each other. Moreover, we present a comparative study for FVMAM and annular Zernike polynomials which are very well known to be widely used to represent optical aberrations. The results show that the free-vibration modes can not only be used to replace annular Zernike polynomials but also can be more effective.
In this paper, the finite element parameterized model of 1.2 meter terahertz antenna is established for near-field holographic measurement. The structure of 1.2m antenna, which consists of reflector body and tower base, is developed to a prototype of the 5-m Dome A Terahertz Explorer (DATE5). The reflector is made of carbon fiber-reinforced plastics, and tower base is made of steel. For the evaluation of the antenna performances, the gravity load effects of 1.2m antenna have been analyzed by the model. The numerical analysis results show that reflector surface RMS errors due to gravity load decrease with the increase of elevation angle, and the ranges of values of the surface RMS errors are from 0.14μm, to 0.81μm, which has been met the performance requirements of 1.2m antenna. Moreover, the mode shapes and the eigenfrequencies are also studied. The results suggest that the trends of the dependence of first three orders eigenfrequency upon elevation angles are well agreement with those of DATE5: the eigenfrequencies of the first and second orders of the model also decrease with the increase of elevation angle, while the eigenfrequencies of the third order increase with the increase of elevation angle.
A novel wavefront-based algorithm for the beam simulation of both reflective and refractive optics in a complicated quasi-optical system is proposed. The algorithm can be regarded as the extension to the conventional Physical Optics algorithm to handle dielectrics. Internal reflections are modeled in an accurate fashion, and coating and flossy materials can be treated in a straightforward manner. A parallel implementation of the algorithm has been developed and numerical examples show that the algorithm yields sufficient accuracy by comparing with experimental results, while the computational complexity is much less than the full-wave methods. The algorithm offers an alternative approach to the modeling of quasi-optical systems in addition to the Geometrical Optics modeling and full-wave methods.
A near-field millimeter-wave holography system operating in the 3-mm waveband have been developed as a prototype for DATE5, a 5-m terahertz telescope proposed to be deployed at Dome A, Antarctica. Experimental measurements at 92 GHz have been made on a 1.45-m test antenna. During the night time at which the ambient temperature doesn’t vary rapidly, a 75-minute repeatability (repeating measurement 3 times) of ~2.3 μm rms has been achieved with an aperture resolution of 46 mm. A local surface change of known value is correctly detected. After long-time repeating measurements, thermal-induced feed displacement is also detected with an accuracy of approximately 20 μm. Random error factors of the experiment system are evaluated and their contributions to the derived surface error are also simulated, showing that relative poor pointing of the test antenna is the major factor limiting the measurement repeatability.
The observation bands of the 5 meter Dome A Terahertz Explorer (DATE5) are primarily over the wavelength of 350 and 200 μm. However, the pointing performance of DATE5 is affected by the unsteady wind, which either acts directly on the telescope structure or transmits through the ice and foundation. According to the above performance requirements of DATE5, the pointing error caused by the wind disturbance must be less than 2 arcsec. The main influence of the disturbances acting on the telescope is forces and torques due to wind gusts. Alternating forces and torques cause displacements of the telescope as well as structural oscillations. Both effects lead to pointing errors and therefore have to be compensated as much as possible by the main axes servo controllers. Wind acting on the telescope can be treated as random event, whose expected values depend on the specific site. The wind velocity throughout a given time interval can be described as a randomly varying velocity superimposed upon a constant average or mean velocity. For the dynamic analysis, the two components are separated and only the fluctuating component is used. In this paper, the dynamic analysis (mode analysis and spectrum analysis) of DATE5 is carried out based on the physically realistic environmental disturbances of dome A.
Dome A 5m Terahertz Explorer (DATE5) is a proposed telescope to be deployed at Dome A, Antarctica to explore the excellent terahertz observation condition unique to the site. One of the key challenges of the telescope is to realize and maintain the required 10 μm rms overall reflector surface accuracy under the extreme site conditions and unmanned operating mode. Aluminum panels on carbon fiber backup structures is one of the candidate options for the 5 meter main reflector. For aluminum panels, three major technical risks were identified: 1) the large CTE of aluminum causes significant panel deformation due to the large seasonal soak temperature change; 2) internal stress may cause additional surface deformation when operating under a cold environment; 3) reflector panels working at Dome A run high risks of icing (which degrades antenna efficiency and increases noise) and automatic active de-icing mechanisms has to be implemented on the panels. In order to verify the feasibility of the aluminum panels for DATE5 and identify possible technical risks, a prototype panel was fabricated and went through rigorous tests. The manufacture error at the room temperature is 3.2 μm rms, which meets the budget. The panel surface is then measured at various ambient temperatures down to -60°C in a climate chamber using photogrammetric techniques. The additional surface error at the low temperatures is found to be mainly contributed by defocusing error, and the dependence of the panel focal length on temperature is well predictable. No additional surface error caused by internal stress has been observed. Next, the icing condition of the panel is analyzed and a prototype de-icing system based on polyimide film heaters was installed on the panel. The performance of the de-icing system was tested in a climate chamber as well as in the field experiments to simulate a variety of operating environments. The experiments indicate that the power required for de-icing the entire main reflector is less than 1kW and the temperature field produced by the de-icing system has trivial effect on the surface accuracy of the panel. This study indicates that aluminum panels have the potential to meet the reflector surface error budget under the harsh environment of Dome A.
DATE5 antenna, which is a 5m telescope for terahertz exploration, will be sited at Dome A, Antarctica. It is necessary to keep high surface accuracy of the primary reflector panels so that high observing efficiency can be achieved. In antenna field, carbon fiber reinforced composite (CFRP) sandwich panels are widely used as these panels are light in weight, high in strength, low in thermal expansion, and cheap in mass fabrication. In DATE5 project, CFRP panels are important panel candidates. In the design study phase, a CFRP prototype panel of 1-meter size is initially developed for the verification purpose. This paper introduces the material arrangement in the sandwich panel, measured performance of this testing sandwich structure samples, and together with the panel forming process. For anti-icing in the South Pole region, a special CFRP heating film is embedded in the front skin of sandwich panel. The properties of some types of basic building materials are tested. Base on the results, the deformation of prototype panel with different sandwich structures and skin layers are simulated and a best structural concept is selected. The panel mold used is a high accuracy one with a surface rms error of 1.4 μm. Prototype panels are replicated from the mold. Room temperature curing resin is used to reduce the thermal deformation in the resin transfer process. In the curing, vacuum negative pressure technology is also used to increase the volume content of carbon fiber. After the measurement of the three coordinate measure machine (CMM), a prototype CFRP panel of 5.1 μm rms surface error is developed initially.
The optimization of a primary mirror support system is one of the most critical problems in the design of large telescopes. Here, we propose a hybrid optimization methodology of variable densities mesh model (HOMVDMM) for the axial supporting design, which has three key steps: (1) creating a variable densities mesh model, which will partition the mirror into several sparse mesh areas and several dense mesh areas; (2) global optimization based on the zero-order optimization method for the support of primary mirror with a large tolerance; (3) based on the optimization results of the second step, further optimization with first-order optimization method in dense mesh areas by a small tolerance. HOMVDMM exploits the complementary merits of both the zero- and first-order optimizations, with the former in global scale and the latter in small scale. As an application, the axial support of the primary mirror of the 2.5-m wide-field survey telescope (WFST) is optimized by HOMVDMM. These three designs are obtained via a comparative study of different supporting points including 27 supporting points, 39 supporting points, and 54 supporting points. Their residual half-path length errors are 28.78, 9.32, and 5.29 nm. The latter two designs both meet the specification of WFST. In each of the three designs, a global optimization value with high accuracy will be obtained in an hour on an ordinary PC. As the results suggest, the overall performance of HOMVDMM is superior to the first-order optimization method as well as the zero-order optimization method.
An upgrade program is proposed for the Delingha 13.7-m radio telescope to implement active surface for multi-beam
observation at 3 mm wavelength. The upgrade involves three critical development aspects. One is the displacement
actuator, which must fit the existing position, space and connections of the panels and backup structure, meanwhile, must be as compact and lightweighted as possible. The second is that a new sub-reflector is necessitated by the multi-beam observation, where a new hyperbolic surface figure is optimized. The third, more crucial and difficult, is to realize active control of the actuators and real-time closed-loop of the full active surface. This paper is to present the progress of the development work, test and experiments associated with the three areas. With one of the spare panels of the telescope, an experiment system is carried out with six sets of actuator and control electronics. Another experiment system of a novel laser-based closed-loop measurement concept is also conducted with four smaller dummy panels. Both experiment setups have output expected results and further experiments are going on with them. In this paper, based on the two experiments, we will describe the special design and test of the actuator, including the design of its special mounting and connecting mechanisms. The design and manufacture and measurement of the new hyperbolic sub-reflector will be detailed as well as the principle, simulation and realization of the laser-based measurement system. Besides, the control strategy of the large scale use of the hundreds of actuators and EMI suppression are also covered.
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