The CAFE (Census of warm-hot intergalactic medium, Accretion, and Feedback Explorer) and LyRIC (Lyman UV Radiation from Interstellar medium and Circum-galactic medium) have been proposed to the space agencies in China respectively. CAFE was first proposed as a joint scientific CAS-ESA small space mission in 2015. LyRIC was proposed as the independent external payload operating on the Chinese Space Station (CSS) in 2019. Both missions are dedicated to mapping the Lyman UV emissions ( ionized oxygen (OVI) resonance lines at 103.2 and 103.8 nm, and Lyman series) for the diffuse sources either in our Galaxy or the circum-galactic mediums of the nearby galaxies. We present the primary science objectives, mission concepts, the enabling technologies, as well as the current status.
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.
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.
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.
WFST is a proposed 2.5m wide field survey telescope intended for dedicated wide field sciences. The telescope is to operate at six wavelength bands (u, g, r, i, z, and w), spanning from 320 to 1028 nm. Designed with a field of view diameter of 3 degree and an effective aperture diameter of 2.29 m, the WFST acquires a total optical throughput over 29.3 m2deg2. With such a large throughput, WFST will survey up to 6000deg2 of the northern sky in multiple colors each night, reaching 23th magnitude for high-precision photometry and astrometry. The optical design is based on an advanced primary-focus system made up of a 2.5 m f/2.48 concave primary mirror and a primary-focus assembly (PFA) consisting of five corrector lenses, atmospheric dispersion corrector (ADC), filters, and the focal-plane instrument. For zenith angles from 0 to 60 degrees, 80% of the polychromatic diffracted energy falls within a 0.35 arcsec diameter. The optical design also highlights an enhanced transmission in the UV bands. The total optical transmission reaches 23.5% at 320 nm, allowing unique science goals in the U band. Other features include low distortion and ease of baffling against stray lights, etc. The focal-plane instrument is a 0.9 gigapixel mosaic CCD camera comprising 9 pieces of 10K×10K CCD chips. An active optics system (AOS) is used to maintain runtime image quality. Various design aspects of the WFST including the optical design, active optics, mirror supports, and the focal-plane instrument are discussed in detail.
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.
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