Guohua Zhou

The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST)

The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST, also called the Guo Shou Jing Telescope) is a special reflecting Schmidt telescope. LAMOST’s special design allows both a large aperture (effective aperture of 3.6 m–4.9 m) and a wide field of view (FOV) (5 ° ). It has an innovative active reflecting Schmidt configuration which continuously changes the mirror’s surface that adjusts during the observation process and combines thin deformable mirror active optics with segmented active optics. Its primary mirror (6.67 m×6.05 m) and active Schmidt mirror (5.74 m×4.40 m) are both segmented, and composed of 37 and 24 hexagonal sub-mirrors respectively. By using a parallel controllable fiber positioning technique, the focal surface of 1.75 m in diameter can accommodate 4000 optical fibers. Also, LAMOST has 16 spectrographs with 32 CCD cameras. LAMOST will be the telescope with the highest rate of spectral acquisition. As a national large scientific project, the LAMOST project was formally proposed in 1996, and approved by the Chinese government in 1997. The construction started in 2001, was completed in 2008 and passed the official acceptance in June 2009. The LAMOST pilot survey was started in October 2011 and the spectroscopic survey will launch in September 2012. Up to now, LAMOST has released more than 480 000 spectra of objects. LAMOST will make an important contribution to the study of the large-scale structure of the Universe, structure and evolution of the Galaxy, and cross-identification of multiwaveband properties in celestial objects.

Panel positioning error and support mechanism for a 30-m THz radio telescope

A 30-m TeraHertz (THz) radio telescope is proposed to operate at 200μmxa0with an active primary surface. This paper presents sensitivity analysis of active surfacexa0panel positioning errors with optical performance in terms of the Strehl ratio.xa0Based on Ruze’s surface error theory and using a Monte Carlo simulation, the effectsxa0of six rigid panel positioning errors, such as piston, tip, tilt, radial, azimuthal and twistxa0displacements, were directly derived. The optical performance of the telescope wasxa0then evaluated using the standard Strehl ratio. We graphically illustrated the variousxa0panel error effects by presenting simulations of complete ensembles of full reflectorxa0surface errors for the six different rigid panel positioning errors. Study of the panelxa0error sensitivity analysis revealed that the piston error and tilt/tip errors are dominantxa0while the other rigid errors are much less important. Furthermore, as indicated by thexa0results, we conceived of an alternative Master-Slave Concept-based (MSC-based) activexa0surface by implementating a special Series-Parallel Concept-based (SPC-based)xa0hexapod as the active panel support mechanism. A new 30-m active reflector basedxa0on the two concepts was demonstrated to achieve correction for all the six rigid panelxa0positioning errors in an economically feasible way.

An active reflector antenna using a laser angle metrology system

An active reflector is one of the key technologies for constructing largexa0telescopes, especially for millimeter/sub-millimeter radio telescopes. This article introducesxa0a new efficient laser angle metrology system for an active reflector antennaxa0on large radio telescopes. Our experiments concentrate on developing an active reflectorxa0for improving the detection precisions and the maintenance of the surface shape inxa0real time on the 65-meter prototype radio telescope constructed by Nanjing Institutexa0of Astronomical Optics and Technology (NIAOT; http://65m.shao.cas.cn/). The testxa0results indicate that the accuracy of the surface shape segmentation and maintenancexa0has the dimensions of microns, and the time- response can be on the order of minutes.xa0Our efforts proved to be workable for sub- millimeter radio telescopes.

A new efficient laser angle metrology system for maintaining the large radio telescope active reflecting antenna

Radio telescopes with much more larger aperture collect much more signals and therefore sought after by astronomers. The primary reflecting antenna is traditionally segmented and perfectly optically aligned at the central altitude among the whole observation sky area for minimizing the gravitational deformation during operation and passively open-loop maintained at any other altitude. A new laser segmentation sensing and maintaining method based on normal deflection angle measurement is proposed in this paper. After the introduction of the theory, the method is simulated and tested on a special prototype of radio panel segmentation system. It provides real-time monitoring and measurement of the global segmentation status of all panels and is proved to be a high accurate, high efficient and low cost method. Finally several conclusions are reached.

An active surface upgrade for the Delingha 13.7-m Radio Telescope

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.

Progress of the active reflector antenna using laser angle metrology system

An active reflector is one of the key technologies for constructing large telescopes, especially for the millimeter/sub-millimeter radio telescopes. This report presents a new and substantial progress on the efficient laser angle metrology system for the active reflector antenna of the large radio telescopes, with a plenty of experiments based on a four-panel prototype system constructed by Nanjing Institute of Astronomical Optics and Technology (NIAOT). The test results prove that this technology is workable for sub-millimeter radio telescopes both in accuracy and time-response. Thus it can be applied to the reconstruction of the active reflector antenna in China and play a central role in promoting the new area of sub-mm radio astronomy.

Conceptual design of a 5-m terahertz telescope at Dome A

A 5-meter terahertz telescope is proposed by the Chinese Center for Antarctic Astronomy (CCAA) for the East Antarctica site of the Dome A plateau. The Dome A 5-m terahertz telescope (DATE 5) will be operated at sub-millimeter waveband taking the unique advantage of the transparent atmospheric windows between 200 and 350 μm wavelengths at Dome A. A preliminary design has been conducted according to the given technical requirements and the special environmental conditions at Dome A. A symmetric R-C Cassegrain optical system is designed for the telescope, with a primary f-ratio of 0.4 and a wide field of view of 10 arcmin. The magnification of the sub-reflector is 9.4, leading to the final focal ratio of 3.76 and the focus 0.2 m below the vertex of the primary reflector. To ensure surface accuracy of the reflectors precise as small as 10 um RMS, we consider using Carbon Fiber Reinforced Plastics (CFRP) to build the backup structure (BUS) of the primary reflector and the sub-reflector itself. An alt-azimuthal mounting is adopted and a tall base structure beneath the telescope is set up to lift the telescope above the low atmosphere turbulent layer. All the mechanics, as well as control electronics, are strictly designed to fit the lower temperature operation in the Dome A environment. This paper is to generally present the mentioned systematic optical, structural and electronic design of the DATE 5 telescope.

Research progress of co-phasing inductance edge sensor for Chinese extremely large telescope

Edge sensor is one of the most important technologies for the extremely large segmented primary telescopes like Keck, Thirty Meter Telescope (TMT), European Extremely Large Telescope (E-ELT) and Chinese Future Giant Telescope (CFGT) for control of out-of-plane degrees of freedom. Different from the capacity edge sensor from Keck and TMT, one kind of an inductance edge sensor is proposed and applied with the similar principle and configuration, fine aligned and tested in this paper to try to realize the same co-focusing or co-phasing maintenance purpose and high accuracy of relative piston and tip/tilt degrees of freedom of the segments. The sensor is also considered and modified to much more sensitive to dihedral angle between the neighboring segments. Finally some preliminary conclusions are reached.

Study on a novel panel support concept for radio telescopes with active surface

Generally, panels of radio telescopes are mainly shaped in trapezoid and each is supported/positioned by four adjustors beneath its vertexes. Such configuration of panel supporting system is essentially hyper-static, and the panel is overconstrained from a kinematic point of view. When the panel is to be adjusted and/or actuated, it will suffer stress from its adjusters and hence its shape is to be distorted. This situation is not desirable for high precision panels, such as glass based panels especially used for sub-millimeter and shorter wavelength telescopes with active optics/active panel technology. This paper began with a general overview of panel patterns and panel supports of existing radio telescopes. Thereby, we proposed a preferable master-slave active surface concept for triangular and/or hexagonal panel pattern. In addition, we carry out panel error sensitivity analysis for all the 6 degrees of freedom (DOF) of a panel to identify what DOFs are most sensitive for an active surface. And afterwards, based on the error sensitivity analysis, we suggested an innovative parallel-series concept hexapod well fitted for an active panel to correct for all of its 6 rigid errors. A demonstration active surface using the master-slave concept and the hexapod manifested a great save in cost, where only 486 precision actuators are needed for 438 panels, which is 37% of those actuators needed by classic segmented mirror active optics. Further, we put forward a swaying-arm based design concept for the related connecting joints between panels, which ensures that all the panels attached on to it free from over-constraints when they are positioned and/or actuated. Principle and performance of the swaying-arm connecting mechanism are elaborated before a practical cablemesh based prototype active surface is presented with comprehensive finite element analysis and simulation.

Upgradation progress of 13.7m millimeter radio telescope reflector surface maintenance test

The real-time maintenance sensor for the active reflector is one of the key technologies for the active reflector upgradation plan of 13.7m millimeter radio telescope from Purple Mountain Observatory, China. A new type of maintenance integration sensor based on PSD and laser module based on normal angle and distance detection is proposed in this paper. After the brief introduction of the maintenance theory of the radio telescope segmented primary reflector, the method is simulated and tested on the real backup panel from the telescope in the active reflector lab in Nanjing Institute of Astronomical Optics and Technology, China. The method is proved to be a high accurate, engineering feasible for that real-time maintenance of the whole primary. Finally some conclusions are reached.