Dehua Yang

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.

Measuring seeing with a Shack-Hartmann wave-front sensor during an active-optics experiment

We describe the measurement of atmospheric enclosure seeing along a 120-m light path by use of a Shack-Hartmann wave-front sensor (S-H WFS) for the first time to our knowledge in the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) outdoor active-optics experiment system, based on the differential image motion method and a S-H WFS. Seeing estimates that were gained with the S-H WFS were analyzed and found to be in close agreement with the actual seeing conditions, the estimates of refractive-index structure constant, and the thin-mirror active optics results, which usually include the shape sensing precision and the active correction precision of the experimental system. Finally, some countermeasures against poor seeing conditions were considered and adopted.

Active support system of LAMOST reflecting Schmidt plate

The reflecting Schmidt plate MA of LAMOST is with 5.7m × 4.4m reflecting area and consists of 24 segmented hexagonal sub-mirrors. Each sub-mirror is 25mm in thickness and 1.1m in diagonal. To correct the spherical aberration of the primary mirror, during observation, the aspherical shape of MA should be changed in every 1.5 minutes. To achieve the good image during observation, the active support system of MA will not only create the correct off-axis aspherical shape on each sub-mirror, but also maintain the co-focus for all 24 sub-mirrors. This paper presents the studying design with finite element analysis and experiments on the active support system of MA, including its axial and lateral supports, force actuators, optimization of the stiffness of the force actuator, sub-mirror cell, the mirror support structure etc. There are 30 force actuators and three position actuators, which support each sub-mirror and connected by sub-mirror cell. Total 24 sub-mirror cells located on the top of the MA main support structure. All force actuators work as both active and passive supports for each sub-mirror. It showed that the support system is complex but should work properly within the optical requirement.

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.

Structure Design and Analysis of the Special Mounting and Tracking System of the LAMOST

The Large sky Area Multi-Object fiber Spectroscopic Telescope is a very special reflecting Schmidt telescope with a 40 m long optical axis between the reflecting Schmidt correcting plate and the spherical main mirror. In the middle is located the spherical focal plane of 1.75 m in diameter. The reflecting Schmidt correcting plate serves not only to correct wavefront by active optics but also to point and track celestial objects by normal tracking with collaboration of the focal plane to form a special mounting and tracking system. In this paper, the operational principle and technical specification of the tracking system is briefed. Design and test measurement as well as driving mode of both the Schmidt plate and the focal plane are investigated with structural calculations and analyses. The paper is closed with the conclusion that the mounting and tracking system is to meet global technical specifications of the LAMOST excellently.

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.

Study on functional integration of the SKA and the solar thermal power system

A separate building of solar power plants may take hundreds of millions of euros. The dish-stirling system is one of the concentrating solar thermal power (CSP) technologies. Considering the dish-stirling system is structurally similar to a radio telescope, with its diameter similar to the antenna that is used in the SKA, It is assumed that a radio telescope and the dish-stirling system could be functionally integrated in the design for time-based sharing, thus to reduce the SKA and the dish-stirling system in the repeated construction costs on the reflecting surface, the two-axis tracking mechanism, the civil engineering, and the roads, etc. Based on the above idea on the functional integration of devices, whilst taking account on the functional requirements of the SKA and the dish-stirling system, the Principle design of functional integration is conducted. In addition, the control system and multi-functional reflector regarding its processing and coating technology is covered.