Daxing Wang

Progress of Antarctic Schmidt Telescopes (AST3) for Dome A

Prelimenary site testing led by Chinese Center of Antarctic Astronomy (CCAA) shows that the highest point of the Antarctic Plateau Dome A has very clear sky, good seeing, slow wind, low boundary layer and very low precipitable water vapour which make it the best site on earth for optical/IR and sub-mm observations. Chinese Small Telescope ARray (CSTAR) was installed at Dome A in 2008 and have automatically observed for about 3 antarctic winters. The three Antarctic Schmidt telescopes(AST3) with entrance pupil diameter 500mm are the second antarctic project proposed by CCAA and the first AST are being constructed in NIAOT now which is planned to be mounted on Dome A at the beginning of 2011. All the tracking components were tested in the low temperature chamber and an adaptive defrosting method is designed to prevent the frost building up on the schmidt plate.

Status of the first Antarctic Survey Telescopes for Dome A

The preliminary site testing carried out since the beginning of 2008 shows the Antarctic Dome A is very likely to be the best astronomical site on earth even better than Dome C and suitable for observations ranging from optical wavelength to infrared and sub-millimeter. After the Chinese Small Telescope Array (CSTAR) which is composed of four small fixed telescopes with diameter of 145mm and mounted on Dome A in 2008 for site testing and variable star monitor, three Antarctic Survey Telescopes (AST3) were proposed for observations of supernovas and extrasolar planets searching. AST3 is composed of 3 large field of view catadioptric telescopes with 500mm entrance diameter and G, R, I filter for each. The telescopes can point and track autonomously along with a light and foldable dome to keep the snow and icing build up. A precise auto-focusing mechanism is designed to make the telescope work at the right focus under large temperature difference. The control and tracking components and assembly were successfully tested at from normal temperature down to -80 Celsius degree. Testing observations of the first AST3 showed it can deliver good and uniform images over the field of 8 square degrees. The first telescope was successfully mounted on Dome A in Jan. 2012 and the automatic observations were started from Mar. 2012.

Development of automated small telescopes as Dome A site testing DIMM

The extreme environment of Antarctic greatly benefits astronomical observations. Site testing works already show the excellent seeing and transmission on Dome C. And the higher, colder inland plateau Dome A is widely predicted as even better astronomical site than Dome C. Preliminary site testing carried out since the beginning of 2008 shows that Dome A has lower boundary layer and lower precipitable water vapour. Now the automated seeing monitor is urgently needed to quantify the sites optical character which is necessary for the telescope design and deployment. We modify the commercial telescopes with diameter of 35cm to function as site testing DIMM and make it monitor both seeing and isoplanatic angle at the same time automatically on Dome A at different height. Part of the processed data will be transferred back by Iridium satellite network every day. The first DIMM will be deployed on Dome A in early 2011.

One Arc PMSM for telescope tracking system

This paper explores one Arc PMSM for Direct Drive Telescope tracking system. By the Arc PMSM, we can very easily manufacture one direct drive system for large telescope. Direct drive system has many advantages over more traditionally used friction and rack/pinion drive. The advantages include high stiffness, no friction, easy alignment and low maintenance. The paper discusses the design process of the Arc PMSM, especially the methods to reduce the torque ripple.

One direct drive system for Telescope

The paper discusses one direct drive telescope experiment bed (DDTEB), which is designed to simulate the modern telescope tracking system. The main task is to find the problem and the reliability which might be met in the real direct drive tracking system of the telescope and how to handle them. More information and experience will be acquired and accumulated to use the direct drive technology in the telescope complex motion system of Chinese telescope in the future.

The AST3 project: Antarctic Survey Telescopes for Dome A

The AST3 project consists of three large field of view survey telescopes with 680mm primary mirror, mainly for observations of supernovas and extrasolar planets searching from Antarctic Dome A where is very likely to be the best astronomical site on earth for astronomical observations from optical wavelength to thermal infrared and beyond, according to the four years site testing works by CCAA, UNSW and PRIC. The first AST3 was mounted on Dome A in Jan. 2012 and automatically run from March to May 2012. Based on the onsite winterization performance of the first AST3, some improvements such as the usage of high resolution encoders, defrosting method, better thermal control and easier onsite assembly et al were done for the second one. The winterization observation of AST3-2 in Mohe was carried on from Nov. 2013 to Apr. 2014, where is the most northern and coldest part of China with the lowest temperature around -50°. The technical modifications and testing observation results will be given in this paper. The third AST3 will be optimized from optical to thermal infrared aiming diffraction limited imaging with K band. Thus the whole AST3 project will be a good test bench for the development of future larger aperture optical/infrared Antarctic telescopes such as the proposed 2.5m Kunlun Dark Universe Survey Telescope project.

Control system for the first three Antarctic Survey Telescopes (AST3-1)

The first Three Antarctic Survey Telescope (AST3-1), a 50/68cm Schmidt-like equatorial-mount telescope, is the first automated Chinese telescope operating on the Antarctic plateau. It is planned to be in operations at Dome A, the highest peak on the Antarctic plateau, in 2012. The telescope is unmanned during night-time operations in the Austral winter. The telescope optics and mechanics, as well as the motors and position sensors, are exposed to a very harsh environment. The mechanics is enclosed with a foldable tent-like dome to prevent snow, diamond dust and ice. While the drive boxes, most circuit, power supply and computers are located inside the warm instrumental cabin. This article describes the challenges the telescope control system encountered in night-time operations, such as the power supply limit, the harsh meteorological condition, unattended testing, automatic operation, remote control and telemetry, etc. Some solutions are also discussed in this paper, which are applied on the AST3-1 and waiting for validation. AST3-1 is also an exploration of a larger telescope on the Antarctic.

The study on servo-control system in the large aperture telescope

Large astronomical telescope or extremely enormous astronomical telescope servo tracking technique will be one of crucial technology that must be solved in researching and manufacturing. To control technique feature of large astronomical telescope or extremely enormous astronomical telescope, this paper design a sort of large astronomical telescope servo tracking control system. This system composes a principal and subordinate distributed control system, host computer sends steering instruction and receive slave computer functional mode, slave computer accomplish control algorithm and execute real-time control. Large astronomical telescope servo control use direct drive machine, and adopt DSP technology to complete direct torque control algorithm, Such design can not only increase control system performance, but also greatly reduced volume and costs of control system, which has a significant occurrence. The system design scheme can be proved reasonably by calculating and simulating. This system can be applied to large astronomical telescope.

Error analysis of friction drive elements

Friction drive is used in some large astronomical telescopes in recent years. Comparing to the direct drive, friction drive train consists of more buildup parts. Usually, the friction drive train consists of motor-tachometer unit, coupling, reducer, driving roller, big wheel, encoder and encoder coupling. Normally, these buildup parts will introduce somewhat errors to the drive system. Some of them are random error and some of them are systematic error. For the random error, the effective way is to estimate their contributions and try to find proper way to decrease its influence. For the systematic error, the useful way is to analyse and test them quantitively, and then feedback the error to the control system to correct them. The main task of this paper is to analyse these error sources and find out their characteristics, such as random error, systematic error and contributions. The methods or equations used in the analysis will be also presented detail in this paper.

Design of one large telescope direct drive control system based on TMS320F28xx

The mount drive control is the key technique which mostly affects astronomical telescope’s resolution and its speed. However, the ultra -lower speed and the giant moment of inertia make it very difficult to be controlled. In this paper, one segmented permanent-magnet synchronous motor (PMSM), 4m diameter, is suggested for the mount driving. A method is presented to drive the motor directly, which is based on TMS320F28XX and Insulated Gate Bipolar Transistor (IGBT) , also, HEIDENHAIN tape is used to detect the absolute position of the motor together with the Hall sensor. The segmented PMSM can work stable and the mount drive can realize nice tracking performance at ultra -lower speed with this drive system.