The imaging quality and resolution of telescopes are deeply affected by the vibration that caused by electromechanical system and wind shake. Normally, vibration is caused by insufficient damping of the structure. In this paper, an active damper system based on linear motor is proposed to suppress vibration. The model of the whole control system is established at the beginning of this paper. LQR (Linear Quadratic Regulator) algorithm is proposed and the simulation is performed based on actual parameters of system. The results show that the system has a higher stability with higher Q value. The dynamic characteristics of the structure was obtained by analyzing the modal test data from accelerators. The experiments have been carried out to test the performance of the system. The results indicated that the active vibration damper can reduce the structure vibration 93.8% at 5.5Hz and increase the stiffness of structure.
The site testing shows that Antarctic Dome A is one of the best site on earth for astronomical observations, for wavelength ranging from visible to infrared and sub-millimeter. Continuous observation for nearly four months in polar nights makes Dome A quite suitable for time domain astronomy. In the past decade CCAA already led a series of Antarctic astronomy activities and telescope projects which will be introduced in this paper. The first generation telescope is Chinese Small Telescope Array known as CSTAR, which was composed of four identical telescopes with 145mm entrance pupil, 20 square degrees FOV and different filters, all pointing to the celestial South Point, mainly used for variable stars detection and site testing. The telescope was deployed in Dome A in Jan. 2008, and followed by automatic observations for four consecutive winters. Three Antarctic Survey Telescopes (AST3) is the second generation telescope capable of pointing and tracking in very low temperature, with 500mm entrance pupil, 8.5 square degree FOV. AST3-1 and AST3-2 were respectively mounted on Dome A in Jan. 2012 and 2015, fully remotely controlled for supernovae survey and exoplanets searching. In Aug. 2017, AST3-2 successfully detected the optical counterpart of LIGO Source GW 170817. Now AST3-3 is under development for both optical and near infrared sky survey by matching different cameras. Based on the experience of the above smaller sized optical telescopes, the 2.5m Kunlun Dark Universe Survey Telescope (KDUST) was proposed for high resolution imaging over wide field of view. Currently the KDUST proposal was submitted to the government and waiting for project review.
Due to its extremely cold, dry, tenuous, and stable atmosphere, the Antarctica plateau is widely considered to be an excellent astronomical site. The long periods of uninterrupted darkness at polar sites such as Dome A provide a possibility of continuous observation for more than 3 months, which is quite suitable for time-domain astronomy. The second Antarctic Survey Telescope (AST3-2), the largest optical telescope in Antarctica so far, is a 0.5m entrance diameter large field of view optical imaging telescope which was deployed to Dome A, Antarctic in January 2015. It was used to study variable objects, such as supernova explosions and the afterglow of gamma-ray bursts, and to search for extrasolar planets. For the remoteness of the Antarctic plateau, it is designed to observe autonomously and operate remotely via satellite communication. With only 20 days attending maintenance annually, it has experienced 3 winters. It has observed for 3months in 2015 and 4 months in 2016. In the third year of 2017, the observing time of AST3-2 has covered all the polar night from March to September, the data reached to nearly 30TB with more than 200,000 exposures for searching supernovas and exoplanets. AST3-2 was also the only one telescope in the Antarctic plate that joined the optical observations of LIGO GW170817.
The Antarctic Survey Telescope-AST3 consists of three optical telescopes with 680mm primary mirror and 8 square degree field of view, mainly for observations of supernovas and extrasolar planets searching from Antarctic Dome A. The first two AST3 telescopes (AST3-1 and AST3-2) were successfully installed on Dome A by Chinese expedition team in Jan. 2012 and Jan. 2015 separately. Multi-anti-frost methods were designed for AST3-2 and the automatic observations are keeping on from March 2016. The best limited magnitude is 19.4m with exposure time 60s in G band. The third AST3 will have switchable interface for both optical camera and near infrared camera optimized for k dark band survey. Now the telescope is under development in NIAOT and the K-band camera is under development in AAO.
Currently, more and more telescopes were built and installed in Dome A of Antarctic. The telescopes are remote controlled, unattended operation due to Dome A’s environment. These telescopes must be work successfully at least one year without any failure. According to past experience, the power supply system is the weakest point in whole system. The telescopes have to stop if the power system have a problem, even a minor problem. So the high requirement for power supply system are presented. The requirement include high reliability, the self-diagnosis and perfect monitor system. Furthermore, the optic telescope only can work at night. The power source mainly relay on diesel engine. To protect the Antarctic environment and increase the life of engines. The power capacity is limited during observation. So it need the power supply system must be high power factor, high efficient. To meet these requirement, one power supply system was design and built for Antarctic telescope. The power supply system have the following features. First, we give priority to achieve high reliability. The reliability of power system was calculated and the redundant system is designed to make sure that the spare one can be work immediately when some parts have problems. Second, the perfect monitor system was designed to monitor the voltage, current, power and power factor for each power channel. The status of power supply system can be acquired by internet continuously. All the status will be logged in main computer for future analysis. Third, the PFC (Power Factor Correction) technology was used in power supply system. This technology can dramatically increase the power factor, especially in high power situation. The DC-DC inverter instead of AC-DC inverter was used for different voltage level to increase the efficient of power supply.
Antarctic is perfect site for astronomic observatory. But Antarctic also challenge the telescope design because of low temperature. The low temperature can impact characterization of telescope control system, especially for drive system. The following phenomenon can be produced due to low temperature. 1. The viscosity of grease will increase. 2. The clearance of bearing and gear will decrease. These two factors can lead to the increase in load torque of drive system with temperature drop. This would cause the bad tracking accuracy and low speed creeping. In order to overcome the impact of low temperature and improve the telescope’s track accuracy. In this paper, we describe some methods to overcome the effect of low temperature. First, the motor’s electromagnetism and lubrication in low temperature are analyzed. It shows that motor’s electromagnetism is little affected by temperature if the suitable material is selected. But the characterization of grease change dramatically with temperature. Second, the other lubricant material, solid lubricant, instead of lubricating grease is proposed. Contrasting experiment on two lubricant material proved that the solid lubricant is better than lubricating grease in low temperature environment. Third, besides the mechanical solution, a method from control point view is proposed to reduce the temperature influence. In this paper, the friction feedforward algorithm is used to compensate the torque change. Laboratory testing results will be presented verifying that friction feedforward can increase the tracking accuracy in low temperature environment.
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.
Chinese Antarctic Observatory has been listed as National large research infrastructure during twelfth five-year plan. Kunlun Dark Universe Survey Telescope, one of two major facility of Chinese Antarctic Observatory, is a 2.5-meter optic/infrared telescope and will be built at the Chinese Antarctic Kunlun Station. It is intended to take advantage of the exceptional seeing conditions, as well as the low temperature reducing background for infrared observations. KDUST will adopt an innovative optical system, which can deliver very good image quality over a 2 square degree flat field of view. All of parts of it have been designed carefully to endure the extremely harsh environment. KDUST will be perched on a 14.5-meter-high tower to lift it above the turbulence layer. In this paper, preliminary design and key technology pre-research of KDUST will be introduced.
The KDUST telescope would be installed in Antarctic Dome A, where is extremely cold, high, dry, but have a very stable,
calm atmosphere for astronomical observation. According to project requirement, the position following error should be
less than 1''. To achieve project target, a direct drive method is used in the project. Normal PID control algorithm is used
in controller. It can meet the target in the room temperature. But the following error increased too significantly in the
cryogenic environment. In this paper, the expert PID algorithm is applied to control system. The control parameter can
be adjusted by amplitude and variation of following error. Experiment proved that expert PID has an obvious advantage
in both start-up and tracking process under different temperature. Moreover expert PID also can improve the stability of
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.
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.
No periodical error and free of backlash are the main advantages of friction drive. So friction drive is applied in many ultra-low speed systems in the past years. With the trend that the aperture of optical telescope becomes bigger and bigger, there are some reports about friction drive employed to drive the telescopes. However friction drive also brings up challenge to control system because the inherent nonlinear characteristics of friction drive. This report describes the study on the friction drive finished in an experiment arranged by LAMOST project. It comprises three main parts. First, it introduces the experiment apparatus and presents a friction nonlinear curve to indicate the nonlinear characteristics of
friction drive. Subsequently, this report illuminates the negative result that influenced by the nonlinear characteristic. Secondly, this report use nonlinear PID control algorithm to control friction drive. It achieves ultra-low speed and high precision position control. The ultra-low velocity is 0.2"/S and error is 0.032"(RMS). This report also lists some factors that influence the precision of speed. Lastly, this report gives the analysis fluctuating speed of friction drive and applies acceleration feedback to diminish this fluctuating.