Lichun Zhu

THE FIVE-HUNDRED-METER APERTURE SPHERICAL RADIO TELESCOPE (FAST) PROJECT

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is a Chinese mega-science project funded by the National Development and Reform Commission (NDRC). The National Astronomical Observatories of China (NAOC) is in charge of its construction and the subsequent operation. Upon its expected completion in September of 2016, FAST will surpass the 300-meter Arecibo and the 100-meter GBT in terms of absolute sensitivity in the 70 MHz to 3 GHz bands. In this paper, we report the current status, the key science goals, and the aspiration of its early sciences. A special emphasis is paid to its innovative fatigue-resistant fibers, which are critical for the control and data acquisition under the unique FAST design.

Pulsar Observations with Radio Telescope FAST

FAST, Five hundred meter Aperture Spherical Telescope, is the Chinese effort for the international project SKA, Square Kilometer Array. An innovative engineering concept and design pave a new road to realizing huge single dish in the most effective way. Three outstanding features of the telescope are the unique karst depressions as the sites, the active main reflector which corrects spherical aberration on the ground to achieve full polarization and wide band without involving complex feed system, and the light focus cabin driven by cables and servomechanism plus a parallel robot as secondary adjustable system to carry the most precise parts of the receivers. Besides a general coverage of those critical technologies involved in FAST concept, the progresses in demonstrating model being constructed at the Miyun Radio Observatory of the NAOC is introduced. Being the most sensitive radio telescope, FAST will enable astronomers to jumpstart many of science goals, for example, the natural hydrogen line surveying in distant galaxies, looking for the first generation of shining objects, hearing the possible signal from other civilizations, etc. Among these subjects, the most striking one could be pulsar study. Large scale survey by FAST will not only improve the statistics of the pulsar population, but also may offer us a good fortune to pick up more of the most exotic, even unknown types like a sub-millisecond pulsar or a neutron star – black hole binary as the telescope is put into operation.

Preparatory Study for Constructing FAST, the World's Largest Single Dish

A 500-m aperture spherical telescope (FAST) was funded by the National Development and Reform Commission of China (NDRC) in July 2007 and will be located in the unique Karst region, a sinkhole-like landform, in Guizhou province. FAST can be seen as a modified ldquoArecibordquo type radio telescope using many innovative techniques, with as much as twice the collecting area and a wider sky coverage. FAST has, first, an active reflector, conforming to a paraboloid of revolution from a sphere in real time through actuated control, which enables the realization of wide bandwidth and full polarization capability by using standard feed design. Secondly, it has a light focus cabin suspension system, integrating optical, mechanical, and electronic technologies, reducing effectively the cost of the support structure and control system. With such a huge collecting area of more than 30 football fields, FAST will become the largest single dish ever built. Here we will summarize the FAST concept and the milestones achieved in experiments on its key technologies, i.e., site exploration, active reflector prototyping, focus cabin driving mechanism, measurement and control techniques, and the receiver layout. The Miyun FAST demonstrator also will be presented.

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) project

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is a Chinese mega-science project funded by the National Development and Reform Commission (NDRC). The National Astronomical Observatories of China (NAOC) is in charge of its construction and the subsequent operation. Upon its expected completion in September of 2016, FAST will surpass the 300-meter Arecibo and the 100-meter GBT in terms of absolute sensitivity in the 70 MHz to 3 GHz bands. In this paper, we report the current status, the key science goals, and the aspiration of its early sciences. A special emphasis is paid to its innovative fatigue-resistant fibers, which are critical for the control and data acquisition under the unique FAST design.

Five-Hundred-Meter Aperture Spherical Telescope Project

A Five hundred meter Aperture Spherical Telescope (FAST) is proposed to be built in the unique karst area of southwest China, and will act, in a sense, as a prototype for the Square Kilometer Array (SKA). It will be over twice as large as the Arecibo telescope coupled with much wider sky coverage. Some results from site surveys for such a SKA concept are briefly reported. Technically, FAST is not simply a copy of the existing Arecibo telescope but has rather a number of innovations. Firstly, the proposed main spherical reflector, by conforming to a paraboloid of revolution in real time through actuated active control, enables the realization of both wide bandwidth and full polarization capability while using standard feed design. Secondly, a feed support system which integrates optical, mechanical and electronic technologies will effectively reduce the cost of the support structure and control system. Pre-research on FAST has become a key project in the CAS.

Measurement scheme and simulation for the main reflector of FAST

FAST (five-hundred-meter aperture spherical radio telescope) is a radio telescope being built in a karst depression in Guizhou Province of China, which will be the largest single dish radio telescope in the world [1]. The reflector of the telescope is composed of over 4000 panels, and each panel could adjust its position according to observation requirements. During observations, panels in the illuminated area could form a paraboloid to correct spherical aberration [2]. Therefore, accurate measurement of the positions of panels is crucial for the operation of the telescope. In this paper, we introduce the measurement scheme for the reflector of FAST, and simulate its accuracy using direct linear transform, Gauss–Newton algorithm, Levenberg–Marquardt algorithm and an algorithm referred to as multi-point algorithm. Advantages and disadvantages of using these four methods are compared for analysis at different locations of the panels on the reflector, and suggestions are given in choosing algorithms in implementation.

Development of active reflector of the 30-meter FAST model

FAST is an Arecibo type large radio telescope with 500 meters aperture reflector, which is composed of about 4600 triangle panels. The panels and back structures are installed on the spring cable meshes. FAST adopts the active reflection structure to change the spherical difference, which will form a simultaneous parabola with aperture of 300 meters. To test the feasibility of this new type reflector structure, a FAST model of 30 meters aperture was constructed in 2005. In this paper, the structure of the model is introduced, which includes a circle supporting girder of 30 meters in diameter, 252 panel back structures, 472 main cables, and 145 sets of control cables, nodes, actuators and anchors. The structural design and analysis are processed for these compositions, and the test results of the model reflector are given. The work of the paper will provide a significant reference for the primary design of FAST reflector.

The study on the scheme of measurement and control for FAST

Newly developed method and technology for determining the spatial position of the feeds of the FAST are introduced in this paper. Base on the measurements of the position and orientation of cabin in which the feeds are mounted, a loop feedback control enables accurately driving the feeds along desired tracks. The key technique of this implementation is the precise measurement of 6-freedom coordinates of the cabin in air with high sampling rate. An innovated way for this purpose is put forward and tested, combining data by different type of sensors. The errors of measurements and their influences on the control accuracy are analyzed theoretically, and checked by model tested. The experiment shows the feasibility and effectivity of the scheme of measurement and control for the telescope.

The operation control and data acquisition of the actuators of FAST main reflector

The 2225 actuators are the main and key control devices for the deformation control of FAST (Five-hundred-meter Aperture Spherical radio Telescope) reflector. The control behavior of the reflector deformation such as tracking and scanning, is implemented by the central coordination of the actuators. For each actuator, various operation state data should be uploaded to the monitoring center on time. The actuators are controlled from the upper computer in the control center and by the PLC in the relay room. OPC protocol is used in the acquisition and control process. OPC protocol is configured to set related variables. There are significant importance for the data acquisition of the actuators of FAST main reflector. The results can be used to analyze the life of the components of the actuator. They can also be used to monitor the operation status and to analyze the reason of failure, which may be of great help to the function extension, improvement and upgrading.

Differential correction method applied to measurement of the FAST reflector

The Five-hundred-meter Aperture Spherical radio Telescope(FAST) adopts an active deformable main reflector which is composed of 4450 triangular panels. During an observation, the illuminated area of the reflector is deformed into a 300-m diameter paraboloid and directed toward a source. To achieve accurate control of the reflector shape, positions of 2226 nodes distributed around the entire reflector must be measured with sufficient precision within a limited time, which is a challenging task because of the large scale. Measurement of the FAST reflector makes use of stations and node targets. However, in this case the effect of the atmosphere on measurement accuracy is a significant issue. This paper investigates a differential correction method for total stations measurement of the FAST reflector. A multi-benchmark differential correction method, including a scheme for benchmark selection and weight assignment, is proposed. Onsite evaluation experiments show there is an improvement of 70%–80% in measurement accuracy compared with the uncorrected measurement, verifying the effectiveness of the proposed method.