The Five-hundred-meter Aperture Spherical radio Telescope (FAST) project locates in the mountainous region of Guizhou Province, China. Due to the huge scale of the project and the precise observation performance requirements of the telescope, the reflector unit is required to have characteristics of small quality and high precision. Due to the high humidity on the site, it is necessary to ensure that the reflective surface unit has good anti-corrosion properties. This article studies how to solve the problem of the structural performance of the reflective surface unit and its implementation method. Based on the research in this paper, the error of the surface accuracy of the reflecting surface unit is less than 2.5 mm, and the central deflection of the block constituting the unit is less than 1 mm. In addition, this type of unit has good anti-corrosion properties. This paper also proposes the method of accuracy assurance in the construction process. In the end, the research results were successfully applied to the FAST project.
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.
The thermal problem is one of the important research contents of the design and operation about giant radio antenna. This kind of influence to the antenna has been concerned in the astronomy field. Due to the instantaneous temperature load and uncertainty, it is difficult to accurately analysis and effectively control about its effect. It has important significance to analyze the thermal problem of giant radio antenna to its design and operation. The research of solar cookers and temperature field on Five-hundred-meter Aperture Spherical radio Telescope (FAST) were preceded in detail. The tests of temperature distribute about 30 meters antenna in Mi-yun observatory station were performed. The research work including the parameters related to the sun, the flow algorithm of telescope site, mathematical model of solar cooker, analysis results of temperature field and corresponding control strategy, the temperature distribution test of 30 meters model. The results showed that: solar cookers could be weakened and controlled effectively of FAST. This work will provide a reference to design and operation of the FAST and same big antenna. It has certain theory significance, engineering significance and application value.
Upon its completion, the Five-hundred-meter Aperture Spherical radio Telescope (FAST) will be the largest single dish
radio telescope ever in the world. The construction has been initiated in March 2011 in Guizhou province of China. The
whole construction process is expected to be completed in September 2016, with duration of 5.5 years.
With an aperture of 500 meters and an illumination aperture of 300 meters, the active reflector is one of the most
important parts of FAST. The reflector is composed of a ring beam, a cable net and thousands of panels, tie-down cables,
actuators and anchors. For the observation process of source switching and source tracking, the parabola shape of the
reflector is achieved by drawing back of the tie-down cables by the actuators. The motion performance and the reliability
of the actuators are of great importance to the telescope.
In this paper, the motion models of the actuators are analyzed for the observation process of source switching and source
tracking. Several design schemes are proposed, including mechanical and hydraulic design. The electric, mechanical and
hydraulic characteristics of these designs are discussed. Related experimental studies are performed to investigate the
electric and mechanical performances of these actuator prototypes. Based on the analysis and test results, a final type of
actuator will be optimally concluded to meet the requirements of the reflector of FAST.
The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is currently under construction at a Karst
depression in the Guizhou province of China. The active reflector of the telescope is composed of 4395 triangular panels
laid on a cable-net structure. The aperture of the spherical surface is 500 meters, with open angle of about 110~120
degrees. Acting as the nodes of the reflector, the joint of these panels are adjusted by 2235 down-tie cables drawn by
actuators. The RMS error of the parabola reflector is expected to be 5mm.
To form the parabola shape of the reflector, for each of the actuators, a minimal working stroke of 950mm is required,
with maximal speed of 1.6mm/s at the load of 50kN. Considering the elastic deformation of the down-tie cable and other
factors, a positioning error within 0.25mm is required for the actuators.
In this paper, the base formula for the motion of a general actuator at a typical observation time is studied analytically.
The results are used to estimate the control error of the actuators and the pointing error of the whole reflector. Based on
the designed error budgets, a statistical method is employed to estimate the overall surface error of the parabola reflector.
The overall surface error is a comprehensive result of the panel design error, panel fabrication error, thermal deformation
error, panel wind load induced error, cable-net error, installation error, measurement and control error etc. The results
may be used as a reference in the measurement and control of the active reflector when in operation.
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.
FAST, five-hundred-meter aperture spherical radio telescope will be the largest radio telescope in the world which has
been established science and research items recently. One of the innovative engineering concepts is the active main
reflector which corrects spherical aberration on the ground to achieve full polarization and a wide band without
involving a complex feed system. Besides the reflector simulation, it is very important to study the supporting
structure for the reflecting surface. As the cable-net structure has been adopted, the in-depth study of back-structure is
very important which is connected between cable-net and panel. In this paper, structure forms and parameters are studied
in detail due to catch the costs and technical requirements. Throughout analysis, parameters are compared and modified.
Meanwhile, Comparing experiments has carried out on some sample frames. The stiffness experiments with different
load situations are going to confirm the feasibility of certain back-structure. Some conclusions is obtained, which can
avail in further study.
The reflector of FAST (Five-hundred-meter Aperture Sphere Telescope) is a net mesh structure and can be considered as
a flexible parallel motion mechanism array which can form the varying paraboloid surface by controlling the motion of
the net mesh nodes. As a parallel mechanism, the motion of the nodes are coupled together. In order to release the
coupling, or to estimate the surface error of the reflector, the motion of FAST 30m Model was simulated combined with
ADAMS and SIMULINK. The net mesh mechanism was modeled as springs and spheres with mass in ADAMS software.
To control the large amount of actuators, and to analyze the motion of the net mesh motion mechanism, a control model
in SIMULINK has been built, which includes astronomical plan, actuator controlling and surface analysis. The model
can be used as the test tool of the actuator control strategy and optimization for the net mesh structure. With the
combined simulation, the amount of the couple phenomenon is estimated precisely. The paraboloid shape forming and
moving in the observing course is simulated, and the variation of the surface error of the reflector and the forces of each
cable are given. By the simulation, it can be concluded that the couple effect is small in the FAST 30m Model, and such a
method can be applied to the FAST prototype.
This paper presents a preliminary study dedicated to a spatial three-degree-of-freedom (3-DoF) parallel mechanism intended to be used as the active reflector surface of a large spherical radio telescope. The forward and inverse kinematic problems of the mechanism are addressed, and solved in analytical form. Since the mechanism has only three degrees of freedom, constraint equations describing the inter-relationship between the six Cartesian coordinates are derived. Furthermore, the Jacobian matrix of the mechanism is obtained. Finally, the dexterity of the mechanism and the parasitic motion are discussed. A simulation result is reported.
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.
Polarization independent semiconductor optical amplifiers are highly desirable for optical communication. In this paper, the influence of graded index waveguides on the gain difference between TE0 and TM0 modes of semiconductor optical amplifiers is studied in detail. A new numerical procedure called complex shooting method was proposed at first to solve the eigenvalues of waveguides with graded complex refractive index. The results show that a graded index waveguide will increase the polarization sensitivity of the modal gain while an unplanar waveguide can decrease it. A polarization independent semiconductor optical amplifier can be obtained by adopting an unplanar waveguide.