On the morning of the 4th, the last steel cable was installed in the 500-meter spherical radio telescope (FAST) in Pingtang, Guizhou. The cable net manufacturing and installation project was completed. This means that the construction of the FAST support frame is completed and enters the reflective panel assembly stage.
FAST is the largest radio telescope in the world, built with natural circular lava pits. FAST's mirror frame is a 1500-meter-long circular steel beam, while the steel cable is supported by steel beams, which are staggered and have a spherical network structure.
The cable net structure is the main support structure of the FAST active reflecting surface, and is the key point for the active displacement of the reflecting surface. Cable net manufacturing and installation engineering is also one of the main technical difficulties of the 500-meter spherical radio telescope project. The key technical problems include: design of super-long span cable net installation, development of ultra-high fatigue performance cable structure, and ultra-high-precision cable structure. Manufacturing process, etc. The successful completion of the cable network project means that the FAST project has achieved substantial breakthroughs in the above-mentioned key technical difficulties.
The FAST cable net structure is 500 meters in diameter and is divided by a geodesic grid. The discontinuous design is adopted, that is, the main cable is disconnected through the node. Some key indicators of the cable net structure are much higher than the normative requirements of related fields at home and abroad: for example, the control accuracy of the main cable section must be within 1 mm, the position accuracy of the main cable joint must be 5 mm, and the fatigue strength of the cable member must not be less than 500 MPa. . The entire cable network has a total of 6,670 main cables, 2,225 main cable nodes and the same number of pull-down cables. The total weight of the cable net is about 1,300 tons, and there are 16 kinds of specifications for the main cable section, and the cross-sectional area is between 280 and 1319 square millimeters. Due to site conditions, all cable structures must be assembled in the sky.
The cable net adopts the unique working mode of active displacement, that is, according to the orientation of the observed celestial body, the actuator is used to control the pull-down cable, and a paraboloid with a diameter of 300 meters is formed in different areas of the 500-meter aperture reflecting surface to realize the celestial body observation.
The FAST cable network is the world's largest and most accurate cable network structure, and the world's first cable network system that uses displacement work. The technical difficulty is self-evident, and the technical problems that need to be overcome run through the entire process of design, manufacture and installation of the cable net. Taking the development of high-stress steel cables as an example, the FAST engineering has twice the fatigue performance requirements of the cable, which is equivalent to twice the standard value. There is no experience or information to be used for reference at home and abroad. The research and development work has undergone repeated "failure-recognition-modification-improvement" process, and it took a year and a half to complete the technical research. The results obtained have been approved by foreign expert groups at the international expert review meeting and successfully applied in the FAST project. With the continuous recovery of many technical problems of the cable network, 12 independent innovation patents have been formed, including 7 invention patents. These achievements have greatly improved the level of cable construction in China.
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