Revealing the world’s largest "pot cover": the reflecting surface is equivalent to 30 football fields (Figure)

  Xinhua News Agency, Guiyang, July 3 rd Title: Revealing the world’s largest "pot cover": 4,450 reflection units spell out the world’s largest and strongest "Eye of the Sky"

  Xinhua news agency reporter

  Remember what the "pot cover antenna" looks like?

  On July 3, 2016, the world’s largest "pot cover" with a diameter of 500 meters was erected in Guizhou karst tiankeng.

  It is the 500-meter spherical radio telescope, the largest and most powerful single-aperture radio telescope in the world.

  It is called "Eye of the Sky", which is used to listen to the sounds in the depths of the universe and observe the mysteries of the universe.

  Start with Xue Huadian on old TV.

  When the old TV can’t receive the signal, the screen is not blank, but Xue Huadian is flashing. In fact, these Xue Huadian are electromagnetic wave signals, including radio emission from space.

  In 1933, scientists in bell laboratory accidentally discovered the stable radio emission from the center of the Milky Way with a highly sensitive receiver, which opened the door to radio astronomy.

  Anyone who has used the "lid antenna" knows that the larger the lid aperture, the clearer the TV picture. For radio telescopes, the larger the aperture, the farther you can see. Radio astronomers all over the world are pursuing to build a larger-caliber "pot cover" to improve the sensitivity of radio telescopes.

  Peng bo, a researcher at the National Astronomical Observatory of the Chinese Academy of Sciences and deputy manager of the 500-meter spherical radio telescope project, said that the radio telescope had been short of funds at the beginning of its design and construction, but scientists were unwilling to reduce its caliber no matter what it was reduced.

  "Space is mixed with all kinds of radiation, and distant signals are like cicadas in thunder, and there is no super-sensitive ‘ Ear ’ I can’t tell it at all. " Nan Rendong, chief scientist and chief engineer of the 500-meter spherical radio telescope project at the National Astronomical Observatory of the Chinese Academy of Sciences, said.

  Previously, the most sensitive radio telescopes in the world were the 100-meter telescope in Bonn, Germany and the 300-meter telescope in Arecibo, USA. The former can move and "shake its head", while the latter is built with the help of karst potholes on Puerto Rico island.

  At the 1993 International Radio Union Congress, astronomers from 10 countries, including China, proposed to build a new generation of radio "big telescopes", eager to go back to the original universe and solve many difficult problems in astronomy before the radio wave environment was completely destroyed.

  "Building the world’s first large-caliber radio telescope is the dream of teacher Nan Rendong and several predecessors, which embodies the ambitious ambition of China astronomers." Peng bo said.

  At the end of 1995, more than 20 universities and research institutes in the United Nations of Beijing Observatory set up the China Promotion Committee of Radio "Large Telescope", and put forward the karst engineering concept of building a spherical reflector, namely "Arecibo antenna array", by using Guizhou karst depression.

  Since then, scientists in China have further promoted the concept of karst and proposed to independently develop a new karst unit, namely a 500-meter spherical radio telescope.

  In order to set up a new generation of radio "big telescopes", scientists have turned over the karst mountain areas in Guizhou through satellite remote sensing. Peng bo recalled that at that time, the Observatory commissioned two institutes to conduct independent search and select from more than 300 candidate potholes. As a result, Dawodang, located in Pingtang County, Qiannan Prefecture, got the highest score twice.

  The conditions provided by natural karst potholes in Guizhou have always been the most unique and the largest and strongest foundation for China Radio Telescope in the world.

  Not just a big circle — — What is the strength of China Radio Telescope?

  Whether you are near a large radio telescope, climbing the observation deck on a nearby hill or watching a virtual reality video, you can intuitively feel its first feature — — Big. Scientists describe it as a "giant eye for watching the sky".

  Wang Qiming, chief engineer of the 500-meter spherical radio telescope project at the National Astronomical Observatory of Chinese Academy of Sciences, said that more than 10,000 tons of steel were used only for the ring beam, cable net and six towers supporting the feed cabin.

  "The total reflecting surface of the telescope is 250,000 square meters, which is equivalent to the size of 30 standard football fields. Although the reflective panel is only 1 mm thick, it also uses more than 2,000 tons of aluminum alloy. " Wang Qiming said.

  However, the large radio telescope is by no means a "stupid" metal pile, it is the most sophisticated astronomical instrument. Due to the adoption of the feed platform with optical, mechanical and electrical integration and the secondary adjustment of the parallel robot in the feed cabin, it can realize millimeter-level pointing tracking without rigid connection between the feed and the reflecting surface, ensuring accurate gathering and monitoring of weak radio signals in the universe.

  The construction technology of the large radio telescope is also improving. Wang Qiming said that due to strict requirements, this big scientific project has promoted the improvement of equipment manufacturing capabilities in many fields:

  — — The cable net with active reflection surface has the characteristics of high elasticity, tensile resistance and fatigue resistance, and its ultra-high stress amplitude of 500 MPa is 2.5 times that of the national standard;

  — — More than 2,000 hydraulic actuators that help the reflector to be displaced can achieve accurate positioning and coordinated movement through expansion and contraction, and can also report their own state information to the control system to meet the movement requirements such as timely tracking and source change.

  — — Dynamic optical cable, which undertakes the mission of transmitting all kinds of data and information, can withstand repeated bending, winding and torsion and other mechanical properties and harsh natural environment tests.

  "Our original design concept originated from the Arecibo telescope in the United States. But compared with Arecibo, the active reflector system is our biggest innovation. " Peng bo said that the cable net structure of a large radio telescope can change with the movement of celestial bodies, driving 4,450 reflecting units on the cable net to form a 300-meter instantaneous paraboloid in the direction of radio power supply, which greatly improves the observation efficiency.

  Arecibo telescope is a fixed telescope, which can only scan a 20-degree strip area in the sky by changing the position of antenna collapse. The active reflector allows the China Radio Telescope to have a wider observation range, covering 40-degree zenith angle.

  The working frequency of large radio telescopes is relatively wide. Peng bo said that the feed cabin is equipped with a multi-band and multi-beam feed and receiver system covering the frequency of 70 MHz ~ 3 GHz.

  Zheng Xiaonian, deputy director of the National Astronomical Observatory of the Chinese Academy of Sciences, said that the German Bonn telescope with a diameter of 100 meters was once called "the largest machine on the ground", and the sensitivity of the China Radio Telescope was improved by about 10 times. The 300-meter-caliber Arecibo telescope in the United States has been unsurpassed for more than 50 years. Compared with it, the comprehensive performance of China Radio Telescope has been improved by about 10 times.

  Take root in the karst sinkhole and look at the deep space of the universe

  "Like other radio telescopes, the two main scientific goals of the China Radio Telescope are to patrol the neutral hydrogen in the universe and observe pulsars. The former is to study the large-scale physics of the universe to explore the origin and evolution of the universe, and the latter is to study the material structure and physical laws in extreme States." Zheng Xiaonian said.

  The earth’s atmosphere leaves two windows for human beings to explore the universe, one is optics and the other is radio. For astronomers, if the optical telescope is a microscope, then the radio telescope is a CT machine, which can obtain the ultra-fine structure of celestial bodies.

  "There are seven sets of receivers, because the frequency of observation in different bands is different, and the observation and research goals are different." Peng bo said that in the eyes of large radio telescopes, the universe and cosmic celestial bodies are a three-dimensional presentation.

  For more than half a century, the energy collected by all radio telescopes in the world has not turned a page, and the joining of China Radio Telescope will greatly accelerate this speed. And the energy collected means the amount of information to interpret the mysteries in the depths of the universe.

  "Since the birth of the radio telescope, humans have discovered about 2,500 pulsars. If the working hours of the China Radio Telescope are all used to observe pulsars, it is expected to double this number within one year." Peng bo said that pulsars can be used for pulsar navigation, pulsar timing array and other application targets.

  Nan Rendong believes that large radio telescopes may also find some unprecedented pulsar phenomena, such as a pulsar paired with a black hole, which may produce a breakthrough theory.

  Every little progress in the development of physics is accompanied by great difficulties and twists and turns. But at every stage of human civilization progress, physics has always stood at the forefront of liberating productive forces. Peng bo said that scientists used Arecibo telescope to discover gravitational waves and won the Nobel Prize in physics, while China Radio Telescope provided a great opportunity for natural science, especially physics-related fields.

  "The answer is yes to whether the large radio telescope that the public is very concerned about can be used to find extraterrestrial civilization." Peng bo said that it is a weapon to detect exoplanets, especially terrestrial planets. Because of its improved sensitivity, it can see farther and fainter celestial bodies. By detecting interstellar molecules and searching for possible interstellar communication signals, the probability of finding extraterrestrial civilization is 5 to 10 times higher than that of existing equipment.

  On July 3rd, after the installation of the feed cabin and the reflector panel was completed as planned, the large radio telescope will be debugged for more than two months, and it will be officially completed and put into use at the end of September. However, in order to optimize all functional parameters, it needs to be continuously debugged and improved in two or three years of observation.

  "After the completion of the large radio telescope, it will become the ‘ Sharp weapon ’ To maintain the status of world-class equipment in the next 10 to 20 years. " Zheng Xiaonian said, "I hope that China scientists will use it to produce results as soon as possible." (Note holder Qi Jian; Participating reporters Wu Jingjing, Hu Xing and Yang Weihan)