The world's largest and most sensitive single-aperture radio telescope——
"Chinese Sky Eye", listen to the voice of the universe (open the book to learn new things)
Jiang Peng
"People's Daily" (20th edition on April 29, 2021)
On March 31, 2021, the "Chinese Sky Eye" (FAST) was officially opened to astronomers around the world.
What is the "Chinese Sky Eye"?
It is a single-aperture spherical radio telescope with independent intellectual property rights in my country for exploring the universe.
With it, it can promote the understanding and exploration of the deep space of the universe, and provide new possibilities for the development of astronomy.
How big is the "Chinese Sky Eye"?
It has a caliber of 500 meters and a launch area equivalent to 30 standard football fields.
If you fill it with mineral water, 7 billion people in the world can divide 4 bottles per person on average.
How far can it see?
It can see through an area of more than 13 billion light-years, close to the edge of the universe.
At present, the "China Sky Eye" is the largest and most sensitive single-aperture radio telescope in the world.
Learn from the principle of parabolic antennas to listen to signals from the universe from the earth
The scientific name of "China Sky Eye" is a 500-meter-caliber radio telescope.
Unlike common optical telescopes that observe through visible light, radio telescopes "observe" the universe by receiving radio waves that are invisible in the universe.
There are two "windows" in the thick atmosphere above us: one is a visible light window through which humans have observed the universe for thousands of years; the other is a radio window, which was the pioneer of radio astronomy Karl Jansky in the 1930s The signal from the center of the Milky Way was discovered by accident, and the curtain of radio astronomy was opened, pushing human beings to understand the origin of the universe and the origin of life.
The "Chinese Sky Eye" is the "heavy tool" of radio astronomy today.
What is the basic principle?
We all know that parallel electromagnetic waves will converge to the focal point after being reflected by a parabolic surface.
For radio telescopes, the reflecting surface is made into a parabolic shape, and then a receiver is placed at the focal point to collect the electromagnetic wave signals emitted by celestial bodies for astronomical observation.
The larger the area of the parabola, the more signals it collects, and the more faint and distant celestial bodies can be detected.
Therefore, since Karl Jansky accidentally discovered the radio astronomy observation window, astronomers from all over the world have been working to build giant radio telescopes with as large a reflecting surface as possible.
At the same time, with the large-scale use of radio by humans, more and more radio waves have been generated, which interferes with the reception of signals from space by humans.
At the 1993 International Radio Conference, many countries, including China, put forward an initiative to build a radio telescope with a super-large aperture before the earth's electromagnetic environment is destroyed.
In the following year, Chinese scientists represented by Mr. Nan Rendong began the exploration of the "Chinese Sky Eye", opening the journey of "turning the impossible into possible".
Difficulty and many breakthroughs, "China Sky Eye" occupies the commanding heights in sensitivity
How large a telescope can be built depends on how large a depression is eventually found.
Suitable depression is very difficult to find, because it must meet the four major conditions at the same time.
First, it must be large enough and round enough, otherwise the cost of excavation and support will make this project impossible; secondly, it must be far away from densely populated areas, so as to ensure a good radio environment; again, no water can accumulate, otherwise the life of the equipment will be difficult Guarantee; Finally, there must be good geological conditions, otherwise large-scale, high-precision astronomical observation equipment cannot be built.
From 1994 to 2006, Nan Rendong led the team to select more than 300 depressions from more than 8,000 maps, and then further narrowed the scope to dozens.
The team walked almost all over these depressions, on-site surveys, eating and sleeping.
In the end, the site was set at the Dawotai Depression in Kedu Town, Pingtang County, Guizhou Province.
After the site is determined, how to design, how to realize, how to debug and use it after completion, there is no ready-made experience to learn from: there is no precedent for key technologies, and key materials need to be developed from scratch.
The design of "China Sky Eye" is different from the existing single-aperture radio telescopes in the world, which is firstly reflected in the design of "retina" and "pupil".
"Retina" refers to the reflective surface; "pupil" refers to the feed cabin, that is, the cabin where the device system for receiving signals from outside the universe is placed.
As the world's first, the "retina" of the "Chinese Sky Eye" is an active reflective surface that can change its shape, a spherical surface for a while, and a parabolic surface for a while.
Specifically, this huge movable "retina" is a cable net made of 6670 steel cables, hung on a ring beam with a diameter of 500 meters supported by 50 huge steel columns; the cable net is covered with 4450 pieces and more than 380 kinds of reflective surface units; under the cable net are 2225 pull-down cables, each of which is fixed to an actuator on the ground, and the shape of the cable net is changed by manipulating the actuator and pulling the pull-down cable , So as to collect and observe astronomical signals.
The "pupil" of "China Sky Eye" is the feed cabin, which is also a bold breakthrough design.
The "pupil" position of most traditional radio telescopes is fixed or can only be fine-tuned.
The "China Sky Eye" is completely different. It uses a new light-weight cable-driven control system, which allows the "pupil" of the "China Sky Eye" to freely change the angle and position, and more effectively collect, track, and monitor more abundant cosmic electromagnetic waves.
In terms of size, the feed cabin of the world's largest radio telescope weighed more than 1,000 tons, and the feed cabin of the "China Sky Eye" weighed only about 30 tons.
Small size brings many advantages, such as effectively reducing light path occlusion and reducing interference signals, so that the beam is very clean, which is more conducive to astronomical observation.
The breakthrough and innovation of "China Sky Eye" in design has brought huge challenges to the manufacturing of "from drawings to reality".
The process of meeting the challenge is exactly the process of domestic precision manufacturing constantly creating miracles.
For example, to realize the world’s first design that the shape of the reflective surface (ie the cable net) can be changed, the steel cables constituting the cable net are required to have a certain degree of flexibility like a spring, and the fatigue strength is more than twice the existing standard, which is unprecedented in the world ; It is also required that the machining accuracy of each steel cable reaches 1 mm, which has raised the traditional standard by an order of magnitude.
In the past two years, scientists have continued to improve the cable body technology in all directions, and a steel cable has to undergo 2 million fatigue tests.
After nearly a hundred failures, this key problem was finally successfully solved, and three world pioneering achievements were realized: ultra-large span, ultra-high-precision, and actively shifted cable net structure.
After the completion of the construction, "China Sky Eye" entered the commissioning stage.
The debugging of giant telescopes involves many disciplines such as astronomy, measurement, control, electronics, mechanics, structure, etc. It is a highly interdisciplinary applied research. The debugging cycle of traditional large radio telescopes in the world is rarely less than 4 years.
"China Sky Eye" has created a new model, and its debugging work is also more challenging.
Up to now, tracking, drifting, motion scanning, weaving scanning, etc. have been implemented, and functional debugging has been completed in advance.
In terms of performance debugging, the "China Sky Eye" has a diameter of 500 meters, but it is quite difficult to achieve millimeter-level accuracy.
At present, the accuracy of the telescope measurement reference network has been improved to less than 1 millimeter. Among them, the sensitivity level is 2.5 times that of the world's second largest telescope. This is the first time that a telescope built in China has a commanding height in the sensitivity parameter.
In addition, the 19-beam has been installed, and its significance is also very significant: it can expand the telescope's field of view to 19 times the original, greatly improving the efficiency of the telescope's sky survey.
"China Sky Eye" patented technology is used in many fields, and continues to incubate new scientific achievements
The "China Sky Eye" team dares to think and do. It is difficult and challenging. The process of design and construction is not only a process of overcoming difficulties, but also a process of successively producing innovative results.
Many patented technologies with my country's independent intellectual property rights have been born and applied.
For example, ultra-high fatigue performance steel cable structures are used in large stadiums, and high-precision cable structure production systems are used in the construction of the Hong Kong-Zhuhai-Macao Bridge.
Many national and provincial construction methods have also been produced during the entire manufacturing and installation process.
For example, in the process of laying the "retina" for the "China Sky Eye", 4450 reflecting units, 6,670 steel cables, and tens of thousands of joint bearings were assembled by workers one by one at an altitude of tens of meters. When completed, the fault tolerance rate is zero.
These complex construction methods will help the precise construction of large and complex projects in the future.
It can be said that the "China Sky Eye" is a modern engineering miracle. It has condensed the hard work of more than 20 scientific research institutions and hundreds of scientific researchers, and has gathered the sweat of thousands of front-line workers.
The construction conditions are difficult, and many people will get red bumps after working on the site for a few days.
There is no air conditioning or heating in the damp, cold work shed, and everyone's quilt is so wet that water is about to be squeezed out.
It is often said that only China can make the "eyes of the sky". I think that to make the eyes of the sky depends on this kind of spirit of never giving up and forming a city.
In October 2017, the first batch of scientific achievements of "China Sky Eye" was made public.
Today, more than 70 high-level papers have been published based on the "China Sky Eye" data; the number of pulsars discovered has exceeded 300, which is three times the sum of all other telescopes found in the world during the same period.
Why is the discovery of pulsars important?
Pulsars are rapidly rotating neutron stars with extremely high density, weighing hundreds of millions of tons per cubic centimeter.
It scatters light like a lighthouse and scans the universe all the time; it rotates very fast and has a precise rotation period, making it the most accurate clock in the universe.
Therefore, grasping pulsars is conducive to the establishment of a "cosmic navigation system" and will help mankind realize the dream of interstellar travel in the future.
Next, "China Sky Eye" will further explore the frontiers of low-frequency gravitational wave detection, the origin of fast radio bursts, and interstellar molecules, strengthen openness and sharing at home and abroad, promote the output of major achievements, and climb the world's technological peak.
Our younger generation of scientists will also work hard to "use" the "eyes" that have condensed the efforts of the four generations of scientists in China, to produce more scientific research results, and to promote human exploration and cognition of the universe.
(The author is the chief engineer of FAST)
Recommended reading:
"Walking in the Starry Sky of China": by Qi Rui and Wan Haoyi; published by Science Popularization Publishing House.
"A New Introduction to Astronomy" (Fifth Edition): edited by Su Yi; published by Science Press.
"The Mystery of Chanjuan-The Origin and Evolution of the Moon": edited by Hu Zhongwei; published by Science Press.