FAST

Reported+By+Leng+Linwei

When looking at the sky, people always think: who are we? Where are we from? Whether are we lonely... In the vast universe, if there are other civilized societies? The philosopher Bertrand Russell said: “there are only two answers for this question, no matter yes or no, both will make us feel surprised.”

Under the mysterious and deep sky, the world's largest telescope FAST (Five - hundred - meter Aperture Spherical radio Telescope) is standing proudly in the mountains. It is like an eye looking at the space, helping us to explore the mysteries of the universe. Because of it, “Knowledge is Power”journalists went to the FAST engineering office in the national astronomical observatory, Chinese academy of sciences for interview. In the concise and spacious conference room, the staff in FAST engineering office introduced the project construction and the role about FAST project.

When was China's FAST radio telescopes on the agenda? What advantages does it have compared with other radio telescopes in the world?

Office: since the 1960s, our country has built a batch of radio telescopes. In 1993, at the conference of the international union of radio science, astronomers from 10 countries including China put forward the suggestion of constructing a new generation of radio "telescope" .In the end of 1995, leading by the Beijing astronomical observatory from Chinese academy of sciences (now the national observatory), more than 20 domestic universities and research institutes set up the promoting committee of radio “telescope”, they raised the concept of building the “karst engineering” by using the karst depressions of Chinas Guizhou. In reference to the experience of building the radio telescope in foreign countries, Chinese astronomers put forward the concept of "karst engineering", advised to build the world's largest single caliber radio telescope - the spherical radio telescope with a aperture of 500 meters.

When was China's FAST radio telescopes on the agenda? What advantages does it have compared with other radio telescopes in the world?

Office: since the 1960s, our country has built a batch of radio telescopes. In 1993, at the conference of the international union of radio science, astronomers from 10 countries including China put forward the suggestion of constructing a new generation of radio "telescope" .In the end of 1995, leading by the Beijing astronomical observatory from Chinese academy of sciences (now the national observatory), more than 20 domestic universities and research institutes set up the promoting committee of radio “telescope”, they raised the concept of building the “karst engineering” by using the karst depressions of Chinas Guizhou. In reference to the experience of building the radio telescope in foreign countries, Chinese astronomers put forward the concept of "karst engineering", advised to build the world's largest single caliber radio telescope - the spherical radio telescope with a aperture of 500 meters.

Compared with the similar large diameter telescope, it has three "unmatched" independent innovation achievements:

1. Use the natural karst depression in Guizhou as sites, decrease the cost of telescope project greatly;

2. Put thousands of pieces to form the spherical cap active reflective surface of 500 meters in the depression, the spherical cap reflector forms the instantaneous paraboloid of 300 meters, which make the telescope receiver located at the focal point as the traditional parabolic antenna.

3. Use the light rope drag mechanism and parallel robot, realizing the high precision positioning of the telescope receiver.

Brand-new design concept, coupled with the advantage of unique sites, make the FAST break through the limit of 100 meters for the radio telescope, start the new model to build the giant radio telescope. It has a reception area as large as 30 football field, which will be the largest single diameter telescope in the world. Its sensitivity increases by 10 times compared with the so called “largest machine on the ground”——Bonn,the German telescope of 100 meters; One of the top ten big projects in the 20th century is the Arecibo radio telescope of America, which ranks in front of the Apollo moon landing, compared with the Arecibo radio telescope, the FASTs comprehensive performance increased about 10 times. As the worlds largest single diameter telescope, FAST will maintain the status of world-class equipment in the next 20 to 30 years.

Predictably, FAST with a diameter of 500 meters must be another observation tool for people to explore the universe. However, how does this big guy work?

Office: the radio astronomy uses radio telescopes to “see” objects in radio waves, the basic structure of a radio telescope has three main parts——reflecting surface, receiver, and pointing device. Traditional parabolic telescope converge the incident plane electromagnetic wave to the focal point, while the ball reflector are converged into a focal line, limiting the application of the wideband polarization receiver. To overcome this difficulty, the spherical cap reflecting surface of FAST forms aninstantaneous paraboloid at the radio source direction, which makes the receiver in the feed tank locating at the same focus as the traditional parabolic antenna.

FAST ball reflective surface will be divided into 4600 pieces of reflective surface unit, controlled by actuator, realized the active deformation of the reflection surface. As for the huge space between the receiver and the reflective surface, its difficult to establish a high precision rigid connection. FAST adopts the rope supporting light feed platform, and the secondary adjusting device inside the feed cabin, achieving the space positioning of the receiver. FAST adopts the measure and control technologies of big range, high precision and high sampling rate, realizing the active deformation of the reflection surface and the precise point to track.

The multi-beam receiver of international advanced quality is equipped in the feed tank, it collects the cosmic radio waves converged on the reflective surface, transfers the waves to the terminal equipment through broadband optical fiber, and analyzes the astrophysical information.

Compared with the American Arecibo telescope of 300 meters, FAST has increased 2.25 times in sensitivity. And the work limit for Arecibos zenith angle of 20°limits the observation area, especially limits the networking observation capability.

Guizhou is mountainous, so the path to FAST construction site is bumpy, we cant help asking why will FAST locate in Dawohan of Guizhou? What kind influence on the local environment for FAST construction?

Office: the reasons to choose such a natural giant col of “Dawohan” are to using the natural hallow pit in the construction of FAST, and the landscape develops only in karst area. Since 1994, the project team has begun the multidisciplinary evaluation work in the karst area of southern Guizhou. They made the preliminary assessment in the aspects of natural geography, landscape development controlling factors, morphological characteristics of the depression, hydrogeology, engineering geology, meteorology and wave environment. Many experts at home and abroad, including two former leaders of the Arecibo observatory, have been to FASTs primary zone for inspection. The experts of FAST team also visited the Arecibo in 1999, everyone agreed that the primary zone in Guizhou depression will be the unmatched address of large spherical radio telescope.

FAST is so large, how was it built? What problems did it encounter in the construction, and how to solve them?

Office: since FAST project was set up, it has experienced intense research and experiment process. Now the ring beam and part of the supporting tower have been installed, devices are placed by step, the next step is to install cable network and reflective surface. In addition, except for the concrete construction, the development of system is also on the way. In 2016, the telescope system alignment will be conducted. The entire project is expected to be completed in September 2016.

The FAST project is combining scientific research and engineering, there is no ready-made standard and mature technology, every step is a highly groundbreaking. It is needed to apply the scientific ideas and design to the practical engineering. In the actual construction, there were all kinds of problems, therefore constant design, updating, deepening and research are needed. In addition, each step of progress for the project is promoting the scientific development of our country. For example, the supporting tower should have good stability; the measuring and receiving system should have high precision. On the construction technology, new material and process have been studied. For example, for the requirement of fatigue, the special wire beyond the national standard is developed; the optical fiber is used to transfer the cosmic signal accepted from feed source to the terminal handling equipment, as the feed source keeps moving, the optical fiber is always in a state of bending down, therefore such new type of optical fiber is developed.