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China Hopes to Build World's Largest Radio Telescope
European CRAFT Secretary-General T. Spoelstra gives a speech at an international academic symposium sponsored by Beijing Observatory, according to Beijing Review.
China is planning to construct a 500-meter Aperture Spherical Telescope (FAST), which will be the largest in the world, in the unique karst area of its southwestern province of Guizhou. This news has quickly attracted wide public attention.
Telescopes are essential tools used by astronomers to probe the mysteries of the universe. Since Galileo invented the refracting telescope in 1609, various kinds of astronomical telescopes have emerged along with the progress of technology, and have helped in achieving great discoveries in the field of modern astronomy.
As everyone knows, a bigger aperture telescope provides a more distant view into space. Therefore, building larger telescopes has always been the goal of astronomers throughout the world. The 305-meter diameter Arecibo telescope run by the United States is the largest fixed radio telescope in the world's at present. Some 30 years ago, Germany built the world's largest fully steerable radio telescope with a 100-meter aperture.
¡°FAST is our dream and our goal,¡± said Dr. Peng Bo of China's National Astronomical Observatory. To act, in a sense, as the prototype for the proposed Square Kilometer Array (SKA), Peng noted, FAST will be a new generation radio telescope that will be over twice as large as Arecibo and will provide approximately a one order of magnitude increase in sensitivity over the existing fully steerable radio telescope.
A Huge International ProjectAccording to Peng, who is also a member of the International SKA Steering Committee (ISSC), FAST is one of the candidate options for the SKA concept ¡ªthe first such project in the field of radio astronomy that has been "born globally."
In 1993, at the 24th General Assembly of the International Union of Radio Science held in Kyoto, Japan, radio astronomers from 10 countries, including China, jointly proposed the construction of a new generation Large Telescope (LT) with a collection area of 1 square km. Estimated investment in the project, which is now known as SKA, will be about US$1 billion.
This research project has caused excitement in the international astronomical community because realization of the project could bring fundamental changes to radio astronomy. Upon completion, the SKA could detect hydrogen elements more than 10 billion light years away. This would enable astronomers to study the formation of the early universe, helping them to prove and improve their existing theories and establish new theories concerning the structure of the universe. It also would play a crucial role in the observation of catastrophes in near space, the study of deep space communication and the search for extraterrestrial intelligence.
Considered as Earth's "celestial eyes", the SKA will be an interferometric array of individual antenna stations. Its collection area would be distributed over 30 stations, each having a 200-meter diameter telescope, and the array will extend over an area of several hundred or even 1,000 km. But the main part of the array will be concentrated in a 50-km area.
To construct such a high-cost project that involves sophisticated technology is impossible without international collaboration. Therefore, the Kyoto conference established a Large Telescope Working Group, which sponsors international meetings twice a year to coordinate relevant international research and development efforts.
The SKA project can be accomplished through different technological designs. Returning from the Kyoto conference, scientists of various countries dedicated themselves to their respective designs, engineering pre-studies and site selection. Obviously, they all hope their solutions eventually can be accepted so that the project can be built in their own country.
To date, more than 10 countries have provided their designs, of which five have been chosen as candidate options. They respectively belong to Australia, Canada, China, the Netherlands and the United States.
Each design has its own features, Peng said. According to him, the American design comprises many small radio telescopes, which would have good directability but be complicated to coordinate. Canada proposed a large low-profile reflector of very long focal length lying on the ground, with the receiver supported by an aerostat at prime focus, thus creating a problem with the stability of the feed support system that remains to be solved. The Dutch design, a fixed planar array, puts high demands on technology and materials, with the price of key parts equal their weight in gold. If constructed, however, it would create very good industrial prospects. The Australian solution, an array of spherical Luneburg lenses, which was submitted just one year ago, still has many technological problems to tackle.
The Chinese Option¡ªFAST More than 70 Chinese scientists from 22 institutions of higher learning and scientific institutes have participated in the design of FAST. The LT Promoting Committee of China was established in 1995, accelerating the research process.
According to Dr. Peng, southern Guizhou Province, which encompasses hundreds of karst depressions, is an ideal region for a SKA concept. Astronomers have noted that radio telescopes are increasingly affected by man-made radio-frequency interference (RFI). Preliminary RFI monitoring in the region has shown encouraging results.
Besides the geographical advantage, Chinese scientists have made technological innovations in their design, Peng said. China's option, FAST, has an overall diameter of 500 meters, which is composed of about 2,000 panels, each one 15 meters square. Looking like a parabolic satellite antenna, it has an area as large as 25 football fields. The cost is estimated at 600 million yuan. It will provide an observation area four times wider than Arecibo with a 2.3-fold increase in sensitivity.
Currently, breakthroughs have been achieved in two key technologies¡ªthe actuated active main reflector and the feed support system.
The prototype of the actuated active main reflector was built recently. The proposed main spherical reflector is to be pieced together with 2,000 smaller elements, each having its own actuator, and can be dynamically shaped to form a parabolic. It can be adjusted continuously to fit a paraboloid of revolution in real time while tracking an object.
Designing and testing of the feed support system will soon be completed. Similar foreign feed systems are normally supported by fixed platforms. Such a huge, heavy platform would have a high cost. The Chinese scientists are creating a design that integrates optical, mechanical and electronic technologies, which will make the support platform several hundred times lighter than those manufactured by traditional techniques, and the cost will be much lower. In order to ensure completion of the work by March, researchers at Xidian and Tsinghua universities are working day and night in their labs.
Neither fully steerable nor fully fixed, FAST combines the advantages of the two types to a certain extent, Peng said. China's solution won high praise from Dr. Sebastian Von Hoerner, a world renowned German radio engineering expert, who is famed as the father of Germany's 100-meter aperture radio telescope. The 79-year-old German scientist visited China in 1998 and inspected the FAST design. He maintained that FAST is more feasible than the other proposals.
Of the 18 seats in the ISSC, China and India each hold one, Canada and Australia each occupy two, and the United States and Europe share the rest. Is such a situation disadvantageous to China during ISSC¡® s final selection?¡°Scientists are not businessmen nor politicians," Peng said. "Scientists make decisions mainly out of scientific requirements." It will be a good thing if China's option could be accepted by the ISSC, Peng said, for then the SKA possibly would be built in China. "However, we have been determined from the very beginning not to rely excessively on the international factor. We will build an independent, complete system in light of our national financial capability. Then, China would possess the world's largest radio telescope for at least 30 years in the foreseeable future." In addition, no matter where the SKA is built, China will undertake part of the work, Peng assured.
What Will FAST and SKA Bring? The influence of the new generation of radio telescopes on astronomy is obvious, Peng said. Radio astronomy was born in the 1930s. Different from optical telescopes, radio telescopes receive radio wave radiated by celestial objects. Since radio waves are able to penetrate cosmic dust that blocks light waves, radio telescopes can see through the dust into the more remote, unexplored reaches of the universe. Moreover, radio waves are free from the impact of sunshine and climate, so radio telescopes can operate in almost all weather without interruption. Given these advantages, the four greatest astronomical discoveries in the last century were achieved with the aid of radio telescopes. So far, five of the seven Nobel prizes awarded for work in astronomy were given to observational achievements related to radio astronomy. Therefore, radio astronomy has been regarded as the cradle of the Nobel Prize.
"I hope China will establish a niche in this area someday," said Peng. Participating in the SKA project will help China foster a considerable number of talented individuals in the field and improve the level of its astronomy as well as some other basic research.
When built, FAST would carry out remote monitoring and tracking of deep space flight vehicles. Besides its scientific value, the construction of FAST will motivate the development of relevant industries, especially those in Guizhou, a relatively underdeveloped western province. The province has placed great hope in the project. Provincial Party committee secretary Liu Fangren said the project will produce a great influence, not only on scientific and technological undertakings in Guizhou, but also on its social and economic development. The province will give full support to the project, he ensured.
Where Will the Money Come From?Apart from numerous technological difficulties, funding is a big problem nagging the Chinese scientists. According to Peng, researchers in the 22 institutions involved have acquired 150,000 yuan from the astronomical sector annually during the past years of pre-study, only about 2,000 yuan per person.
Gratifyingly, with the progress in FAST research, the project has attracted increasing attention and support from related State departments, Peng noted. Since 1999, the Ministry of Science and Technology and the Chinese Academy of Sciences have allocated several million yuan to the FAST project.
A stable financial source is key to the project when construction begins. Where will the money come from?
State support will play the key role. According to sources, the Ministry of Science and Technology has listed the FAST scheme as one of the candidates for major scientific projects to be included in the nation¡®s 10th Five-Year Plan (2001-05). If the project gets approval from the various State departments concerned, basic funding will be guaranteed. Optimistic estimates suggest that State investments may range from 400 to 500 million yuan.
However, it is impossible for the project to rely totally on State investment. It is reported that Paul Allen, one of the founders of Microsoft, has contributed US$12 million to support the Allen Telescope project, the United States' option for a SKA concept. Allen is not the only person to do so. The 10-meter aperture Keck Telescope, the largest optical telescope operating in the world, was built with the contribution of the American entrepreneur Keck. ¡°But we do not know how Chinese non-governmental organizations or business circles will respond to the FAST project,¡± Peng said. The LT Promotion Committee of China did have some discussions about such possibilities.¡°It perhaps will make a decision that those who contribute a certain amount of funds will be granted the right to name the telescope.¡±
International cooperation will be another approach. Officials from relevant departments of the Ministry of Science and Technology say that China welcomes international business participation in the construction of FAST.
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