NEWS Proposal to construct a five hundred meter aperture (active) spherical telescope (FAST)

RADIO astronomy aims at exploring the universe by means of radio technology. Since the first de- tection of galactic radio radiation in 1932, radio astronomy has witnessed rapid progress thanks to the modern technologies of electronic communication and computer science, and the pursuit of high sensitivity and high angular resolution has also brought about a revolution in electronics and related areas. Radio astronomy has been the birthplace of major astronomical discoveries, the cradle of Nobel Prize winners in astronomy, and it has shown great vitality and continues to have immense potential. At the 24th URSI Meeting in Kyoto in 1993, radio astronomers from Australia, Canada, China, France, Germany, India, the Netherlands, Russia, UK, and USA launched a proposal to construct a large radio telescope (LT) with a receiving area of 1 km2. Its sensitivity will be two orders of magnitude higher than that of the current largest telescope in the world. The As- tronomical Observatory of the Chinese Academy of Sciences set up a Chinese Committee to pro- mote the LT two years ago, and they put forward a proposal to build a spherical reflector array, composed of about 30 units of Arecibestyle antenna, the KARST (kilometer-square area radio synthesis telescope) Project in the karst depressions in Guizhou, China. Most

Chinese Science Bulletin Vol .43 No. 15 August 1998 NEWS radio astronomers believe that the project should proceed in two steps, and the first step is to build one unit according to individual plans. After comprehensive investigation and comparison, a suit- able concept for the LT can now be selected. The astronomers from Beijing Astronomical Observatory suggest that the fitstep be aimed at build- ing a single-dish spherical radio telescope. Its main properties (comprehensive proprties like receiving area and sky coverage) should be one (instead of two) order of magnitude better than those of the largest ex- isting fully steerable dotelescope. And it should be finished at the of the 21st century. It will certainly bring China to the leading position in world astronomy. - The spherical reflector, to be installed in a 500-m diameter karst depression, might be made up of small spherical units, with the position and orientation to be adjustable in real-time by a computer. This real-time adjustment for the source direction within the 300-m illuminated aper- ture will produce a proper paraboloid of revolution, which will overcome spherical aberration at the focus, and greatly simplify the feed system; therefore wide-band, polarization and multibeam (sky survey and multi-objective) observations can be carried out with the techniques of parabolic feed system illumination. The operating frequency will range (continuously) from 200-5 000 MHz. As the depression may be as large as 500 m, the area of sky coverage will be greatly en- hanced. FAST will have a larger area of sky coverage than the Arecibo antenna, and the mass of its feed and supporting systems will be lower by 1-2 orders of magnitude. The total cost will be far lower than that of the 100-m antenna, and its receiving area will be nearly one order of magnitude higher than that of the largest fully steerable single-antenna in the world. The advantageous to- pography of the Guizhou karst will enable us to fully realize the project. Once this system is successfully developed, it will have a working efficiency in centimeter bands one order of magnitude greater than what will be possible with any large telescope in the world in the foreseeable future. Its sensitivity will consequently be pushed to a greater depth (the number of sources discovered in radio astronomy is less than 10- that in optical astronomy, not to mention that many radio astronomical discoveries were made accidentally). Another possible use for FAST could be as a communication dish for deep space satellite missions. It would help fill a gap which exists in earth coverage at present. This FAST element can serve as a pioneer LT unit to encourage the international astronomi- cal community to locate LT in KARST concept in China. This proposal has been widely supported by experts in China. Profs. Chen Fangyun, , Wang Shouguan and Chen Jiansheng have recommended the proposal on pre-research made by Beijing Astronomical Observatory to the Ministry of Science and Technology of China and Chi- nese Academy of Sciences. It will surely attract international investment owing to its advanta- geous locality and prospects. The budget of the project is estimated at R. M. B. 200 M ( -US $25M). This project will not only promote theoretical research and deep-space communication in related areas but improve the development of related industries as well.

1320 Chinese Science Bulletin Vol .43 No. 15 August 1998