10-02-2016, 12:34 PM
The Five-hundred-meter Aperture Spherical radio Telescope (FAST; Chinese: 五百米口径球面射电望远镜), nicknamed Tianyan (天眼, lit. "Heavenly Eye" or "The Eye of Heaven"), is a radio telescope located in the Dawodang depression (大窝凼洼地), a natural basin in Pingtang County, Guizhou Province, south China.[4] It consists of a fixed 500 m (1,600 ft) dish constructed in a natural depression in the landscape. It is the world's largest filled-aperture radio telescope,[5] and the second-largest single-dish aperture after the sparsely-filled RATAN-600 in Russia.[2][6]
It has a novel design, using an active surface for pointing and focusing, rather than only correcting residual errors,[7] and suspending the receiver on a computer-controlled winch system without any rigid connection to the primary.
Construction on the FAST project began in 2011 and it achieved first light in September 2016. It is currently undergoing testing and commissioning.
The telescope was first proposed in 1994. The project was approved by the National Development and Reform Commission (NDRC) in July 2007.[8][7] A 65-person village was relocated from the valley to make room for the telescope[9] and an additional 9,110 people living within a 5 km radius of the telescope were relocated to create a radio-quiet area.[9][10]
On 26 December 2008, a foundation laying ceremony was held on the construction site.[11] Construction started in March 2011,[12][13] and the last panel was installed on the morning of 3 July 2016.[9][13][14][15]
Originally budgeted for CN¥700 million,[2]:49[12] the final cost was CN¥1.2 billion (US$180 million).[9] Significant difficulties encountered were the site's remote location and poor road access, and the need to add shielding to suppress radio-frequency interference from the primary mirror actuators.[7] There are still ongoing problems with the failure rate of the primary mirror actuators.[7]
Testing and commissioning began with first light on 25 September 2016.[16] The first observations are being done without the active primary reflector, configuring it in a fixed shape and using the Earth's rotation to scan the sky.[7] Subsequent early science will take place at lower frequencies[17] while the active surface is brought to its design accuracy;[18] longer wavelengths are less sensitive to errors in reflector shape. It will take three years to calibrate the various instruments so it can become fully operational.[16] Once it does, it will likely require hundreds of astronomers. However, due to the shortage of astronomers, the telescope will not operate at full capacity for a long time.[19][verification needed]
Local government efforts to develop a tourist industry around the telescope are causing some concern among astronomers worried about nearby mobile telephones.[20]
The primary driving force behind the project[7] is Nan Rendong (南仁东), a researcher with the Chinese National Astronomical Observatory, part of the Chinese Academy of Sciences. He holds the positions of chief scientist[15] and chief engineer[7] of the project.
The basic design of FAST is similar to the Arecibo Observatory radio telescope. Both are fixed primary reflectors installed in natural hollows, made of perforated aluminum panels with a movable receiver suspended above. There are, however, four significant differences in addition to the size.[22][26][27]
First, Arecibo's dish is fixed in a spherical shape. Although it is also suspended from steel cables with supports underneath for fine-tuning the shape, they are manually operated and adjusted only for maintenance.[22] It has a fixed spherical shape and two additional reflectors suspended above to correct for the resultant spherical aberration.[28]
Second, Arecibo's receiver platform is fixed in place. To support the greater weight of the additional reflectors, the primary support cables are static, with the only motorised portion being three hold-down winches which compensate for thermal expansion.[22]:3 The antennas are mounted on a rotating arm below the platform.[22]:4 This smaller range of motion limits it to viewing objects within 19.7° of the zenith.[29]
Third, the FAST dish is significantly deeper, contributing to a wider field of view. Although 64% larger in diameter, FAST's radius of curvature is 300 m (980 ft),[13]:3 barely larger than Arecibo's 270 m (870 ft),[29] so it forms a 113° arc[13]:4[dubious – discuss] (vs. 70° for Arecibo). Although Arecibo's full aperture of 305 m (1,000 ft) can be used when observing objects at the zenith, the effective aperture for more typical inclined observations is 221 m (725 ft).[22]:4
Fourth, Arecibo's larger secondary platform also houses several transmitters, making it one of only two instruments in the world capable of radar astronomy.[citation needed] The NASA-funded Planetary Radar System allows Arecibo to study solid objects from Mercury to Saturn, and to perform very accurate orbit determination on near-earth objects, particularly potentially hazardous objects. Arecibo also includes several NSF funded radars for ionospheric studies, the 430 MHz at 2.5 TW[citation needed], 47 MHz at 300 MW[citation needed], and 8 MHz at 6 MW. FAST's smaller receiver platform makes radar studies of the ionosphere impossible, so it will not be able to participate in planetary defense.[citation needed]
The Arecibo observatory has the advantage of location closer to the equator, so the Earth's rotation scans a larger fraction of the sky. Arecibo is located at 18.35° N latitude, while FAST is sited about 7.5° farther north, at about 25.80° N.[citation needed] FAST's wider field of view more than makes up for this.[citation needed]
https://en.wikipedia.org/wiki/Five_hundr..._Telescope
It has a novel design, using an active surface for pointing and focusing, rather than only correcting residual errors,[7] and suspending the receiver on a computer-controlled winch system without any rigid connection to the primary.
Construction on the FAST project began in 2011 and it achieved first light in September 2016. It is currently undergoing testing and commissioning.
The telescope was first proposed in 1994. The project was approved by the National Development and Reform Commission (NDRC) in July 2007.[8][7] A 65-person village was relocated from the valley to make room for the telescope[9] and an additional 9,110 people living within a 5 km radius of the telescope were relocated to create a radio-quiet area.[9][10]
On 26 December 2008, a foundation laying ceremony was held on the construction site.[11] Construction started in March 2011,[12][13] and the last panel was installed on the morning of 3 July 2016.[9][13][14][15]
Originally budgeted for CN¥700 million,[2]:49[12] the final cost was CN¥1.2 billion (US$180 million).[9] Significant difficulties encountered were the site's remote location and poor road access, and the need to add shielding to suppress radio-frequency interference from the primary mirror actuators.[7] There are still ongoing problems with the failure rate of the primary mirror actuators.[7]
Testing and commissioning began with first light on 25 September 2016.[16] The first observations are being done without the active primary reflector, configuring it in a fixed shape and using the Earth's rotation to scan the sky.[7] Subsequent early science will take place at lower frequencies[17] while the active surface is brought to its design accuracy;[18] longer wavelengths are less sensitive to errors in reflector shape. It will take three years to calibrate the various instruments so it can become fully operational.[16] Once it does, it will likely require hundreds of astronomers. However, due to the shortage of astronomers, the telescope will not operate at full capacity for a long time.[19][verification needed]
Local government efforts to develop a tourist industry around the telescope are causing some concern among astronomers worried about nearby mobile telephones.[20]
The primary driving force behind the project[7] is Nan Rendong (南仁东), a researcher with the Chinese National Astronomical Observatory, part of the Chinese Academy of Sciences. He holds the positions of chief scientist[15] and chief engineer[7] of the project.
The basic design of FAST is similar to the Arecibo Observatory radio telescope. Both are fixed primary reflectors installed in natural hollows, made of perforated aluminum panels with a movable receiver suspended above. There are, however, four significant differences in addition to the size.[22][26][27]
First, Arecibo's dish is fixed in a spherical shape. Although it is also suspended from steel cables with supports underneath for fine-tuning the shape, they are manually operated and adjusted only for maintenance.[22] It has a fixed spherical shape and two additional reflectors suspended above to correct for the resultant spherical aberration.[28]
Second, Arecibo's receiver platform is fixed in place. To support the greater weight of the additional reflectors, the primary support cables are static, with the only motorised portion being three hold-down winches which compensate for thermal expansion.[22]:3 The antennas are mounted on a rotating arm below the platform.[22]:4 This smaller range of motion limits it to viewing objects within 19.7° of the zenith.[29]
Third, the FAST dish is significantly deeper, contributing to a wider field of view. Although 64% larger in diameter, FAST's radius of curvature is 300 m (980 ft),[13]:3 barely larger than Arecibo's 270 m (870 ft),[29] so it forms a 113° arc[13]:4[dubious – discuss] (vs. 70° for Arecibo). Although Arecibo's full aperture of 305 m (1,000 ft) can be used when observing objects at the zenith, the effective aperture for more typical inclined observations is 221 m (725 ft).[22]:4
Fourth, Arecibo's larger secondary platform also houses several transmitters, making it one of only two instruments in the world capable of radar astronomy.[citation needed] The NASA-funded Planetary Radar System allows Arecibo to study solid objects from Mercury to Saturn, and to perform very accurate orbit determination on near-earth objects, particularly potentially hazardous objects. Arecibo also includes several NSF funded radars for ionospheric studies, the 430 MHz at 2.5 TW[citation needed], 47 MHz at 300 MW[citation needed], and 8 MHz at 6 MW. FAST's smaller receiver platform makes radar studies of the ionosphere impossible, so it will not be able to participate in planetary defense.[citation needed]
The Arecibo observatory has the advantage of location closer to the equator, so the Earth's rotation scans a larger fraction of the sky. Arecibo is located at 18.35° N latitude, while FAST is sited about 7.5° farther north, at about 25.80° N.[citation needed] FAST's wider field of view more than makes up for this.[citation needed]
https://en.wikipedia.org/wiki/Five_hundr..._Telescope
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