Five-hundred-meter Aperture Spherical Telescope
Under construction in 2015. Final form is a metallic dish.
|Location(s)||Jinke Village, People's Republic of China|
|Wavelength||0.10 m (3.0 GHz)-4.3 m (70 MHz)|
|Built||2011 –3 July 2016|
|First light||3 July 2016|
|Telescope style||radio telescope|
|Diameter||600 m (1,968 ft 6 in)|
|Illuminated diameter||300 m (984 ft 3 in)|
|Collecting area||196,000 m2 (2,110,000 sq ft)|
|Illuminated area||70,690 m2 (760,900 sq ft)|
|Focal length||140 m (459 ft 4 in)|
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. "Eye of the Sky/Heaven") is a radio telescope located in the Dawodang depression (大窝凼洼地), a natural basin in Pingtang County, Guizhou, southwest China. It consists of a fixed 500 m (1,600 ft) diameter dish constructed in a natural depression in the landscape. It is the world's largest filled-aperture radio telescope, and the second-largest single-dish aperture after the sparsely-filled RATAN-600 in Russia.
It has a novel design, using an active surface made of metal panels that can be tilted by a computer to help change the focus to different areas of the sky. The cabin containing the feed antenna suspended on cables above the dish is also moved using a digitally-controlled winch by the computer control system to steer the instrument to receive from different directions.
Construction on the FAST project began in 2011 and it achieved first light in September 2016. It is currently undergoing testing and commissioning. It observes at wavelengths of 10 cm to 4.3 m.:11
The telescope made its first discovery of two new pulsars in August 2017. The new pulsars PSR J1859-01 and PSR J1931-02, which are also referred to as FAST pulsar #1 and #2 (FP1 and FP2), were detected on 22 and 25 August and are 16,000 and 4,100 light years away, respectively. They were independently confirmed by the Parkes Observatory in Australia on 10 September. The telescope had discovered 44 new pulsars by September 2018.
The telescope was first proposed in 1994. The project was approved by the National Development and Reform Commission (NDRC) in July 2007. A 65-person village was relocated from the valley to make room for the telescope and an additional 9,110 people living within a 5 km radius of the telescope were relocated to create a radio-quiet area. About 500 families tried to sue the local government. Villagers accused the government of forced demolitions, unlawful detentions and not giving compensation. The Chinese government spent around $269 million in poverty relief funds and bank loans for the relocation of the local residents, while the construction of the telescope itself cost US$180 million.
On 26 December 2008, a foundation laying ceremony was held on the construction site. Construction started in March 2011, and the last panel was installed on the morning of 3 July 2016.
Originally budgeted for CN¥700 million,:49 the final cost was CN¥1.2 billion (US$180 million). Significant difficulties encountered were the site's remote location and poor road access, and the need to add shielding to suppress radio-frequency interference (RFI) from the primary mirror actuators. There are still ongoing problems with the failure rate of the primary mirror actuators.
Testing and commissioning began with first light on 25 September 2016. 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. Subsequent early science will take place at lower frequencies while the active surface is brought to its design accuracy; 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.
Local government efforts to develop a tourist industry around the telescope are causing some concern among astronomers worried about nearby mobile telephones acting as sources of RFI. A projected 10 million tourists in 2017 will force officials to decide on the scientific mission versus the economic benefits of tourism.
FAST has a fixed primary reflector located in a natural sinkhole in the landscape (karst), focusing radio waves on a receiving antenna in a "feed cabin" suspended 140 m (460 ft) above it. The reflector is made of perforated aluminium panels supported by a mesh of steel cables hanging from the rim.
FAST's surface is made of 4450 triangular panels, 11 m (36 ft) on a side, in the form of a geodesic dome. 2225 winches located underneath make it an active surface, pulling on joints between panels, deforming the flexible steel cable support into a parabolic antenna aligned with the desired sky direction.
Above the reflector is a light-weight feed cabin moved by a cable robot using winch servomechanisms on six support towers.:13 The receiving antennas are mounted below this on a Stewart platform which provides fine position control and compensates for disturbances like wind motion.:13 This produces a planned pointing precision of 8 arcseconds.:24:179
Although the reflector diameter is 500 metres (1,600 ft), only a circle of 300 m diameter is used (held in the correct parabolic shape and "illuminated" by the receiver) at any one time.:13 Thus, the name is a misnomer: the aperture is not 500 m, nor is it spherical.
Its working frequency range of 70 MHz to 3.0 GHz, with the upper limit set by the precision with which the primary can approximate a parabola. It could be improved slightly, but the size of the triangular segments limits the shortest wavelength which can be received. This range is covered by nine receivers under the feed cabin,:30 with the 1.23–1.53 GHz band around the hydrogen line using a 19-beam receiver built by the CSIRO as part of the ACAMAR collaboration between the Australian Academy of Science and the Chinese Academy of Sciences.
The Next Generation Archive System (NGAS), developed by the International Center for Radio Astronomy (ICRAR) in Perth, Australia and the European Southern Observatory will store and maintain the large amount of data that it collects.
The FAST website lists the following science objectives of the radio telescope:
- Large scale neutral hydrogen survey
- Pulsar observations
- Leading the international very long baseline interferometry (VLBI) network
- Detection of interstellar molecules
- Detecting interstellar communication signals (Search for extraterrestrial intelligence)
- Pulsar timing arrays
The primary driving force behind the project was Nan Rendong, a researcher with the Chinese National Astronomical Observatory, part of the Chinese Academy of Sciences. He held the positions of chief scientist and chief engineer of the project. He died on 15 September 2017 in Boston due to lung cancer.
The Academy has been having difficulty finding staff for the telescope. Its size requires a large staff, but they are having difficulty attracting astronomers to its remote location, making it unlikely that the telescope will operate at full capacity for some time. As China has few radio astronomers, they are soliciting staff internationally, but the pay offered is low, and many are worried about heavy-handed management for this high-profile project.
The Academy has likewise been searching for a qualified director of scientific operations for FAST since May 2017, but has not been able to fill the position. Although an offer of US$1.2 million is widely quoted, this is primarily a one-time research grant, not salary or ongoing support.
Comparison with Arecibo Observatory
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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 aluminium panels with a movable receiver suspended above. And both have an effective aperture smaller than the physical size of the primary. There are, however, five significant differences in addition to the size.
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. It has a fixed spherical shape and two additional reflectors suspended above to correct for the resultant spherical aberration.
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.:3 The antennas are mounted on a rotating arm below the platform.:4 This smaller range of motion limits it to viewing objects within 19.7° of the zenith.
Third, Arecibo can receive higher frequencies. The finite size of the triangular panels making up FAST's primary reflector limits the accuracy with which it can approximate a parabola, and thus the shortest wavelength it can focus. Arecibo's more rigid design allows it to maintain sharp focus down to 3 cm wavelength (10 GHz); FAST is limited to 10 cm (3 GHz). Improvements in position control of the secondary might be able to push that to 6 cm (5 GHz), but then the primary reflector becomes a hard limit.
Fourth, 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),:3 barely larger than Arecibo's 270 m (870 ft), so it forms a 113° arc:4 (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).:4 (This is partially compensated for by Arecibo's 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.)
Fifth, Arecibo's larger secondary platform also houses several transmitters, making it one of only two instruments in the world capable of radar astronomy. 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. These powerful transmitters are too large and heavy for FAST's small receiver cabin, so it will not be able to participate in planetary defence.
- Chinese space program
- Square Kilometre Array – a proposed 1 km2 telescope array in Australia and South Africa
- KARST – a 1990s Chinese proposal to host the SKA
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The report said officials were moving 2,029 families, a total of 9,110 people, who live within about three miles of the telescope in the area of Pingtang and Luodian Counties in the southwestern province of Guizhou. Depopulating the area will create "a sound electromagnetic wave environment" for the telescope, Xinhua said.
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- Five-hundred-meter Aperture Spherical radio Telescope - website
- on YouTube
- on YouTube (25 September 2016)