Wavelength 10 cm to 4.3 m First light 25 September 2016 | Built 2011–2016 | |
Location(s) Pingtang County, Guizhou Province, China Telescope style Deformable fixed primary, spherical reflector Diameter 500 m (1,600 ft)(physical)
300 m (980 ft) (effective) | ||
The Five-hundred-meter Aperture Spherical radio Telescope (FAST) (Chinese: 五百米口径球面射电望远镜), nickname Tianyan (天眼, literally "The Eye of Heaven"), is a radio telescope located in a natural basin of the Dawodang depression (大窝凼洼地), in Pingtang County, Guizhou Province, southwest China. It consists of a fixed 500 m (1,600 ft) diameter spherical dish constructed in a natural depression sinkhole caused by karst processes in the region. 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.
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Rather than suspending the receiver on a computer-controlled winch system to correct residual errors without any rigid connection to the primary, an active surface is used to attain higher accuracy for pointing and focusing.
FAST project began constructing in 2011 and achieved its first light in September 2016. It is currently undergoing testing and commissioning.
History
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.Around 8,000 people had to be relocated.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 $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, 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 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. 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.
Local government efforts to develop a tourist industry around the telescope are causing some concern among astronomers worried about nearby mobile telephones.
The primary driving force behind the project 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 and chief engineer of the project.
Overview
FAST has a fixed primary reflector located in a natural hollow in the landscape (karst), focusing radio waves on a receiver 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. The receiving antennas are mounted below this on a Stewart platform which provides fine position control and compensates for disturbances like wind motion. This produces a planned pointing precision of 8 arcseconds.
FAST is capable of pointing anywhere within ±40° from the zenith. The effective aperture is reduced by vignetting at angles above ±30°.
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. 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 9 receivers on the feed cabin, 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.
Science mission
FAST website lists 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
- Pulsar timing arrary
Comparison with Arecibo Observatory
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.
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. The antennas are mounted on a rotating arm below the platform. This smaller range of motion limits it to viewing objects within 19.7° of the zenith.
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), barely larger than Arecibo's 270 m (870 ft), so it forms a 113° arc‹See TfD› (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).
Fourth, 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 defense.
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..