Five-hundred-meter Aperture Spherical Telescope
World's largest single-dish radio telescope, located in Guizhou, China.
The Five-hundred-meter Aperture Spherical Telescope (FAST), nicknamed Tianyan, is a radio telescope in a natural basin in Pingtang County, Guizhou, southwestern China. With a 500 m diameter dish, it is the world's largest single-dish telescope. Its novel design uses an active surface of metal panels and a movable feed cabin to observe at wavelengths from 10 cm to 4.3 m.
Quick Facts
- Location
- Dawodang depression, Pingtang County, Guizhou, China
- Diameter
- 500 m / 1,640 ft
- First light
- September 2016
- Fully operational
- 11 January 2020
- Construction start
- 2011
- Cost
- $180 million
Facts from the source article.
History
The telescope was first proposed in 1994, and the project was approved by the National Development and Reform Commission in July 2007. A 65-person village was relocated from the valley, and an additional 9,110 people living within a 5 km radius were relocated to create a radio-quiet area. The Chinese government spent poverty relief funds and bank loans for relocations, while construction cost $180 million. A foundation-laying ceremony was held on 26 December 2008, construction started in March 2011, and the last panel was installed on 3 July 2016. Significant difficulties included the remote site and poor road access, and the need to add shielding to suppress radio-frequency interference from the primary mirror actuators; the actuators were redesigned and installation completed in 2015, with no interference detected since. Testing and commissioning began with first light on 25 September 2016, and it took three years to calibrate instruments for full operation. Local government efforts to develop tourism around the telescope cause concern among astronomers about mobile telephones as RFI sources. The primary driving force was Nan Rendong, who died on 15 September 2017 in Boston due to lung cancer.
Overview
FAST has a reflecting surface 500 m in diameter located in a natural sinkhole in karst rock, focusing radio waves on a receiving antenna in a feed cabin suspended 140 m above. The reflector is made of perforated aluminium panels supported by a mesh of steel cables. The surface consists of 4,450 triangular panels, 11 m on a side, in a geodesic dome form. There are 2,225 winches underneath that deform the flexible steel cable support into a parabolic antenna aligned with the desired sky direction. Above the reflector, a lightweight feed cabin is moved by a cable robot using winch servomechanisms on six support towers, with receiving antennas mounted on a Stewart platform for fine position control, producing a planned pointing precision of 8 arcseconds. The maximum zenith angle is 40 degrees when the effective illuminated aperture is reduced to 200 m, and 26.4 degrees when the effective illuminated aperture is 300 m without loss. Only a circle of 300 m diameter is useful at any one time. Its working frequency ranges from 70 MHz to 3.0 GHz. Currently, only the FAST L-band Receiver-array of 19 beams (FLAN) is installed and operational between 1.05 GHz and 1.45 GHz. The Next Generation Archive System (NGAS) will store and maintain the data.
Science mission
Science objectives include large scale neutral hydrogen survey, pulsar observations, leading the international VLBI network, detection of interstellar molecules, detecting interstellar communication signals (SETI), and pulsar timing arrays. FAST joined the Breakthrough Listen SETI project in October 2016. In February 2020, scientists announced the first SETI observations with the telescope. It will be open to the global scientific community starting in April 2021, becoming effective in August 2021.
Comparison with Arecibo telescope
FAST's basic design is similar to the former Arecibo Telescope, both using reflectors in natural hollows in karst limestone with perforated aluminium panels and a movable receiver suspended above. However, Arecibo's dish was fixed in a spherical shape with manually operated supports, while FAST has an active surface. Arecibo's receiver platform was fixed, with static support cables and limited azimuth adjustment, viewing objects within 19.7° of the zenith; FAST can point to different sky positions by illuminating a 300 m section of the 500 m aperture. Arecibo could receive higher frequencies, down to 3 cm wavelength (10 GHz), while FAST is limited to 10 cm (3 GHz) due to the finite size of its triangular panels. The FAST dish is significantly deeper, contributing to a wider field of view; its radius of curvature is 300 m, forming a larger arc than Arecibo's.
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