One of the more impressive engineering feats of the past 25 years is the FAST (Five-hundred-meter Aperature Spherical Telescope) in China. According to Wikipedia: “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.” According to Don McLeod, President and General Manager of Applied Motion Products in Watsonville, CA:
Initiated in 1994, the FAST telescope is a key national scientific and technological infrastructure project in China. Standing in a region of typical Karst (sinkhole) depressions in Guizhou province, the dish-like telescope will be as large as 30 football fields. The FAST’s main spherical reflector will be composed of thousands of panels, and its observation sensitivity will be 10 times more powerful than the 100-meter aperture steerable radio telescope in Germany. Its overall capacity will also be 10 times larger than what is now the world’s largest (300 m) Arecibo radio telescope developed by the United States (in Puerto Rico), according to Nan Rendong, the chief scientist of the project and an NAO researcher.
CONSTRUCTION OF FAST TELESCOPE
Construction began in 2011 and it achieved first light in September 2016. It is currently undergoing testing and commissioning. The FAST telescope is similar in performance to Arecibo, though with servo-adjustable positioning on each panel, the system might achieve results not available to the Arecibo dish. “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 , operated by AMP Servos, 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.” Some of the technical details and a comparison of the capabilities between the two dishes are available from a post on Wikipedia:
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, 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 limit 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 defense.
SERVO TECHNOLOGY BEHIND FAST TELESCOPE
Much of what makes the new FAST telescope possible are the servo-adjustable receiver electronics with servos provided by AMP and networked together to form one synchronous system. Applied Motion Products (AMP), today a fully owned subsidiary of Moons Industries of Shanghai, is one of the world’s larger manufacturers of stepper and servo motors and controls. Here is a great video on the construction of FAST and its usefulness.
Most recently, AMP announced the release of a new range of fully integrated StepServo motors, similar to the integrated stepper motors available for several years. StepServo motors combine the low cost of stepper motors with the high holding torque of a true servo motor:
StepSERVO is the Next Evolution in Step Motor Technology. Starting with a proven integrated motor design, we add a high-resolution incremental encoder and closed-loop servo firmware to create a motor that offers the best step motor performance available today. StepSERVO integrated motors offer the same high-torque-at-low-speed and excellent holding torque characteristics of open loop stepping motors, with the advantages of true closed-loop control. These advantages include the ability to create peak torques up to 50% higher than open loop motors, as well as cooler and quieter operation.
AMP continues to lead innovation among drive manufacturers with high value solutions that focus on flexibility. AMP supports most major industrial communications protocols on the market today including basic Step and Direction, RS232/422, EthernetIP, CanOpen, Sinet, Modbus RTU or TCP and soon EtherCat.