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Metrology

Laser Tracker to be Used in 500-Meter Radio Telescope

World’s biggest telescope is accurately positioned using sensor and laser tracker

Published: Thursday, July 29, 2010 - 06:00

A dish-style radio telescope is being constructed in China that will allow astronomers to detect galaxies and pulsars at unprecedented distances. Not only will the Five-hundred-meter Aperture Spherical Telescope (FAST) be almost 200 meters larger than the current largest telescope in the world, it will be the only telescope of its kind with the ability to change shape and move the position of its focus. The dimension of the telescope, once completed, will be equal to 30 standard football fields, making FAST the biggest telescope in the world. The sensitivity will be 10 times better than the 100 m telescope in Bonn Germany, and the comprehensive performance will be 10 times better than Arecibo 300 in America.

As shown below, the Karst depression in the Guizhou province of China provides a unique topographical condition ideal for building the FAST.

Figure 1: Artist rendition of FAST installed in Karst depression. The feed cabin is the purple object in the middle.

One of the key components of the telescope is the feed cabin that hangs high above the basin. The feed cabin will be held over the dish by six cables (see figure 1). In order for the huge telescope to be precisely positioned to observe a celestial body, the feed cabin must remain steady and accurate. To compensate for the natural shaking of the feed cabin, Automated Precision Inc. (API) and the National Astronomical Observatories Chinese Academy Sciences (NAOC) have developed a flexible platform that will be controlled in real time using data provided from API’s Tracker3 laser tracker and its SmartTRACK Sensor.

Figure 2: A base platform equipped with sensor and laser tracker to measure movement of the feed cabin

API Tracker3 laser tracker and 6D SmartTRACK Sensor

The purple center of figure 1 contains several parts, which are shown in schematic form in figure 2. There is a large base platform, which is designed as part of the rigging. The base platform holds the 6D SmartTRACK Sensor so that the system will know if the center starts moving or swaying. Coming out of the base platform are six sliding legs, which are attached to the motion platform—these legs are the only thing holding the motion platform. The motion platform contains the feed cabin. When the whole structure starts to move, it is detected and recorded by the SmartTRACK Sensor and Tracker3, at which point the sliding legs move the motion platform (and therefore the feed cabin) to compensate for that movement. This system allows FAST to maintain the high-precision positioning of the feed cabin needed to use the telescope.

An API spokesperson says that the frequency response and range-of-motion for the system will not be known until the system is built and tested. API predicts that the system will be able to respond at typical Tracker3 and servo drive (sliding legs) speeds. The Tracker3, SmartTRACK sensor, and servo drive will all collect data and respond in real time.

In December 2009, the CEO of Automated Precision Inc., Kam Lau, and delegates visited the National Astronomical Observatories Chinese Academy Sciences (NAOC). The two organizations held in-depth discussions and concluded a cooperation agreement to achieve real-time dynamic measurement of FAST’s feed cabin.

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Dirk Dusharme @ Quality Digest’s picture

Dirk Dusharme @ Quality Digest

Dirk Dusharme is Quality Digest’s editor in chief.