Motors Keep Telescope Operating in Record-Low Antarctic Temperatures
- Friday, 01 April 2011
At Concordia Station in Antarctica, there is a telescope mount that has been operating for a few years. Recently, there was a new record temperature at the Dome C site: -84.6 °C, or -199 °F. Not many things operate well in such conditions, but the telescope mount — which has to move continuously — used for scientific studies by the Laboratoire Universitaire d’Astrophysique de Nice (LUAN) is one of them.
Astro-Physics (Machesney Park, IL) designs and manufactures telescope mounts, and has proven that they work well in Antarctica through the installation of a number of their 900GTO and 1200GTO mounts that have been operating continuously at Dome C since the early 2000s. This is important because maintenance is so difficult. Low temperatures and dangerous wind conditions prevent technicians from working outdoors, and the mount must be reliable 24 hours a day for the entire polar night, lasting six months. Their latest mount installed at the site, the 3600GTO, is the largest mount used at Dome C to date.
One of the most important aspects of every telescope in the world is the gear reduction system used in the mounting apparatus. In order for a telescope to maintain a consistent bead on a particular star or system, it must move continuously. If a telescope is not driven, the image of a star, for example, would be out of view very quickly. The higher the telescope magnification, the faster that target will appear to move.
So, in order for a target to stay “fixed” in the viewing field of a telescope, the mount has to move continuously. Astro-Physics’ precision mounting systems are for use with telescopes ranging from 50 pounds to the one used in Antarctica that weighs a quarter-ton.
Motor Features Make the Grade
AstroPhysics uses maxon motors in each system they build. The grease used in the motor’s bearings is ideal for harsh/extreme temperatures, such as the severe conditions experienced at Dome C in Antarctica. Once in place, the motors do not need to be greased, which would never work in such severe conditions as those at Dome C. The motors also feature an ironless core designed with neodymium magnets, which provide the highest power available relative to motor volume. For mechanical commutation, the motors are provided with either graphite or precious metal brushes. And for the applications on mounts, the motors offer linear characteristics making them easy to implement.
There are two axes designed into each mount. One axis, the right ascension axis, is mounted parallel to the Earth’s axis and follows the Earth’s movement. Actually, the motor is driven in the opposite direction of the Earth’s rotation so that the target object looks as though it is fixed in the sky. The reduction drive is designed by Astro-Physics, which uses maxon’s motor and encoder.
The declination axis is mounted at a right angle from the ascension axis. With the two axes mounted at right angles from one another, the operator can aim the telescope anywhere they want. The encoder is used so that the motor can adjust and correct its position on an intermittent basis.
AstroPhysics uses A-max motors for smaller mounts and RE25 motors for mounts like the one at Dome C. The RE25 offers the highest torque per unit size in its class. The motors also have no cogging — or detent — which is the jerky motion most iron core motors exhibit while operating slowly. The motors use an ironless core design that eliminates cogging, even at slow speeds like those needed for telescope mounting systems.
This article was contributed by maxon precision motors, Fall River, MA. For more information, visit http://info.hotims.com/34453-322.