Brushless DC gearmotor helps create simulated stars.

The Organisation for Applied Scientific Research (TNO) has created a projection method to be used on the Very Large Telescope (VLT). Complex optical tube assemblies form precise display devices that create mock stars. Highly dynamic brushless DC pancake motors fitted with reduction planetary gearboxes, linear drive mechanism and feedback sensors create a precise position system to control lasers.

Considered by many as the most effective astronomical observatory on the globe, the European Southern Observatory (ESO) has provided researchers with critical data and discoveries since 1962. At the forefront is the VLT in South America, a location that provides excellent environments for observing light spectrums. Four telescopes with 8.2 and 1.8 meter optical mirror diameters create the world’s most technically superior optical device. To assist with accurate focusing and to provide guidance points of light in the sky the Netherlands Organisation for Applied Scientific Research (TNO) created a guided laser system for the VLT. Optical tube assemblies (OTAs) are multifarious systems for the creation of simulated stars. Made up of four 20 W lasers fired 90 km into the sky, the device assists with correcting visual distortions that are created by air turbulence

Telescopes typically take light from space and focus it for instrumentation. In contrast, in the OTA equipment the optics are utilised to project lasers into the atmosphere creating light points. These light points stimulate sodium atoms causing them to radiate. This is obtained with a position accuracy of just 45mm as high as 90km. The illuminated points create mock stars used as a proximity guide or refer-ence points.

maxon brushless DC motors within.
Internally the OTA consists of a x20 times laser expander and an elastomeric mounted pan tilt mirror. This device is called the Field Selector Mechanism (FSM). A membrane spring and strut combination supports the 100mm mirror for tip and tilt motions. Brushless DC motors drive the mirror around the two axes that are at right angles to each other. The linear actuation components are self-locking and there sensors mounted directly to the mirror for positioning accuracy.

Brushless DC maxon motors are accountable for the correct movement of the mirror in the FSM and accordingly for the accurate position of the lasers location in the atmosphere. In a telescope, two mo-tors are used per FSM unit. The self-locking feature of the maxon linear actuators allowed TNO use standard maxon motor spindle drives that contain integrated planetary gearboxes.
The first implementation for the device on the TNO will be in 2015 and it is intended that the technology will also be used on the world’s largest telescope, the Extremely Large Telescope project.

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