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News -> GBT Active Surface

[The GBT]

Contacts:

Charles E. Blue
Public Information Officer
National Radio Astronomy Observatory
Charlottesville, Virginia
(434) 296-0323 -- office
(434) 296-0278 -- fax
cblue@nrao.edu


Major Milestone for the GBT: Active Surface Sharpens View

The Robert C. Byrd Green Bank Telescope (GBT), the world's largest fully steerable radio telescope, has achieved a technology first by the successful deployment of the active surface of its dish.

"The active surface is a fundamental and critical feature of the GBT," said Phil Jewell, site director of the National Radio Astronomy Observatory (NRAO) in Green Bank, West Virginia. "This innovative element helps to keep the dish in sharp focus, the particularly at low and very high elevation angles where gravity would normally deform the shape of the dish."

The surface of the GBT's dish is made up of 2004 individually adjustable panels. These reflective panels are mounted at their corners on actuators (drive pistons), which can make tiny adjustments to the positions of the panels, keeping the telescope perfectly in focus.

On March 27, NRAO astronomers made the first observations with the GBT using its active surface. To do this, they used a computer model to predict how the structure and surface deform under gravity. This information was fed to the active surface control system, which then moved the 2004 panels to ensure that it maintained as nearly as possible a perfect parabolic shape during the observations.

The data received during these observations convincingly show a very impressive improvement in the efficiency of the telescope with the active surface on. "There will undoubtedly be a long campaign to refine the performance of the GBT and its active surface, but nonetheless, this is a major achievement," said Jewell.

Eventually, the active surface will be tied to another cutting-edge feature of the GBT, a novel laser-ranging system, which monitors the shape of the dish, and allows the actuators to correct its shape for the natural distortions caused by gravity and temperature fluctuations.

All of the observations during this run were made at 20 GHz, close to the highest frequency ever used on the GBT. The observations were of the radio source NGC 7027, which is a planetary nebula located about 3,000 light-years from Earth in the direction of the constellation Cygnus.

The GBT was commissioned in August of 2000. During its early science observations, the telescope also has undergone tests and outfitting of its sensitive electronics. Press releases on recent discoveries with the GBT can be found on:

-- Charles E. Blue National Radio Astronomy Observatory Charlottesville, Virginia (434) 296-0323 -- office (434) 296-0278 -- fax cblue@nrao.edu Modified on [an error occurred while processing this directive]