About: Active surface

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An active surface is a surface of a radio telescope that is under active computer control of its shape. Large (more than 10 m in diameter or length) radio telescopes always bend during operation, due to their enormous weight and the fact that even the strongest materials are not perfectly stiff. This bending, in the range of a few millimetres, does not affect low frequency operation much, but dramatically reduces the efficiency of the telescope at higher frequencies where the wavelengths are comparable to the distortion. Typically, the efficiency of a telescope drops appreciably when the deviation from the desired shape is more than 1/10 of the considered wavelength. An active surface uses numerous small actuators to move the surface panels with respect to the underlying frame, and thus ma

Attributes	Values
rdf:type	yago:WikicatAstronomicalInstruments bone yago:Artifact100021939 yago:AstronomicalTelescope102751295 yago:Device103183080 yago:Instrument103574816 yago:Instrumentality103575240 yago:Magnifier103709206 yago:Object100002684 yago:PhysicalEntity100001930 yago:RadioTelescope104044716 yago:ScientificInstrument104147495 yago:Telescope104403638 yago:Whole100003553 yago:WikicatRadioTelescopes
rdfs:label	Active surface (en)
rdfs:comment	An active surface is a surface of a radio telescope that is under active computer control of its shape. Large (more than 10 m in diameter or length) radio telescopes always bend during operation, due to their enormous weight and the fact that even the strongest materials are not perfectly stiff. This bending, in the range of a few millimetres, does not affect low frequency operation much, but dramatically reduces the efficiency of the telescope at higher frequencies where the wavelengths are comparable to the distortion. Typically, the efficiency of a telescope drops appreciably when the deviation from the desired shape is more than 1/10 of the considered wavelength. An active surface uses numerous small actuators to move the surface panels with respect to the underlying frame, and thus ma (en)
dcterms:subject	Astronomical imaging Astronomical instruments Radio astronomy
Wikipage page ID	19918926 (xsd:integer)
Wikipage revision ID	1000149132 (xsd:integer)
Link from a Wikipage to another Wikipage	Noto Radio Observatory Radio telescope Large Millimeter Telescope Five hundred meter Aperture Spherical Telescope Astronomical imaging Astronomical instruments Radio astronomy Green Bank Telescope Sardinia Radio Telescope
Link from a Wikipage to an external page	http://www.sciencepubs.com/news/2016/09/world-s-largest-radio-telescope-will-search-dark-matter-listen-aliens http://www.ursi.org/Proceedings/ProcGA02/papers/p0639.pdf https://web.archive.org/web/20110522141417/http:/www.ursi.org/Proceedings/ProcGA02/papers/p0639.pdf
sameAs	Active surface Active surface Active surface Active surface
dbp:wikiPageUsesTemplate	dbt:Cite_conference dbt:Cite_journal dbt:Cite_news dbt:Convert
has abstract	An active surface is a surface of a radio telescope that is under active computer control of its shape. Large (more than 10 m in diameter or length) radio telescopes always bend during operation, due to their enormous weight and the fact that even the strongest materials are not perfectly stiff. This bending, in the range of a few millimetres, does not affect low frequency operation much, but dramatically reduces the efficiency of the telescope at higher frequencies where the wavelengths are comparable to the distortion. Typically, the efficiency of a telescope drops appreciably when the deviation from the desired shape is more than 1/10 of the considered wavelength. An active surface uses numerous small actuators to move the surface panels with respect to the underlying frame, and thus maintain the correct shape. An active surface can try to compensate for many different types of errors. The first is gravity—this is simplest since previous measurements, or even a mathematical model, can be used to predict (and correct) any bending. More difficult is correction for wind and thermal errors, since these require measuring and correcting in real time. Some examples of active surfaces are: * Green Bank Telescope * Large Millimeter Telescope * Sardinia Radio Telescope * Noto Radio Observatory The Chinese Five hundred meter Aperture Spherical Telescope uses a uniquely ambitious form of active surface, not only correcting errors, but applying deflections of up to 47 centimetres (19 in) in order to aim and focus the telescope. (en)
gold:hypernym	Surface
prov:wasDerivedFrom	wikipedia-en:Active_surface?oldid=1000149132&ns=0
page length (characters) of wiki page	3128 (xsd:nonNegativeInteger)
foaf:isPrimaryTopicOf	wikipedia-en:Active_surface
is Link from a Wikipage to another Wikipage of	Noto Radio Observatory Active optics Haystack Observatory Large Millimeter Telescope Green Bank Telescope Sardinia Radio Telescope Five-hundred-meter Aperture Spherical Telescope
is foaf:primaryTopic of	wikipedia-en:Active_surface

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