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6 August 2010The mechanical performances and the metrology system of the European ALMA antenna
The Atacama Large Millimeter Array (ALMA) consists of a large number of 12 m diameter antennas that will operate up
to 950GHz. The mechanical performances in terms of surface accuracy, pointing stability and residual delay are very
tight. The antennas must work at full performances in free air during night and day with also the request to observe the
sun. The mechanical performances are affected by all the not repeatable error sources and in particular by the
temperature variations and wind component blowing from different directions. The design of the antenna has been done
in order to have a very light and stiff structure, in particular all the elevation structure is in carbon fibre with also a very
low thermal expansion coefficient, but to achieve the ALMA specification, two different systems able to predict the
above error sources have been implemented in the control of the antenna.
The first system is composed by a determined number of thermal sensors distributed in the alidade of the antenna (is the
only part in steel ) and compensates the elevation axis deformation due to the temperature variation by means of a
The second system is based on two high accuracy inclinometers with a very short recovery time opportunely placed on
the antenna and correct the wind induced errors.
These innovative systems and instruments have been design and tested in the prototype antenna to the production phase.
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F. Rampini, G. Marchiori, R. Biasi, S. Stanghellini, L. Ghedin, "The mechanical performances and the metrology system of the European ALMA antenna," Proc. SPIE 7733, Ground-based and Airborne Telescopes III, 773314 (6 August 2010); https://doi.org/10.1117/12.859265