D. Plathner [1]
April 8, 1999
Keywords: 12m radiotelescope, submillimeter telescope, IRAM, carbon fibre back structure, aluminum panels
The present design of a 12m telescope is based on the IRAM report "The 15m (12.8m) Telescopes for the MMA/LSA Projects" which was recently published as MMA Memo 254. The earlier 15m telescope already met the requirements for millimeter and sub- millimeter work. The proposed 12m telescope features the same high quality standard and is modified only in areas where recent studies promise technical and scientific advantages. So the main reflector back structure and the tripod are still from carbon fibre reinforced plastic tubes to obtain thermal stability, and the panels and the subreflector from machined aluminum.
The optical layout is based on a pure Cassegrain arrangement with a fully symmetrical main reflector and a secondary. The elevation axis is displaced again; in this case by typically 2m from the optical axis and by 1m from the azimuth axis.
We have also kept the mechanically advantageous three-point connection between reflector assembly and the mount structure. The originally proposed linear elevation drive, however, has been replaced by a pinion/gear segment with backlash compensation by doubled gear trains as for the Plateau de Bure 15m antennas. This drive system is also applied for the rotation in azimuth and is combined with a single, big roller bearing.
These changes required a more compact design of the mount, which has now become a welded box structure instead of a truss configuration. The lower end of the mount is equipped with a ring flange, which can easily be bolted to counterparts on the foundation. The system permits one to align the telescope to a vertical position when it is still carried by the transporter. And it is in this position fixed to the ground which releases many constraints concerning the precision requirements for the foundations or actuated fixation systems.
Such an aligned telescope structure favours also the installation of a load-free substructure (similar to ideas of J. Lugten, NRAO) which is placed close to the ground fixation area, but above the azimuth bearing. This telescope-independent temperature stabilized structure is equipped at its upper end with displacement sensors to monitor non- repeatable motions of the elevation axis, and it is linked to the elevation encoder, which is directly fixed to the reflector backup structure.
[1] IRAM
View a PDF version of MMA Memo #259.
Download a 1.3MB gzipped postscript version of MMA Memo #259 from
Last modified: 09 December, 1999
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