Telescope Construction Progress
Following the final selection of the LMT site, Volcán Sierra Negra,
in 1997, work started on the access roads to the summit of the
mountain and the excavations for the concrete
foundation that required 37 piles to a depth of 20m. When completed
in 2000, the foundation consisted of a 40m diameter basic box
structure, 6m deep, that now provides a number of large rooms that
have been converted into laboratory space, living quarters and control
rooms. The foundation also provides the base for a central 15m high
concrete tower which supports, at the top, the azimuth pintle bearing
which holds the telescope under lateral loads.
The LMT is a single-dish millimeter-wavelength telescope with a
primary aperture of 50-m diameter, and a secondary mirror of 2.5m
diameter. The optical design
provides a field-of-view of up to 8 arcminutes (diameter) with minimal
aberration. The telescope alidade is supported by 16 wheels (housed
in 4 bogies) that provide azimuthal rotation on a steel track. The
alidade structure also contains the telescope control room and receiver
cabins, where individual instruments are served by a tertiary
mirror and additional warm coupling-optics.
The telescope reflector consists of 180 surface-segments, arranged in
5 concentric rings. A total of 720 actuators will provide an
open-loop active surface to maintain the required surface accuracy
under normal operating conditions.
The major structural components of the telescope (track, alidade,
wheels, ballast counterweights, primary reflector backstructure,
secondary mirror quadrapod, control-room and receiver-cabin) are close
to completion.
Progress of the on-site construction of the telescope, which began in
2001, is summarized in this
link.
Reflector surface
The primary reflector surface of the LMT is the last
major structural item that remains to be
completed before scientific commissioning of the telescope begins.
The design and production of the surface-pan
el segments
(with approximate dimensions of 3 x 5 meters) has already
started. A typical segment consists
of 8 smaller sub-panels, each formed from thin electro-formed
Nickel surface-skins bonded to an aluminum honeycomb (fabricated by
Media Lario in Italy). Similar panels have been
successfully tested on the European ALMA prototype telescope.
The active surface system consisting of 720 actuators and
an array of thermal sensors will compute and correct for
thermal and gravitational deformation of the reflector surface
elements using the finite element model. Simulations
indicate that the LMT should be able to maintain the required surface
accuracy of 70µm and pointing-accuracy during
night-time conditions in the presence of winds up to 10 m/s.
