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Large Millimeter Telescope Description

The Large Millimeter Telescope will be a 50m-diameter millimeter-wave radio telescope. At this time, the telescope is complete with the inner 32m-diameter of its reflecting surface in place. This configuration allows the full system, including two scientific instruments, to be tested and debugged, and it offers the opportunity to pursue initial scientific programs with the telescope in 2011-2012. The LMT has now achieved first light at millimeter wavelengths and is currently undergoing its initial campaign of commissioning, testing and debugging.

Reflector surface

The full 50m-diameter reflector surface is comprised of 180 surface segments with dimension on the order of 5m. At this time, the inner 84 of these segments have been completed, installed, and aligned, and this set of panels is now being used to test the LMT as a functional telescope. The LMT segments are made of precision subpanels fabricated by Media Lario (the builder of panels for the European ALMA antennas). The subpanels are attached to a supporting structure and then to the antenna backstructure at four points which may be adjusted by a set of actuators that comprise the LMT's active surface.
LMT Refector Surface

The primary mirror is active, meaning that the positions of all reflector segments are adjusted to compensate for gravitational (and eventually thermal) deformations. The system of actuators required for the inner 32m-diameter has been installed and is in operation. Actuators were demonstrated in the laboratory with a positioning accuracy of 5 microns rms. For our initial astronomical tests, the reflector surface has been set to a single elevation using holographic measurements of geostationary satellites at 12GHz.

Telescope Optics

The LMT is a bent Cassegrain optical system with a 2.5m-diameter secondary mirror and a flat tertiary mirror located on the telescope's elevation axis. The secondary is a machined aluminum mirror with an rms of 30 microns. It is attached to the telescope with a positioning system which allows optimization of the focus, lateral offsets, and tilts. The tertiary mirror tracks the telescope elevation angle and delivers the beam to the receivers. LMT M2 LMT M3 and Positioning System

Telescope Drive System

The antenna drive system has been complete for some time. Through the use of an optical telescope mounted on the antenna, it has been possible to evaluate the pointing and tracking behavior of the telescope mount. These measurements having demonstrated tracking accuracies well below one arcsec, and absolute pointing observations that are consistent with errors of 3 arcsec RMS. The RMS for offset pointing from nearby sources, demonstrated with the optical camera, is considerably better and approaches the specification of 1 arcsec RMS.

Telescope Control System and Data Collection System

The LMT's Telescope Control System has been fully developed for some time and was put to use on the FCRAO 14m telescope during its final years of operation. This early testing has proved to be very useful as we have used LMT for the first time. The LMT's Data Collection System, which coordinates operation of the telescope and its instruments to produce scientific data, is a new software component that has been developed based on our experiences with the 14m telescope. This new system has been used successfully with our test instruments (Optical Camera and Holography System) and with our two initial scientific instruments (AzTEC and Redshift Search Receiver).

Site Infrastructure

The telescope has been built atop Sierra Negra, a 4600m peak in the state of Puebla, Mexico. This site, the 6th highest mountain in Mexico, was selected for its excellent observing characteristics which allow seasonal access to the 1mm and and submillimeter atmospheric windows and year round access to lower millimeter-wave frequencies in the 3mm atmospheric window. All site infrastructure is complete at this time, including road access, power, communications, and water. A new visitor's center is nearing completion at the summit. Facilities to support operation of the telescope are well advanced, with completion of the new LMT Base Camp in the nearby town, Ciudad Serdan, during the past year.
LMT Visitor Center. Orizaba in background LMT Base Camp View of Orizaba (left) and Sierre Negra (right) from Base Camp