The MMT Observatory, a joint venture of the Smithsonian Institution and the University of Arizona, operates the 6.5-m MMT telescope on the summit of Mount Hopkins approximately 45 miles south of Tucson, AZ. The upgraded telescope has been in routine operation for nearly fifteen years and, as such, is a very reliable and productive general purpose astronomical instrument. The telescope can be configured with one of three secondary mirrors that feed more than ten instruments at the Cassegrain focus. In this paper we provide an overview of the the telescope, its current capabilities, and its performance. We will review the existing suite of instruments and their different modes of operation. We will describe some of the general operations challenges and strategies for the Observatory. Finally, we will discuss plans for the near-term future including technical upgrades, new instrumentation and routine queue operation of MMIRS and Binospec.
As part of the effort to increase the reliability of the MMT Observatory (MMTO) 6.5m Primary Mirror Coating System, the specified filament has changed from a configuration in which the aluminum charge is hand wound around a tungsten filament to a configuration in which the aluminum is integrally wound with the tungsten at the time of filament manufacture. In the MMTO configuration, this filament consists of the three strands of tungsten wire and one strand of aluminum wire. In preparation of a full system test utilizing two hundred filaments fired simultaneously, an extensive testing program was undertaken to characterize these filaments using a four filament configuration in the MMTO small coating chamber (0.5m) and then a forty filament configuration in the University of Arizona Steward Observatory coating chamber (2m). The testing using the smaller coating chambers has shown these filaments provide very predicable coatings from test to test, and with the proper heating profile, these filaments greatly reduce the likelihood of aluminum drips. The initial filament design was modified during the course of testing by shortening the unwound filament length to closer match the aluminum load required in the MMTO coating chamber. This change increased the aluminum deposition rates without increasing the power delivered of the filament power supplies (commercial welders). Filament power levels measured at the vacuum chamber feed throughs, currents, and deposition rates from multiple coating tests, including a full system test, are presented.
Strategies for thermal control of the 6.5-meter diameter borosilicate honeycomb primary (M1) mirror at the MMT
Observatory have included: 1) direct control of ventilation system chiller setpoints by the telescope operator, 2) semiautomated
control of chiller setpoints, using a fixed offset from the ambient temperature, and 3) most recently, an
automated temperature controller for conditioned air. Details of this automated controller, including the integration of
multiple chillers, heat exchangers, and temperature/dew point sensors, are presented here. Constraints and sanity checks
for thermal control are also discussed, including: 1) mirror and hardware safety, 2) aluminum coating preservation, and
3) optimization of M1 thermal conditions for science acquisition by minimizing both air-to-glass temperature
differences, which cause mirror seeing, and internal glass temperature gradients, which cause wavefront errors.
Consideration is given to special operating conditions, such as high dew and frost points. Precise temperature control of
conditioned ventilation air as delivered to the M1 mirror cell is also discussed. The performance of the new automated
controller is assessed and compared to previous control strategies. Finally, suggestions are made for further refinement
of the M1 mirror thermal control system and related algorithms.
Originally commissioned in 1979, the Multiple Mirror Telescope was a highly innovative and successful facility that pioneered many of the technologies that are used in the new generation of 8 to 10 m class telescopes. After 19 years of operations the MMT was decommissioned in March of 1998: the enclosure was modified, the optics support structure was replaced, and a single 6.5-meter primary mirror was installed and aluminized in-situ. First light for the new MMT was celebrated on May 13, 2000. Operations began with an f/9 optical configuration compatible with existing instruments. Work has continued commissioning two new optical configurations that will serve a suite of new instruments: an f/15 deformable secondary mirror and adaptive optics facility that has obtained diffraction-limited images; and an f/5.4 secondary mirror and refractive corrector that provides a one-degree diameter field of view. The wide-field instrument suite includes two fiber-fed bench spectrographs, a robotic fiber positioner, and a wide-field imaging camera.