We summarize the operational realities of re-aluminizing 8.4-meter primary mirrors in-situ on the Large Binocular Telescope. We review the evaporative coating system design, and summarize its performance in the 16 coatings since 2005. A mostly manual system with long-handled mops and traditional chemicals is used to remove the old coating and to clean the glass surface. After cleaning, the telescope is moved to horizon-pointing orientation and the aluminizing belljar is mounted to the primary mirror cell using the overhead crane internal to the enclosure. We report on the multi-year struggle to understand variations in deposition rate among the 28 crucibles that evaporate the aluminum. We describe the challenges of making operational improvements to a system that must reliably coat one of the two primary mirrors every year, and we report on some lessons learned along the way.
Rubin Observatory’s Commissioning Camera (ComCam) is a 9 CCD direct imager providing a testbed for the final telescope system just prior to its integration with the 3.2-Gigapixel LSSTCam. ComCam shares many of the same subsystem components with LSSTCam in order to provide a smaller-scale, but high-fidelity demonstration of the full system operation. In addition, a pathfinder version of the LSSTCam refrigeration system is also incorporated into the design. Here we present an overview of the final as-built design, plus initial results from performance testing in the laboratory. We also provide an update to the planned activities in Chile both prior to and during the initial first-light observations.
The Large Synoptic Survey Telescope (LSST) Commissioning Camera (ComCam) is a smaller, simpler version of the full LSST camera (LSSTCam). It uses a single raft of 9 (instead of twenty-one rafts of 9) 4K x 4K LSST Science CCDs, has the same plate scale, and uses the same interfaces to the greatest extent possible. ComCam will be used during the Project’s 6-month Early Integration and Test period beginning in 2020. Its purpose is to facilitate testing and verification of system interfaces, initial on-sky testing of the telescope, and testing and validation of Data Management data transfer, infrastructure and algorithms prior to the delivery of the full science camera.
Facility Instruments at the Large Binocular Telescope (LBT) include the Large Binocular Camera (LBC), a pair of wide-field imagers at the prime focus, the LUCIFER (or LUCI) near-infrared imager and spectrograph pair, and the Multi-Object Double Spectrograph (MODS), a pair of long-slit spectrographs. The disciplines involved in instrument support are reviewed, as well as scheduling of support personnel. A computerized system for instrument maintenance scheduling and spare parts inventory is described. Instrument problems are tracked via an online reporting system, and statistics on types of instrument problems are discussed, as well as applicability of the system to troubleshooting.
After several years of operation the enclosure rotation system of the LBT is exhibiting wear and other performance
issues that may impact operations. This paper reviews the system design and assumptions used, describes the current
performance and observed symptoms, and discusses recent improvements made to improve performance and reliability.
The rotating enclosure of the LBT is a 2200 ton structure riding on four bogies with a total of 20 wheels. Identified
deficiencies include wheel bearing capacities, bogie misalignment, and rail loading. These are partially due to excess
enclosure weight, which was supposed to be 1600 tons, but also due to design errors.
The most serious problem was the failure of several wheel bearings. The bearings were not designed for field
serviceability, so a crash program began to determine how to replace them. This got us back on sky quickly, but a
review of the engineering calculations identified an error which led to the use of undersized bearings. A method of
installing a larger bearing was found, and these have been installed.
One set of bogie wheels are misaligned so severely the structure makes loud popping and banging noises when the
direction of building rotation changes. The bogie needs to be rotated about its vertical axis, but there was no provision in
the design for this.
The circular rail the bogies roll on is wearing faster than expected. The rails are extremely difficult to replace, so the
short term plan is to study the problem.
The Large Binocular Telescope's hydrostatic bearing system is operational, and tuning for optimal performance is
currently underway. This low friction system allows for the precise control of the 700 ton telescope at temperatures
ranging from -20°C to +25°C. It was a challenge to meet the performance requirements on such a massive telescope
with a wide range of operating temperatures. This required changes to the original design, including significantly
improving oil temperature control, and adding variable capillary resistors to allow for precise flow control to each pocket
on each bearing. We will present a system description and report on lessons learned.
The recently commissioned system for aluminizing the 8.408 meter diameter Large Binocular
Telescope mirrors has a variety of unusual features. Among them are aluminizing the mirror in the
telescope, the mirror is horizon pointing when aluminized, boron nitride crucibles are used for the
sources, only 28 sources are used, the sources are powered with 280 Volts at 20 kHz, high vacuum
is produced with a LN2 cooled charcoal cryo-panel, an inflatable edge seal is used to isolate the
rough vacuum behind the mirror from the high vacuum space, and a burst disk is mounted in the
center hole to protect the mirror from overpressure. We present a description of these features.
Results from aluminizing both primary mirrors are presented.
At the Navy Prototype Optical Interferometer (NPOI), during stellar fringe acquisition and tracking, optical stations along the NPOI vacuum line array remain in passive mode. Optical drift amplitude and rate must remain below certain limits lest stellar acquisition and fringe tracking become unachievable. Subsequent to each observation, relay mirrors are reconfigured within the long delay line stations to provide appropriate constant delays. The placement of these mirrors must be reliable and repeatable within certain tolerances. We describe the results of drift tests conducted on the current long delay line stations.
At the Navy Prototype Optical Interferometer (NPOI) we have developed a two-stage method for preparation and installation of the optical feed relay stations (elevators). This method reduces contamination, increases consistency, and allows greater management in testing and upgrades. In stage one, we prepare a pre-alignment facility in a laboratory. Using this facility we accurately position the feed stations, internal optics and detector optics relative to the NPOI array line-of-sight. The feed station is cleaned, assembled, internally aligned, tested and placed in its vacuum canister. It is stored under vacuum until transported to the array. In stage two, we align the station on the array by global five-axis adjustments of the vacuum canister. No further independent internal alignments are necessary. The canister is continuously under vacuum during global alignments. We describe the methodology and techniques for installing the optical feed stations.