Blogs

January 28, 2019 - The LSST Primary/Tertiary Mirror (M1M3) is currently in the Richard F Caris Mirror Lab at the University of Arizona for optical testing. In January, the M1M3 on its support system was positioned at the bottom of the lab’s interferometry tower in anticipation of two test campaigns. The first, which has just concluded, took place from January 14-25. The second campaign is scheduled for February 11-22.

The tests use specialized optical equipment to evaluate the figures of the M1 and M3 mirror surfaces. Separate instruments, called interferometers, are used to perform measurements on each of the two mirrors that make up the monolith. The interferometer used to test M1 is at the very top of the tower, and the one used to test M3 is lower down, on a movable bridge. The mirror surfaces are tested separately, first M1, then M3, then M3 again, then M1. When M1 is being tested, the lower interferometer is moved out of the optical path.

During the test process, the interferometer in use emits two beams of light. One travels to the mirror and bounces back, and the other goes to a reference within the interferometer. The interaction between the two beams of light is recorded in an image called an interferogram (the black and white image in the photo to the left). The lines in the image are called interference fringes, and each one represents approximately 300 nanometers. A tight grouping of lines indicates a steep change in the height of the surface, much like tight lines on a topographic map indicate steep terrain. A “perfect” mirror interferogram would be a solid color, because its measurements would be recorded as a single fringe. But according to LSST Telescope and Site Mechanical Engineer Tucker Booth, achieving perfection on individual mirrors isn’t the goal. Instead, it’s the optimization of the entire M1M3 monolith that will ensure the best possible images during LSST Operations.

Allowing adequate time for optical testing, analysis, and optimization in Tucson reduces the work that will have to be done to prepare for operations once the telescope is assembled in Chile. Additionally, the unique testing environment available at the Richard F Caris Mirror Lab isn’t available in the summit facility building, so LSST is fortunate to have access to this world-class facility for the M1M3 optical test campaigns. M1M3 is currently scheduled to ship from the U.S. to Chile in May.
 

January 14, 2019 - The 233rd Meeting of the American Astronomical Society (AAS) wrapped up on January 10; this year’s winter meeting took place in Seattle, WA, with more than 3000 people registered. LSST staffed an exhibitor booth during the meeting within the National Science Foundation’s (NSF) Pavilion, giving project updates and answering questions from conference attendees. Numerous posters and talks were presented by LSST Project and Science Collaboration members.

November 12, 2018 - It looked a lot like a space ship before it was wrapped for shipping, but it’s actually a very earth-bound piece of cargo: the Coating Chamber for the mirrors of the Large Synoptic Survey Telescope (LSST). The Coating Chamber arrived on the summit of Cerro Pachón in Chile on November 11, 2018, and is now positioned on the service floor of the LSST summit facility building. The Coating Chamber and its associated equipment will share this level with the camera maintenance rooms, the vertical platform lift, and the shipping and receiving area. The Coating Chamber will be used to coat LSST’s mirrors when they arrive on Cerro Pachón, and to re-coat the mirrors periodically during Operations.

One of the activities included in Factory Acceptance Testing of the Telescope Mount Assembly (TMA) is installation and removal of the camera surrogate, a steel structure that approximates the mass of the LSST camera assembly, using the camera lifting fixture. The camera lifting fixture, like the TMA, was fabricated at the Asturfeito factory in Spain. Using a camera surrogate for these tests ensures that any issues arising during the installation or removal process can be addressed long before the real—and far more delicate—camera is integrated with the TMA in Chile. This video contains footage of the installation and removal of the surrogate camera using the camera lifting fixture.

October 30, 2018 - On the morning of October 25th, at the Richard F. Caris Mirror Lab on the University of Arizona campus, the LSST Primary/Tertiary Mirror (M1M3) was successfully lifted out of its transport container and onto the M1M3 Cell. The mirror lift was performed with a special lifting fixture, outfitted with 54 vacuum pads, that was designed specifically to safely lift and lower the 37,000 lb (16,780 kg) glass monolith. The M1M3 Mirror was lifted onto the Cell, interfacing successfully with the 355 static supports (wire rope isolators), that hold it above the upper surface of the mirror cell.

In order to minimize the risk of damage to the glass, the M1M3 Mirror will only be lifted in this manner this four times during the entirety of LSST construction and operations. This lift was the second; the first lift occurred in February of 2015, when the Mirror’s fabrication was complete and it was lifted into its protective transport container. The third lift will occur when it’s time to put the Mirror back into its protective box for transport to Chile, and the fourth will integrate M1M3 and the Cell for the last time in the LSST summit facility. Once M1M3 is integrated with the Cell at the observatory site, it will not be removed from the Cell again—not even for coating. The M1M3 Mirror can be coated while installed on the Cell, thanks to an internal cylindrical vacuum barrier. When rolled into place under the Coating Chamber lid using the transport cart, the Cell takes the place of the bottom half of the Coating Chamber, allowing a vacuum to be drawn and the M1M3 Mirror to be coated.

Over the next few weeks, work in the Mirror Lab will focus on the integration of the Mirror and Cell, which includes installing hardpoints, actuators, and electronics. These activities will be followed by functional testing of the assembled system. The Mirror is scheduled to move under the Mirror Lab’s interferometery tower for optical testing in January, 2019.

October 26, 2018 - A week after the Primary/Tertiary Mirror (M1M3) Cell was moved to the Richard F. Caris Mirror Lab on the University of Arizona campus, the M1M3 Mirror was also moved to the Mirror Lab from a hangar at Million Air, where it has been stored since its fabrication in 2015.

The Mirror left the hangar at Tucson International Airport on a specialized trailer from Precision Heavy Haul and arrived at the Mirror Lab at approximately 4:00 a.m. on October 18th. As with the M1M3 Cell move last week, the Mirror waited outside the Lab until the outside air temperature warmed to the accepted level, and then was moved inside the building. The designated LSST workspace inside the Mirror Lab now accommodates the Mirror, the Mirror Cell, and the Mirror lifting fixture, so some strategic rearranging was done to ensure the space was used as efficiently as possible.

Later the same day, the lid on the Mirror's protective shipping container was removed and the Mirror was revealed for the first time since being placed in storage. The next day, the Mirror's protective blue polymer coating, originally applied before it was stored, was refreshed with a new layer.

Now that both the Cell and the Mirror are in the Lab, the next step is the installation of the Mirror onto the M1M3 Cell using the vacuum lifter.
 

October 19, 2018 - This is a truck you definitely don't want to be stuck behind. Very early in the morning (3:10 a.m., to be exact) on Wednesday, October 10, the vehicle carrying the LSST Primary/Tertiary Mirror (M1M3) Cell departed CAID Industries in Tucson. The M1M3 Cell, which is the steel structure that will support LSST's 8.4-meter mirror, weighs approximately 55,000 lbs.

The Cell had been loaded and secured on the truck the day before the move by teams from Precision Heavy Haul (PHH) and CAID, with oversight from Tucker Booth, LSST Telescope and Site Mechanical Engineer. The move itself was scheduled for the quiet morning hours to minimize disruption of traffic, and to minimize stops for the truck, which required more than two lanes of clearance when loaded with the Cell. Accompanied by three pilot vehicles and two state troopers, the truck and its oversized cargo made its way to the Richard F. Caris Mirror Lab on the University of Arizona campus, arriving just before 4:00 a.m.

There was a pause in the action once the truck arrived, because the big, rolling door through which the Cell would enter the Mirror Lab couldn't be opened until the outside air temperature was within 10 degrees Fahrenheit of the Lab's inside temperature. This regulation exists to protect the mirrors currently being fabricated in the Lab from damage caused by abrupt temperature swings. While the group waited for the temperature to rise, the interior of the Mirror Lab was prepared for the acceptance of the Cell.

Teams from PHH and the Mirror Lab also used this time to move the truck into place and position the crane that would lift the Cell into the building. They also performed some test lifts of the Cell using the crane and nylon slings, to ensure the load was balanced correctly. At about 7:30 a.m., the door was cleared to open and the Cell was lifted off the truck and into the Mirror Lab.

"Everything went smoothly, thanks to the crews from CAID, PHH, and the Mirror Lab," said Booth. "Because they had things so well under control, my biggest challenge that morning was finding a 24-hour donut shop."

This week, a similar process will take place with the M1M3 Mirror itself, which will be moved from its airport storage facility to the Mirror Lab. Over the next few months, the Mirror and Cell will be integrated, and the fully assembled system will be tested thoroughly before being disassembled and shipped to Chile in 2019.

https://gallery.lsst.org/bp/#/folder/2689925/82785166