The Vera Rubin Observatory hosts a large (8.4 meter) wide-field (3.5 degree) survey telescope4. The Secondary Mirror (M2) Assembly6 and Camera5 utilize large hexapods3 to facilitate optical positioning relative to the Primary/Tertiary Mirror. These hexapods were designed, fabricated, assembled, tested and met all their requirements1. Unfortunately, both hexapods were damaged prior to integration. The camera hexapod was damaged from overheating induced separation of the low temperature grease into constituents. The M2 hexapod was damaged from water intrusion during shipping. In both cases the critical linear encoders/tapes interior to the hexapod actuators were affected. These encoders are used by the control system to determine the length of the actuator during hexapod operations. If these encoders require servicing while deployed on the telescope, the hexapod needs to be unloaded by removing its optical payload (camera or M2), and the hexapod disassembled. The hexapod actuator then needs to be disassembled and repaired. This procedure produces an unacceptable risk to equipment, and an excessive disruption of observing. To rectify this, the actuators were redesigned to allow on-telescope servicing of these encoders. The encoder to tape orientation was inverted, and an access cover was added. This facilitates servicing the encoder/tape while on the telescope, reducing the servicing time from days to minutes. To improve reliability, alterations were also applied to the electrical system. The limit switch wiring was rearranged, and the cabling to the hexapod legs was upgraded. Also, multiple software upgrades were incorporated to improve function, performance, and compatibility with the other observatory systems.
KEYWORDS: Mirrors, Field programmable gate arrays, LabVIEW, Telescopes, Control systems, Observatories, Human-machine interfaces, Control systems design, Telecommunications, Actuators, Borosilicate glass
The Rubin Observatory’s Simonyi Survey Telescope M1M3 is a lightweight honeycomb 8.4 meter Ohara E- 6 borosilicate glass mirror, cast by the University of Arizona (UofA) Mirror Lab. It combines primary and tertiary mirror surfaces, hence its acronym. Its control software might be referenced as a 3rd generation UofA mirror active control system - after the Multiple Mirror Telescope’s (MMT) and the Large Binocular Telescope Observatory’s (LBTO). The control software uses a combination of LabVIEW Field Programmable Gate Array (FPGA),1 C++ (”back office”), and Python/Web (Graphical User Interface (GUI)/Engineering User Interface (EUI) to control the mirror. With the telescope’s first light expected soon, details of control software evolution, performed changes, as well as new development and status are described.
The Rubin Observatory Commissioning Camera (ComCam) is a scaled down (144 Megapixel) version of the 3.2 Gigapixel LSSTCam which will start the Legacy Survey of Space and Time (LSST), currently scheduled to start in 2024. The purpose of the ComCam is to verify the LSSTCam interfaces with the major subsystems of the observatory as well as evaluate the overall performance of the system prior to the start of the commissioning of the LSSTCam hardware on the telescope. With the delivery of all the telescope components to the summit site by 2020, the team has already started the high-level interface verification, exercising the system in a steady state model similar to that expected during the operations phase of the project. Notable activities include a simulated “slew and expose” sequence that includes moving the optical components, a settling time to account for the dynamical environment when on the telescope, and then taking an actual sequence of images with the ComCam. Another critical effort is to verify the performance of the camera refrigeration system, and testing the operational aspects of running such a system on a moving telescope in 2022. Here we present the status of the interface verification and the planned sequence of activities culminating with on-sky performance testing during the early-commissioning phase.
In the last couple of years, the Rubin telescope and site subsystem has made tremendous progress and overcome a few challenges. The insulated cladding on the dome is done and work is now focused on finishing the louvers, weatherproof cladding, interior work, light baffles, and the final fabrications. This has been done concurrently with the installation of the telescope mount, now mostly complete and approaching the beginning of functional testing in September-October, 2022. While work is being done on these two major subsystems, other major components and systems are being integrated and tested in a system spread configuration: M1M3 & M2 mirrors, the camera hexapod/rotator and the control software, including elements of the active optics control and the commissioning camera. Finally, the calibration system - an important contributor to achieving the exquisite photometry required by the Legacy Survey of Space and Time (LSST) - is being finalized.
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 Vera C. Rubin Observatory is now under construction on Cerro Pachon in Chile. This ground-based facility is designed to conduct the Legacy Survey of Space and Time (LSST), which is a decade-long time-domain optical survey of the night sky. The system aberrations introduced by temperature gradients, hysteresis and other non-predictable errors can prevent the telescope from delivering a consistently high-quality image over its 3.5 degrees field of view, necessary to the LSST scientific goals. Therefore, the active optics system (AOS) uses a combination of an open-loop and a closed-loop correction. The AOS open-loop is planned to correct for typical gravity variations while the AOS closed-loop will correct the real-time (within 30s) system aberrations. The components used for this task consist mainly of: two mirrors with active support systems (M1M3 and M2), two hexapods and curvature wavefront sensors integrated to the focal plane of the science detector. By the beginning of 2019, both M1 and M3 mirrors had been extensively tested using interferometry techniques, providing necessary measurements to refine our Finite Element models. This will help to achieve higher image quality when integrating all mirrors on the telescope. Progress has also been made on the active optics pipeline, which allows for conversion of the wavefront sensor images into corrective data for the mirrors and hexapods. In this paper, we will present the main results from the mirror testing as well as predicted performance of the AOS using these results. Finally, we will discuss the test plan for commissioning the AOS on the telescope.
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.
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