The M2 secondary mirror of the Vera C. Rubin Observatory, scheduled to be commissioned on-sky in 2024, will be the first active secondary mirror of 3.5m diameter in operation. Its substantial dimensions and advanced functionalities place it in league with the secondary mirrors of the upcoming 30m class telescopes. Characterizing its performance serves as a critical step towards comprehending and controlling the optics of the next generation of Extremely Large Telescopes (ELTs). This study focuses on testing and validating the M2 cell in the Observatory’s integration hall and at the Telescope Mount Assembly (TMA). We also report on the integration steps of the M2 cell onto the TMA itself, including installing the light baffle. During the testing campaign, the M2 cell is equipped with an aluminum mirror surrogate for safety reasons regarding the glass mirror. To ensure integrity when the thin glass mirror (10cm) is installed onto the telescope, the M2 support system must be actively controlled during any M2 cell movement. This prompted the development of a dedicated control system to enable closed loop mode for transporting the M2 cell with the glass mirror from the integration hall to the telescope. The tests in the integration hall were conducted with the M2 cell mounted on a rotating cart, allowing different orientations with respect to gravity as it will experience on the telescope. Upon reaching the telescope, static and dynamic tests are conducted at progressively higher telescope performance, increasing slewing speed, acceleration, and jerk. A significant novelty introduced by Rubin to astronomical instrumentation is the Verification & Validation architecture as part of the model-based Systems Engineering approach where requirements, test procedures and executions are merged into an interlaced and dynamic flow. This report presents the experimental results from the distinct test campaigns covering a wide range of M2 cell functionalities. These include characterization of actuator behavior in terms of maximum stroke and force limits, evaluation of closed-loop (active) and open-loop (passive) support system operation for the M2, system settling time and Force Balance response to different slewing speeds of the telescope.
The Simonyi Survey Telescope (formerly known as the Large Synoptic Survey Telescope) of the Rubin Observatory is an 8.4m telescope now in construction on Cerro Pachón, in Chile. This telescope has been designed to conduct a 10 years’ survey of the sky in which it will map the entire night sky every three nights. The Mirror Cell Assembly system is a 9x9m steel structure that provides positioning, support, figure correction and temperature control to the primary and tertiary mirror. It is composed of two main systems, the Support System and the Thermal Control System. The Support System provides positioning, support and figure control of the mirror as well as dynamic forces compensation. The Thermal Control System will control the bulk temperature and temperature variations throughout the mirror. The temperature variations produce thermal distortions of the mirror which produce image degrading distortion of the optical surface. Variations between the bulk temperature and the ambient degrade local seeing and can produce condensation. The mirror cell assembly was designed and build in Tucson, Arizona by the LSST engineering team, and was tested, to confirm correct integration, at the Richard F Caris Mirror Lab to confirm the optical performance of the system using the real glass mirror. After successful testing, the mirror cell assembly was disassembled, packed and shipped to the Cerro Pachón summit in Chile where it was integrated with the surrogate mirror, and installed on the telescope mount assembly (TMA) for system performance test. Once system performance test concluded, the mirror cell was transported to the maintenance level to remove the metal surrogate mirror, install the glass and coat. After coating the mirror, the mirror cell assembly will be integrated with the telescope mount assembly to conduct final testing and verification.
The Vera C. Rubin Observatory is an astronomical survey facility nearing completion in Chile. Its mission is to accomplish the 10-year Legacy Survey of space and Time (LSST) survey - a 6-color optical imaging survey of the southern sky. The science mission for the LSST resulted in demanding requirements for optical performance and system dynamics. Producing a Telescope and an Observatory meeting these requirements resulted in multiple technical challenges which were encountered and resolved during the design and construction of the project. Resolving these challenges has impacted the assembly and integration of the overall system. Analyses were performed and solutions were developed. This paper provides a general overview of these challenges and highlights some specific examples where resolutions were found and implemented.
The Vera C. Rubin Observatory is currently under construction on Cerro Pachón, in Chile. It was designed to conduct a 10-year multi-band survey of the southern sky with frequent re-visits (with both an intra- and extra-night cadence) to identify transient and moving objects. The mirror cell assembly was designed in Tucson, Arizona by the Rubin Observatory engineering department, and was tested twice in Tucson. The first testing campaign was performed at CAID industries, where the mirror cell was fabricated, using a steel mirror surrogate that has the same geometry and mass of the glass mirror2,4. The glass mirror is a single monolith that contains both the primary and tertiary mirrors on a single substrate. The testing results confirmed that the mirror support system was performing within the design specifications, and that it was safe to install the glass mirror on the cell. The second test campaign was performed at the Richard F. Caris Mirror Lab of the University of Arizona using the actual glass mirror16. This test campaign was performed under the test tower, which contains a vibration insensitive interferometer to measure mirror figure. This confirmed the mirror support system could achieve proper optical surface figure control for both primary and tertiary mirrors. After successful test campaigns at CAID, and the mirror Lab, the mirror cell assembly was disassembled, packed and shipped to the Rubin Observatory site at the Cerro Pachón summit in Chile. Upon arrival, the mirror cell has been integrated with the mirror surrogate once again to perform the third test campaign that confirmed the system has arrived safe and operational to the summit. This integrated system will be tested on the telescope mount assembly to verify that it still meets it requirements under the effects of variations in gravitational orientation, and dynamic (slewing) loads.
The construction of the Vera C. Rubin Observatory is well underway, and when completed the telescope will carry out a precision photometric survey, scanning the entire sky visible from Chile every three days. The photometric performance of the survey is expected to be dominated by systematics; therefore, multiple calibration systems have been designed to measure, characterize and compensate for these effects, including a dedicated telescope and instrument to measure variations in the atmospheric transmission over the LSST bandpasses. Now undergoing commissioning, the Auxiliary Telescope system is serving as a pathfinder for the development of the Rubin Control systems. This paper presents the current commissioning status of the telescope and control software, and discusses the lessons learned which are applicable to other observatories.
The lowest spectroscopic band devised for the Atacama Large Millimeter Array (ALMA), the so-called Band 1,
covers the frequency range from 31 to 45 GHz. This band was not implemented during the rst construction
phase of the telescope, but will be included during a second ALMA development phase. During the past 4
years our group has been working on the development of technology to cover this band, complying with the
demanding ALMA specications. Among the most burdensome challenges are the stringent specications on
noise temperature, the large required bandwidth, and the limited space available for this receiver within the
ALMA cryostat. In this paper we present some of the technologies we have developed, including the design of
key components like horn, lens, ortho-mode transducer, and low noise ampliers. We also present an evaluation
of third-party components which can be used in the receiver. The work is used to present a preliminary layout
of the Band 1 receiver.
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