We outline the scientific motivation for reducing the systematics in the image sensors used in the LSST. Some examples are described, leading to lab investigations. The CCD250 (Teledyne-e2v) and STA3900 Imaging Technology Laboratory (ITL) charge-coupled devices (CCDs) used in Rubin Observatory’s LSSTCam are tested under realistic LSST f/1.2 optical beam in a lab setup. In the past, this facility has been used to characterize these CCDs, exploring the systematic errors due to charge transport. Now, this facility is being used to optimize the clocking scheme and voltages. The effect of different clocking schemes on the on-chip systematics such as non-linear crosstalk, noise, persistence, and photon transfer is explored. The goal is to converge on an optimal configuration for the LSSTCam CCDs, which minimizes resulting dark energy science systematics.
The Vera C. Rubin Observatory is nearing completion, and we are embarking on a campaign to optimize the image quality during its upcoming 10-year optical survey. Here, we present the tools and methods we are implementing to disentangle and quantify the different sources of image degradation, as well as our plans to correct and mitigate as many of these different contributions to seeing as possible. The tools include an on-site Differential Image Motion Monitor (DIMM) for measuring atmospheric seeing, multiple 2D and 3D sonic anemometers for measuring in-dome wind speed and turbulence, and direct dome seeing monitors. We also implement a guider mode that allows data to be taken at 9Hz over small regions and a stuttered and streaked imaging mode that allows us to measure mount tracking and jitter and perform atmospheric tomography. Additionally, we use curvature wavefront sensing to estimate the residual wavefront error to support the telescope’s alignment and focus. This is the same algorithm that we will use for the Simonyi Survey Telescope. Many of these tools, as well as additional techniques to quantify the contribution of astigmatism to seeing, have been tested at the Auxiliary Telescope (AuxTel). This 1.2m telescope acts as a pathfinder for the Rubin Observatory. We present initial results and the creation of an image quality budget table for AuxTel to characterize and monitor significant sources of image quality degradation. We then discuss plans for implementing these techniques on the 8.4m Simonyi Survey Telescope.
The LSST Camera is a complex, highly integrated instrument for the Vera C. Rubin Observatory. Now that the assembly is complete, we present the highlights of the LSST Camera assembly: successful installation of all Raft Tower Modules (RTM) into the cryostat, integration of the world’s largest lens with the camera body, and successful integration and testing of the shutter and filter exchange systems. While the integration of the LSST Camera is a story of success, there were challenges faced along the way which we present: component failures, late design changes, and facility infrastructure issues.
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.
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 Integration and Verification Testing and characterization of the expected performance of the Large Synoptic Survey Telescope (LSST) Camera is described. The LSST Camera will be the largest astronomical camera ever constructed, featuring a 3.2 Gpixel focal plane mosaic of 189 CCDs. In this paper, we describe the verification testing program developed in parallel with the integration of the Camera, and the results from our performance characterization of the Camera. Our testing program includes electro-optical characterization and CCD height measurements of the focal plane, at several steps during integration, as well as a complete functional and characterization program for the finished focal plane. It also includes a suite of functional tests of the major Camera mechanisms: shutter, filter exchange system and thermal control. Finally, we expect to test the fully assembled Camera prior to its scheduled completion and delivery to the LSST observatory in early calendar 2021.
The Integration and Verification Testing of the Large Synoptic Survey Telescope (LSST) Camera is described. The LSST Camera will be the largest astronomical camera ever constructed, featuring a 3.2 giga-pixel focal plane mosaic of 189 CCDs with in-vacuum controllers and readout, dedicated guider and wavefront CCDs, a three element corrector with a 1.6-meter diameter initial optic, six optical filters covering wavelengths from 320 to 1000 nm with a novel filter exchange mechanism, and camera-control and data acquisition capable of digitizing each image in two seconds. In this paper, we describe the integration processes under way to assemble the Camera and the associated verification testing program. The Camera assembly proceeds along two parallel paths: one for the focal plane and cryostat and the other for the Camera structure itself. A range of verification tests will be performed interspersed with assembly to verify design requirements with a test-as-you-build methodology. Ultimately, the cryostat will be installed into the Camera structure as the two assembly paths merge, and a suite of final Camera system tests performed. The LSST Camera is scheduled for completion and delivery to the LSST observatory in 2020.
The LSST Camera focal plane comprises twenty-one raft tower modules (RTMs), each with nine CCD sensors and their associated electronics. RTMs are assembled at Brookhaven National Lab and shipped to SLAC National Lab, where they must be re-verified before being assembled into the full focal plane. The process for accepting an RTM at SLAC has been thoroughly documented, including unpacking a raft from its shipping container, verifying aliveness of the electrical connections, performing metrology and electro-optical testing in an environment similar to the full Camera, and finally storing the RTM until it can be installed into the LSST Camera
An electronic traveler system has been implemented for the LSST Camera. Its purpose is to guide execution of procedures on the hardware and associate any resulting test data, analysis results and configurations with the tested devices. The system is accessible from a web browser or via a REST API and uses a MySQL database to provide a history of the assembly hierarchy, hardware locations and test procedure instances, along with locations of the resulting test data. Components of the system are entirely experiment-independent with the exception of the Data Portal web application, which provides expert knowledge by querying the eTraveler database.
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