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.
The Vera C. Rubin Observatory is the result of a public-private partnership between the USA National Science Foundation (NSF), the lead Federal Agency of the project, the Department of Energy and the Association Of Universities For Research In Astronomy (AURA), and the LSST Corporation. EIE GROUP has developed the Detail Design, the Manufacturing, and the Erection on Site of the giant Rotating Building. In this regard, 2021 was a year full of successes for the development of the project.
The Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST) will perform precision photometry of resolved and unresolved objects over the visible sky at a 3-day cadence using an 8.4-meter diameter telescope that forms an image of the sky on a 3.2 Gigapixel focal plane array. Meeting and exceeding the photometric precision requirements is a significant challenge and necessitates the calibration and correction of multiple forms of systematic error. This paper describes multiple novel hardware systems that Rubin is developing to measure and compensate for numerous sources of systematic errors, particularly errors impacting photometry measurements.
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.
The Vera C. Rubin Observatory (Rubin Obs) (formerly Large Synoptic Survey Telescope - LSST) is an 8.4-m telescope, now under construction in Chile. In the last couple of years, the telescope has achieved tremendous progress, though like many other projects, progress has been curtailed for over six months due to the worldwide pandemic. This paper provides the high-level status of each of the telescope's subsystem. The summit facility (Cerro Pachon) and base facility (La Serena) have been substantially completed. The dome is expected to be finished by October of 2021, which will also allow the completion of integration and testing of the Telescope Mount Assembly (TMA). The integration and verification of the TMA is planned to be completed by the end of 2021. The two mirror systems, M1M3 and M2, have been fully tested under interferometers, showing they both satisfy their performance requirement, and both have been received at the summit facility. The M2 mirror has been successfully coated with protected aluminum, which is the first scientific coating produced by the new Rubin coating plant. The M1M3 mirror is planned to be coated with the same plant at the beginning of 2022. The auxiliary telescope and its principal spectrograph instrument, which will allow for real-time atmospheric characterization, has been commissioned. The Rubin environment awareness system (EAS), which includes the DIMM, weather station, all-sky camera, and facility environmental control, is operational. Significant progress has been made on the software for all of the above-mentioned subsystems, as well as the comprehensive telescope control system and the telescope operator interfaces.
The Vera C. Rubin Observatory is a joint NSF and DOE construction project with facilities distributed across multiple sites. These sites include the Summit Facility on Cerro Pachón, Chile; the Base Facility in La Serena, Chile; the Project and Operations Center in Tucson, AZ; the Camera integration and testing laboratories at SLAC National Accelerator Laboratory in Menlo Park, CA; and the data support center based at the National Center for SuperComputing Applications at Urbana-Champaign, IL. The Rubin Observatory construction Project has entered its system integration and testing phase where major subsystem components are coming together and being tested and verified at a system level for the first time. The system integration phase of the Project requires a closely coordinated and organized plan to merge, manage, and be able to adapt the complex set of subsystems and activities across the entire observatory as real effects are discovered. In this paper we present our strategy to successfully complete integration, test and commissioning of the systems making up the Rubin Observatory. We include discussion on (i) our strategy for integration activities and the verification of requirements (ii) a brief summary of construction status at the time of this paper, (iii) early integration activities that are used to mitigate risks including the use of the Rubin Observatory's commissioning camera (ComCam), planning for the integration, testing and verification of the primary science instrument - LSSTCam, and lastly, (v) Science Verification through short concentrated survey-like campaigns. Throughout this paper we identify where key performance metrics are addressed that directly impact the Rubin Observatory's 10{year Legacy Survey of Space and Time (LSST) science capabilities - e.g. image quality, telescope dynamics, alert latency, etc...
A measurement platform including a Shack-Hartmann Wavefront Sensor (SHWFS) has been designed, integrated and tested at Imagine Optic, Orsay France and delivered to the Rubin Observatory (previously known as the LSST). This instrument will be used for the initial on-axis optical alignment and testing of the LSST telescope. The optical configuration of the Rubin Telescope without the presence of the main LSST camera requires advanced capabilities in term of quantities of aberrations to measure, linearity, accuracy and sensitivity for usage on a natural star. The HASO 128 GE 2, available from Imagine Optic, was identified as the most relevant WFS to meet all those requirements. In that paper, we provide details about the simulations that led to the choice of the HASO 128 GE 2. We also provide the specifics regarding the opto-mechanical design allowing the relay imaging of the pupil compatible with the fast aperture of the telescope, a reference source for the on-site calibration of the system and the optical output made available for a viewer camera.
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 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 optical axis of a Nasmyth telescope should be perpendicular to the Elevation axis and pass through the rotational center of the Tertiary mirror turret rotator. Realized by aligning a laser beam to the rotational center of the two field derotators. A high precision Pentaprism mounted on the Tertiary mirror rotator deviates the laser beam by 90° defining the optical axis onto which the Primary and Secondary mirrors are mounted and aligned. We present method, procedure, tools and results for two examples of Nasmyth Telescopes; the 4.1m SOAR and the LSST's 1.2m Auxiliary Telescope.
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.
KEYWORDS: Systems modeling, Large Synoptic Survey Telescope, Data modeling, Systems engineering, Integrated modeling, Model-based design, Safety, Telescopes
This paper describes the evolution of the processes, methodologies and tools developed and utilized on the Large Synoptic Survey Telescope (LSST) project that provide a complete end-to-end environment for verification planning, execution, and reporting. LSST utilizes No Magic’s MagicDraw Cameo Systems Modeler tool as the core tool for systems modeling, a Jira-based test case/test procedure/test plan tool called Test Management for Jira for verification execution, and Intercax’s Syndeia tool for bi-directional synchronization of data between Cameo Systems Modeler and Jira. Several additional supporting tools and services are also described to round out a complete solution. The paper describes the project’s needs, overall software platform architecture, and customizations developed to provide the end to- end solution.
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.
The Large Synoptic Survey Telescope (LSST) Project1 received its construction authorization from the National Science Foundation in August 2014. The LSST Telescope and Site (T and S) group has achieved significant progress in the development and delivery of an integrated telescope system solution to meet the LSST science mission requirements. The summit facility construction has been completed on Cerro Pachón in Chile, construction of the base facility and data center continues in La Serena, and many major vendor subsystem integration and verification efforts are currently in progress. This paper summarizes the status of the T and S group, which is responsible to provide the summit and base facilities and infrastructure necessary to support the wide, fast, deep LSST survey mission. The major elements of the telescope system are well into factory assembly and testing, in anticipation of shipping, integration and final acceptance testing and verification on the summit. Progress continues on the dome system assembly atop the lower enclosure of the summit facility. The M1M3 primary/tertiary and M2 secondary mirror assembly systems are undergoing integrated system testing prior to shipment to Chile. Factory testing has been achieved on the telescope mount assembly, hexapod and rotator systems, coating plant, and the auxiliary calibration telescope. Other in-house efforts including software for observatory supervisory functions, scheduling of the survey, and active optics control has also advanced. The summary status of these subsystems and future integration and verification plans are presented.
The LSST Coating Plant consists of a Coating Chamber for high reflective optical coatings deposition and a Cleaning and Stripping Station for the M1M3 and M2 mirrors. The Coating Chamber sputtering process will be capable of depositing bare and protected Silver/Aluminum coating recipes. The Cleaning and Stripping Station consists of a rotating washing/drying boom, perimeter platforms, and an effluent handling system within the M1/M3 mirror cell. This paper describes the status of the Coating Plant construction effort at the Von Ardenne and MAN facilities. Progress on factory testing, review of the design features and reflective/coating requirements, and results are presented.
KEYWORDS: Telescopes, Finite element methods, Systems modeling, Solid modeling, Mirrors, Actuators, 3D modeling, Large Synoptic Survey Telescope, Computer aided design, Large Synoptic Survey Telescope, Space telescopes
During this early stage of construction of the Large Synoptic Survey Telescope (LSST), modeling has become a crucial system engineering process to ensure that the final detailed design of all the sub-systems that compose the telescope meet requirements and interfaces. Modeling includes multiple tools and types of analyses that are performed to address specific technical issues. Three-dimensional (3D) Computeraided Design (CAD) modeling has become central for controlling interfaces between subsystems and identifying potential interferences. The LSST Telescope dynamic requirements are challenging because of the nature of the LSST survey which requires a high cadence of rapid slews and short settling times. The combination of finite element methods (FEM), coupled with control system dynamic analysis, provides a method to validate these specifications. An overview of these modeling activities is reported in this paper including specific cases that illustrate its impact.
This paper describes the status and details of the large synoptic survey telescope1,2,3 mount assembly (TMA). On June 9th, 2014 the contract for the design and build of the large synoptic survey telescope mount assembly (TMA) was awarded to GHESA Ingeniería y Tecnología, S.A. and Asturfeito, S.A. The design successfully passed the preliminary design review on October 2, 2015 and the final design review January 29, 2016. This paper describes the detailed design by subsystem, analytical model results, preparations being taken to complete the fabrication, and the transportation and installation plans to install the mount on Cerro Pachón in Chile. This large project is the culmination of work by many people and the authors would like to thank everyone that has contributed to the success of this project.
All of the components of the LSST subsystems (Telescope and Site, Camera, and Data Management) are in production. The major systems engineering challenges in this early construction phase are establishing the final technical details of the observatory, and properly evaluating potential deviations from requirements due to financial or technical constraints emerging from the detailed design and manufacturing process. To meet these challenges, the LSST Project Systems Engineering team established an Integrated Modeling (IM) framework including (i) a high fidelity optical model of the observatory, (ii) an atmospheric aberration model, and (ii) perturbation interfaces capable of accounting for quasi static and dynamic variations of the optical train. The model supports the evaluation of three key LSST Measures of Performance: image quality, ellipticity, and their impact on image depth. The various feedback loops improving image quality are also included. The paper shows application examples, as an update to the estimated performance of the Active Optics System, the determination of deployment parameters for the wavefront sensors, the optical evaluation of the final M1M3 surface quality, and the feasibility of satisfying the settling time requirement for the telescope structure.
Construction of the Large Synoptic Survey Telescope system involves several different organizations, a situation that poses many challenges at the time of the software integration of the components. To ensure commonality for the purposes of usability, maintainability, and robustness, the LSST software teams have agreed to the following for system software components: a summary state machine, a manner of managing settings, a flexible solution to specify controller/controllee relationships reliably as needed, and a paradigm for responding to and communicating alarms. This paper describes these agreed solutions and the factors that motivated these.
At the core of the Large Synoptic Survey Telescope (LSST) three-mirror optical design is the primary/tertiary (M1M3) mirror that combines these two large mirrors onto one monolithic substrate. The M1M3 mirror was spin cast and polished at the Steward Observatory Mirror Lab at The University of Arizona (formerly SOML, now the Richard F. Caris Mirror Lab at the University of Arizona (RFCML)). Final acceptance of the mirror occurred during the year 2015 and the mirror is now in storage while the mirror cell assembly is being fabricated. The M1M3 mirror will be tested at RFCML after integration with its mirror cell before being shipped to Chile.
The Large Synoptic Survey Telescope (LSST) is an 8-meter class wide-field telescope now under construction on Cerro Pachon, near La Serena, Chile. This ground-based telescope is designed to conduct a decade-long time domain survey of the optical sky. In order to achieve the LSST scientific goals, the telescope requires delivering seeing limited image quality over the 3.5 degree field-of-view. Like many telescopes, LSST will use an Active Optics System (AOS) to correct in near real-time the system aberrations primarily introduced by gravity and temperature gradients. The LSST AOS uses a combination of 4 curvature wavefront sensors (CWS) located on the outside of the LSST field-of-view. The information coming from the 4 CWS is combined to calculate the appropriate corrections to be sent to the 3 different mirrors composing LSST. The AOS software incorporates a wavefront sensor estimation pipeline (WEP) and an active optics control system (AOCS). The WEP estimates the wavefront residual error from the CWS images. The AOCS determines the correction to be sent to the different degrees of freedom every 30 seconds. In this paper, we describe the design and implementation of the AOS. More particularly, we will focus on the software architecture as well as the AOS interactions with the various subsystems within LSST.
The Large Synoptic Survey Telescope (LSST) is currently under construction and upon completion will perform precision photometry over the visible sky at a 3-day cadence. To meet the stringent relative photometry goals, LSST will employ multiple calibration systems to measure and compensate for systematic errors. This paper describes the design and development of these systems including: a dedicated calibration telescope and spectrograph to measure the atmospheric transmission function, a collimated beam projector to characterize the spatial dependence of the LSST transmission function and an at-field screen illumination system to measure the high-frequency variations in the global system response function.
In the construction phase since 2014, the Large Synoptic Survey Telescope (LSST) is an 8.4 meter diameter wide-field (3.5 degrees) survey telescope located on the summit of Cerro Pachón in Chile. The reflective telescope uses an 8.4 m f/1.06 concave primary, an annular 3.4 m meniscus convex aspheric secondary and a 5.2 m concave tertiary. The primary and tertiary mirrors are aspheric surfaces figured from a monolithic substrate and referred to as the M1M3 mirror. This unique design offers significant advantages in the reduction of degrees of freedom, improved structural stiffness for the otherwise annular surfaces, and enables a very compact design. The three-mirror system feeds a threeelement refractive corrector to produce a 3.5 degree diameter field of view on a 64 cm diameter flat focal surface. This paper describes the current status of the mirror system components and provides an overview of the upcoming milestones including the mirror coating and the mirror system integrated tests prior to summit integration.
The Large Synoptic Survey Telescope (LSST) is a large (8.4 meter) wide-field (3.5 degree) survey telescope, which will be located on the Cerro Pachón summit in Chile. Both the Secondary Mirror (M2) Cell Assembly and Camera utilize hexapods to facilitate optical positioning relative to the Primary/Tertiary (M1M3) Mirror. A rotator resides between the Camera and its hexapod to facilitate tracking. The final design of the hexapods and rotator has been completed by Moog CSA, who are also providing the fabrication and integration and testing. Geometric considerations preclude the use of a conventional hexapod arrangement for the M2 Hexapod. To produce a more structurally efficient configuration the camera hexapod and camera rotator will be produced as a single unit. The requirements of the M2 Hexapod and Camera Hexapod are very similar; consequently to facilitate maintainability both hexapods will utilize identical actuators. The open loop operation of the optical system imposes strict requirements on allowable hysteresis. This requires that the hexapod actuators use flexures rather than more traditional end joints. Operation of the LSST requires high natural frequencies, consequently, to reduce the mass relative to the stiffness, a unique THK rail and carriage system is utilized rather than the more traditional slew bearing. This system utilizes two concentric tracks and 18 carriages.
The Large Synoptic Survey Telescope (LSST) primary/tertiary (M1M3) mirror cell assembly supports both on-telescope operations and off-telescope mirror coating. This assembly consists of the cast borosilicate M1M3 monolith mirror, the mirror support systems, the thermal control system, a stray light baffle ring, a laser tracker interface and the supporting steel structure. During observing the M1M3 mirror is actively supported by pneumatic figure control actuators and positioned by a hexapod. When the active system is not operating the mirror is supported by a separate passive wire rope isolator system. The center of the mirror cell supports a laser tracker which measures the relative position of the camera and secondary mirror for alignment by their hexapods. The mirror cell structure height of 2 meters provides ample internal clearance for installation and maintenance of mirror support and thermal control systems. The mirror cell also functions as the bottom of the vacuum chamber during coating. The M1M3 mirror has been completed and is in storage. The mirror cell structure is presently under construction by CAID Industries. The figure control actuators, hexapod and thermal control system are under developed and will be integrated into the mirror cell assembly by LSST personnel. The entire integrated M1M3 mirror cell assembly will the tested at the Richard F Caris Mirror Lab in Tucson, AZ (formerly Steward Observatory Mirror Lab).
The civil work, site infrastructure and buildings for the summit facility of the Large Synoptic Survey Telescope (LSST) are among the first major elements that need to be designed, bid and constructed to support the subsequent integration of the dome, telescope, optics, camera and supporting systems. As the contracts for those other major subsystems now move forward under the management of the LSST Telescope and Site (T and S) team, there has been inevitable and beneficial evolution in their designs, which has resulted in significant modifications to the facility and infrastructure. The earliest design requirements for the LSST summit facility were first documented in 2005, its contracted full design was initiated in 2010, and construction began in January, 2015. During that entire development period, and extending now roughly halfway through construction, there continue to be necessary modifications to the facility design resulting from the refinement of interfaces to other major elements of the LSST project and now, during construction, due to unanticipated field conditions. Changes from evolving interfaces have principally involved the telescope mount, the dome and mirror handling/coating facilities which have included significant variations in mass, dimensions, heat loads and anchorage conditions. Modifications related to field conditions have included specifying and testing alternative methods of excavation and contending with the lack of competent rock substrate where it was predicted to be. While these and other necessary changes are somewhat specific to the LSST project and site, they also exemplify inherent challenges related to the typical timeline for the design and construction of astronomical observatory support facilities relative to the overall development of the project.
The Large Synoptic Survey Telescope (LSST) has a 10 degrees square field of view which is achieved through a 3 mirror optical system comprised of an 8.4 meter primary, 3.5 meter secondary (M2) and a 5 meter tertiary mirror. The M2 is a 100mm thick meniscus convex asphere. The mirror surface is actively controlled by 72 axial electromechanical actuators (axial actuators). Transverse support is provided by 6 active tangential electromechanical actuators (tangent links). The final design has been completed by Harris Corporation. They are also providing the fabrication, integration and testing of the mirror cell assembly, as well as the figuring of the mirror. The final optical surface will be produced by ion figuring. All the actuators will experience 1 year of simulated life testing to ensure that they can withstand the rigorous demands produced by the LSST survey mission. Harris Corporation is providing optical surface metrology to demonstrate both the quality of the optical surface and the correctablility produced by the axial actuators.
The LSST M1/M3 combines an 8.4 m primary mirror and a 5.1 m tertiary mirror on one glass substrate. The combined mirror was completed at the Richard F. Caris Mirror Lab at the University of Arizona in October 2014. Interferometric measurements show that both mirrors have surface accuracy better than 20 nm rms over their clear apertures, in nearsimultaneous tests, and that both mirrors meet their stringent structure function specifications. Acceptance tests showed that the radii of curvature, conic constants, and alignment of the 2 optical axes are within the specified tolerances. The mirror figures are obtained by combining the lab measurements with a model of the telescope’s active optics system that uses the 156 support actuators to bend the glass substrate. This correction affects both mirror surfaces simultaneously. We showed that both mirrors have excellent figures and meet their specifications with a single bending of the substrate and correction forces that are well within the allowed magnitude. The interferometers do not resolve some small surface features with high slope errors. We used a new instrument based on deflectometry to measure many of these features with sub-millimeter spatial resolution, and nanometer accuracy for small features, over 12.5 cm apertures. Mirror Lab and LSST staff created synthetic models of both mirrors by combining the interferometric maps and the small highresolution maps, and used these to show the impact of the small features on images is acceptably small.
KEYWORDS: Telescopes, Domes, Large Synoptic Survey Telescope, Cameras, Device simulation, Systems modeling, Monte Carlo methods, Thermal modeling, Performance modeling, 3D modeling
Begin Dome seeing is a critical effect influencing the optical performance of ground based telescopes. A previously reported combination of Computational Fluid Dynamics (CFD) and optical simulations to model dome seeing was implemented for the latest LSST enclosure geometry. To this end, high spatial resolution thermal unsteady CFD simulations were performed for three different telescope zenith angles and four azimuth angles. These simulations generate time records of refractive index values along the optical path, which are post-processed to estimate the image degradation due to dome seeing. This method allows us to derive the distribution of seeing contribution along the different optical path segments that composed the overall light path between the entrance of the dome up to the LSST science camera. These results are used to recognize potential problems and to guide the observatory design. In this paper, the modeling estimates are reviewed and assessed relative to the corresponding performance allocation, and combined with other simulator outputs to model the dome seeing impact during LSST operations.
KEYWORDS: Large Synoptic Survey Telescope, Systems modeling, Systems engineering, Cameras, Telescopes, Observatories, Imaging systems, Data modeling, Control systems, Optical filters
The Large Synoptic Survey Telescope project was an early adopter of SysML and Model Based Systems Engineering
practices. The LSST project began using MBSE for requirements engineering beginning in 2006 shortly after the initial
release of the first SysML standard. Out of this early work the LSST’s MBSE effort has grown to include system
requirements, operational use cases, physical system definition, interfaces, and system states along with behavior
sequences and activities. In this paper we describe our approach and methodology for cross-linking these system
elements over the three classical systems engineering domains – requirement, functional and physical - into the LSST
System Architecture model. We also show how this model is used as the central element to the overall project systems
engineering effort. More recently we have begun to use the cross-linked modeled system architecture to develop and
plan the system verification and test process. In presenting this work we also describe “lessons learned” from several
missteps the project has had with MBSE. Lastly, we conclude by summarizing the overall status of the LSST’s System
Architecture model and our plans for the future as the LSST heads toward construction.
The LSST will utilize an Active Optics System to optimize the image quality by controlling the surface figures of the
mirrors (M1M3 and M2) and maintain the relative position of the three optical systems (M1M3 mirror, M2 mirror and
the camera). The mirror surfaces are adjusted by means of figure control actuators that support the mirrors. The relative
rigid body positions of M1M3, M2 and the camera are controlled through hexapods that support the M2 mirror cell
assembly and the camera. The Active Optics System (AOS) is principally operated off of a Look-Up Table (LUT) with
corrections provided by wave front sensors.
The LSST is an integrated, ground based survey system designed to conduct a decade-long time domain survey of the
optical sky. It consists of an 8-meter class wide-field telescope, a 3.2 Gpixel camera, and an automated data processing
system. In order to realize the scientific potential of the LSST, its optical system has to provide excellent and consistent
image quality across the entire 3.5 degree Field of View. The purpose of the Active Optics System (AOS) is to optimize
the image quality by controlling the surface figures of the telescope mirrors and maintaining the relative positions of the
optical elements. The basic challenge of the wavefront sensor feedback loop for an LSST type 3-mirror telescope is the
near degeneracy of the influence function linking optical degrees of freedom to the measured wavefront errors. Our
approach to mitigate this problem is modal control, where a limited number of modes (combinations of optical degrees
of freedom) are operated at the sampling rate of the wavefront sensing, while the control bandwidth for the barely
observable modes is significantly lower. The paper presents a control strategy based on linear approximations to the
system, and the verification of this strategy against system requirements by simulations using more complete, non-linear
models for LSST optics and the curvature wavefront sensors.
The Large Synoptic Survey Telescope instrument include four guiding and wavefront sensing subsystems called corner
raft subsystems, in addition to the main science array of 189 4K x 4K CCDs. These four subsystems are placed at the
four corners of the instrumented field of view. Each wavefront/guiding subsystem comprises a pair of 4K x 4K guide
sensors, capable of producing 9 frames/second, and a pair of offset 2K x 4K wavefront curvature sensors from which the
images are read out at the cadence of the main camera system, providing 15 sec integrations. These four
guider/wavefront corner rafts are mechanically and electrically isolated from the science sensor rafts and can be installed
or removed independently from any other focal plane subsystem. We present the implementation of this LSST
subsystem detailing both hardware and software development and status.
The Large Synoptic Survey Telescope (LSST) Telescope integration and test plan is phased to ensure that subsystems and services are available to support the integration flow. It begins with the summit facility construction and shows how the major subsystems feed into the activities through final testing. In order to minimize the amount of hardware mated for the first time during that period, the approach is to favor all hardware mated and pre-tested at vendors’ facilities with associated hardware and software prior to delivery onsite. The integration and test plan exploits the diffraction limited on-axis image quality of the three-mirror design. In addition, fiducials will be used during optical acceptance testing at vendors’ facilities to capture the optical axis geometry of each optical element. These fiducials will be used during the integration and tests sequence to facilitate the telescope optical alignment. In this paper, we describe the major steps of the LSST telescope integration and test sequence prior to the start of commissioning with the science camera.
The Large Synoptic Survey Telescope (LSST) has recently completed its Final Design Review and the Project is preparing for a 2014 construction authorization. The telescope system design supports the LSST mission to conduct a wide, fast, deep survey via a 3-mirror wide field of view optical design, a 3.2-Gpixel camera, and an automated data processing system. The observatory will be constructed in Chile on the summit of Cerro Pachón. This paper summarizes the status of the Telescope and Site group. This group is tasked with design, analysis, and construction of the summit and base facilities and infrastructure necessary to control the survey, capture the light, and calibrate the data. Several early procurements of major telescope subsystems have been completed and awarded to vendors, including the mirror systems, telescope mount assembly, hexapod and rotator systems, and the summit facility. These early contracts provide for the final design of interfaces based upon vendor specific approaches and will enable swift transition into construction. The status of these subsystems and future LSST plans during construction are presented.
The Large Synoptic Survey Telescope (LSST) is an 8.4 meter, 3.5 degree, wide-field survey telescope. The survey mission requires a short slew, settling time of 5 seconds for a 3.5 degree slew. Since it does not include a fast steering mirror, the telescope has stringent vibration limitations during observation. Meeting these requirements will be facilitated by a stiff compact Telescope Mount Assembly (TMA) riding on a robust pier and by added damping. The TMA must also be designed to facilitate maintenance. The design is an altitude over azimuth welded and bolted assembly fabricated from mild steel.
KEYWORDS: Telescopes, Camera shutters, Domes, Large Synoptic Survey Telescope, Space telescopes, Capacitors, Mirrors, Stray light, Control systems, Bridges
The Large Synoptic Survey Telescope (LSST) is a large (8.4 meter) wide-field (3.5 degree) survey telescope, which will be located on the Cerro Pachón summit in Chile. As a result of the wide field of view, its optical system is unusually susceptible to stray light; consequently besides protecting the telescope from the environment the rotating enclosure (Dome) also provides indispensible light baffling. All dome vents are covered with light baffles which simultaneously provide both essential dome flushing and stray light attenuation. The wind screen also (and primarily) functions as a light screen providing only a minimum clear aperture. Since the dome must operate continuously, and the drives produce significant heat, they are located on the fixed lower enclosure to facilitate glycol water cooling. To accommodate day time thermal control, a duct system channels cooling air provided by the facility when the dome is in its parked position.
The Large Synoptic Survey Telescope (LSST) relies on a set of calibration systems to achieve the survey photometric performances over a wide range of observing conditions. Its purpose is to consistently and accurately measure the observatory instrumental response and the atmospheric transparency during LSST observing. The instrumental response calibration will be performed regularly to monitor any variation of the transmission during the duration of the survey. The atmospheric data will be acquired nightly and processed to atmospheric models. In this paper, we describe the calibration screen system that will be used to perform the instrumental response calibration and the atmospheric calibration system including the auxiliary telescope dedicated to the acquisition of spectral data to determine the atmospheric transmission.
The Large Synoptic Survey Telescope (LSST) is a large (8.4 meter) wide-field (3.5 degree) survey telescope, which will
be located on the Cerro Pachón summit in Chile. Both the Secondary Mirror (M2) Cell Assembly and Camera utilize
hexapods to facilitate optical positioning relative to the Primary/Tertiary (M1M3) Mirror. Geometric considerations
preclude the use of a conventional hexapod arrangement for the M2 Hexapod. A rotator resides between the Camera and
its hexapod to facilitate tracking. The requirements of the M2 Hexapod and Camera Hexapod are very similar;
consequently to facilitate maintainability both hexapods will utilize identical actuators.
The Large Synoptic Survey Telescope (LSST) optical design calls for a large annular 3.4 m diameter meniscus convex aspheric Secondary Mirror (M2). The M2 has a mass of approximately 1.5 metric tons and the optimized mirror support system consists of 72 axial actuators, mounted at the mirror back surface, and 6 tangent link lateral supports mounted around the outer edge. A fully integrated M2 Finite Element Model (FEM) including the mirror and the support systems has been developed to investigate the performance of the M2 assembly and to determine the image degradation due to dynamic wind loading. Detailed wind response analysis was performed based on the input from Computational Fluid Dynamics (CFD) simulations. Image quality calculations of the time history responses and Power Spectrum Density (PSD) are addressed.
This paper describes Computational Fluid Dynamic (CFD) analyses combined with thermal
analyses for modeling the effects of passive ventilation, enclosure-building configuration and
topography on the optical performance of the Large Synoptic Survey Telescope (LSST). The
primary purpose of the analyses was to evaluate the seeing contribution of the major enclosure-facility
elements and to select the features to be adopted in the baseline design from among
various configurations being explored by the LSST project and the contracted architectural
design team.
In addition, one of several simulations for different telescope orientations is presented including
various wind-telescope relative azimuth angles. Using a post-processing analysis, the effects of
turbulence and thermal variations within the airflow around the buildings and inside the
telescope-enclosure configuration were determined, and the optical performance due to the
thermal seeing along the optical path was calculated.
The 3.5-meter diameter Large Synoptic Survey Telescope (LSST) secondary (M2) mirror utilizes a 100mm thick
meniscus ULE™ blank completed by Corning Incorporated in 2009. Sub-aperture interferometry will guide the
polishing process to meet mirror structure function requirements. The convex asphere is actively supported by 72
axial actuators and 6 tangential links. These tangent links utilize an embedded lever system to meet the
requirements. The axial actuators have force limiting devices. The control system utilizes a higher level "outer loop
controller" for monitoring and commanding the tangent links and axial actuators. Numerous sensors determine the
assembly status. To prevent thermally induced image degradation, the interior air of the M2 cell is conditioned.
Results from determining the optical turbulence profile (OTP) on the LSST site, El
Peñon, located on Cerro Pachón (Chile) are presented. El Peñón appears to be an
excellent observatory site with a surface layer seeing contribution on the order of 0.15”
with most of this seeing being produced below 20m. These measurements also helped to
confirm that the telescope is elevated high enough above ground. As part of the LSST site
characterization campaign, microthermal measurements were taken in order to determine
the contribution of the surface layer turbulence to the atmospheric seeing. Such
measurements are commonly used for this purpose where pairs of microthermal sensors
mounted on a tower measure atmospheric temperature differences. In addition, the lunar
scintillometer LuSci was installed on El Peñon for short campaigns near full moon for the
same purpose. LuSci is a turbulence profiler based on measuring spatial correlation of
moonlight scintillations. The comparison of the results from both instruments during
simultaneous data acquisition showed a remarkable temporal correlation and very similar
mean OTPs.
KEYWORDS: Telescopes, Cameras, Mirrors, Large Synoptic Survey Telescope, Space telescopes, Monochromatic aberrations, Optical alignment, Optical testing, Active optics, System integration
The planned construction and completion of the Large Synoptic Survey Telescope (LSST) Project consists of phased
activities. The initial telescope construction period will transition to a multi-year commissioning phase, which will
conclude with final hand off to science operations. The initial telescope alignment will utilize laser tracker fiducials
and nodal aberration theory (NAT) to demonstrate Engineering First Light with a three-mirror optical system and
test camera, prior to the integration of the science camera. This plan exploits the diffraction limited on-axis image
quality of the three-mirror design. Commissioning consists of final integration of the three LSST subsystems
(Telescope, Camera, and Data Management), followed by on-sky science verification to show compliance with the
survey performance specifications.
The Large Synoptic Survey Telescope will be located on a seismically active Chilean mountain. Seismic ground
accelerations produce the telescope's most demanding load cases. Consequently, accurate prediction of these
accelerations is required. These seismic accelerations, in the form of Peak Spectral Acceleration (PSA), were compared
for site specific surveys, the Chilean building codes and measured seismic accelerations. Methods were also investigated
for adjusting for variations in damping level and return period. The return period is the average interval of time between
occurrences of a specific intensity.
The LSST project has updated the all-sky IR camera that was installed on Cerro Pachón in Chile to continue its
investigations in cloud monitoring and quantifying photometric conditions. The objective is to provide the survey
scheduler with real-time measured conditions of the sky/clouds, including high cirrus to better optimize the observing
strategy. This paper describes the changes done to improve the detection performance of the first generation system and
presents comparison results of visible and IR images.
KEYWORDS: Large Synoptic Survey Telescope, Systems modeling, Imaging systems, Telescopes, Observatories, Cameras, Systems engineering, Data modeling, Control systems, Computer architecture
The Large Synoptic Survey Telescope is a complex hardware - software system of systems, making up a highly
automated observatory in the form of an 8.4m wide-field telescope, a 3.2 billion pixel camera, and a peta-scale data
processing and archiving system. As a project, the LSST is using model based systems engineering (MBSE)
methodology for developing the overall system architecture coded with the Systems Modeling Language (SysML).
With SysML we use a recursive process to establish three-fold relationships between requirements, logical & physical
structural component definitions, and overall behavior (activities and sequences) at successively deeper levels of
abstraction and detail. Using this process we have analyzed and refined the LSST system design, ensuring the
consistency and completeness of the full set of requirements and their match to associated system structure and
behavior. As the recursion process proceeds to deeper levels we derive more detailed requirements and specifications,
and ensure their traceability. We also expose, define, and specify critical system interfaces, physical and information
flows, and clarify the logic and control flows governing system behavior. The resulting integrated model database is
used to generate documentation and specifications and will evolve to support activities from construction through final
integration, test, and commissioning, serving as a living representation of the LSST as designed and built. We discuss
the methodology and present several examples of its application to specific systems engineering challenges in the LSST
design.
The LSST camera is located above the LSST primary/tertiary mirror and in front of the secondary mirror in the shadow
of its central obscuration. Due to this position within the optical path, heat released from the camera has a potential
impact on the seeing degradation that is larger than traditionally estimated for Cassegrain or Nasmyth telescope
configurations. This paper presents the results of thermal seeing modeling combined with Computational Fluid
Dynamics (CFD) analyzes to define the thermal requirements on the LSST camera.
Camera power output fluxes are applied to the CFD model as boundary conditions to calculate the steady-state
temperature distribution on the camera and the air inside the enclosure. Using a previously presented post-processing
analysis to calculate the optical seeing based on the mechanical turbulence and temperature variations along the optical
path, the optical performance resulting from the seeing is determined. The CFD simulations are repeated for different
wind speeds and orientations to identify the worst case scenario and generate an estimate of seeing contribution as a
function of camera-air temperature difference. Finally, after comparing with the corresponding error budget term, a
maximum allowable temperature for the camera is selected.
The LSST Telescope has critical requirements on tracking error to meet image quality specifications, and will require
closing a guiding loop, with the telescope servo control, to meet its mission. The guider subsystem consists of eight
guiding sensors located inside the science focal plane at the edge of the 3.5deg field of view. All eight sensors will be
read simultaneously at a high rate, and a centroid average will be fed to the telescope and rotator servo controls, for
tracking error correction. A detailed model was developed to estimate the sensors centroid noise and the resulting
telescope tracking error for a given frame rate and telescope servo control system.
The centroid noise depends on the photo-electron flux, seeing conditions, and guide sensor specifications. The model for
the photo-electron flux takes into consideration the guide star availability at different galactic latitudes, the atmospheric
extinction, the optical losses at different filter bands, the detector quantum efficiency, the integration time and the
number of stars sampled. A 7-layer atmospheric model was also developed to estimate the atmospheric decorrelation
between the different guide sensors due to the 3.5deg field of view, to predict both correlated and decorrelated
atmospheric tip/tilt components, and to determine the trade-offs of the guider servo loop.
We present a new lunar scintillometer, LuSci. A simple and accurate way to determine the Ground Layer (GL)
turbulence profile is through measuring lunar and solar scintillation. The contribution of the first 10-100 m to
the total seeing is usually significant. Measuring the seeing in this GL is important to evaluate sites, especially
to set the height of future domes and to translate existing seeing data to higher domes. This holds in particular
to Antarctic sites where the GL seeing is dominant, with obvious implications for AO and interferometry. We
develop robust methods for turbulence profile restoration from LuSci data, incorporating the effect of lunar
phases. We present restored profiles from initial campaigns. We also extract a simple model for the wind profile
from the rich information present in the scintillation spectrum.
The LSST project has acquired an all sky IR camera and started to investigate its effectiveness in cloud monitoring. The
IR camera has a 180-degree field of view. The camera uses six filters in the 8-12 micron atmospheric window and has a
built in black body reference and visible all sky camera for additional diagnostics. The camera is installed and in nightly
use on Cerro Pachon in Chile, between the SOAR and Gemini South telescopes. This paper describes the measurements
made to date in comparison to the SOAR visible All Sky Camera (SASCA) and other observed atmospheric throughput.
The objective for these tests is to find an IR camera design to provide the survey scheduler with real-time measured
conditions of clouds, including high cirrus to better optimize the observing strategy.
A wind pressures PSD measured on the Gemini South Telescope was applied to the FEA model of
the LSST telescope to determine the RMS motions of the principal optical systems. These motions
were then converted to the time domain. The time domain motions were analyzed in the ZEMAX®
software to determine the wind induced image degradation. This degradation was shown to be
tolerable.
The Large Synoptic Survey Telescope (LSST) baseline design includes aluminum coating for the large mirrors in its 3 element modified Paul Baker optical design. The 8.4 meter diameter of the primary provides a significant challenge to the LSST coating plans however such coatings have successfully achieved for this size aperture. LSST also recognizes that the use of mirror coatings with higher reflectivity and durability would significantly benefit its science by increasing its overall throughput and improving its operational efficiency. LSST has identified Lawrence Livermore National Laboratory (LLNL) blue-shifted protected silver coating as a possible candidate to provide this blue wavelength performance. A study has been started to assess the performance of these and other coatings in the observatory environment. We present the details of this ongoing program, the results obtained so far, and related coating tests results. LSST has also engaged in collaboration with the Gemini Telescope in the development and testing of an Al-Ag coating based on their current recipe. The first results of these tests are also included in this report.
The project for the proposed Large Synoptic Survey Telescope (LSST) performed more than two years of data
collection, site evaluation, and analysis to support the selection of its prime site. LSST assessment was based on
using an existing site with existing infrastructure and historical performance information. A large and diverse set of
comparative information was compiled for potential sites using results from other site campaigns, measurements
from existing large telescopes, new astro-climate measurements, logistical and feasibility information, and from
existing satellite and climate databases. Several analyses were performed on these data including the assessment of
survey performance using the LSST operation simulator. An independent site selection committee of experts
provided recommendations to the Project leading to three finalist sites, one in Mexico, and two in northern Chile.
The finalist sites were assessed thoroughly with additional data collection from all-sky cameras and site proposals.
Cerro Pachon in Chile was selected to be the site for LSST after a difficult decision between the high quality final
candidates. This paper describes the data, analysis and approach used to support the site evaluation.
The proposed science missions of the LSST require a telescope with an optical etendue of greater than 250 meters square degrees square. The current LSST Baseline Configuration has a field of view of 3.5 degrees and an optical etendue of 302 m2d2. The etendue calculation includes the effect of gradual vignetting by the camera as the field angle increases. A current optical point design includes spun cast light-weighted borosilicate mirrors (primary and tertiary) of 8.4 and 5 m diameter respectively. Thermal control systems are needed to optimize telescope seeing and to minimize the thermal distortion of the mirrors. The goals of this study are to determine the airflow requirements for the specified ambient temperature rate of change, to identify thermal time constants and to predict the magnitude and form of thermal distortions that can be developed by environmental conditions. Operational data taken at the 6.5 m MMT (Multi-Mirror Telescope Observatory) and at the Magellan Observatory are presented for comparison with this study. Finally, the results from the thermal analysis were used to simulate the LSST focus control over one night of observation and to estimate the effect on the image quality for different correction frequencies.
The current LSST Baseline Configuration has a field of view of 3.5 degrees and an optical etendue of 302 meters square degrees square. The etendue calculation includes the effect of gradual vignetting by the camera as the field angle increases. A current optical point design includes an 8.4 m spun cast light-weighted borosilicate primary mirror, a 3.2 m secondary mirror and a 5.0 m tertiary mirror. The goal of this study is to determine if these mirrors can be actively supported and retain figure control over elevation angles without closed-loop control based on wave-front measurement. Support systems for the tertiary and primary mirrors are adapted from proven systems utilized on 6.5 and 8.4 m class primaries developed by the University of Arizona's Mirror Laboratory. The number and locations of axial and lateral supports is determined for each mirror and the gravitational and support induced surface distortions are calculated and are shown to be within budgeted limits. The support components and their performance are described and it is demonstrated that predicted mirror distortion attributable to the support system is consistent with the known performance of the support components.
The Large Synoptic Survey Telescope (LSST) is an 8-meter class telescope with a proposed field of view between 3.0 and 3.5 degrees. The scientific goals of the survey establish a cadence that sets the telescope performance. The proposed cadence of the LSST telescope will typically require movements and settling of the telescope of approximately 3 degrees in 5 seconds. This dictates a high bandwidth to the telescope servo and thus a high locked rotor resonant frequency. In this study, the structure must accommodate three optical surfaces, the 8.4-meter primary, the 3-meter class secondary, and a 5-meter class tertiary in a long-tube configuration. The instrument must be accommodated in a "Trapped Focus" in the middle of the telescope. This imposes very stringent requirements on the structure and drives. This structure will require performance beyond the existing class of 8-meter telescopes. This can be achieved with the C-ring and azimuth platform concept demonstrated with the Large Binocular Telescope. The structure requires a low rotational inertia and a very high locked rotor resonant frequency at all angles of the sky. This is a challenging problem that can be overcome with this innovative solution.
The 8.4m Large Synoptic Survey Telescope (LSST) is a wide-field telescope facility that will add a qualitatively new capability in astronomy. For the first time, the LSST will provide time-lapse digital imaging of faint astronomical objects across the entire sky. The LSST has been identified as a national scientific priority by diverse national panels, including multiple National Academy of Sciences committees. This judgment is based upon the LSST's ability to address some of the most pressing open questions in astronomy and fundamental physics, while driving advances in data-intensive science and computing. The LSST will provide unprecedented 3-dimensional maps of the mass distribution in the Universe, in addition to the traditional images of luminous stars and galaxies. These mass maps can be used to better understand the nature of the newly discovered and utterly mysterious Dark Energy that is driving the accelerating expansion of the Universe. The LSST will also provide a comprehensive census of our solar system, including potentially hazardous asteroids as small as 100 meters in size. The LSST facility consists of three major subsystems: 1) the telescope, 2) the camera and 3) the data processing system. The baseline design for the LSST telescope is a 8.4m 3-mirror design with a 3.5 degree field of view resulting in an A-Omega product (etendue) of 302deg2m2. The camera consists of 3-element transmisive corrector producing a 64cm diameter flat focal plane. This focal plane will be populated with roughly 3 billion 10μm pixels. The data processing system will include pipelines to monitor and assess the data quality, detect and classify transient events, and establish a large searchable object database. We report on the status of the designs for these three major LSST subsystems along with the overall project structure and management.
The multi-conjugate adaptive optics (MCAO) system design for the Gemini-South 8-meter telescope will provide near-diffraction-limited, highly uniform atmospheric turbulence compensation at near-infrared wavelengths over a 2 arc minute diameter field-of-view. The design includes three deformable mirrors optically conjugate to ranges of 0, 4.5, and 9.0 kilometers with 349, 468, and 208 actuators, five 10-Watt-class sodium laser guide stars (LGSs) projected from a laser launch telescope located behind the Gemini secondary mirror, five Shack-Hartmann LGS wavefront sensors of order 16 by 16, and three tip/tilt natural guide star (NGS) wavefront sensors to measure tip/tilt and tilt anisoplanatism wavefront errors. The WFS sampling rate is 800 Hz. This paper provides a brief overview of sample science applications and performance estimates for the Gemini South MCAO system, together with a summary of the performance requirements and/or design status of the principal subsystems. These include the adaptive optics module (AOM), the laser system (LS), the beam transfer optics (BTO) and laser launch telescope (LLT), the real time control (RTC) system, and the aircraft safety system (SALSA).
The idea of achieving Adaptive Optics over the majority of the sky using sodium laser guide stars is reaching maturity on Mauna Kea. However, Mauna Kea is a shared astronomical site with 13 institutions and 11 telescopes. Coordination between observatories with laser guide stars and facilities without laser guide stars must be accomplished to prevent sodium light (Rayleigh scatter and the laser guide star itself) from interfering with science observations at the non-laser facilities. To achieve this goal, a technical working group was organized with participation from several Mauna Kea observatories to discuss and agree upon an automated system for avoiding laser “beam” collisions with other telescopes. This paper discussed the implementation of a Laser Traffic Control System (LTCS) for Mauna Kea including a brief history of the coordination effort, technical requirements and details surrounding implementation of laser beam avoidance software, critical configuration parameters, algorithmic approaches, test strategies used during deployment, and recommendations based upon experiences to date for others intending to implement similar systems.
The Acquisition and Guiding Unit of the Gemini Telescope is able to support two major signal-processing functions: off axis active optics correction, and off axis fast guiding and focus. Both functions are performed by using up to two different Shack-Hartmann wavefront sensors working in the visible (called the Peripheral Wavefront Sensors). In addition to these wavefront sensors, each facility instrument includes its On Instrument Wavefront Sensor, which provides on or off axis fast guiding, and in some cases focus and astigmatism correction. In this paper, we will describe the different wavefront sensors and the results obtained in closed loop in terms of image quality and temporal performance.
The Gemini Observatory is planning to implement a Multi Conjugate Adaptive Optics System as a facility instrument for the Gemini-South telescope. The system will include 5 Laser Guide Stars, 3 Natural Guide Stars, and 3 Deformable mirrors optically conjugated at different altitudes to achieve near-uniform atmospheric compensation over a 1 arc minute square field of view. The control of such a system will be split in 3 main functions: the control of the opto- mechanical assemblies of the whole system (including the Laser, the Beam Transfer Optics and the Adaptive Optics bench), the control of the Adaptive Optics System itself at a rate of 800 frames per second and the control of the safety system. The control of the adaptive Optics System is the most critical in terms of real time performance. In this paper, we will describe the requirements for the whole Multi Conjugate Adaptive Optica Control System, preliminary designs for the control of the opto-mechanical devices and architecture options for the control of the Adaptive Optics system and the safety system.
A Prime Focus Wavefront Sensor (PFWFS) has been designed and built at the Gemini Observatory. The system contains a Shack- Hartmann (SH) wavefront sensor and has been designed to use commercial components. The primary mirror of the 8 m Gemini Telescope has a complex active optics system that needs to be calculated during commissioning. The wavefront sensor was built to measure the image quality at prime focus, this eliminates the secondary mirror introducing supplementary aberrations. It has been successfully used during commissioning, to test the active optics.
We discuss the design of the laser guide star system to be implemented with ALTAIR, the Gemini North adaptive optics system. We give an overview of the sodium physics in order to understand why some lasers are more efficient than others to produce bright artificial stars. We present some simulation results which set the laser output power requirement when launching a perfect beam to the sky. Preliminary designs for the beam transfer optics, the laser launch telescope and the safety systems are also presented.
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