The Giant Magellan Telescope (GMT) is a next-generation ground-based segmented telescope. In the last few years, significant progress has been made by the GMT team and partners to design a natural guide-star wavefront control strategy that can reliably correct wavefront error, including the discrete piston aberration between segment gaps. After an extensive set of simulations and external reviews, the team proposed a design of a Pyramidal Wavefront Sensor (PWFS) combined with a Holographic Dispersed Fringe Sensor (HDFS) and started building a prototype for integrating a GMT simulator (High Contrast AO Testbed) with a PWFS and an HDFS. The prototype was developed in collaboration with the University of Arizona, INAF-Arcetri, and the GMT observatory. The software development of the adaptive optics controllers and the interfaces between all testbed components were done using the GMT software frameworks, as they will be implemented for the final observatory software. The GMT framework is model-based, and the software component interfaces are defined using a domain-specific language (DSL). In this paper, we show how the design of the testbed software fits within GMT's component-based architecture and what each partner was responsible for delivering. We discuss the challenge of a multidisciplinary team from multiple institutions in different time zones working together on the same software, describe how the software architecture and development process helped to ensure seamless integration and highlight other accomplishments and lessons learned.
The Giant Magellan Telescope (GMT) wavefront control system provides active optics control and optical turbulence correction for every instrument on the 25.4 m diameter GMT. The GMT has four first-generation wavefront control modes that balance image quality, field of view, sky coverage, and development risk: Natural Seeing, Ground-Layer AO, Natural Guide Star AO, and Laser Tomography AO. Several aspects of the GMT wavefront control design have been recently updated. The Acquisition, Guiding, and Wavefront Sensing Subsystem, used in all control modes, has completed final design and a full-scale prototype sensor is being assembled. A Holographic Dispersed Fringe Sensor has been developed to improve the segment phasing capture range and stability of the Natural Guide Star AO mode. In the Laser Tomography AO mode, a high-speed infrared imager in each instrument will measure segment phasing disturbances using phase retrieval on a faint natural guide star, replacing an inter-segment differential laser metrology truss as the primary phasing sensor. High-fidelity simulations of all wavefront control modes have been developed, and we are developing wavefront sensor prototypes on laboratory testbeds that replicate the GMT optical design. We review the performance expectations in each control mode, and describe our plan to complete the wavefront control system development.
The Giant Magellan Telescope will be a 25.4-m visible and infrared telescope at Las Campanas Observatory. The optical design consists of 7 8.4-m primary mirror segments that reflect light to 7 secondary mirror segments in a doubly segmented direct Gregorian configuration. GMT is developing a Telescope Metrology System (TMS) to decrease the complexity of alignment and increase observatory efficiency. The TMS has been developed to Preliminary Design Review level. A prototyping, modelling, and analysis effort has been completed. All components of the system were matured, and the edge-sensing strategy was significantly revised. This paper describes the current TMS design.
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...
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 Vera C. Rubin Observatory Primary Tertiary Mirror (M1M3), together with the fully-assembled mirror support system, underwent two optical testing campaigns at the University of Arizona Richard F. Caris Mirror Lab. The objectives of the testing campaigns were: (1) optimizing the M1M3 surfaces with support forces, and (2) characterizing how the surfaces respond to actuator forces, including measuring the bending modes and single actuator influence functions. Both objectives were successfully achieved. The differences between the measured bending modes and the Finite Element Analysis (FEA) predicted modes were shown to be less than a few percent. The surface optimizations routinely resulted in Root-Mean-Square (RMS) surface errors below 30 nm for M1 and M3, simultaneously. The entire system was shown to be robust and repeatable. In this paper, we present the results of the optical testing and the analyses performed using the data acquired.
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 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.
High spatial resolution thermal unsteady CFD simulations of LSST are performed and processed to provide image degradation due to dome seeing in FWHM. An analysis of the sensitivity of the image quality to certain important geometric features and aerothermal properties is presented. More specifically, the influence of the LSST vent light baffles and windscreen, the wind speed and the surface temperature of components such as the primary and secondary mirrors, the camera, the telescope structure and dome exterior is assessed and conclusions are drawn. The secondary mirror and camera surface temperatures are found to be among the most critical in minimizing LSST dome seeing.
The Large Synoptic Survey Telescope (LSST) is under construction in Chile. To make the delivered system meet the science goals, the project defines a set of performance metrics, and constantly monitors the system performance by evaluating the metrics against their requirements. In this paper, we describe the latest updates to the comprehensive tool set we have developed for evaluating the LSST system performance, which we collectively refer to as the LSST integrated model, and recent work on utilizing these tools for system verification. We also broaden our set of performance metrics and introduce an integrated-étendue-based metrics framework, which is useful for not just system verification, but also mitigation and optimization. Most of the major metrics currently being monitored fit under this framework, including image quality, system throughput, the single-visit point source 5σdetection limit, etc. We also mointor the Point Spread Function (PSF) ellipticity, which isn't part of this metrics framework, but is an output of the integrated model.
KEYWORDS: Large Synoptic Survey Telescope, Imaging systems, System integration, Cameras, Telescopes, Observatories, Data processing, Interfaces, Control systems, Computing systems
The Commissioning Phase of the LSST Project is the final stage in the combined NSF and DOE funded LSST construction project. The LSST commission phase is planned to start early in 2020 and be completed near the end of 2022, ending with the LSST Observatory system ready to start survey operations. Commissioning includes the assembly of the three principal subsystems (Telescope, Camera and Data Management) into the LSST Observatory System and the integration and test (AI&T) efforts as well as the science verification activities. The LSST System AI&T and Commissioning Plan is driven by a combination of engineering and scientifically oriented activities to show compliance with technical requirements and readiness to conduct science operations (acquiring data, processing data, and serving data and derived data products to users). LSST System AI&T and Commissioning will be carried out over four phases of activity: Phase-0) Pre-commissioning preparations (work breakdown structure; Phase-1) Early System AI&T with a commissioning camera (ComCam); Phase-2) Full System AI&T when the LSST Science Camera is shipped to Chile, integrated on the telescope and the data management system (DMS) is exercised with full scale data; and Phase-3) Science Validation where a series of mini-surveys are used to characterize the system with respect to the survey performance specifications in the SRD/LSR and functionality of the, leading to operations readiness. The Science Validation Phase concludes with an Operations Readiness Review (ORR).
The LSST System Assembly, Integration and Test and Commissioning effort has been planned out over several phases The first phase of commissioning under Early AI&T is designed to test and verify the system level interfaces using ComCam – a 144Mpixel imager utilizing the same control components as the full science camera. During this period, the telescope active optics system will be brought into compliance with system requirements; the scheduler will be exercised and all safety checks verified for autonomous operation; and early DM algorithm testing will be performed with on-sky data from ComCam using a commissioning computing cluster at the Base Facility.
The second phase of activities under Full System AI&T is designed to complete the technical integration of the three principal subsystems and EPO, show full compliance with system level requirements as detailed in the Observatory System Specifications and system level interface control documents, and provide full scale data for further DM/EPO software and algorithmic testing and development. System level requirements that flow directly to subsystems without any further derivation will be tested for compliance, at the subsystem level and below, under the supervision of Project Systems Engineering. This document includes the general approach and goals for these tests. It is expected that roughly four (4) months into the Full System AI&T phase the telescope and camera will be fully integrated and routinely producing science grade images over the full field of view (FOV), at which point “System First Light” will be declared. Following System First Light will be an intensive data acquisition period design to test the image processing pipelines and validate the derived science products that are to be delivered by the LSST survey.
The third and final phase of activities under Science Validation is designed to fully characterize the system performance specifications detailed in LSST System Requirements Document and the range of demonstrated performance per the LSST Science Requirements. These activities are based on the measured “On-Sky” performance and informed simulations of the LSST system.
In this paper we describe the inputs and assumptions to the commissioning plan, a summary of the activities in each phase, management strategies and expected outcomes.
The Large Synoptic Survey Telescope is an 8.4m telescope now in construction on Cerro Pachón, in Chile. This telescope is designed to conduct a 10-year survey of the southern sky in which it will map the entire night sky every few nights. In order to achieve this goal, the telescope mount has been designed to achieve high accelerations that will allow the system to change the observing field in just 2 seconds. These rapid slews will subject the M1M3 mirror to high inertial and changing gravitational forces that has to be actively compensated for in order to keep the mirror safe, aligned, and properly figured during operations. The LSST M1M3 active support system is composed of six “hard point” actuators and 156 pneumatic actuators. The hard points define the mirror position in the mirror cell (with little or no applied force) and hold that position while observing in order to maintain the alignment of the telescope optics. The pneumatic actuators provide the force-distributed mirror support plus a known (static) figure correction as well as dynamic optical figure optimizations coming from other components of the Active Optics System. Optimizing this mirror support system required the introduction of innovative control concepts in the control loops (Inner and Outer). The Inner Loop involves an extensive pressure control loop to ensure precise force feedback for each pneumatic actuator while the Outer Loop includes telescope motion sensors to provide the real-time feedback to compensate for the changing external inertial and gravitational forces. These optimizations allow the mirror support system to maximize the hard point force-offloading while keeping the glass safe when slewing and during seismic events.
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.
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.
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.
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.
We make a detailed quantitative comparison of the wavefront recovery algorithms between those developed for Dark Energy Camera (DECam) and the Large Synoptic Survey Telescope (LSST). Samples used in this study include images of out of focus stars collected by the DECam at the Blanco 4-meter telescope and artificial simulated donut images. The data from DECam include wavefront images collected by the wavefront sensors and out-of-focus images where the entire DECam sensor array is used. For simulated images, we have used both the forward Fraunhofer diffraction and a LSST-like ZEMAX optical model where the images are convolved with Kolmogorov atmosphere. All samples are analyzed with the forward wavefront retrieval algorithm developed for DECam and the transport of intensity algorithm for LSST. Good quantitative agreement between results by the two implemented algorithms is observed.
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.
To optimize the observing strategy of a large survey such as the LSST, one needs an accurate model of the night sky emission spectrum across a range of atmospheric conditions and from the near-UV to the near-IR. We have used the ESO SkyCalc Sky Model Calculator1, 2 to construct a library of template spectra for the Chilean night sky. The ESO model includes emission from the upper and lower atmosphere, scattered starlight, scattered moonlight, and zodiacal light. We have then extended the ESO templates with an empirical fit to the twilight sky emission as measured by a Canon all-sky camera installed at the LSST site. With the ESO templates and our twilight model we can quickly interpolate to any arbitrary sky position and date and return the full sky spectrum or surface brightness magnitudes in the LSST filter system. Comparing our model to all-sky observations, we find typical residual RMS values of ±0.2-0.3 magnitudes per square arcsecond.
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 (LSST) uses an Active Optics System (AOS) to maintain system alignment and surface figure on its three large mirrors. Corrective actions fed to the LSST AOS are determined from 4 curvature based wavefront sensors located on the corners of the inscribed square within the 3.5 degree field of view. Each wavefront sensor is a split detector such that the halves are 1mm on either side of focus. In this paper we describe the development of the Active Optics Pipeline prototype that simulates processing the raw image data from the wavefront sensors through to wavefront estimation on to the active optics corrective actions. We also describe various wavefront estimation algorithms under development for the LSST active optics system. The algorithms proposed are comprised of the Zernike compensation routine which improve the accuracy of the wavefront estimate. Algorithm development has been aided by a bench top optical simulator which we also describe. The current software prototype combines MATLAB modules for image processing, tomographic reconstruction, atmospheric turbulence and Zemax for optical ray-tracing to simulate the closed loop behavior of the LSST AOS. We describe the overall simulation model and results for image processing using simulated images and initial results of the wavefront estimation algorithms.
The Large Synoptic Survey Telescope (LSST) has a 3.5º field of view and F/1.2 focus that makes the performance quite
sensitive to the perturbations of misalignments and mirror surface deformations. In order to maintain the image quality,
LSST has an active optics system (AOS) to measure and correct those perturbations in a closed loop. The perturbed
wavefront errors are measured by the wavefront sensors (WFS) located at the four corners of the focal plane. The
perturbations are solved by the non-linear least square algorithm by minimizing the rms variation of the measured and
baseline designed wavefront errors. Then the correction is realized by applying the inverse of the perturbations to the
optical system. In this paper, we will describe the correction processing in the LSST AOS. We also will discuss the
application of the algorithm, the properties of the sensitivity matrix and the stabilities of the correction. A simulation
model, using ZEMAX as a ray tracing engine and MATLAB as an analysis platform, is set up to simulate the testing and
correction loop of the LSST AOS. Several simulation examples and results are presented.
The Large Synoptic Survey Telescope (LSST) is a proposed ground based telescope that will perform a comprehensive
astronomical survey by imaging the entire visible sky in a continuous series of short exposures. Four special purpose
rafts, mounted at the corners of the LSST science camera, contain wavefront sensors and guide sensors. Wavefront
measurements are accomplished using curvature sensing, in which the spatial intensity distribution of stars is measured
at equal distances on either side of focus by CCD detectors. The four Corner Rafts also each hold two guide sensors. The
guide sensors monitor the locations of bright stars to provide feedback that controls and maintains the tracking of the
telescope during an exposure. The baseline sensor for the guider is a Hybrid Visible Silicon hybrid-CMOS detector. We
present here a conceptual mechanical and electrical design for the LSST Corner Rafts that meets the requirements
imposed by the camera structure, and the precision of both the wavefront reconstruction and the tracking. We find that a
single design can accommodate two guide sensors and one split-plane wavefront sensor integrated into the four corner
locations in the camera.
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