The Giant Magellan Telescope (GMT) primary mirror subsystem (M1S) consists of seven 8.4m diameter borosilicate primary mirrors that must be maintained at the ambient nighttime air temperature as it changes throughout the observing night to prevent seeing effects at the mirror surface. Additionally, thermal gradients internal to the mirrors must be minimized to prevent figure errors caused by distortions of the mirror due to the non-zero thermal expansion coefficient of the glass. To address these requirements, the GMT M1S team is fabricating a prototype thermal control system design that consists of a sub-critical refrigeration system utilizing high pressure (~30 to ~60 bar) CO2 (R744) refrigerant. This paper describes the design and status of the M1 Subsystem Thermal Control (M1STC).
GMTO has developed a full-scale prototype of the cell that can house an 8.4-meter borosilicate mirror. This test cell is populated with all the active support control hardware and a mass simulator that simulates the mirror weight and the moment of inertia. GMTO has implemented the control software with all the core features needed to operate the active support system. A series of tests have been carried out to verify the functions, performance, and safety of the active support control system. The tests were carried out at several different orientations of the cell to demonstrate that the active support system works with the changing zenith angle and location of the mirror on the telescope mount. This paper describes the results of important safety and dynamic response tests of the active support system.
Large aperture telescopes require active control to maintain focus, collimation, and correct figure errors in the Primary Mirror (M1) due to gravity and thermal deformations. The Giant Magellan Telescope M1 active optics and thermal control systems called the M1 Subsystem (M1S) consists of the hardware and software that controls the shape, position, and thermal state of each mirror segment. A full-scale off-axis M1S prototype called the Test Cell is being fabricated and tested. The primary objective of the Test Cell is to mitigate risk by verifying that the mirror figure and position can be controlled within the image quality error budget and that the thermal control system vibration is within its system level allocation. The M1S components for the active optics support system have been fabricated, assembled, tested at the component level, and integrated into the Test Cell. The team completed the Test Readiness Review and started system level testing with the M1 Device Control Software. Lessons learned throughout the component and integrated system testing of the Test Cell will be incorporated into the M1S design for the production phase. This paper will summarize the progress of the Test Cell and results presented at the Test Readiness Review.
Large aperture telescopes require active control to maintain focus, collimation, and correct figure errors in the Primary Mirror (M1) due to gravity and thermal deformations. The Giant Magellan Telescope (GMT) M1 active optics subsystem consists of the hardware and software that controls the shape, position, and thermal state of each mirror segment. Pneumatic force actuators support the weight and control the surface figure while linear position actuators control the six solid-body degrees of freedom of each mirror segment. A forced convection system comprised of fan-heat exchanger units control the mean temperature and thermal gradient of each mirror segment. The M1 Subsystem design leverages existing technology and employs innovations driven by more demanding requirements compared to heritage systems. These differences led to the identification of three key GMT project risks: determining if the vibration environment induced by the fan-heat exchanger units and the error in the applied influence functions required to shape the mirror are within image quality budget allocations. The third risk is incorporating damping to the force actuators to meet the seismic requirements. GMT is currently mitigating these risks by integrating a fully functional off-axis M1 Test Cell at the University of Arizona’s Richard F. Caris Mirror Lab. This paper summarizes our requirements and design presented at the M1 Subsystem Preliminary Design Review in June 2019, describes our risk burn-down strategy for the M1 Subsystem, and presents our integration and test progress of the M1 Test Cell.
The Primary Mirror Device Control System (M1 DCS) is one of the many Device Control Systems (DCS) included in the Giant Magellan Telescope (GMT) control system and is responsible for the overall control and operation of the GMT primary mirror segments. The primary mirror is composed of seven 8.4m diameter segments, six off-axis and one in the center. The active support system of each segment comprises 170 support actuators for the off-axis segments and 154 actuators for the center segment to control the mirror figure, and 6 hardpoints to control the six degrees of freedom of rigid body motion. The software design follows a component model-based architecture, implemented using the GMT core software frameworks. Software components of the M1 DCS are specified using a custom Domain Specific Language (DSL) and inherit all key features of the core components such as communication ports, default behaviors, telemetry, logs, alarms, faults, state machines and engineering user-interface without the need of a separate implementation. The communication between the real time software and the controlled devices is implemented by an EtherCAT Fieldbus in a ring topology. This master-slave standard protocol enables the control system to reach 100 Hz closed loop rate for active support control. This paper describes the software of the M1 DCS, the tests performed with different software and hardware simulators, and the strategy to ensure software readiness with the final optical mirror.
The new Keck Observatory Telescope Control System is now deployed for regular operations on Keck 2 and the deployment on both telescopes, Keck 1 and Keck 2, is expected to be completed by the time this paper is published. Two new instruments, KCWI and NIRES, were commissioned with the new control system on Keck 2. The upgrade project was a major undertaking replacing the original software architecture and modules, as well as many obsolete hardware components. During the long testing phase, we discovered deficiencies, which we corrected with modifications of the original design. This paper gives a summary of the achieved performance, the issues involving deploying a new system while remaining in full operation, and lessons learned in design and implementation of such a large system.
Since the start of operations in 1993, the twin 10 meter W. M. Keck Observatory telescopes have continued to maximize their scientific impact and to produce transformative discoveries that keep the observing community on the frontiers of astronomical research. Upgraded capabilities and new instrumentation are provided though collaborative partnerships with Caltech and UC instrument development teams. The observatory adapts and responds to the observers’ evolving needs as defined in the observatory’s strategic plan, periodically refreshed in collaboration with the science community. This paper summarizes the performance of recently commissioned infrastructure projects, technology upgrades, and new additions to the suite of instrumentation at the observatory. We will also provide a status of projects currently in the design or development phase, and since we need to keep our eye on the future, we mention projects in exploratory phases that originate from our strategic plan. Recently commissioned projects include telescope control system upgrades, OSIRIS spectrometer and imager upgrades, and deployments of the Keck Cosmic Web Imager (KCWI), the Near-Infrared Echellette Spectrometer (NIRES), and the Keck I Deployable Tertiary Mirror (KIDM3). Under development are upgrades to the NIRSPEC instrument and adaptive optics (AO) system. Major instrumentation in design phases include the Keck Cosmic Reionization Mapper and the Keck Planet Finder. Future instrumentation studies and proposals underway include a Ground Layer Adaptive Optics system, NIRC2 upgrades, the energy sensitive instrument KRAKENS, an integral field spectrograph LIGER, and a laser tomography AO upgrade. Last, we briefly discuss recovering MOSFIRE and its return to science operations.
Launched in 2009, Keck Observatory’s Telescope Control System Upgrade (TCSU) project set out to improve Keck’s telescope pointing, tracking, and offsetting performance as well as increase maintainability and reliability. The project went online full time on the Keck 2 telescope in October 2017 and on the Keck 1 telescope in March 2018 after a notable delay due to a re-design of the azimuth and elevation encoder mounting systems. This paper discusses the details and challenges of implementing this large and complicated system while never requiring a shutdown of either telescope. The TCSU project replaced all of the major elements of the telescope controls, rotator and secondary mirror controls, and safety system. National Instrument’s reconfigurable I/O technology (i.e. NI RIO), with their embedded field programmable gate arrays (FPGAs), are used as the core of the telescope’s digital velocity control loop, structural filter, and tachometer filter. They were also used to create a monitoring and safety system for the rotator velocity controller as well as reading the newly installed tilt meters used to greatly improve pointing performance. Delta Tau’s family of “Brick” programmable multi-axis controllers, i.e. PMAC or BRICK, are used to control the rotator and secondary mirror. They enable better tuning and faster slew speeds for these subsystems. An Allen Bradley’s ControlLogix® controller and the family of FLEX™ Input/Output (IO) modules were used to create a distributed safety system able to handle a wide variety of signal types. This technology refresh based on commercial off the shelf equipment replaced much of our obsolete and custom equipment. A significant part of the project was the installation of new telescope azimuth and elevation position encoders based on Heidenhain’s 40 micron grading tape scales. Interpolated to a 10 nanometer resolution, the new encoders provide true 4 mas resolution in azimuth and 1 mas resolution in elevation. This is a big improvement to Keck’s position sensing when compared to the old rotary incremental encoders. The installation required a significant amount of mechanical infrastructure to house them. Additionally, two tilt meters were installed to sense the telescope’s varying vertical angle as a function of azimuth, mainly due to the azimuth bearing’s axial runout. The encoders and tilt meters are the primary reason for achieving the greatly improved pointing and tracking performance [1]. Finally, a switching solution using solid state relays and dual network switches was installed to provide seamless and rapid switching between the old and new control systems during commissioning. Although this component is a simple design and does not boast of any new technology, it is one of the key components that enabled the successful testing of the new equipment while keeping the old system operational as a backup for night time observing as well as for baseline performance comparisons. It allowed us to switch a variety of signal types and was very cost effective when compared to available products.
Pointing and tracking performance is one of the key metrics that characterize a telescope's overall efficiency. The pointing performance of the Keck telescopes, which use rotary friction encoders to provide position feedback to the control system, has been surpassed by newer large telescopes with more precise encoder systems. While poor tracking can be compensated with guiding, poor blind pointing performance can lead to loss of observing time. In this paper we present a history of the efforts to reduce the impact of poor pointing, as well as the improvements achieved after the installation of new tape encoders. We will discuss the calibration and testing methods and the tools for monitoring and maintaining the desired pointing performance. A comparative analysis of the pointing performance before and after the telescope control system upgrade will also be presented.
KEYWORDS: Electroluminescence, Control systems, Telescopes, Computer programming, Radium, Phase modulation, Linear filtering, Amplifiers, Field programmable gate arrays, Analog electronics
The Keck I and II telescopes have been operational respectively since 1990 and 1996. Operational improvements are
sought to decrease the settling time in response to short moves. The structural response of the open loop system has been
re-identified and the mount control design has been re-examined. Changes to the mount control compensators and
command shaping architecture have been proposed in order to achieve improved response. Results from these studies are
presented, both theoretical and experimental.
Natural Guide Star (NGS) and Laser Guide Star (LGS) Adaptive Optics (AO) have been offered for routine science
operations to the W. M. Keck Observatory community since 2000 and late 2004, respectively. The AO operations team
is now supporting ~100 nights of AO observing with four different instruments, including over fifty nights of LGS AO
per semester. In this paper we describe improvements to AO operations to handle the large number of nights and to
accommodate the recent upgrade to the wavefront sensor and wavefront controller. We report on the observing
efficiency, image quality, scientific productivity, impact analysis from satellite safety procedures and discuss the support
load required to operate AO at Keck. We conclude the paper by presenting our plans for dual LGS AO operations with
Keck I - Keck II LGS, starting in 2009.
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