On June 9th, 2014, the design/build contract for the Large Synoptic Survey Telescope (LSST) Mount Assembly (TMA) system was awarded to GHESA Ingeniería y Tecnología, S.A. and Asturfeito, S.A. This paper describes the current status of the fabrication, assembly, and verification, along with the logistic plans to ship the mount and equipment to Cerro Pachón in Chile. The design of the mount successfully passed the final design review on January 29, 2016, and is currently under full-scale construction at Asturfeito’s factory in Avilés, Spain.
A detailed description the critical design, fabrication challenges, and the state of testing is presented for the following subsystems:
Azimuth track assembly: The 16-m diameter azimuth track which was fabricated in four large sectors provides the mounting surfaces for the axial and radial hydrostatic bearings. This high precision surface has been machined to high flatness and circularity to meet the high pointing repeatability requirements.
Azimuth structure: The azimuth structure consists of 20 large weldments. These large heat-treated weldments were designed to minimize pointing hysteresis and yet be small enough to be transported by truck.
Elevation structure: The elevation structure consists of a large central ring structure that supports both the M1M3 mirror cell and the optical support for the M2 and camera.
Azimuth mechanicals: The azimuth structure uses 16 linear motors designed and fabricated by Phase Motion Control. All motors, motion control, and capacitor banks have been delivered to the factory and are being prepared for installation
Hydrostatic bearings: All hydrostatic bearings have been designed and fabricated by SKF. The oil supply system was designed by SKF and HYDX hydraulic solutions. The azimuth bearings have been installed and tested using the azimuth platform.
Mount control system hardware and software: The hardware, engineering interface and the software that connects to the telescope control system was designed, assembled, and tested by iK4 Tekniker. This system has been tested using the camera cable wrap and the M1M3 mirror covers at Tekniker. The system is now being installed the factory to begin testing on the assembled mount.
Camera cable wrap: The top end of the telescope requires a complex cable wrap for all of the cameras services and utilities. This wrap successfully passed verification testing and is now installed on the telescope top end.
M1M3 mirror cover: This unique four-fan design was developed and tested at ik4 Tekniker. After verification at Tekniker it was shipped to the factory and is now assembled on the azimuth ring assembly.
Utility distribution: Fluid distribution system includes a large network of coolants, refrigerants, air, fibers optics, and data communication lines. The unique challenges to routing throughout the telescope all of these services required coordinated design and implementation and four cable wraps. The azimuth cable wrap is a motorized drape design designed by Empresarios Agrupados and Tekniker. The two elevation drapes were designed by Empresarios Agrupados and Kabbleschlepp.
An overview of the logistics required for shipping, ground transportation, and cranes will be described.
The Zwicky Transient Facility (ZTF) will be a major upgrade to the 48” Schmidt Camera at Palomar Observatory, which was initially commissioned in 1948. Although the optical design for ZTF is a relatively small part of the project, system requirements placed special constraints on the optical design. This paper presents the optical design for ZTF as well as the system requirements that drove the optical design.
Proc. SPIE. 9911, Modeling, Systems Engineering, and Project Management for Astronomy VI
KEYWORDS: Actuators, Telescopes, Mirrors, 3D modeling, Space telescopes, Finite element methods, Computer aided design, Large Synoptic Survey Telescope, Large Synoptic Survey Telescope, Systems modeling, Solid modeling
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 telescope<sup>1,2,3</sup> mount assembly (TMA). On June 9<sup>th</sup>, 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.
On 15 October 2006 a large earthquake damaged both telescopes at Keck observatory resulting in weeks of observing downtime. A significant portion of the downtime was attributed to recovery efforts repairing damage to telescope bearing journals, radial pad support structures and encoder subsystems. Inadequate damping and strength in the seismic restraint design and the lack of break-away features on the azimuth radial pads are key design deficiencies. In May, 2011 a feasibility study was conducted to review several options to enhance the protection of the telescopes with the goal to minimize the time to bring the telescopes back into operation after a large seismic event. At that time it was determined that new finite element models of the telescope structures were required to better understand the telescope responses to design earthquakes required by local governing building codes and the USGS seismic data collected at the site on 15 October 2006. These models were verified by comparing the calculated natural frequencies from the models to the measured frequencies obtained from the servo identification study and comparing the time history responses of the telescopes to the October 2006 seismic data to the actual observed damages. The results of two finite element methods, response spectrum analysis and time history analysis, used to determine seismic demand forces and seismic response of each telescope to the design earthquakes were compared. These models can be used to evaluate alternate seismic restraint design options for both Keck telescopes.
Strategies for thermal control of the 6.5-meter diameter borosilicate honeycomb primary (M1) mirror at the MMT
Observatory have included: 1) direct control of ventilation system chiller setpoints by the telescope operator, 2) semiautomated
control of chiller setpoints, using a fixed offset from the ambient temperature, and 3) most recently, an
automated temperature controller for conditioned air. Details of this automated controller, including the integration of
multiple chillers, heat exchangers, and temperature/dew point sensors, are presented here. Constraints and sanity checks
for thermal control are also discussed, including: 1) mirror and hardware safety, 2) aluminum coating preservation, and
3) optimization of M1 thermal conditions for science acquisition by minimizing both air-to-glass temperature
differences, which cause mirror seeing, and internal glass temperature gradients, which cause wavefront errors.
Consideration is given to special operating conditions, such as high dew and frost points. Precise temperature control of
conditioned ventilation air as delivered to the M1 mirror cell is also discussed. The performance of the new automated
controller is assessed and compared to previous control strategies. Finally, suggestions are made for further refinement
of the M1 mirror thermal control system and related algorithms.
Over the past three decades, the staff of the MMT observatory used a variety of techniques to predict the summit wind
characteristics including wind tunnel modeling and the release of smoke bombs. With the planned addition of a new
instrument repair facility to be constructed on the summit of Mt. Hopkins, new computational fluid dynamic (CFD)
models were made to determine the building's influence on the thermal environment around the telescope. The models
compared the wind profiles and density contours above the telescope enclosure with and without the new building. The
results show the steeply-sided Mount Hopkins dominates the summit wind profiles. In typical winds, the height of the
telescope remains above the ground layer and is sufficiently separated from the new facility to insure the heat from the
new building does not interfere with the telescope. The results also confirmed the observatories waste heat exhaust duct
location needs to be relocated to prevent heat from being trapped in the wind shadow of the new building and lofting
above the telescope. These useful models provide many insights into understanding the thermal environment of the
The Laser Adaptive Optics system of the 6.5 m MMT telescope has now been commissioned with Ground Layer
Adaptive Optics operations as a tool for astronomical science. In this mode the wavefronts sampled by each of five laser
beacons are averaged, leading to an estimate of the aberration in the ground layer. The ground layer is then compensated
by the deformable secondary mirror at 400 Hz. Image quality of
0.2-0.3 arc sec is delivered in the near infrared bands
from 1.2-2.5 μm over a field of view of 2 arc minutes. Tomographic wavefront sensing tests in May 2010 produced open
loop data necessary to streamline the software to generate a Laser Tomography Adaptive Optics (LTAO) reconstructor.
In addition, we present the work being done to achieve optimal control PID wavefront control and thus increase the
disturbance rejection frequency response for the system. Finally, we briefly describe plans to mount the ARIES near
infrared imager and echelle spectrograph, which will support the 2 arc min ground-layer corrected field and will exploit
the diffraction limit anticipated with LTAO.
The 6.5m MMT telescope currently has three focal configurations. The f/5 optical configuration has a system of optical
baffles to prevent stray light from entering the focal plane. The system consists of a cone baffle supported on the
secondary (M2) structure and set of concentric rings suspended between the secondary and the primary (M1). This paper
reviews the optical configurations, mechanical design, alignment, installation, and measured performance of the system.
The Large Binocular Telescope Observatory (LBT) encoded their elevation and azimuth axis with Farrand Inductosyn tape encoders. The authors present the unique design requirements to achieve high precision tracking and pointing. This paper describes the mechanical hardware used to meet these goals. The telescope elevation axis uses two tapes to encode 14m diameter tracks machined into the optical support structure. Each elevation tape is encoded with two custom read heads machined to fit the surfaces. The read heads are mounted on spring loaded flexures with rollers to insure consistent alignment of the heads to the tapes and to allow for radial run out. The azimuth is encoded with two tapes set end to end. Four custom read heads have been installed on similar flexures. The tape mounting hardware has been designed to maintain uniform and constant tension over the lifetime of the tape. We also describe the equipment and procedures used during installation to insure uniform tension of the tape in the track.
The 6.5m Multiple Mirror Telescope Observatory (MMTO) installed a new f/5 secondary system in April 2003. We describe the design and performance of the mirror cell and supports for the 1.7 m diameter Zerodur mirror. Pneumatic actuators divided into one lateral and three axial zones support this 318 kg mirror. The control feedback for the high bandwidth pressure transducers for these four zones is obtained from six load cells attached to rigid positioning rods. The mirror cell includes thermal control, force limiters, passive supports, installation and handling, and alignment metrology. Optical test results are described and compared to the original design specifications.
Originally commissioned in 1979, the Multiple Mirror Telescope was a highly innovative and successful facility that pioneered many of the technologies that are used in the new generation of 8 to 10 m class telescopes. After 19 years of operations the MMT was decommissioned in March of 1998: the enclosure was modified, the optics support structure was replaced, and a single 6.5-meter primary mirror was installed and aluminized in-situ. First light for the new MMT was celebrated on May 13, 2000. Operations began with an f/9 optical configuration compatible with existing instruments. Work has continued commissioning two new optical configurations that will serve a suite of new instruments: an f/15 deformable secondary mirror and adaptive optics facility that has obtained diffraction-limited images; and an f/5.4 secondary mirror and refractive corrector that provides a one-degree diameter field of view. The wide-field instrument suite includes two fiber-fed bench spectrographs, a robotic fiber positioner, and a wide-field imaging camera.
We present results from a study of the performance of the MMT
thermal system. The 6.5-m MMT primary mirror consists of a
borosilicate honeycomb structure that is thermally controlled with
a forced-air ventilation system. We will give an overview of both
the measurement and control systems. Our goal is to define an
algorithm for control of the ventilation system such that the
primary mirror temperature closely tracks ambient while minimizing
thermal gradients. Future work will include a study of correlations
between the thermal state of the primary mirror and both seeing and
wavefront errors. The thermal system is currently controlled by
the telescope operators, but the results from this work will assist in fully automating the system.
We describe the active support system and optimization of support forces for the 6.5 m primary mirror for the Multiple Mirror Telescope Conversion. The mirror was figured to an accuracy of 26 nm rms surface error, excluding certain flexible bending modes that will be controlled by support forces in the telescope. On installation of the mirror into its telescope support cell, an initial optimization of support forces is needed because of minor differences between the support used during fabrication and that in the telescope cell. The optimization is based on figure measurements made interferometrically in the vibration- isolated test tower of the Steward Observatory Mirror Lab. Actuator influence functions were determined by finite- element analysis and verified by measurement. The optimization is performed by singular value decomposition of the influence functions into normal modes. Preliminary results give a wavefront accuracy better than that of the atmosphere in 0.11 arcsecond seeing.
Operated by the Multiple Mirror Telescope Observatory (MMTO), the multiple mirror telescope (MMT) is funded jointly by the Smithsonian Institution (SAO) and the University of Arizona (UA). The two organizations equally share observing time on the telescope. The MMT was dedicated in May 1979, and is located on the summit of Mt. Hopkins (at an altitude of 2.6 km), 64 km south of Tucson, Arizona, at the Smithsonian Institution's Fred Lawrence Whipple Observatory (FLWO). As a result of advances in the technology at the Steward Observatory Mirror Laboratory for the casting of large and fast borosilicate honeycomb astronomical primary mirrors, in 1987 it was decided to convert the MMT from its six 1.8 m mirror array (effective aperture of 4.5 m) to a single 6.5 m diameter primary mirror telescope. This conversion will more than double the light gathering capacity, and will by design, increase the angular field of view by a factor of 15. Because the site is already developed and the existing building and mount will be used with some modification, the conversion will be accomplished for only about $20 million. During 1995, several major technical milestones were reached: (1) the existing building was modified, (2) the major steel telescope structures were fabricated, and (3) the mirror blank was diamond wheel ground (generated). All major mechanical hardware required to affect the conversion is now nearly in hand. Once the primary mirror is polished and lab-tested on its support system, the six-mirror MMT will be taken out of service and the conversion process begun. We anticipate that a 6 - 12 month period will be required to rebuild the telescope, install its optics and achieve f/9 first light, now projected to occur in early 1998. The f/5.4 and f/15 implementation will then follow. We provide a qualitative and brief update of project progress.
In order to collect as much information as possible from the universe, the latest generation of astronomical telescopes have exceptionally large diameter primary mirrors. This dramatic increase in mirror diameter, and corresponding increase in weight, has placed ever increasing demands on the technical performance of the mirror support system. In this paper the authors discuss the mechanical design, fabrication, and testing of the six servo controlled position-actuators that mechanically link the 6.5 m honeycomb mirror to six rigidly reinforced locations in the multiple mirror telescope conversion mirror cell. During telescope operation, these adjustable length actuators assure that the natural frequency of the mirror does not degrade the optical performance of the telescope. Flexures are provided on each end of the actuators to minimize any moments applied to the attachment of the actuator to the mirror. These actuators provide a precise measurement of the external forces applied to the mirror, such as wind loads, for the control of the pneumatic force system that supports the weight of the mirror. The total length of each actuator can be measured to sub-micron resolution upon request. Each actuator has a reliable fail-safe system that limits the compressive and tensile forces that can be applied to the mirror. The position-actuators meet all of the above technical specifications in both tension and compression.
This paper will describe and discuss the methods which are being developed to support the large borosilicate honeycomb mirrors from the Steward Observatory Mirror Lab which are being used in the MMT 6.5 m conversion and the Large Binocular Telescope. The technique is similar to previous work carried out for the 3.5 m Phillips Lab mirror support.