The Hobby-Eberly Telescope (HET) is an innovative large telescope of 9.2 meter aperture, located in West Texas at the
McDonald Observatory (MDO). The HET operates with a fixed segmented primary and has a tracker which moves the
four-mirror corrector and prime focus instrument package to track the sidereal and non-sidereal motions of objects. A
major upgrade of the HET is in progress that will increase the pupil size to 10 meters and the field of view to 22′ by
replacing the corrector, tracker and prime focus instrument package. In addition to supporting the existing suite of
instruments, this wide field upgrade will feed a revolutionary new integral field spectrograph called VIRUS, in support
of the Hobby-Eberly Telescope Dark Energy Experiment (HETDEXχ). This paper discusses the current status of this
upgrade.
In support of the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX), the Center for Electromechanics at The
University of Texas at Austin was tasked with developing the new Tracker and control system to support the HETDEX
Wide-Field Upgrade. The tracker carries the 3,100 kg Prime Focus Instrument Package and Wide Field Corrector
approximately 13 m above the 10 m diameter primary mirror. Its safe and reliable operation by a sophisticated control
system, over a 20 year life time is a paramount requirement for the project. To account for all potential failures and
potential hazards, to both the equipment and personnel involved, an extensive Failure Modes and Effects Analysis
(FMEA) was completed early in the project. This task required participation of all the stakeholders over a multi-day
meeting with numerous follow up exchanges. The event drove a number of significant design decisions and requirements
that might not have been identified this early in the project without this process. The result is a system that has multiple
layers of active and passive safety systems to protect the tens of millions of dollars of hardware involved and the people
who operate it. This paper will describe the background of the FMEA process, how it was utilized on HETDEX, the
critical outcomes, how the required safety systems were implemented, and how they have worked in operation. It should
be of interest to engineers, designers, and managers engaging in complex multi-disciplinary and parallel engineering
projects that involve automated hardware and control systems with potentially hazardous operating scenarios.
A near-infrared spectrograph (NIRS) has been designed and proposed for utilization as a first-light instrument on the
Giant Magellan Telescope (GMT). GMTNIRS includes modular JHK, LM spectrograph units mounted to two sides of a
cryogenic optical bench. The optical bench and surrounding, protective radiation (thermal) shield are containerized
within a rigid cryostat vessel, which mounts to the GMT instrument platform. A support structure on the secondary side
of the optical bench provides multi-dimensional stiffness to the optical bench, to prevent excessive displacements of the
optical components during tracking of the telescope. Extensive mechanical simulation and optimization was utilized to
arrive at synergistic designs of the optical bench, support structure, cryostat, and thermal isolation system. Additionally,
detailed steady-state and transient thermal analyses were conducted to optimize and verify the mechanical designs to
maximize thermal efficiency and to size cryogenic coolers and conductors. This paper explains the mechanical and
thermal design points stemming from optical component placement and mounting and structural and thermal
characteristics needed to achieve instrument science requirements. The thermal and mechanical simulations will be
described and the data will be summarized. Sufficient details of the analyses and data will be provided to validate the
design decisions.
A multi-axis, high precision drive system has been designed and developed for the Wide Field Upgrade to the Hobby-
Eberly Telescope at McDonald Observatory. Design, performance and controls details will be of interest to designers of
large scale, high precision robotic motion devices. The drive system positions the 20-ton star tracker to a precision of
less than 5 microns along each axis and is capable of 4 meters of X/Y travel, 0.3 meters of hexapod actuator travel, and
46 degrees of rho rotation. The positioning accuracy of the new drive system is achieved through the use of highprecision drive hardware in addition to a meticulously tuned high-precision controller. A comprehensive understanding of the drive structure, disturbances, and drive behavior was necessary to develop the high-precision controller. Thorough testing has characterized manufacture defects, structural deflections, sensor error, and other parametric uncertainty. Positioning control through predictive algorithms that analytically compensate for measured disturbances has been developed as a result of drive testing and characterization. The drive structure and drive dynamics are described as well as key results discovered from testing and modeling. Controller techniques and development of the predictive algorithms are discussed. Performance results are included, illustrating recent performance of several axes of the drive system. This paper describes testing that occurred at the Center for Electromechanics in Austin Texas.
A high precision, dual drive system has been designed and developed for the Wide Field Upgrade to the Hobby-Eberly
Telescope* at McDonald Observatory in support of the Hobby-Eberly Telescope Dark Energy Experiment. Analysis,
design and controls details will be of interest to designers of large scale, high precision robotic motion devices. The drive
system positions the 19,000 kg star tracker to a precision of less than 5 microns along its 4-meter travel. While
positioning requirements remain essentially equal to the existing HET, tracker mass increases by a factor greater than 5.
The 10.5-meter long tracker is driven at each end by planetary roller screws, each having two distinct drive sources
dictated by the desired operation: one slowly rotates the screw when tracking celestial objects and the second rotates the
nut for rapid displacements. Key results of the roller screw rotordynamics analysis are presented. A description of the
complex bearing arrangement providing required degrees of freedom as well as the impact of a detailed Failure Modes
and Effects Analysis addressing necessary safety systems is also presented. Finite element analysis results demonstrate
how mechanical springs increase the telescope's natural frequency response by 22 percent. The critical analysis and
resulting design is provided.
The Hobby-Eberly Telescope (HET) is an innovative large telescope of 9.2 meter aperture, located in West Texas at the
McDonald Observatory (MDO). The HET operates with a fixed segmented primary and has a tracker which moves the
four-mirror corrector and prime focus instrument package to track the sidereal and non-sidereal motions of objects. A
major upgrade of the HET is in progress that will increase the pupil size to 10 meters and the field of view to 22' by
replacing the corrector, tracker and prime focus instrument package. In addition to supporting the existing suite of
instruments, this wide field upgrade will feed a revolutionary new integral field spectrograph called VIRUS, in support
of the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). This paper discusses the current status of this
upgrade.
The Wide Field Upgrade presents a five-fold increase in mass for the Hobby-Eberly Telescope's* tracker system. The design of the Hobby-Eberly Telescope places the Prime Focus Instrument Package (PFIP) at a thirty-five degree angle from horizontal. The PFIP and its associated hardware have historically been positioned along this uphill axis (referred to as the telescope's Y-axis) by a single screw-type actuator. Several factors, including increased payload mass and design for minimal light obscuration, have led to the design of a new and novel configuration for the Y-axis screw-drive as part of the tracker system upgrade. Typical screw-drive designs in this load and travel class (approximately 50 kilonewtons traveling a distance of 4 meters) utilize a stationary screw with the payload translating with the moving nut component. The new configuration employs a stationary nut and translating roller screw affixed to the moving payload, resulting in a unique drive system design. Additionally, a second cable-actuated servo drive (adapted from a system currently in use on the Southern African Large Telescope) will operate in tandem with the screw-drive in order to significantly improve telescope safety through the presence of redundant load-bearing systems. Details of the mechanical design, analysis, and topology of each servo drive system are presented in this paper, along with discussion of the issues such a configuration presents in the areas of controls, operational and failure modes, and positioning accuracy. Findings and results from investigations of alternative telescope safety systems, including deformable crash barriers, are also included.
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