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 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.
The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX )at the University of Texas McDonald
Observatory will deploy the Visible Integral-Field Replicable Unit Spectrograph (VIRUS) to survey large areas of
sky. VIRUS consists of up to 192 spectrographs deployed as 96 units. VIRUS units are fiber-fed and are housed in
four enclosures making up the VIRUS Support Structure (VSS). Initial design studies established an optimal array
size and an upper and lower bound on their placement relative to the existing telescope structure. Tradeoffs
considering IFU (optical fiber) length, support structure mass and ease of maintenance have resulted in placement of
four 3 × 8 arrays of spectrograph pairs, about mid-point in elevation relative to the fixed HET structure. Because of
the desire to minimize impact on the modal performance of the HET, the VSS is required to be an independent, selfsupporting
structure and will only be coupled at the base of the telescope. Analysis shows that it is possible to
utilize the existing azimuth drives of the telescope, through this coupling, which will greatly simplify the design and
reduce cost. Each array is contained in an insulated enclosure that will control thermal load by means of heat
exchangers and use of facility coolant supply. Access for installation and maintenance on the top, front, and rear of
the enclosures must be provided. The design and analysis presented in this paper must provide an optimum balance
in meeting the stringent requirements for science and facility constraints such as cost, weight, access, and safety.
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.
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 quantity and length of optical fibers required for the Hobby-Eberly Telescope* Dark Energy eXperiment
(HETDEX) create unique fiber handling challenges. For HETDEX‡, at least 33,600 fibers will transmit light from the
focal surface of the telescope to an array of spectrographs making up the Visible Integral-Field Replicable Unit
Spectrograph (VIRUS). Up to 96 Integral Field Unit (IFU) bundles, each containing 448 fibers, hang suspended from the
telescope's moving tracker located more than 15 meters above the VIRUS instruments. A specialized mechanical system
is being developed to support fiber optic assemblies onboard the telescope. The discrete behavior of 448 fibers within a
conduit is also of primary concern. A life cycle test must be conducted to study fiber behavior and measure Focal Ratio
Degradation (FRD) as a function of time. This paper focuses on the technical requirements and design of the HETDEX
fiber optic support system, the electro-mechanical test apparatus for accelerated life testing of optical fiber assemblies.
Results generated from the test will be of great interest to designers of robotic fiber handling systems for major
telescopes. There is concern that friction, localized contact, entanglement, and excessive tension will be present within
each IFU conduit and contribute to FRD. The test apparatus design utilizes six linear actuators to replicate the movement
of the telescope over 65,000 accelerated cycles, simulating five years of actual operation.
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