The Visible Integral-field Replicable Unit Spectrograph (VIRUS) consists of 156 identical spectrographs fed by 35,000 fibers from the upgraded 10-meter Hobby-Eberly Telescope (HET). VIRUS is in a phased deployment. At the submission of this paper, over half of the units are installed and the full support infrastructure is operational. This paper will describe the VIRUS infrastructure which includes the physical support system, the air cooling, the cryogenic cooling, and the temperature control of VIRUS. The paper will also discuss the various installation, maintenance, and operational procedures based on growing experience with the VIRUS array.
Following a 7-year, multi-million dollar effort to fabricate a 730 kg, 4 element Wide Field Corrector (WFC) for the Hobby-Eberly Telescope (HET) Wide Field Upgrade (WFU), it needed to be transported 820 km to its destination at the McDonald Observatory in West Texas. The final system optical test for the assembly required repeatability in the +/- 2μm range. Due to the size, mass, and ultimate destination of the payload, the only option available for transport was via roadway on a flat-bed trailer. While the route was primarily interstate highway, it presented a great variety of vibrational inputs due to poor paving conditions, and mountain roadways. Consideration also had be given to avoiding high ambient temperatures. Early in the design of the corrector assembly it was assumed that cable isolators would be the key element to isolate the payload from vibrational inputs, however, few documented references were available to provide the assurances required for transporting a load so key to the success of the telescope program. Tests were designed to simulate the load conditions, and inputs and outputs to the test load were measured for verification of the isolator performance. This was followed up with monitoring of vibration throughput during the actual shipment of the WFC. Upon arrival at the destination, the alignment of the assembly was checked and found to have no appreciable change in the alignment. Data and lessons learned are presented on the performance of air-ride trailers as well as the performance of cable isolators.
The Visible Integral-field Replicable Unit Spectrograph (VIRUS) consists of 156 identical spectrographs (arrayed as 78 pairs) fed by 35,000 fibers, each 1.5 arcsec diameter, at the focus of the upgraded 10 m Hobby-Eberly Telescope (HET). VIRUS has a fixed bandpass of 350-550 nm and resolving power R~700. VIRUS is the first example of industrial-scale replication applied to optical astronomy and is capable of surveying large areas of sky, spectrally. The VIRUS concept offers significant savings of engineering effort, cost, and schedule when compared to traditional instruments. The main motivator for VIRUS is to map the evolution of dark energy for the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX‡), using 0.8M Lyman-alpha emitting galaxies as tracers. The VIRUS array is undergoing staged deployment during 2016 and 2017. It will provide a powerful new facility instrument for the HET, well suited to the survey niche of the telescope, and will open up large spectroscopic surveys of the emission line universe for the first time. We will review the production, lessons learned in reaching volume production, characterization, and first deployment of this massive instrument.
VIRUS is a massively replicated spectrograph built for HETDEX, the Hobby Eberly Telescope Dark Energy Experiment. It consists of 156 channels within 78 units fed by 34944 fibers over the 22 arcminute field of the upgraded HET. VIRUS covers a relatively narrow bandpass (350-550nm) at low resolution (R ~ 700) to target the emission of Lyman-alpha emitters (LAEs) for HETDEX. VIRUS is a first demonstration of industrial style assembly line replication in optical astronomy. Installation and testing of VIRUS units began in November of 2015. This winter we celebrated the first on sky instrument activity of the upgraded HET, using a VIRUS unit and LRS2-R (the upgraded facility Low Resolution Spectrograph for the HET). Here we describe progress in VIRUS installation and commissioning through June 2016. We include early sky data obtained to characterize spectrograph performance and on sky performance of the newly upgraded HET. As part of the instrumentation for first science light at the HET, the IFU fed spectrographs were used to test a full range of telescope system functionality including the field calibration unit (FCU).We also use placement of strategic IFUs to map the new HET field to the fiber placement, and demonstrate actuation of the dithering mechanism key to HETDEX observations.
The Hobby-Eberly Telescope (HET) is an innovative large telescope, located in West Texas at the McDonald Observatory. 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. We have completed a major multi-year upgrade of the HET that has substantially increased the pupil size to 10 meters and the field of view to 22 arcminutes by replacing the corrector, tracker, and prime focus instrument package. The new wide field HET will feed the revolutionary integral field spectrograph called VIRUS, in support of the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX§), a new low resolution spectrograph (LRS2), an upgraded high resolution spectrograph (HRS2), and later the Habitable Zone Planet Finder (HPF). The upgrade is being commissioned and this paper discusses the completion of the installation, the commissioning process and the performance of the new HET.
The Visible Integral-Field Replicable Unit Spectrograph (VIRUS) instrument will be installed at the Hobby-Eberly
Telescope† in the near future. The instrument will be housed in two enclosures that are mounted adjacent to the
telescope, via the VIRUS Support Structure (VSS). We have designed the enclosures to support and protect the
instrument, to enable servicing of the instrument, and to cool the instrument appropriately while not adversely affecting
the dome environment. The system uses simple HVAC air handling techniques in conjunction with thermoelectric and
standard glycol heat exchangers to provide efficient heat removal. The enclosures also provide power and data transfer
to and from each VIRUS unit, liquid nitrogen cooling to the detectors, and environmental monitoring of the instrument
and dome environments. In this paper, we describe the design and fabrication of the VIRUS enclosures and their subsystems.
The Hobby-Eberly Telescope (HET) is undergoing an upgrade to increase the field of view to 22 arc-minutes with the
dark energy survey HETDEX the initial science goal [1]. Here we report on the design, alignment, and deployment of a
suite of instruments located at prime focus of the upgraded HET. This paper reviews the integration of motion control
electronics and software and alignment of those electromechanical systems. Use of laser trackers, alignment telescopes,
and other optical alignment techniques are covered. Deployment onto the upgraded telescope is discussed.
The Hobby-Eberly Telescope (HET) is an innovative large telescope located in West Texas at the McDonald Observatory. The HET operates with a fixed segmented primary and has a tracker, which moves the four-mirror optical 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 substantially increase the pupil size to 10 meters (from 9.2 m) and the field of view to 22 arcminutes (from 4 arcminutes) by replacing the corrector, tracker, and prime focus instrument package. In addition to supporting existing instruments, and a new low resolution spectrograph, 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§). The upgrade is being installed and this paper discusses the current status.
A major upgrade of the HET is in process that increases the pupil size to 10 meters and the field of view to 22’ by replacing the four-mirror corrector and prime focus instrument package to track the sidereal and non-sidereal motions of astronomical targets. To support the new payload a new Tracker, comprising 13 axes, and weighing 20 tons, was designed, built and tested at the University of Texas Center for Electromechanics, in Austin, Texas. It was then disassembled and installed on the HET. Structural modifications were performed on the upper hexagon of the telescope structure to support the net increase of 15% to the total mass of the system and maintain fundamental mode performance of 5Hz. Testing in the laboratory, as well as subsequent commissioning tests on the HET, confirm that the Tracker will position the payload to acquire and track within the specified +/-9.5um de-center, +/-15um de-focus, and +/-4.4 arc-sec tip/tilt requirement*.
A major upgrade of the HET is in progress that will substantially increase the pupil size to 10 meters and the field of view to 22 arc-minutes by replacing the spherical aberration corrector. The new Wide Field Corrector is a 4-element assembly weighing 750kg and measuring 1.34 meters diameter by 2.1 meter in length. Special fixtures were required in order to support the mirrors of the Wide-Field Corrector and adapt them to the coaters chamber, during the vacuum coating process. For the 1 meter-class mirrors, the only suitable support interface was located on a 80mm wide cylindrical surface on the periphery of each mirror. The vacuum compatible system had to support the mirrors with the surface facing downward, and accommodate thermal ranges from ambient to 100C without inducing stresses in the substrate. The fixture also had to accommodate washing, as well as support of witness samples during testing and production runs, and provide masking for alignment fixtures in the center apertures of each mirror. Design principles, materials, implementation details, as well as lessons learned are covered*.
VIRUS is the massively replicated fiber-fed spectrograph being built for the Hobby-Eberly Telescope to support
HETDEX (the Hobby-Eberly Telescope Dark Energy Experiment). The instrument consists of 156 identical
channels, fed by 34,944 fibers contained in 78 integral field units, deployed in the 22 arcminute field of the
upgraded HET. VIRUS covers 350-550nm at R ≈ 700 and is built to target Lyman α emitters at 1.9 < z < 3.5 to
measure the evolution of dark energy. Here we present the assembly line construction of the VIRUS spectrographs,
including their alignment and plans for characterization. We briefly discuss plans for installation on the telescope.
The spectrographs are being installed on the HET in several stages, and the instrument is due for completion
by the end of 2014.
The Visible Integral-field Replicable Unit Spectrograph (VIRUS) consists of a baseline build of 150 identical
spectrographs (arrayed as 75 unit pairs) fed by 33,600 fibers, each 1.5 arcsec diameter, at the focus of the upgraded 10
m Hobby-Eberly Telescope (HET). VIRUS has a fixed bandpass of 350-550 nm and resolving power R~700. VIRUS is
the first example of industrial-scale replication applied to optical astronomy and is capable of surveying large areas of
sky, spectrally. The VIRUS concept offers significant savings of engineering effort, cost, and schedule when compared
to traditional instruments.
The main motivator for VIRUS is to map the evolution of dark energy for the Hobby-Eberly Telescope Dark Energy
Experiment (HETDEX), using 0.8M Lyman-α emitting galaxies as tracers. The full VIRUS array is due to be deployed starting at the end of 2014 and will provide a powerful new facility instrument for the HET, well suited to the
survey niche of the telescope, and will open up large area surveys of the emission line universe for the first time.
VIRUS is in full production, and we are about half way through. We review the production design, lessons learned in
reaching volume production, and preparation for deployment of this massive instrument. We also discuss the application
of the replicated spectrograph concept to next generation instrumentation on ELTs.
VIRUS is the visible, integral-field replicable unit spectrograph for the Hobby-Eberly-Telescope (HET) consisting of 75
integral-field-units that feed 150 spectrographs. The full VIRUS instrument features over 33,000 fibres, each projecting
to 1.5 arcseconds diameter on sky, deployed at the prime focus of the upgraded 10m HET. The assembly and acceptance
testing for all IFUs includes microscopic surface quality inspections, astrometry of fibre positions, relative throughput
measurements, focal-ratio-degradation evaluation, and system acceptance using a VIRUS reference spectrograph to
verify the image quality, spectral transmission, stability, or to detect any stray light issues.
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.
The Hobby-Eberly Telescope (HET) Wide-Field Upgrade (WFU) will be equipped with new closed-loop metrology systems to actively control the optical alignment of the new four-mirror Wide-Field Corrector (WFC) as it tracks sidereal motion with respect to the fixed primary mirror. These systems include a tip/tilt camera (TTCam), distance measuring interferometers (DMI), guide probes (GP), and wavefront sensors (WFS). While the TTCam and DMIs are to monitor the mechanical alignment of the WFC, the WFSs and GPs will produce direct measurement of the optical alignment of the WFC with respect to the HET primary mirror. Together, these systems provide fully redundant alignment and pointing information for the telescope, thereby keeping the WFC in focus and suppressing alignment driven field aberrations. In addition to these closed-loop metrology systems, we will have a pupil viewing camera (PVCam) and a calibration wavefront sensor (CWFS). The PVCam will be used for occasional reflectance measurement of the HET primary mirror segments in the standard R,G,B colors. The CWFS will provide the reference wavefront signal against which the other two WFS are calibrated. We describe the current snapshot of these systems and discuss lab/on-sky performance test results of the systems.
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.
The Visible Integral-field Replicable Unit Spectrograph (VIRUS) consists of a baseline build of 150 identical
spectrographs (arrayed as 75 units, each with a pair of spectrographs) fed by 33,600 fibers, each 1.5 arcsec diameter,
deployed over the 22 arcminute field of the upgraded 10 m Hobby-Eberly Telescope (HET). The goal is to deploy 82
units. VIRUS has a fixed bandpass of 350-550 nm and resolving power R~700. VIRUS is the first example of
industrial-scale replication applied to optical astronomy and is capable of spectral surveys of large areas of sky. This
approach, in which a relatively simple, inexpensive, unit spectrograph is copied in large numbers, offers significant
savings of engineering effort, cost, and schedule when compared to traditional instruments.
The main motivator for VIRUS is to map the evolution of dark energy for the Hobby-Eberly Telescope Dark Energy
Experiment (HETDEX) using 0.8M Lyman-α emitting galaxies as tracers. The full VIRUS array is due to be deployed
by early 2014 and will provide a powerful new facility instrument for the HET, well suited to the survey niche of the
telescope. VIRUS and HET will open up wide-field surveys of the emission-line universe for the first time. We present
the production design and current status of VIRUS.
The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) uses a novel technique of replicated spectrographs (VIRUS) to measure dark energy at intermediate redshifts (2 < z < 4). VIRUS contains over 30,000 fibers and over 160 independent and identical channels. Here we report on the construction and characterization of the initial batch of VIRUS spectrograph cameras. Assembly of the first batch of 16 is in progress. A brief overview of the assembly is presented, and where available performance is compared to specification.
The Hobby-Eberly Telescope (HET) is undergoing an upgrade to increase the field of view to 22 arc-minutes with the
dark energy survey HETDEX the initial science goal [1]. Here we report on the engineering development of a suite of
instruments located at prime focus of the upgraded HET. The Prime Focus Instrument Package (PFIP) contains
acquisition, guiding, and wave front sensing instrumentation [2], the fiber feeds for the facility spectrographs (VIRUS,
HRS, MRS, LRS2), and ancillary hardware. This paper reviews the design and functions of the PFIP and presents
details of the mechanical design, integration and testing.
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 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.
A 4-mirror prime focus corrector is under development to provide seeing-limited images for the 10-m aperture Hobby-
Eberly Telescope (HET) over a 22 arcminute wide field of view. The HET uses an 11-m fixed elevation segmented
spherical primary mirror, with pointing and tracking performed by moving the prime focus instrument package (PFIP)
such that it rotates about the virtual center of curvature of the spherical primary mirror. The images created by the
spherical primary mirror are aberrated with 13 arcmin diameter point spread function. The University of Arizona is
developing the 4-mirror wide field corrector to compensate the aberrations from the primary mirror and present seeing
limited imaged to the pickoffs for the fiber-fed spectrographs. The requirements for this system pose several challenges,
including optical fabrication of the aspheric mirrors, system alignment, and operational mechanical stability.
The engineering and design of systems as complex as the Hobby-Eberly Telescope's* new tracker require that multiple
tasks be executed in parallel and overlapping efforts. When the design of individual subsystems is distributed among
multiple organizations, teams, and individuals, challenges can arise with respect to managing design productivity and
coordinating successful collaborative exchanges. This paper focuses on design management issues and current practices
for the tracker design portion of the Hobby-Eberly Telescope Wide Field Upgrade project. The scope of the tracker
upgrade requires engineering contributions and input from numerous fields including optics, instrumentation, electromechanics,
software controls engineering, and site-operations. Successful system-level integration of tracker subsystems
and interfaces is critical to the telescope's ultimate performance in astronomical observation. Software and process
controls for design information and workflow management have been implemented to assist the collaborative transfer of
tracker design data. The tracker system architecture and selection of subsystem interfaces has also proven to be a
determining factor in design task formulation and team communication needs. Interface controls and requirements
change controls will be discussed, and critical team interactions are recounted (a group-participation Failure Modes and
Effects Analysis [FMEA] is one of special interest). This paper will be of interest to engineers, designers, and managers
engaging in multi-disciplinary and parallel engineering projects that require coordination among multiple individuals,
teams, and organizations.
To enable the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX), the McDonald Observatory (MDO) and
the Center for Electro-mechanics (CEM) at the University of Texas at Austin are developing a new HET tracker in
support of the Wide-Field Upgrade (WFU) and the Visible Integral-Field Replicable Unit Spectrograph (VIRUS). The
precision tracker is required to maintain the position of a 3,100 kg payload within ten microns of its desired position
relative to the telescope's primary mirror. The hardware system to accomplish this has ten precision controlled
actuators. Prior to installation on the telescope, full performance verification is required of the completed tracker in
CEM's lab, without a primary mirror or the telescope's final instrument package. This requires the development of a
laboratory test stand capable of supporting the completed tracker over its full range of motion, as well as means of
measurement and methodology that can verify the accuracy of the tracker motion over full travel (4m diameter circle,
400 mm deep, with 9 degrees of tip and tilt) at a cost and schedule in keeping with the HET WFU requirements. Several
techniques have been evaluated to complete this series of tests including: photogrammetry, laser tracker, autocollimator,
and a distance measuring interferometer, with the laser tracker ultimately being identified as the most viable method.
The design of the proposed system and its implementation in the lab is presented along with the test processes, predicted
accuracy, and the basis for using the chosen method*.
The Visible Integral-Field Replicable Unit Spectrograph (VIRUS) is an integral field spectrograph to support
observations for the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). The VIRUS instrument is fed by
more than 33,000 optical fibers and consists of 150 spectrographs in 75 individual, identical units. This paper discusses
the evolution in mechanical design of the VIRUS unit spectrographs to maximize the cost benefit from volume
production. Design features which enable volume manufacture and assembly are discussed. Strategies for reducing
part count while enabling precision alignment are detailed. Design considerations for deployment, operation, and
maintenance en mass at the Hobby-Eberly Telescope are also made. In addition, several enabling technologies are
described including the use of cast aluminum in vacuum housings, use of cast Invar, and processing cast parts for
precision tolerances.
The upcoming Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) has provided motivation for upgrading
the Hobby-Eberly Telescope (HET) at the McDonald Observatory. This upgrade includes an increase in
the field-of-view to accommodate the new and revolutionary Visible Integral-field Replicable Unit Spectrograph
(VIRUS). VIRUS is the instrument designed to conduct the HETDEX survey and consists of 150 individual
integral-field spectrographs fed by 33,600 total optical fibers covering the 22 arc-minute field-of-view of the
upgraded HET. The spectrographs are mounted in four enclosures, each 6.0×3.0×1.4 meters in size. Each
spectrograph contains a CCD detector that must be cryogenically cooled, presenting an interesting cryogenic
and vacuum challenge within the distribution system. In this paper, we review the proposed vacuum jacketed,
thermal siphon, liquid nitrogen distribution system used to cool the array of detectors and discuss recent developments.
We focus on the design, prototyping, and testing of a novel "make-break" thermal connector, built
from a modified cryogenic bayonet, that is used to quickly detach a single spectrograph pair from the system.
The Hobby-Eberly Telescope (HET) will be undergoing a major upgrade as a precursor to the HET Dark Energy
Experiment (HETDEX‡). As part of this upgrade, the Prime Focus Instrument Package (PFIP) will be replaced with a
new design that supports the HETDEX requirements along with the existing suite of instruments and anticipated future
additions. This paper describes the new PFIP control system hardware plus the physical constraints and other
considerations driving its design.
Because of its location at the top end of the telescope, the new PFIP is essentially a stand-alone remote automation island
containing over a dozen subsystems. Within the PFIP, motion controllers and modular IO systems are interconnected
using a local Controller Area Network (CAN) bus and the CANOpen messaging protocol. CCD cameras that are
equipped only with USB 2.0 interfaces are connected to a local Ethernet network via small microcontroller boards
running embedded Linux. Links to ground-level systems pass through a 100 m cable bundle and use Ethernet over fiber
optic cable exclusively; communications are either direct or through Ethernet/CAN gateways that pass CANOpen
messages transparently. All of the control system hardware components are commercially available, designed for rugged
industrial applications, and rated for extended temperature operation down to -10 °C.
The Hobby-Eberly Telescope (HET) Wide-Field Upgrade (WFU) will be equipped with new metrology systems to
actively control the optical alignment of the new four-mirror Wide-Field Corrector (WFC) as it tracks sidereal motion
with respect to the fixed primary mirror. These systems include a tip/tilt sensor (TTS), distance measuring
interferometers (DMI), guide probes (GP), and wavefront sensors (WFS). While the TTS and DMIs are to monitor the
mechanical alignment of the WFC, the WFSs and GPs will produce direct measurement of the optical alignment of the
WFC with respect to the HET primary mirror. Together, these systems provide fully redundant alignment and pointing
information for the telescope, thereby keeping the WFC in focus and suppressing alignment-driven field aberrations.
We describe the current snapshot of these systems and discuss their roles, expected performance, and operation plans.
The Visible Integral-field Replicable Unit Spectrograph (VIRUS) consists of a baseline build of 150 identical
spectrographs (arrayed as 75 units, each with a pair of spectrographs) fed by 33,600 fibers, each 1.5 arcsec diameter,
deployed over the 22 arcminute field of the upgraded 10 m Hobby-Eberly Telescope (HET). The goal is to deploy 96
units. VIRUS has a fixed bandpass of 350-550 nm and resolving power R~700. VIRUS is the first example of
industrial-scale replication applied to optical astronomy and is capable of spectral surveys of large areas of sky. The
method of industrial replication, in which a relatively simple, inexpensive, unit spectrograph is copied in large numbers,
offers significant savings of engineering effort, cost, and schedule when compared to traditional instruments.
The main motivator for VIRUS is to map the evolution of dark energy for the Hobby-Eberly Telescope Dark Energy
Experiment (HETDEX+) using 0.8M Lyman-α emitting galaxies as tracers. The full VIRUS array is due to be deployed
in late 2011 and will provide a powerful new facility instrument for the HET, well suited to the survey niche of the
telescope. VIRUS and HET will open up wide field surveys of the emission-line universe for the first time. We present
the design, cost, and current status of VIRUS as it enters production, and review performance results from the VIRUS
prototype. We also present lessons learned from our experience designing for volume production and look forward to
the application of the VIRUS concept on future extremely large telescopes (ELTs).
The Hobby-Eberly Telescope (HET) is an existing innovative large telescope of 9.2 meter aperture, located at the
McDonald Observatory in West Texas. The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) requires a
major upgrade to the HET, including a substantial increase in the telescope field of view, as well as the development and
integration of a revolutionary new integral field spectrograph called VIRUS. The Visible Integral-Field Replicable Unit
Spectrograph (VIRUS) is an instrument comprising approximately 150 individual IFU-fed spectrographs which will be
mounted on the telescope structure. Each spectrograph has a CDD camera detector package which must be cryogenically
cooled during scientific operation. In order to cool each of these camera systems a liquid nitrogen system has been
proposed and design study completed. The proposed system includes: a liquid nitrogen source, vacuum jacket
distribution system, local storage on the telescope, and distribution under a thermal siphon to the individual
spectrographs and local thermal connectors.
The Hobby-Eberly Telescope (HET) is an innovative large telescope of 9.2 meter aperture, located in West Texas at the
McDonald Observatory. The HET operates with a fixed segmented primary and has a tracker which moves the fourmirror
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 substantially increase the field of view 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 Hobby-Eberly Telescope Dark Energy eXperiment [HETDEX] will employ over 43,000 optical fibers to feed light
to 192 Visible Integral-Field Replicable Unit Spectrographs [VIRUS]. Each VIRUS instrument is fed by 224 fibers. To
reduce cost, the spectrographs are combined into pairs; thus, two bundles of 224 fibers are combined into a single
Integral Field Unit [IFU] of 448 fibers. On the input end the fibers are arranged in a square 'dense-pack' array at the
HET focal surface. At the output end the IFU terminates in two separate linear arrays which provide entry slits for each
spectrometer unit. The IFU lengths must be kept to an absolute minimum to mitigate losses; however, consideration of
overall project cost and duration of the science mission have resulted in the generation of two competing concepts.
Multiple axes of motion are imposed on the IFUs as they span the shortest distance from the focal surface to each
VIRUS unit. Arranging and supporting 96 IFUs, that have a total mass over 450 kg, in a manner that is compatible with
these complex translations, together with the management of accompanying forces on the tracking mechanism of the
HET, presents a significant technical challenge, which is further compounded by wind buffeting. The longer IFU
concept is favored due to overall project cost, but requires tests to assure that the fibers can withstand forces associated
with a height differential of 16.25 meters without FRD losses or breakage.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.