The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 35 million galaxies and quasars over 14000 sq deg will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fiber optic positioners. The fibers in turn feed ten broad-band spectrographs. We will describe the extensive preparations of the Mayall telescope and its environs for DESI, and will report on progress-to-date of the installation of DESI itself.
The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 40 million galaxies over 14,000 sq. deg. will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fiber optic positioners. The fibers in turn feed ten broad-band spectrographs. We describe the ProtoDESI experiment, planned for installation and commissioning at the Mayall telescope in the fall of 2016, which will test the fiber positioning system for DESI. The ProtoDESI focal plate, consisting of 10 fiber positioners, illuminated fiducials, and a guide, focus and alignment (GFA) sensor module, will be installed behind the existing Mosaic prime focus corrector. A Fiber View Camera (FVC) will be mounted to the lower surface of the primary mirror cell and a subset of the Instrument Control System (ICS) will control the ProtoDESI subsystems, communicate with the Telescope Control System (TCS), and collect instrument monitoring data. Short optical fibers from the positioners will be routed to the back of the focal plane where they will be imaged by the Fiber Photometry Camera (FPC) or back-illuminated by a LED system. Target objects will be identified relative to guide stars, and using the GFA in a control loop with the ICS/TCS system, the guide stars will remain stable on pre-identified GFA pixels. The fiber positioners will then be commanded to the target locations and placed on the targets iteratively, using the FVC to centroid on back-illuminated fibers and fiducials to make corrective delta motions. When the positioners are aligned with the targets on-sky, the FPC will measure the intensities from the positioners’ fibers which can then be dithered to look for intensity changes, indicating how well the fibers were initially positioned on target centers. The final goal is to operate ProtoDESI on the Mayall telescope for a 6-hour period during one night, successfully placing targets on the intended fibers for the duration of a typical DESI science exposure.
Motivated by a desire to improve the KPNO Mayall 4m telescope’s pointing and tracking performance prior to the start of the DESI installation and by a need to improve the maintainability of its telescope control system (TCS), we recently completed a major modernization of that system based heavily on recent changes made at the CTIO Blanco 4m, as described by Warner et al (2012). We describe here the things we did differently from the Blanco upgrade. We also present results from the as-built performance of the new servo and pointing systems.
The Dark Energy Spectroscopic Instrument (DESI) is under construction for installation on the Mayall 4 Meter telescope. The use of a liquid cooling system is proposed to maintain the DESI prime focus assembly temperature within ±1°C of ambient. Due to concerns of fluid deposition onto optical surfaces from possible leaks, systematic tests were performed of the effects on first surface aluminized mirrors of ethylene glycol and two other candidate coolants. Objective measurement of scattering and reflectivity was an important supplement to visual inspection. Rapid cleanup of a coolant spill followed by a hand wash of the mirror limited surface degradation to the equivalent of a few months of general environmental exposure. Prolonged exposure to corrosive coolants dissolved the aluminum, necesitating mirror recoating.
The Mayall 4-meter telescope recently went through a major modernization of its telescope control system in preparation for DESI. We describe MPK (Mayall Pointing Kernel), our new software for telescope control. MPK outputs a 20Hz position-based trajectory with a velocity component, which feeds into Mayall’s new servo system over a socket. We wrote a simple yet realistic servo simulator that let us develop MPK mostly without access to real hardware, and also lets us provide other teams with a Mayall simulator as test bed for development of new instruments. MPK has a small core comprised of prioritized, soft real-time threads. Access to the core’s services is via MPK’s main thread, a complete, interactive Tcl/Tk shell, which gives us the power and flexibility of a scripting language to add any other features, from GUIs, to modules for interaction with critical subsystems like dome or guider, to an API for networked clients of a new instrument (e.g., DESI). MPK is designed for long term maintainability: it runs on a stock computer and Linux OS, and uses only standard, open source libraries, except for commercial software that comes with source code in ANSI C/C++. We discuss the technical details of how MPK combines the Reflexxes motion library with the TCSpk/TPK pointing library to generically handle any motion requests, from slews to offsets to sidereal or non-sidereal tracking. We show how MPK calculates when the servos have reached a steady state. We also discuss our TPOINT modeling strategy and report performance results.
TripleSpec 4 (TS4) is a near-infrared (0.8um to 2.45um) moderate resolution (R ~ 3200) cross-dispersed spectrograph
for the 4m Blanco Telescope that simultaneously measures the Y, J, H and K bands for objects reimaged
within its slit. TS4 is being built by Cornell University and NOAO with scheduled commissioning in 2015.
TS4 is a near replica of the previous TripleSpec designs for Apache Point Observatory's ARC 3.5m, Palomar
5m and Keck 10m telescopes, but includes adjustments and improvements to the slit, fore-optics, coatings and
the detector. We discuss the changes to the TripleSpec design as well as the fabrication status and expected
sensitivity of TS4.
In an inauspicious start to the ultimately very successful installation of the Dark Energy Camera on the V. M. Blanco 4- m telescope at CTIO, the light-weighted Cer-Vit 1.3-m-diameter secondary mirror suffered an accident in which it fell onto its apex. This punched out a central plug of glass and destroyed the focus and tip/tilt mechanism. However, the mirror proved fully recoverable, without degraded performance. This paper describes the efforts through which the mirror was repaired and the tip/tilt mechanism rebuilt and upgraded. The telescope re-entered full service as a Ritchey- Chrétien platform in October of 2013.
The KPNO Nicholas U. Mayall 4-meter telescope is to be the host facility for the Dark Energy Spectroscopic Instrument (DESI). DESI will record broadband spectra simultaneously for 5000 objects distributed over a 3-degree diameter field of view; it will record the spectra of approximately 20 million galaxies and quasi-stellar objects during a five-year survey. This survey will improve the combined precision of measurement on the dark energy equation of state today (w<sub>0</sub>) and its evolution with redshift (w<sub>a</sub>) by approximately a factor of ten over existing spectroscopy baryon acoustic oscillation surveys (e.g., BOSS<sup>1</sup>) in both co-moving volume surveyed and number of galaxies mapped. Installation of DESI on the telescope is a complex procedure, involving a complete replacement of the telescope top end, routing of massive fiber cables, and installation of banks of spectrographs in an environmentally-controlled lab area within the dome. Furthermore, assembly of the instrument and major subsystems must be carried out on-site given their size and complexity. A detailed installation plan is being developed early in the project in order to ensure that DESI and its subsystems are designed so they can be safely and efficiently installed, and to ensure that all telescope and facility modifications required to enable installation are identified and completed in time.
Filters for astronomical imaging traditionally have a simple bandpass that admits (more or less equally) all the
photons within some bandwith ▵λ around some central wavelength λ0. However, there are situations where
not all photons are equally desirable. We plan to develop and apply multiband filters for practical astronomical
application. A multiband filter is a bandpass filter whose transmission dips to zero at select, undesired wavelength
ranges. Anticipated applications include (i) OH-suppressing filters, especially in the J band (λc ≈ 1.2μm); (ii)
economy of filter slots through multi-band filters used in series with broad blocking filters; and (iii) efficient
searches for object classes with highly structured spectra. We present the design and anticipated photometric
properties of a prototype reduced-background J<sub>R</sub> filter, which we plan to buy and test in 2010.
As astronomical instruments have increased in complexity, cost and production time, sharing a major instrument
between telescopes has become an attractive alternative to duplication. This requires solving technical and logistical
problems of transportation, transferring operational support knowledge between on-site staffs, and developing effective
responses to in-service problems at a different site. The infrared camera NEWFIRM has been operated for two years on
the 4-m Mayall telescope of Kitt Peak National Observatory in Arizona. We have recently temporarily moved it to the 4-
m Blanco telescope of Cerro Tololo Interamerican Observatory in Chile for a limited period of operation. We describe
here our solutions to the challenges involved in relocating this major in-service cryogenic instrument, with an emphasis
on "lessons learned" to date.
NEWFIRM is the wide-field infra-red mosaic camera just delivered and commissioned on the Mayall 4-m telescope
on Kitt Peak. As with other major instrumentation projects, the software was part of a design, development,
implementation and delivery strategy. In this paper, we describe the final implementation of the NEWFIRM
software from acquisition within a MONSOON controller environment, directed by the observation control system,
to the quick-look functionality at the telescope and final delivery of standardized data products via the pipeline.
NEWFIRM is, therefore, the culmination of several years of design and development effort on several fronts.
NEWFIRM, the widefield infrared camera for the NOAO 4-m telescopes, saw first light in February 2007 and is now in
service as a general user instrument. Previous papers have described it conceptually and presented design details. We
discuss experience gained from assembly, laboratory testing, and on-sky commissioning. We present final system
performance characteristics and summarize science use in its the first semester of general availability. NEWFIRM has
met its requirement to provide a high efficiency observing system, optimized end-to-end for survey science.
The Infrared Side Port Imager ISPI is a facility infrared imager for
the CTIO Blanco 4-meter telescope. ISPI has the following capabilities: 1-2.4 micron imaging with an 2K x 2K HgCdTe array, 0.3
arcsec/pixel sampling matched to typical f/8 IR image quality of ~0.6
arcsec and a 10.5 x 10.5 arcmin field of view. First light with ISPI
was obtained on September 24 2002, and since January 2003 ISPI has
been in operation as a common user instrument. In this paper we discuss operational aspects of ISPI, the behavior of the array and we report on the performance of ISPI during the first one and half year of operation.
The NEWFIRM program will provide a widefield IR imaging system optimized for survey programs on the NOAO 4-m telescopes in Arizona and Chile. The camera images a 28 x 28 arcminute field of view over 1-2.4 microns wavelength range with a 4K x 4K pixel array mosaic. We present an overview of camera design features including optics design, manufacture, and mounting; control of internal flexure between input and output focal planes; mosaic array mount design; and thermal design. We also discuss the status of other projects within the program: array control electronics, observation and pipeline reduction software, and production of the science grade array complement. The program is progressing satisfactorily and we expect to deliver the system to the northern 4-m telescope in 2005.
We present case studies on the application of passive compensation in two large astronomical instruments: the Gemini Near Infrared Spectrograph (GNIRS), including actual performance, and the NOAO Extremely Wide Field Infrared Mosaic (NEWFIRM) camera. Image motion due to gravity flexure is a problem in large astronomical instruments. We present solutions for two different cases using passive mechanical compensation of the optical train. For the Gemini Near Infrared Spectrograph (GNIRS), articulation of a single sensitive optic is used. Adjustable cantilevered weights, designed to respond to specific gravity components, are employed to drive tilt flexures connected to the collimator mirror. An additional requirement is that cryocooler vibration must not dynamically excite this mirror. Performance testing of the complete instrument shows that image motion has been satisfactorily compensated. Some image blur due to dynamic excitation by the cryocoolers was noted. A successful damping scheme has been developed experimentally. For the NOAO Extremely Wide Field Infrared Mosaic camera (NEWFIRM), the entire optical support structure is mechanically tuned to deflect and rotate precisely as a rigid body relative to the telescope focal plane. This causes the optical train to remain pointed at a fixed position in the focal plane, minimizing image motion on the science detector. This instrument is still in fabrication.
Wide field-of-view, high-resolution near-infrared cameras on 4-m class telescopes have been identified by the astronomical community as critical instrumentation needs in the era of 8-m and larger telescopes. Acting as survey instruments, they will provide the input source discoveries for large-telescope follow-up observations. The NOAO Extremely Wide Field Infrared Mosaic (NEWFIRM) imaging instrument will serve this need within the US system of facilities. NEWFIRM is being designed for the National Optical Astronomy Observatory (NOAO) 4-m telescopes (Mayall at KPNO and Blanco at CTIO). NEWFIRM covers a 28 x 28 arcmin field of view over the 1-2.4 μm wavelength range with a 4k x 4k pixel detector mosaic assembled from 2k x 2k modules. Pixel scale is 0.4 arcsec/pixel. Data pipelining and archiving are integral elements of the instrument system. We present the science drivers for NEWFIRM, and describe its optical, mechanical, electronic, and software components. By the time this paper is presented, NEWFIRM will be in the preliminary design stage, with first light expected on the Mayall telescope in 2005.
The new operations model for the CTIO Blanco 4-m telescope will use a small suite of fixed facility instruments for imaging and spectroscopy. The Infrared Side Port Imager, ISPI, provides the infrared imaging capability. We describe the optical, mechanical, electronic, and software components of the instrument. The optical design is a refractive camera-collimator system. The cryo-mechanical packaging integrates two LN<sub>2</sub>-cooled dewars into a compact, straightline unit to fit within space constraints at the bent Cassegrain telescope focus. A HAWAII 2 2048 x 2048 HgCdTe array is operated by an SDSU II array controller. Instrument control is implemented with ArcVIEW, a proprietary LabVIEW-based software package. First light on the telescope is planned for September 2002.
A low cost tip-tilt wavefront stabilization system has been put into operation on the Blanco 4-m telescope on Cerro Tololo. A light-weighted f/15 secondary mirror is driven by three commercial piezoelectric actuators. A dichroic at the Cassegrain focus separates optical reference and IR science beams. A steerable high-speed optical CCD sensor, coupled to a dedicated PC for control and image processing, provides positional feedback to the secondary. The IR field is reflected to one of several science sensors. We present a system description, initial performance measures at the telescope, and directions for future improvements.
The Cryogenic Optical Bench (COB) is a 1-4 (mu) IR array camera with multiple cold spectral and spatial filtering capabilities which can be combined in a variety of configurations. The array is driven by a transputer based high speed data system using fiber optic links and dedicated processors. We describe the instrument functions and the mechanical, optical, electronic, and cryogenic implementation. COB is a facility instrument at Kitt Peak National Observatory, available for use by scientists worldwide on the basis of scientific merit.
The Simultaneous Quad-Color Infrared Imaging Device (SQIID) is the first of a new generation of infrared instruments to be put into service at the Kitt Peak National Observatory (KPNO). The camera has been configured to be modular in design and to accept new innovations in detector format as they become available. Currently the camera is equipped with four 256 x 256 platinum silicide arrays with 30 micron pixels for each of the four bands J (1.1-1.4 microns), H (1.5-1.8 microns), K (2.0-2.4 microns), and L' (3.52-4.12 microns). The optics of the instrument have been designed to accept detector arrays as large as 512 x 512, or an equivalent field size of 12.4 mm x 12.4 mm. The instrument is cooled with a pair of closed cycle cryogenic coolers, which are mechanically aligned and electrically phased to eliminate vibration. In addition, a transputer based electronics system has been incorporated to facilitate fast frame rates, co-add frames, and ease the data handling burden.
Hardware and software improvements to the IR speckle camera are reported. The observing experience obtained during the first year of operation allows a preliminary discussion of exposure times, limiting magnitudes, observing strategies and problems, duty-cycle, data handling, and real-time and off-line processing. The results with this system have also helped to define directions for future developments in high resolution IR imaging.