CFHT currently removes heat from the Closed-Cycle Cold Heads of the telescope prime focus instruments, MegaPrime (Wide-Field Optical Imager) and WIRCam (Wide-Field Infrared Camera) by using water-cooled Helium Compressors which provide gas transfer characteristics allowing the dewars to achieve Cryogenic Temperatures. In addition, CFHT uses air-cooled Compressor Units to provide Closed-Cycle cooling for their telescope Cassegrain instrument, SITELLE (Optical imaging Fourier transform spectrometer). With the addition of a new instrument at the end of 2017, SPIRou (near-infrared spectropolarimeter); an upgrade to the Closed-Cycle cooling system was required to remove the extra 10 kW of heat. Therefore the decision to design and develop a more efficient and less complicated cooling system was pursued. The initial concepts were incorporated from Chas Cavedoni of the GEMINI Observatory, the master mind behind their ambient air cooling system. The cool ambient temperatures experienced year round on Mauna Kea (+4° C to +21° C), coupled with the relatively warm (+10° C to +32° C) cooling water required by the Helium Compressor Units; lends itself to a much simpler and less expensive Fluid-Cooling system which essentially utilizes a glorified Radiator (Heat Exchanger). This paper shall describe the Design Considerations, System Design, and System Performance of this new cooling method and share the lessons learned from this innovative concept. This new design will not only provide cooling for the additional 10 kW introduced by SPIRou, but also handle the existing 10 kW (MegaPrime and WIRCam) currently being removed by stand-alone Refrigeration Chillers. An additional 10kW capacity has been incorporated into the new system to provide cooling for future expansion, which ultimately results in a Fluid Cooling System capable of removing a 30 kW heat load.
Fighting vibrations on large telescopes is an arduous task. At Gemini, vibrations originating from cryogenic coolers have been shown to degrade the optical wavefront, in certain cases by as much as 40%. This paper discusses a general solution to vibration compensation by tracking the real time vibration state of the telescope and using M2 to apply corrections. Two approaches are then presented: an open loop compensation at M2 based on the signal of accelerometers at the M1 glass, and a closed loop compensation at M2 based on optical measurements from the wave front sensor. The paper elaborates on the pros and cons of each approach and the challenges faced during commissioning. A conclusion is presented with the final results of vibration tracking integrated with operations.
We report the results of a multi-year program to measure the vibration characteristics of the two Gemini telescopes. Measurements with fast-guiding wavefront sensors and networks of accelerometers show a correlation between image motion and optical vibrations induced mostly by instrument cryocoolers. We have mitigated the strongest vibrations by fast-guiding compensation and active cancellation of vibration sources.
The Gemini Planet Imager (GPI) entered on-sky commissioning and had its first-light at the Gemini South (GS) telescope in November 2013. GPI is an extreme adaptive optics (XAO), high-contrast imager and integral-field spectrograph dedicated to the direct detection of hot exo-planets down to a Jupiter mass. The performance of the apodized pupil Lyot coronagraph depends critically upon the residual wavefront error (design goal of 60nmRMS with <5 mas RMS tip/tilt), and therefore is most sensitive to vibration (internal or external) of Gemini's instrument suite. Excess vibration can be mitigated by a variety of methods such as passive or active dampening at the instrument or telescope structure or Kalman filtering of specific frequencies with the AO control loop. Understanding the sources, magnitudes and impact of vibration is key to mitigation. This paper gives an overview of related investigations based on instrument data (GPI AO module) as well as external data from accelerometer sensors placed at different locations on the GS telescope structure. We report the status of related mitigation efforts, and present corresponding results.
CANOPUS is the facility instrument for the Gemini Multi Conjugate Adaptive Optics System (GeMS) wherein all the
adaptive optics mechanisms and associated electronic are tightly packed. At an early stage in the pre-commissioning
phase Gemini undertook the redesign and implementation of its chilled Ethylene Glycol Water (EGW) cooling system to
remove the heat generated by the electronic hardware. The electronic boards associated with the Deformable Mirrors
(DM) represent the highest density heat yielding components in CANOPUS and they are also quite sensitive to
overheating. The limited size of the two electronic thermal enclosures (TE) requires the use of highly efficient heat
exchangers (HX) coupled with powerful yet compact DC fans.
A systematic approach to comply with all the various design requirements brought about a thorough and robust solution
that, in addition to the core elements (HXs and fan), makes use of features such as high performance vacuum insulated
panels, vibration mitigation elements and several environment sensors. This paper describes the design and
implementation of the solution in the lab prior to delivering CANOPUS for commissioning.
The Laser Service Enclosure (LSE) is an environmentally controlled ISO 7 clean room designed to house, protect and
provide environmental control for the Gemini South multi-conjugate adaptive optics laser system. The LSE is 8.0 meters
long, 2.5 meters wide and 2.5 meters high with a mass of approximately 5,100 kg. The LSE shall reside on a new
telescope Nasmyth platform named the Support Structure (SS). The SS is a three-dimensional beam and frame structure
designed to support the LSE and laser system under all loading conditions. This paper will review the system
requirements and describe the system hardware including optical, environmental, structural and operational issues as
well as the anticipated impact the system will have on the current telescope performance.
The Gemini twins were the first large modern telescopes to receive protected silver coatings on their
mirrors in 2004. The low emissivity requirement is fundamental for the IR optimization. In the mid-IR a
factor of two reduction in telescope emissivity is equivalent to increasing the collecting area by the same
factor. Our emissivity maintenance requirement is very stringent: 0.5% maximum degradation during
operations, at any single wavelength beyond 2.2 μm.
We developed a very rigorous standard to wash the primary mirrors in the telescope without science
down time. The in-situ washes are made regularly, and the reflectivity and emissivity gains are significant.
The coating lifetime has been extended far more than our original expectations. In this report we describe the
in-situ process and hardware, explain our maintenance plan, and show results of the coating performance over
The Gemini Observatory is in the final integration and test phase for its Multi-Conjugate Adaptive Optics (MCAO)
project at the Gemini South 8-meter telescope atop Cerro Pachón, Chile. This paper presents an overview and status of
the laser-side of the MCAO project in general and its Beam Transfer Optics (BTO), Laser Launch Telescope (LLT) and
Safety Systems in particular. We review the commonalities and differences between the Gemini North Laser Guide Star
(LGS) facility producing one LGS with a 10W-class laser, and its southern sibling producing five LGS with a 50W-class
laser. We also highlight the modifications brought to the initial Gemini South LGS facility design based on lessons
learned over 3 years of LGS operations in Hawaii. Finally, current integration and test results of the BTO and on-sky
LLT performance are presented. Laser first light is expected in early 2009.
The Gemini Observatory presents the Helium Closed Cycle Cooling System that provides cooling capacity at cryogenic
temperatures for instruments and detectors. It is implemented by running three independent helium closed cycle cooling
circuits with several banks of compressors in parallel to continuously supply high purity helium gas to cryocoolers
located about 100-120 meters apart. This poster describes how the system has been implemented, the required helium
pressures and gas flow to reach cryogenic temperature, the performance it has achieved, the helium compressors and
cryocoolers in use and the level of vibration the cryocoolers produce in the telescope environment. The poster also
describes the new technology for cryocoolers that Gemini is considering in the development of new instruments.
The Gemini Multi-Conjugate Adaptive Optics project was launched in April 1999 to become the Gemini South
AO facility in Chile. The system includes 5 laser guide stars, 3 natural guide stars and 3 deformable mirrors optically
conjugated at 0, 4.5 and 9km to achieve near-uniform atmospheric compensation over a 1 arc minute square field of
Sub-contracted systems with vendors were started as early as October 2001 and were all delivered by July
2007, but for the 50W laser (due around September 2008). The in-house development began in January 2006, and is
expected to be completed by the end of 2008 to continue with integration and testing (I&T) on the telescope. The on-sky
commissioning phase is scheduled to start during the first half of 2009.
In this general overview, we will first describe the status of each subsystem with their major requirements, risk
areas and achieved performance. Next we will present our plan to complete the project by reviewing the remaining steps
through I&T and commissioning on the telescope, both during day-time and at night-time. Finally, we will summarize
some management activities like schedules, resources and conclude with some lessons learned.
The upgraded 3.8 m UK Infrared Telescope employs active control of the primary mirror figure and secondary mirror alignment to constrain intrinsic wavefront errors, currently to approximately 180 nm, while a fast guider controls a tip- tilt secondary to remove telescope vibrations and tracking errors. It routinely produces images with FWHM below 0.'5 at 2.2 micrometers wavelength (the K-band). The best fully-sampled image yet recorded has FWHM equals 0.'171 and is believed still to be the best ever achieved by a ground-based telescope without the use of higher-order adaptive optics.
A Prime Focus Wavefront Sensor (PFWFS) has been designed and built at the Gemini Observatory. The system contains a Shack- Hartmann (SH) wavefront sensor and has been designed to use commercial components. The primary mirror of the 8 m Gemini Telescope has a complex active optics system that needs to be calculated during commissioning. The wavefront sensor was built to measure the image quality at prime focus, this eliminates the secondary mirror introducing supplementary aberrations. It has been successfully used during commissioning, to test the active optics.
The upgraded 3.8 m UK Infrared Telescope is now provided with: (1) tip-tilt image stabilization by a light-weighted secondary mirror on piezo-electric actuators, controlled by a fast guider sampling at >= 40 Hz on guide stars V <EQ 18.<SUP>m</SUP>6; (2) active primary mirror figure and secondary mirror alignment control, via a regularly-maintained look-up table; (3) active focus measurements and correction by the fast guider, supplementing a focus maintenance model which corrects for elastic and thermal changes; (4) ventilation of the 2600 m<SUP>3</SUP> dome by 16 apertures totalling 50 m<SUP>2</SUP>; (5) insulation of the underside of the concrete dome floor; and (6) internal air circulation during the day, to reduce heating of the upper telescope steelwork.
The 3.8 m UK Infrared Telescope has been the focus of a program of upgrades intended to deliver images which are as close as possible to the diffraction limit at (lambda) equals 2.2 micrometers (FWHM equals 0.'12). This program is almost complete and many benefits are being seen. A high-bandwidth tip-tilt secondary mirror driven by a Fast Guider sampling at <EQ 100 Hz effectively eliminates image movement as long as a guide star with R < 16.<SUP>m</SUP>5 is available within +/- 3.'5 of the target. Low-order active control of the primary mirror and precision positioning of the secondary, using simple lookup tables, provide telescope optics which are already almost diffraction limited at (lambda) equals 2 micrometers . To reduce facility seeing the dome has been equipped with sixteen closable apertures to permit natural wind flushing, assisted in low winds by the building ventilation system. The primary mirror will soon be actively cooled and the concrete dome floor may be thermally insulated against daytime heating if fire safety concerns can be resolved. Delivered images in the K band now have FWHM which is usually <EQ 0.'8, frequently <EQ 0.'6 and quite often approximately 0.'3. Examples of the latter are shown: these approximate the resolution achieved by NICMOS on the HST. We estimate that the productivity of the telescope has approximately doubled, while its oversubscription factor has increased to > 4.
The 3.8 m United Kingdom Infrared Telescope (UKIRT) has recently installed active control of the primary mirror figure, taking advantage of aspects of the original mirror design, which permits the correction of low order aberrations. In this paper, we present results from a campaign of all-sky wavefront sensing carried out UKIRT. As a result of the campaign, a lookup table is being used to correct for attitude dependent astigmatism, while fixed corrections are applied to trefoil and spherical aberrations. Coma is removed by secondary mirror alignment. A continuous, model based, correction of focus for thermal and elastic effects is also applied. Accurate focus is now maintained throughout an observing night.
The 3.8 m UK infrared telescope (UKIRT) is currently the focus of an upgrades program to improve its imaging performance, ideally to approach its diffraction limit in the near-IR at 2.2 micrometer, with FWHM approximately 0.'12. This program is now in its late stages. All the new systems have been designed, most have been manufacture and many have been installed. A new top end carries an adaptive tip-tilt secondary mirror with active precision alignment, which, with low-order active control of the primary mirror, should provide the desired intrinsic optical performance. The adaptive tip- tilt system will correct image motion from telescope vibrations and drive errors and from atmospheric wavefront tilt; delivered images are expected regularly to be less than 0.'5 over wide fields, and within a factor 2 or so of the diffraction limit, at least inside an isoplanatic patch of order an arcmin radius. To reduce facility seeing the primary mirror has been equipped with a ventilation system and will receive a 5 kW cooling system; the dome is being equipped with sixteen closable apertures to permit natural wind flushing, which can be assisted by the building air handling system in low winds. It is hoped that facility seeing -- excluding boundary layer effects -- will be imperceptible during approximately 85% of observable time. The upgraded UKIRT should be well capable of exploiting fully the very best conditions on Mauna Kea.
In order to encourage adequate dome ventilation to reduce or eliminate dome seeing at the 3.8 m United Kingdom Infrared Telescope (UKIRT), a dome ventilation system (DVS) was designed to be installed in the lower dome skirt. The modifications to the dome for the new DVS apertures consisted of installing a reinforcing frame containing an insulated rollup door and adjustable louvers. This paper describes the finite element structural analysis of the reinforcing frame, the detailed design of the frame hardware, the design of the programmable language control (PLC) system for controlling the opening and closing of the rollup doors, and the fabrication and installation of a prototype frame assembly. To date, a prototype assembly has been installed that confirms the design, and fifteen production assemblies are currently under fabrication for installation by September 1996.
The control of the telescope thermal environment at the 3.8-m United Kingdom Infrared Telescope (UKIRT) is based on the requirements that dome seeing should not degrade the image quality by more than 0.05 arcsec (FWHM) and that mirror seeing should be reduced to negligible proportions. After quantifying steady state and transient heat flow around and through the building, we set out on a program to meet these requirements. Major telescope enclosure upgrades to address dome seeing include natural dome ventilation with 16 apertures in the base of the dome and for near still-air nights, forced-air ventilation via the plant room exhaust system. To address mirror seeing, we are in the process of installing a day-time mirror cooling system that can drive and/or keep the primary mirror between 0 degrees Celsius and 2.5 degrees Celsius colder than the predicted night-time local dome air temperature. Nevertheless, during the night, if the primary mirror is warmer than the local dome air, a flushing system is available to blow away warm convective air cells as they form. This paper describes design considerations of the natural dome ventilation system (DVS), the hardware of the primary mirror cooling and flushing system and the performance of the mirror flushing system on a dummy mirror segment.
The Canada-France-Hawaii-Telescope has placed in operation a servo controlled roller-screw support system for its primary mirror. This paper will address the goals of CFHT in upgrading from a fixed `bendix' style mirror supporting defining pads. The main design criteria was to have a system that would define the mirror like the original pads, but have adjustability to remove coma dependent on telescope position.
The design of a multichannel occultation photometer built under NASA contract to SETS Technology, Inc., for the NASA 3-m IR telescope facility (IRTF) and the JPL Table Mountain telescope is described. This instrument acquires data in four selectable passbands (two 1 to 5 micrometers channels and two 10 to 20 micrometers channels), with very high sensitivity and approximately 100% duty cycle on-source during chopping. The optics are optimized for uniform response across an aperture of up to 20 arcseconds on the IRTF. The cryogenic system is a two-can cryostat with one liquid nitrogen can for cooling the radiation shields, optics, filters, and baffles, and a liquid helium can for cooling the IR detectors. The instrument operates two types of IR detector technologies. The 1 to 5 micrometers detectors are low-capacitance, single-element InSb detectors. The 10 micrometers detectors are blocked impurity band detectors. The instrument also has a 64 by 64 visible CCD array as an additional channel for guiding and visible photometry. A global positioning system unit is incorporated into the system for time and location stamping of occultation events. The instrument design and construction are discussed.
This paper describes the design of an IR cold coronagraph (CoCo) built by SETS Technology, Inc., for use at the NASA 3 m IR Telescope Facility (IRTF) at Mauna Kea Observatory, for the imaging of faint IR sources in proximity to bright sources. The coronagraph is designed to obtain high contrast photometric images by use of an occulting mask and a pupil mask. The coronagraph is to be used in combination with the IRTF NSFCAM, which covers 1-5 micrometers and uses a 256x256 InSb array. The platescale can be varied from 0.06'/pixel to 0.15'/pixel, covering a field of view of 14' and 38', respectively. Selectable apodized and hard occulting masks are mounted on a wheel as the first element in the system to reduce scattered light. Selectable pupil masks are cooled to 77K within the CoCo cryostat. The cryostat consists of a liquid nitrogen can for cooling the optics, masks, and baffles. The CoCo dewar is mounted on a slide in a housing to allow it to move out of the beam path so that the NSFCAM may be used with or without the coronagraph during the same observing period.
In the 1970s the pioneering thin-mirror 3.8 m United Kingdom Infrared Telescope (UKIRT) of the UK Science and Engineering Research Council (SERC) was conceived as a low-cost `light bucket', with an 80% encircled-energy diameter <EQ 3'. However the delivered primary mirror had an 80 encircled- energy diameter of approximately 1' and the telescope has regularly delivered sub-arc-second images. To exploit this quality and to keep UKIRT competitive in a 21st century of 8-meter telescopes, in 1991 the SERC initiated an ambitious Upgrades Program, with the goal of routinely providing near- diffraction limited images at 2.2 microns. The major elements of the program are an adaptive tip-tilt secondary system, an active five-axis secondary collimation system, an upgraded primary mirror support system providing active control of the main optical aberrations, and modifications to the telescope and its enclosure to reduce or eliminate dome and mirror seeing, so as to take advantage of the excellent natural seeing on Mauna Kea. This paper outlines the overall project goals, the proposed strategies for upgrading the telescope and the progress to date.
A fast tip-tilt secondary is being implemented on the University of Hawaii 2.2-m telescope, to provide image quality to match the site characteristics of Mauna Kea, and complement the existing wide-field RC secondary.
A telescope aperture of 2.2-m on Mauna Kea that routinely experiences d/r sub 0 = 4 in the near-IR can achieve a factor of 2 gain in angular resolution by tip-tilt correction of atmospheric-induced wavefront errors. To utilize the gains possible from tip-tilt correction, collimation errors and focus errors must also be removed. For its 2.2-m f/31 telescope, the University of Hawaii is in the process of implementing a five-axis fast guiding secondary consisting of a fast steering mirror platform and slow remote detilt, decenter, and despace collimation and focus drives. The near-term goal is to implement closed-loop tip-tilt image motion correction with open-loop collimation and focus control. The long-term goal is to add closed-loop collimation and focus control. This paper documents the progress to date on the fast steering mirror platform and its spider support structure.