This paper presents the design and technical progress of a precision X-Y stage for detector dithering and flexure compensation being developed for the Magellan InfraRed Multi-Object Spectrograph, MIRMOS. Designed to operate at 80 K, the stage will accurately control detector position in two orthogonal degrees of freedom. The piezo-driven flexure stage is very compact providing high-resolution backlash-free motion of the detector. A magneto resistive bridge provides position feedback in each degree of freedom, greatly reducing hysteresis, which is common in piezoelectric actuators. The system is designed to operate in open loop using a lookup table keyed to the Nasmyth rotator angle for flexure control. Here, the optomechanical design of the stage, electrical control system, and performance results from early prototype efforts are presented and discussed.
The instrumentation of the Prime Focus Spectrograph (PFS), a next generation facility instrument on the Subaru telescope, is now in the final phase of its commissioning process and its general, open-use operations for sciences will provisionally start in 2025. The instrument enables simultaneous spectroscopy with 2386 individual fibers distributed over a very wide (∼1.3 degrees in diameter) field of view on the Subaru’s prime focus. The spectra cover a wide range of wavelengths from 380nm to 1260nm in one exposure in the Low-Resolution (LR) mode (while the visible red channel has the Medium-Resolution (MR) mode as well that covers 710−885nm). The system integration activities at the observatory on Maunakea in Hawaii have been continuing since the arrival of the Metrology Camera System in 2018. On-sky engineering tests and observations have also been carried out continually since September 2021 and, despite various difficulties in interlacing commissioning processes with development activities on the schedule and addressing some major issues on hardware and software, the team successfully observed many targeted stars as intended over the entire field of view (Engineering First Light) in September 2022. Then in parallel to the arrival, integration and commissioning of more hardware components, validations and optimizations of the performance and operation of the instrument are ongoing. The accuracy of the fiber positioning process and the speed of the fiber reconfiguration process have been recently confirmed to be ∼ 20−30μm for 95% of allocated fibers, and ∼130 seconds, respectively. While precise quantitative analyses are still in progress, the measured throughput has been confirmed to be consistent with the model where the information from various sub-components and sub-assemblies is integrated. Long integration of relatively faint objects are being taken to validate an expected increase of signal-to-noise ratio as more exposures are taken and co-added without any serious systematic errors from, e.g., sky subtraction process. The PFS science operation will be carried out in a queue mode by default and various developments, implementations and validations have been underway accordingly in parallel to the instrument commissioning activities. Meetings and sessions are arranged continually with the communities of potential PFS users on multiple scales, and discussions are iterated for mutual understanding and possible optimization of the rules and procedures over a wide range of processes such as proposal submission, observation planning, data acquisition and data delivery. The end-to-end processes of queue observations including successive exposures with updated plans based on assessed qualities of the data from past observations are being tested during engineering observations, and further optimizations are being undertaken. In this contribution, a top-level summary of these achievements and ongoing progresses and future perspectives will be provided.
The Spectrograph System (SpS) of Subaru Prime Focus Spectrograph is fed by 2400 fibers and consists of four identical spectrograph modules with 4 arms and 600 fibers each. This paper outlines the overall integration process for the spectrograph module series as completed at the Subaru Telescope. Many partners from the Subaru PFS Collaboration and industry contributed to this large multi-object spectrograph system. The initial integration of the so-called "one-channel prototype" began in 2015. The first spectrograph module was delivered to Subaru in 2019, and the fourth module was delivered in late 2023, with delays due to both technical difficulties and scheduling challenges, including the impact of COVID-19 on the large PFS spectrograph system collaboration. The integration and validation of each spectrograph module were performed at the Laboratoire d’Astrophysique de Marseille (LAM) prior to delivery and full integration at the Subaru Telescope. First, we briefly review the opto-mechanical design and development strategy for the SpS. We present the integration and testing procedures developed for this mini-series of four spectrograph modules. Several specific AIT tools were innovative and key to the process, and are worth reporting, including the software tools required for functional tests, housekeeping, and environment monitoring during integration, analysis of dimensional metrology, test and verification of optical alignment, and overall performance assessment. Specific processes were also developed for analyzing and resolving anomalies and issues encountered. We detail the strategies developed to resolve technical issues: thermal and vacuum performance; dimensional and optical metrology processes to correct for focus/tilt anomalies observed at the focal plane; handling, alignment, and optical testing of large optics such as the 340x340x20mm Volume Phase Holographic Grating (VPHG). We briefly report on a grating orientation issue discovered before the delivery of the last module, which is reported elsewhere. We quickly report the integration logistics: managing the shipping process, custom, and deliveries of many parts and modules among partners since 2014, and the final delivery and installation at the Subaru Telescope at the summit of Mauna Kea in Hawai`i in 2019, 2022, and 2023. We then dedicate a full section to the optical and thermal performance for the largest 8m-class multi-object spectrograph: the spectral channels and camera alignment performance results and the detailed optical performance of the four spectrograph modules (extracted from internal extended performance reports).
The predicted efficiency of the Prime Focus Spectrograph (PFS) for the Subaru telescope at Mauna Kea took a serious hit at the discovery of an error in the mounting of its volume phase holographic gratings (VPHG). Alerted by unexpected jumps in spectral flux between the blue and red channels in the first two spectrograph modules as they became available on sky, inspection of the gratings as mounted into the fourth and last module, still present in the lab, confirmed that all its gratings – three low-resolution (blue, red, NIR) gratings and a medium resolution grating and prism assembly (grism) – were indeed all mounted upside down. In this paper, after reporting on the observations leading to this discovery, we describe the corrective actions taken, illustrating by on-sky spectra full recovery of performance. Finally, we discuss the causes for this potentially catastrophic error, with an emphasis on the difficulty of ensuring verification at all levels (preliminary and final design, procurement, manufacturing, and AIT phases) for the giant instruments we are currently building and designing. We provide guidelines for future instrument designers in order to minimize the risk of such flaws happening again.
We present the conceptual design of a new optical echelle spectrograph for the Astrophysical Research Consortium 3.5-m Telescope at Apache Point Observatory in New Mexico. The Nasmyth-mounted slit spectrograph, intended to replace the existing echelle spectrograph that is over 20 years old, will provide continuous spectra for wavelengths spanning the range 350 nm – 1000 nm with a white pupil design featuring separate blue and red arms. A real-time slit change mechanism will allow three primary modes: 1) Resolution R ~ 32,000 for the median seeing of 1.2 arcsec FWHM, 2) R ~ 40,000 when using a smaller slit with tip-tilt image stabilization, and 3) R ~ 64,000 using a two-slice image slicer. The peak instrument throughput is ~ 38% and at 350 nm the throughput is ~ 22%. High throughput, particularly in the blue, will be enabled through the use of an atmospheric dispersion corrector, high performance coatings, tip-tilt image stabilization, and careful attention to refractive material choices. Expected instrument sensitivity for magnitude 14 stars is SNR per pixel of 50 in 3600 sec at 355 nm (u-band) and about 1800 sec for the centers of griz bands for both the R ~32,000 and R~ 40,000 modes.
SDSS-V is the fifth generation of the Sloan Digital Sky Survey and is an ambitious follow-on to a project that has been producing ground-breaking science for two decades. SDSS-V uses two dedicated 2.5m telescopes – the SDSS telescope at Apache Point Observatory in New Mexico, and the du Pont telescope at Las Campanas Observatory in Chile – feeding BOSS and APOGEE spectrographs at each site. These survey machines generate multi-object, all-sky spectroscopy in the optical and near-IR in support of primary science programs. The new wide field corrector for the SDSS 2.5m telescope is one of several major infrastructure upgrades undertaken for SDSS-V, necessitated by the replacement of the legacy fiber plug plate system with a new robotic Fiber Positioning System (FPS), which places different requirements on the focal characteristics of the telescope. The original 2-element corrector produced a focal surface which was non-telecentric and suffered from axial color, throughput, and image quality issues when used in the H-band with the APOGEE spectrograph. We have designed and built a 3-element, all fused silica corrector which addresses the optical shortcomings in relation to the FPS. In addition, the optomechanical design required very minimal changes to the telescope interfaces and also facilitates in-situ axial adjustment of one lens element to fine-tune the as-built spherical radius of the focal surface, to match the nominal design value to which the FPS was built. This paper discusses the optical and optomechanical design details of the new wide field corrector, concluding with a brief summary of recent commissioning results.
This paper presents thermal system and imaging performance test results from the first of four near infrared cameras for the SuMIRe (Subaru Measurement of Images and Redshifts) Prime Focus Spectrograph (PFS) being developed for the Subaru Telescope. The PFS near infrared camera is a large (330 mm entrance aperture to accommodate a 275 mm collimated beam diameter) cryogenically cooled vacuum Schmidt camera with a 300 mm focal length that images dispersed light onto a 4k x 4k, 15 µm pixel, HgCdTe substrate-removed Teledyne 1.7 µm detector. The 230 kg camera contains just four optical elements: a two-element refractive corrector, a Mangin mirror, and a field flattening lens. This simple optical design produces good imaging performance considering the wide field and wavelength range, and it does so in large part due to the use of a Mangin mirror for the Schmidt primary. Thermal background, both in-band and out-of-band, is reduced to a scientifically acceptable level using cryogenically cooled optics, very black geometrically optimized baffling, and a pair of thermal rejection coatings that reject photons between the edge of the science bandpass and the detector cutoff. System operating temperature is achieved by a pair of closed-cycle cryocoolers, one dedicated to cooling the optics, and one dedicated to cooling the detector. Here we discuss the lab performance of the near infrared camera, both from the perspective of the thermal system and the optical system, including in-band and out-of-band performance.
We present the on-sky performance of the new wide field corrector for the fifth generation of the Sloan Digital Sky Survey (SDSS-V). This new three-element corrector was designed to replace the previous two-element design, which had an aspherical focal surface and was not optimized for the infrared (H-band). The purpose of the new corrector is to improve the imaging performance required for a new robotic Fiber Positioning System (FPS). For commissioning, a Focal Surface Camera (FSC) was developed and used to determine the focal surface location relative to the telescope interface, and to verify imaging performance across the 3-degree field of view of the corrector. This paper discusses the commissioning process in detail, describes how the imaging data were processed, and presents the measured image quality across the field.
PFS (Prime Focus Spectrograph), a next generation facility instrument on the Subaru telescope, is now being tested on the telescope. The instrument is equipped with very wide (1.3 degrees in diameter) field of view on the Subaru’s prime focus, high multiplexity by 2394 reconfigurable fibers, and wide waveband spectrograph that covers from 380nm to 1260nm simultaneously in one exposure. Currently engineering observations are ongoing with Prime Focus Instrument (PFI), Metrology Camera System (MCS), the first spectrpgraph module (SM1) with visible cameras and the first fiber cable providing optical link between PFI and SM1. Among the rest of the hardware, the second fiber cable has been already installed on the telescope and in the dome building since April 2022, and the two others were also delivered in June 2022. The integration and test of next SMs including near-infrared cameras are ongoing for timely deliveries. The progress in the software development is also worth noting. The instrument control software delivered with the subsystems is being well integrated with its system-level layer, the telescope system, observation planning software and associated databases. The data reduction pipelines are also rapidly progressing especially since sky spectra started being taken in early 2021 using Subaru Nigh Sky Spectrograph (SuNSS), and more recently using PFI during the engineering observations. In parallel to these instrumentation activities, the PFS science team in the collaboration is timely formulating a plan of large-sky survey observation to be proposed and conducted as a Subaru Strategic Program (SSP) from 2024. In this article, we report these recent progresses, ongoing developments and future perspectives of the PFS instrumentation.
PFS (Prime Focus Spectrograph), a next generation facility instrument on the Subaru telescope, is a very wide- field, massively multiplexed, and optical and near-infrared spectrograph. Exploiting the Subaru prime focus, 2394 reconfigurable fibers will be distributed in the 1.3 degree-diameter field of view. The spectrograph system has been designed with 3 arms of blue, red, and near-infrared cameras to simultaneously deliver spectra from 380nm to 1260nm in one exposure. The instrumentation has been conducted by the international collaboration managed by the project office hosted by Kavli IPMU. The team is actively integrating and testing the hardware and software of the subsystems some of which such as Metrology Camera System, the first Spectrograph Module, and the first on-telescope fiber cable have been delivered to the Subaru telescope observatory at the summit of Maunakea since 2018. The development is progressing in order to start on-sky engineering observation in 2021, and science operation in 2023. In parallel, the collaboration is trying to timely develop a plan of large-sky survey observation to be proposed and conducted in the framework of Subaru Strategic Program (SSP). This article gives an overview of the recent progress, current status and future perspectives of the instrumentation and scientific operation.
PFS (Prime Focus Spectrograph), a next generation facility instrument on the 8.2-meter Subaru Telescope, is a very wide-field, massively multiplexed, optical and near-infrared spectrograph. Exploiting the Subaru prime focus, 2394 reconfigurable fibers will be distributed over the 1.3 deg field of view. The spectrograph has been designed with 3 arms of blue, red, and near-infrared cameras to simultaneously observe spectra from 380nm to 1260nm in one exposure at a resolution of ~ 1.6-2.7Å. An international collaboration is developing this instrument under the initiative of Kavli IPMU. The project recently started undertaking the commissioning process of a subsystem at the Subaru Telescope side, with the integration and test processes of the other subsystems ongoing in parallel. We are aiming to start engineering night-sky operations in 2019, and observations for scientific use in 2021. This article gives an overview of the instrument, current project status and future paths forward.
The Double Asteroid Redirection Test (DART) is a spacecraft that will impact the smaller body of the binary asteroid Didymos. As a technology demonstration, this will be the first time a kinetic impactor is used to perturb the motion of a near earth object. This technique could someday be used to deflect a dangerous asteroid on a future collision course with Earth. As the only instrument aboard DART, the Didymos Reconnaissance and Asteroid Camera for OpNav (DRACO) serves two purposes. First, DRACO provides images to the Small-body Maneuvering Autonomous Real-Time Navigation (SMARTNav) algorithm, allowing the spacecraft to precisely locate and impact the target. In its final moments, DRACO will also characterize the impact site by providing high resolution, scientific imagery of the surface. Derived from the Long Range Reconnaissance Imager (LORRI) on New Horizons, the telescope is a 208 mm aperture, f/12.6, catadioptric Ritchey-Chrétien, with a 0.29 degree field of view. A lightweight opto-mechanical structure, with low CTE mirror substrates and a composite baffle tube, maintains telescope focus in the low temperature environment of deep space. At the focal plane is a 2560 by 2160 pixel, panchromatic, front-side illuminated complementary metal oxide semiconductor (CMOS) image sensor, with digital output, global shutter, and low read noise. A highly integrated focal plane electronics (FPE) module controls the sensor and relays data to the spacecraft.
PFS (Prime Focus Spectrograph), a next generation facility instrument on the 8.2-meter Subaru Telescope, is a very wide-field, massively multiplexed, optical and near-infrared spectrograph. Exploiting the Subaru prime focus, 2394 reconfigurable fibers will be distributed over the 1.3 deg field of view. The spectrograph has been designed with 3 arms of blue, red, and near-infrared cameras to simultaneously observe spectra from 380nm to 1260nm in one exposure at a resolution of ~1.6 - 2.7Å. An international collaboration is developing this instrument under the initiative of Kavli IPMU. The project is now going into the construction phase aiming at undertaking system integration in 2017-2018 and subsequently carrying out engineering operations in 2018-2019. This article gives an overview of the instrument, current project status and future paths forward.
We describe the conceptual optomechanical design for GMACS, a wide-field, multi-object, moderate-resolution optical
spectrograph for the Giant Magellan Telescope (GMT). GMACS is a candidate first-light instrument for the GMT and
will be one of several instruments housed in the Gregorian Instrument Rotator (GIR) located at the Gregorian focus. The
instrument samples a 9 arcminute x 18 arcminute field of view providing two resolution modes (i.e, low resolution, R ~
2000, and moderate resolution, R ~ 4000) over a 3700 Å to 10200 Å wavelength range. To minimize the size of the
optics, four fold mirrors at the GMT focal plane redirect the full field into four individual "arms", that each comprises a
double spectrograph with a red and blue channel. Hence, each arm samples a 4.5 arcminute x 9 arcminute field of view.
The optical layout naturally leads to three separate optomechanical assemblies: a focal plane assembly, and two identical
optics modules. The focal plane assembly contains the last element of the telescope's wide-field corrector, slit-mask,
tent-mirror assembly, and slit-mask magazine. Each of the two optics modules supports two of the four instrument arms
and houses the aft-optics (i.e. collimators, dichroics, gratings, and cameras). A grating exchange mechanism, and
articulated gratings and cameras facilitate multiple resolution modes. In this paper we describe the details of the
GMACS optomechanical design, including the requirements and considerations leading to the design, mechanism
details, optics mounts, and predicted flexure performance.
We present a conceptual design for a moderate resolution optical spectrograph for the Giant Magellan Telescope (GMT).
The spectrograph is designed to make use of the large field-of-view of the GMT and be suitable for observations of very
faint objects across a wide range of optical wavelengths. We show some details of the optical and mechanical design of
the instrument.
The James Webb Space Telescope will undergo a full system test in the cryogenic vacuum chamber A at the Johnson
Spaceflight Center in order to verify the overall performance of the combined telescope and instrument suite. This will
be the largest and most extensive cryogenic test ever undertaken. Early in the test system development, it was
determined that precise position measurements of the overall hardware would enhance the test results. Various concepts
were considered before selecting photogrammetry for this metrology. Photogrammetry has been used in space systems
for decades, however cryogenic use combined with the size and the optical/thermal sensitivity of JWST creates a unique
set of implementation challenges. This paper provides an overview of the JWST photogrammetric system and mitigation
strategies for three key engineering design challenges: 1) the thermal design of the viewing windows to prevent
excessive heat leak and stray light to the test article 2) cost effective motors and mechanisms to provide the angle
diversity required, and 3) camera-flash life and reliability sufficient for inaccessible use during the number and duration
of the cryogenic tests.
The James Webb Space Telescope (JWST) is a general astrophysics mission which consists of a 6.6m diameter,
segmented, deployable telescope for cryogenic IR space astronomy (~35K). The JWST Observatory architecture
includes the Optical Telescope Element and the Integrated Science Instrument Module (ISIM) element that contains four
science instruments (SI) including a Guider.
The alignment philosophy of ISIM is such that the cryogenic changes in the alignment of the SI interfaces are captured in
the ISIM alignment error budget. The SIs are aligned to the structure's coordinate system under ambient, clean room
conditions using laser tracker and theodolite metrology. The ISIM structure is thermally cycled and temperature-induced
structural changes are concurrently measured with a photogrammetry metrology system to ensure they are within
requirements.
We compare the ISIM photogrammetry system performance to the ISIM metrology requirements and describe the
cryogenic data acquired to verify photogrammetry system level requirements, including measurement uncertainty. The
ISIM photogrammetry system is the baseline concept for future tests involving the Optical Telescope Element (OTE) and
Observatory level testing at Johnson Space Flight Center.
The FourStar infrared camera is a 1.0-2.5 μm (JHKs) near infrared camera for the Magellan Baade
6.5m telescope at Las Campanas Observatory (Chile). It is being built by Carnegie Observatories and
the Instrument Development Group and is scheduled for completion in 2009. The instrument uses four
Teledyne HAWAII-2RG arrays that produce a 10.9' × 10.9' field of view. The outstanding seeing at the
Las Campanas site coupled with FourStar's high sensitivity and large field of view will enable many
new survey and targeted science programs.
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