The fifth Sloan Digital Sky Survey Local Volume Mapper (LVM) is a wide-field integral field unit survey that uses an array of four 160 mm fixed telescopes with siderostats to minimize the number of moving parts. An individual telescope observes the science or calibration field independently and is synchronized with the science exposure. We developed the LVM Acquisition and Guiding Package (LVMAGP)-optimized telescope control software program for LVM observations, which can simultaneously control four focusers, three K-mirrors, one fiber selector, four mounts (siderostats), and seven guide cameras. This software is built on a hierarchical architecture and the SDSS framework and provides three key sequences: autofocus, field acquisition, and autoguide. We designed and fabricated a proto-model siderostat to test the telescope pointing model and LVMAGP software. The mirrors of the proto-model were designed as an isogrid open-back type, which reduced the weight by 46% and enabled reaching thermal equilibrium quickly. In addition, deflection due to bolting torque, self-gravity, and thermal deformation was simulated, and the maximum scatter of the pointing model induced by the tilt of optomechanics was predicted to be 4′.4, which can be compensated for by the field acquisition sequence. We performed a real sky test of LVMAGP with the proto-model siderostat and obtained field acquisition and autoguide accuracies of 0″.38 and 1″.5, respectively. It met all requirements except for the autoguide specification, which will be resolved by more precise alignment among the hardware components at Las Campanas Observatory.
The discovery of a fair sample of Earth-analogues (Earth 2.0’s), i.e. rocky, Earth-mass exoplanets orbiting a Solar-type star in that host star’s habitable zone, and a subsequent search of evidence of bioactivity on those Earth 2.0’s by the detection of biogenically produced molecules in those exoplanetary atmospheres, are two of the most urgent observational programs in astrophysics and science in general. To identify an Earth 2.0, it is necessary to measure the reflex motion radial velocity amplitude of the host star at the 10 cm/sec level, a precision considerably below that which is currently achievable with existing instruments. The follow-on project to search for the biomarkers in an Earth 2.0’s atmosphere may require an effective planet/star contrast of 10-10, again well below the currently achievable level. In this paper, we discuss technical innovations in the implementation of the GMT-Consortium Large Earth Finder (G-CLEF) spectrograph that will enable these observational objectives. We discuss plans to operate G-CLEF at the Magellan Clay telescope with the MagAO-X adaptive optics system and subsequently with GMagAO-X at the Giant Magellan Telescope (GMT).
IGRINS-2 is a high-resolution, near-infrared spectrograph developed by Korea Astronomy and Space Science Institute (KASI) for Gemini Observatory as a new facility instrument. It provides spectral resolving power of ~45,000 and a simultaneous wavelength coverage of 1.49-2.46 μm. IGRINS-2 is an improved version of IGRINS (Immersion GRating INfrared Spectrometer) with minor optical and mechanical design changes, new detector controllers, and operating software to be fully integrated into Gemini operating systems. Since the project began in early 2020, project key milestones including assembly and pre-delivery performance verification were completed, and delivered to Gemini North in early September, 2023. After the successful post-delivery verification and telescope integration, the first light spectra were acquired in October 2023. We present design changes and upgrades made to IGRINS-2 from the original IGRINS, assembly and alignment procedures, and verification of the instrument requirements. We also report the preliminary results of the system performance tests.
We introduce an optical system design of the calibration system for Giant Magellan Telescope Near-Infrared Spectrograph (GMTNIRS), capable of operating across a wavelength range of 1.08 - 5.4 μm. The calibration system fulfills several critical functions, including flat-fielding, wavelength calibration, dark current measurements, and focusing of the spectrograph. The system consists of flat lamp collimator, illuminator, relay optics, and three targets – the USAF 1951 resolution target, a pinhole, and a dark mirror. The focal ratio of the output beam in image space is designed to be 8, replicating the Giant Magellan Telescope. The flatness of the light from the calibration system is evaluated using a non-sequential ray tracing method, confirming over 99% flatness across the slit area.
The optical design of a 400 mm-aperture, f/3, three-mirror freeform telescope for the MESSIER surveyor mission is presented. PhoSim PSF (Point Spread Function) simulations of the linear astigmatism-free optical design and mirror surfaces’ microroughness modeling indicate good manufacturability.
The conventional on-axis reflective systems suffer from a diffraction effect on the Point Spread Function (PSF) due to the secondary mirror obscuration. Meanwhile, the unobscured off-axis reflective systems’ imaging performance may be impacted by linear astigmatism aberration. The Linear Astigmatism Free-Three Mirror System (LAF-TMS) is a confocal off-axis reflective system that eliminates linear astigmatism and enables a wide Field of View (FoV). We present an enhanced design of LAF-TMS, called ”wide-wide”, which has an aperture of D=40mm, an effective focal length of f=75mm, and a wide FoV of 8.25°(Horizontal) × 6.21°(V ertical) combined with a wide spectral bandwidth capability suitable for Unmanned Aerial Vehicle (UAV) applications. To evaluate the performance of this compact and fast optical system design, we use the Photon Simulator (PhoSim) to model physically accurate PSF under different conditions of the mirror surface, mechanical environment, and atmosphere. As a benchmark, we compare and analyze the PhoSim PSF results with other ray tracing software such as Zemax and CodeV. Additionally, PhoSim is capable of simulating infrared spectral imaging cases with a user-defined Spectral Energy Distribution (SED), intensity, and emissivity of each pixel. The comprehensive simulation results demonstrate the high performance of the LAF-TMS with a wide-wide FoV and multispectral capabilities.
GMTNIRS, the Giant Magellan Telescope Near-Infrared Spectrograph, is a high resolution (R = 65,000 - 80,000) near infrared spectrograph selected as a first-generation instrument for the Giant Magellan Telescope (GMT). It simultaneously observes the J, H, K, L, and M bands using five immersion gratings. GMTNIRS will be located on the GMT instrument rotator upper disk and operating in adaptive optics mode. The cryostat and optical bench design is based on the heritage of the highly successful immersion grating spectrograph, IGRINS. The cryostat is octagonal with a width of 1.7 m and a height of 1 m. It consists of top piece, bottom plate, passive radiation shields, and warm window assembly. Cryocoolers, electronics, and vacuum components are installed on the bottom plate. The optical bench system is comprised of two optical benches, bench interface structure, and active radiation shield. It is thermally isolated from the cryostat by eight sets of G10 supports. The sub-bench accommodates the fore-optics, a pupil mask, and an on instrument wave front sensor, while the spectrographs, slit-mask imager, and slit viewing camera are located on the main bench. Structure and thermal analysis have been performed to verify bench flexure by gravity vector change, integrity of the cryostat by vacuum pressure, and temperature distribution at the operating temperature of 70 K. We also present some design strategies to prevent light leakage.
GMTNIRS, the Giant Magellan Telescope Near-Infrared Spectrograph, is a high resolution (R=65,000~80,000) near-infrared spectrograph selected as a first-generation instrument for the Giant Magellan Telescope. The instrument covers J, H, K, L, and M spectral bands in a single shot through 6-channel spectrographs. The L band is shared by two channels. Thanks to the use of silicon immersion gratings, the design is compact for its capability. GMTNIRS will be located on the GMT instrument rotator upper disk and operating in adaptive optics mode. We detail the optical system design, imaging performance, spectral formats, and fabrication/alignment budget.
GMTNIRS, the first-generation instrument of the Giant Magellan Telescope, is a high-resolution (R = 65,000 – 80,000) near-infrared spectrograph. We introduce the preliminary design of optical mounts for slit, beam splitters, mirrors, and gratings installed in the cryogenic spectrograph. Optical components are mounted on aluminum structures and fixed by titanium springs and spring plungers. Static analysis of optical mounts with 1g-force at various directions has been performed to verify the stability of the optical system. In addition, stability in the seismic environment is evaluated with modal analysis and non-linear dynamic analysis. Design and simulation results are compared to the tolerance limits of the system.
GMTNIRS (Giant Magellan Telescope Near-Infrared Spectrograph) is a high resolution (R = 65,000 – 80,000) wide-band near-infrared spectrograph, one of the first-generation instruments of the Giant Magellan Telescope. We present the preliminary design of the electronics system including temperature control, power distribution, vacuum pressure monitoring, moving mechanism, and packaging. Design for infrared detector subsystems for science bands (J, H, K, L, and M) and a slit-view camera is planned. The electronics system makes use of EtherCAT as fieldbus standard according to the requirement of the GMT.
Optical design of the wide field of view telescope is limited by obscuration of the secondary mirror in onaxis system and by serious linear astigmatism in conventional common off-axis system. We have developed an innovative off-axis reflective system in which the optical design is based on the confocal off-axis to completely compensate the linear astigmatism. The main objective of this paper is to compare alignment sensitivity of the confocal system to those of on-axis and common off-axis systems. All three optical designs are based on the classical Cassegrain reflecting telescope and have identical entrance pupil diameter of 1000 mm and F/8 focal ratio. Tilt and decenter of each optical component, and despace which indicates inter-mirror distance are considered as tolerancing parameters that are explored within fabrication tolerance ranges. Encircled energy diameter is evaluated as a criterion of the analysis while tilts of the secondary mirror and the focal position are set to the compensator. The statistical tolerancing method based on Monte-Carlo simulation is also performed to analyze system tolerances. From sensitivity analysis and Monte-Carlo simulation, we concluded that the confocal off-axis system is more sensitive than on-axis and common off-axis systems but it is a feasible system in terms of fabrication and alignment errors.
Linear Astigmatism Free - Three Mirror System (LAF-TMS) is a confocal off-axis system that eliminates linear astigmatism, which is the most critical aberration especially in the large field angle, and therefore, enables the telescope to have a wide field of view. Based on our experience with the telescope, we optimized the LAF-TMS for wavelength ranges of mid-wavelength infrared (3-5 µm) and long-wavelength infrared (8-12 µm) sensors onboard Unmanned Aerial Vehicles (UAVs). It has an entrance pupil diameter of 70 mm, a focal ratio of 1.4, and a wide field of view (FoV) of 6.20° × 4.68°, matching 10.9 mm × 8.2 mm sensor with 17 µ m sized pixels (LAF-TMS D70F1.4). The freeform mirrors of LAF- TMS D70F1.4 are optimized to eliminate the high order aberration. As a result, LAF-TMS D70F1.4 can achieve high- quality optical performance over a wide FoV without any additional correcting lenses. We performed the sensitivity analysis and the Monte-Carlo simulations as the feasibility study. During the sensitivity analysis and the Monte-Carlo simulation, decenter, tilt, despace, and surface RMS errors of three mirrors were analyzed. From the sensitivity analysis, we investigated 80% Energy Encircled Diameter by single factor perturbations. The system tolerance limits were calculated using the Monte-Carlo method with a normal distribution of errors. According to the results, we confirmed that the LAF-TMS D70F1.4 was feasible considering general fabrication and alignment tolerances.
In this study, simulations and measurements were used to investigate stray light properties of the three-mirror off-axis telescope of a new satellite for atmospheric research called Mesospheric Airglow/Aerosol Tomography Spectroscopy (MATS). A 700 mm breadboard baffle for stray light rejection has been designed and tested. Good performance was achieved by coating the baffle’s inside with Vantablack S-VIS R , which has a hemispherical reflectance of 0.2-0.6% across the instrument’s detection band (270-776 nm). A point source transmittance (PST) down to 10−6 was measured for the full-size baffle breadboard. This is in excellent agreement with simulations performed in OpticStudio/LightTools, where scattering was modeled using empirical BRDF data. From the breadboard results, a simulation model of a flight-representative prototype model of the entire instrument was set up in OpticStudio. Strong signals just outside the field of view constitute the biggest challenge, where a PST in the order of 10−6 − 10−4 is required. Simulations suggest that the PST of the prototype limb instrument will be lower than this. Adding to these simulations, an instrument model was developed, which will be utilized by the end-users to remove unwanted features in the data stemming from the instrument itself. Besides stray light, the model also takes into account the most relevant aspects of the instrument, such as image resolution (from measured/simulated point spread functions), image sensor characteristics as well as temperature and wavelength dependencies.
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