We are under integrating off-axis freeform mirrors for the KASI Deep Rolling Imaging Fast Telescope Generation 1 (KDRIFT G1) using a coordinate measuring machine and assembly jig. The telescope is a confocal off-axis freeform threemirror system designed for the detection of extremely low surface brightness structures in the sky. The optical specifications of the K-DRIFT G1 are as follows: the entrance pupil diameter is 300 mm, the focal ratio is 3.5, and the field of view is 4.43° × 4.43°. During the integration stage, we used a coordinate measuring machine to measure the positions of the mirrors, flexures, and bezels within a tolerance range. Following the system integration, we will measure wavefront errors at several edge fields using an interferometer at 633 nm. In this paper, we briefly present the current status of the K-DRIFT G1 and the future plans for the project.
We have developed the KASI Deep Rolling Imaging Fast Telescope (K-DRIFT) to optimally detect Low Surface Bright (LSB) structure and installed a testbed for K-DRIFT performance testing and verification at the Bohyunsan Optical Astronomy Observatory (BOAO). Achieving optimal LSB observations requires minimizing fluctuations in the night sky background value and obtaining high-quality data under stable conditions. For this reason, the remotely controlled K-DRIFT system demands continuous monitoring of the surrounding environment. We have equipped the K-DRIFT testbed with various devices for monitoring the observatory environment. This paper provides an overview of the environmental monitoring system and reports on the performance of the monitoring equipment.
GrainCams is a suite comprising two cameras: SurfCam and LevCam, developed by the Korea Astronomy and Space Science Institute (KASI) for the Commercial Lunar Payload Service (CLPS). SurfCam utilizes a light field camera with a Micro Lens Array (MLA) to capture 3D images of the fairy castle structures on the lunar surface. LevCam is designed to detect dust lofting above the lunar surface. Surviving extreme environments, including launch vibrations, lunar surface temperatures, space radiation, etc., necessitates thorough safety reviews, verification, and reliable ground testing of the system. This paper presents the comprehensive test results of GrainCams engineering qualification model (EQM), along with the cameras' performance following space environment tests such as Total Ionizing Dose (TID), Electro-Magnetic Compatibility (EMC), vibration/shock, and thermal-vacuum tests. Performance test analysis plays a crucial role in ensuring mission success. TID and EMC tests assess the space radiation endurance and electronic compatibility of the electrical components. The vibration/shock test evaluates mechanical stiffness and frequency characteristics during launch. Additionally, GrainCams undergoes temperature variation in the thermal-vacuum test to assess system performance under lunar operational conditions. Our demonstration confirms that GrainCams meet system requirements, and their performance in harsh environments is substantiated by the shared test results.
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.
A mode matching telescope for an EPR squeezer was designed with confocal off-axis configuration. Coupling loss is calculated as 0.02%, and the fabrication is expected to be feasible based on sensitivity analysis and Monte-Carlo simulation.
We fabricated three freeform mirrors for the KASI-Deep Rolling Imaging Fast Telescope pathfinder, which is a confocal off-axis freeform three-mirror system with a 300 mm entrance pupil diameter. During the fabrication process, we light-weighted the primary mirror, reducing its weight by 52%. Front surfaces of these off-axis freeform mirrors were formed by a series of production process, including grinding, polishing, forming, and finishing. Measuring surface profile has been performed by using Coordinate Measuring Machines (CMMs) for the grinding process and an interferometer with Computer Generated Holograms (CGHs) for polishing, forming, and finishing process. The test results for all three mirrors were well within the required value of 20 nm RMS.
We have developed the KASI-Deep Rolling Imaging Fast Telescope (K-DRIFT), adopting a 300 mm aperture off-axis freeform three-mirror design to detect faint and diffuse low-surface-brightness structures. By conducting the on-sky test observations and performing a series of simulations to analyze the performance of the K-DRIFT, we confirmed three main error sources causing optical performance degradation. The imaging performance of the K-DRIFT has successfully improved by correcting low-to-mid spatial frequency wavefront errors based on performance analysis results. This paper presents the K-DRIFT’s optical performance analysis algorithm and the optical performance improvement.
We are developing the KASI-Deep Rolling Imaging Fast Telescope Generation 1 (K-DRIFT G1) based on the on-site performance assessment of the K-DRIFT pathfinder. The telescope is a confocal off-axis freeform three-mirror system designed for the detection of extremely low surface brightness structures in the sky. The optical specifications of the K-DRIFT G1 are as follows: the entrance pupil diameter is 300 mm, the focal ratio is 3.5, the field of view is 4.43° × 4.43°, and the image area is 81.2 mm × 81.2 mm with 10 μm pixels. We performed sensitivity analysis and tolerance simulations to integrate and align the system. We present the analysis results and development plan of the K-DRIFT G1.
The Korea Astronomy and Space Science Institute is working on a project, the Republic of Korea Imaging Test System shortly called ROKITS, which is an optical system that aims to study the formation and occurrence of the aurora. The main objective is to gain insights into the changes occurring in the atmosphere, particularly the upper atmosphere, due to external energy sources from outside the Earth. Additionally, the system will investigate the feasibility of detecting atmospheric waves, specifically atmospheric gravity waves, which spread from the lower atmosphere. To achieve these scientific goals, 90 degrees of a wide field of view and a very narrow bandwidth of filters in a specific wavelength are required, and this paper will present information on the optical design and related analysis.
A catadioptric design has been drawn to be used for semiconductor defect inspection in deep UV, which consists of nine lenses and mirrors. The numerical aperture was 0.8 and the whole length was 95 mm. The optical performances of the system were analyzed and the sensitivities of each component were investigated. Two lenses were found most sensitive and those lenses would be applied for the compensator when the system is going to be assembled. In this paper, the analysis results of the catadioptric system are presented, and the assembly plan is discussed.
We are developing, the second generation of Immersion GRating INfrared Spectrometer, IGRINS-2 which will be a dedicated facility instrument of the Gemini Observatory. IGRINS has been in active operation for more than 8 years since 2014, including recent visits to the Gemini South telescope. House Keeping Package (HKP) of the IGRINS-2 control software monitors temperature, vacuum pressure, and Power Distribution Unit (PDU) of the hardware components, and controls PDU and calibration unit (the motors and the lamps). Slit Camera Package (SCP) and Data Taking Package (DTP) operate the infrared array detectors of Detector Control System (DCS). The interface board for each H2RG detector in IGRINS-2 has been changed from JADE2 to MACIE, which leads us to develop our own control software using the MACIE library in DCS. The IGRINS-2 software will communicate with Gemini Master Process (GMP) through Gemini Instrument Application Programmer Interface (GIAPI). This work presents the design and development process of the IGRINS-2 control software.
This paper describes the deployment of the GMT-Consortium Large Earth Finder (G-CLEF) at the Clay telescope, one of the two Magellan telescopes, in late 2025, moving to the GMT in 2030. G-CLEF is a fiber-fed, ultra-high stability optical band echelle spectrograph designed for extremely precise stellar radial velocity measurement. On the Magellan Clay telescope, G-CLEF will take spectra with resolution up to ~300,000, fully resolving molecular spectral features and opening totally new discovery space for exoplanet atmosphere composition studies. G@M will also be coupled to the Magellan extreme adaptive optics facility, MagAO-X which will allow it to spatially resolve several exoplanets from their host stars. We provide a system description of the G@M instrument as it will be configured at Magellan. A top-level review of optomechanics, electronics and control systems follows, as well as a description of several risk-reduction exercises the team has undertaken.
This conference presentation was prepared for the Ground-based and Airborne Telescopes IX conference at SPIE Astronomical Telescopes + Instrumentation, 2022.
The prototype of KASI-Deep Rolling Imaging Fast-optics Telescope (K-DRIFT) pathfinder is a 300 mm confocal off-axis freeform three-mirror system that has been developed for the detection of extended low surface brightness (LSB; below μV = 28 mag arcsec-2) structures. Until now, it is still very difficult to observe the LSB features due to systematic errors introduced by natural and instrumental effects. To overcome these, we apply the confocal off-axis telescope design theory that removed linear astigmatism, and each mirror made of Zerodur is set as a freeform surface to remove the residual aberration. Through the design, we can get high-quality images in a wide field of view and minimize sky background fluctuations. The size of the entrance pupil of the telescope is 300 mm and the focal length is 1200 mm. The field of view of the telescope is ~1° × 1° and the size of the focal plane is 22.5 mm × 22.5 mm. We have measured root mean square wavefront errors of the system after integration of the mirrors, flexures, and housing. At off-axis fields, the maximum root mean square wavefront error before the alignment is 260 nm, and decreased to 115 nm after alignment. Alignment-induced astigmatism and coma were almost eliminated through the process. In this paper, we briefly present the integration and alignment process of the K-DRIFT pathfinder and the current status of the project.
KEYWORDS: Mirrors, Telescopes, Actuators, Space telescopes, Off axis mirrors, Integrated modeling, Interfaces, Optical instrument design, Phase transfer function, Control systems
The Fast-Steering Secondary Mirror (FSM) of Giant Magellan Telescope (GMT) consists of seven 1.1m diameter segments with effective diameter of 3.2m. Each segment is held by three axial supports and a central lateral support with a vacuum system for pressure compensation. Both on-axis and off-axis mirror segments are optimized under various design considerations. Each FSM segment contains a tip-tilt capability for guiding to attenuate telescope wind shake and mount control jitter. The design of the FSM mirror and support system configuration was optimized using finite element analyses and optical performance analyses. The design of the mirror cell assembly will be performed including sub-assembly parts consisting of axial supports, lateral support, breakaway mechanism, seismic restraints, and pressure seal. . In this paper, the mechanical results and optical performance results are addressed for the optimized FSM mirror and mirror cell assembly, the design considerations are addressed, and performance prediction results are discussed in detail with respect to the specifications
The Fast-steering Secondary Mirror (FSM) of Giant Magellan Telescope (GMT) consists of seven 1.1 m diameter circular segments with an effective diameter of 3.2 m, which are conjugated 1:1 to the seven 8.4 m segments of the primary. Each FSM segment contains a tip-tilt capability for fast guiding to attenuate telescope wind shake and mount control jitter by adapting axial support actuators. Breakaway System (BAS) is installed for protecting FSM from seismic overload or other unknown shocks in the axial support. When an earthquake or other unknown shocks come in, the springs in the BAS should limit the force along the axial support axis not to damage the mirror. We tested a single BAS in the lab by changing the input force to the BAS in a resolution of 10 N and measuring the displacement of the system. In this paper, we present experimental results from changing the input force gradually. We will discuss the detailed characteristics of the BAS in this report.
The Giant Magellan Telescope (GMT) will feature two Gregorian secondary mirrors, an adaptive secondary mirror (ASM) and a fast-steering secondary mirror (FSM). The FSM has an effective diameter of 3.2 m and consists of seven 1.1 m diameter circular segments, which are conjugated 1:1 to the seven 8.4m segments of the primary. Each FSM segment contains a tip-tilt capability for fast guiding to attenuate telescope wind shake and mount control jitter. This tiptilt capability thus enhances performance of the telescope in the seeing limited observation mode. The tip-tilt motion of the mirror is produced by three piezo actuators. In this paper we present a simulation model of the tip-tilt system which focuses on the piezo-actuators. The model includes hysteresis effects in the piezo elements and the position feedback control loop.
The GMT-Consortium Large Earth Finder (G-CLEF) is an instrument that is being designed to exceed the state-of-the-art radial velocity (RV) precision achievable with the current generation of stellar velocimeters. It is simultaneously being designed to enable a wide range of scientific programs, prominently by operating to blue wavelengths (< 3500Å). G-CLEF will be the first light facility instrument on the Giant Magellan Telescope (GMT) when the GMT is commissioned in 2023. G-CLEF is a fiber-fed, vacuum-enclosed spectrograph with an asymmetric white pupil echelle design. We discuss several innovative structural, optical and control system features that differentiate G-CLEF from previous precision RV instruments.
The Giant Magellan Telescope (GMT) will be equipped with two Gregorian secondary mirrors: a fast-steering mirror (FSM) system for seeing-limited operations and an adaptive secondary mirror (ASM) for adaptive optics observing modes. The FSM has an effective diameter of 3.2 m and is comprised of seven 1.1 m diameter circular segments, which are conjugated 1:1 to the seven 8.4m segments of the primary. Each FSM segment has a tip-tilt capability for fast guiding to attenuate telescope wind shake and jitter. To verify the tip-tilt performance at various orientations, we performed tiptilt tests using a conceptual prototype of the FSM (FSMP) which was developed at KASI for R&D of key technologies for FSM. In this paper, we present configuration, methodology, results, and lessons from the FSMP test which will be considered in the development of FSM.
The Fast Steering Secondary Mirror (FSM) for the Giant Magellan Telescope (GMT) will have seven 1.05 m diameter circular segments and rapid tip-tilt capability to stabilize images under wind loading. In this paper, we report on the assembly, integration, and test (AIT) plan for this complex opto-mechanical system. Each fast-steering mirror segment has optical, mechanical, and electrical components that support tip-tilt capability for fine coalignment and fast guiding to attenuate wind shake and jitter. The components include polished and lightweighted mirror, lateral support, axial support assembly, seismic restraints, and mirror cell. All components will be assembled, integrated and tested to the required mechanical and optical tolerances following a concrete plan. Prior to assembly, fiducial references on all components and subassemblies will be located by three-dimensional coordinate measurement machines to assist with assembly and initial alignment. All electronics components are also installed at designed locations. We will integrate subassemblies within the required tolerances using precision tooling and jigs. Performance tests of both static and dynamic properties will be conducted in different orientations, including facing down, horizontal pointing, and intermediate angles using custom tools. In addition, the FSM must be capable of being easily and safely removed from the top-end assemble and recoated during maintenance. In this paper, we describe preliminary AIT plan including our test approach, equipment list, and test configuration for the FSM segments.
The Giant Magellan Telescope (GMT) will be equipped with two Gregorian secondary mirrors; a fast-steering secondary mirror (FSM) for seeing-limited operations and an adaptive secondary mirror (ASM) for adaptive optics observing modes. The FSM has an effective diameter of 3.2 m and is comprised of seven 1.1 m diameter circular segments, which are conjugated 1:1 to the seven 8.4m segments of the primary mirror. Each FSM segment has a tip-tilt capability for fast guiding to attenuate telescope wind shake and jitter. The FSM is mounted on a two-stage positioning system; a macro-cell that positions the entire FSM segments as an assembly and seven hexapod actuators that position and drive the individual FSM segments. In this paper, we present a technical overview of the FSM development status. More details in each area of development will be presented in other papers by the FSM team.
Direct imaging using a starshade is a powerful technique for exoplanet detection and characterization. No current post-processing methods are specialized for starshade images and the ones for coronagraph images have not been applied to images produced by a starshade system ( starshade system means the light sources, starshade and telescope). Here, we report on the first step towards adapting these methods for starshade systems. We have built a starshade imaging model. We generate the image based on a simulation of the real astronomical scene and consider the effects of various starshade defects, misalignment, wavefront error, and detector noise. Future work will add the system dynamics of formation flying between the starshade and the telescope. The ultimate goal is to adapt coronagraphic image processing methods for starshade imaging.
Starshades are a leading technology to enable the direct detection and spectroscopic characterization of Earth-like exoplanets. Two key aspects to advancing starshade technology are the demonstration of starlight suppression to the level required for flight and validation of optical models at this high level of suppression. These technologies are addressed in current efforts underway at the Princeton Starshade Testbed. We report on results from modeling the performance of the Princeton Starshade Testbed to help achieve the milestone 10−9 suppression. We use our optical model to examine the effects that errors in the occulting mask shape and external environmental factors have on the limiting suppression. We look at deviations from the ideal occulter shape such as over-etching during the lithography process, edge roughness of the mask, and random defects introduced during manufacturing. We also look at the effects of dust and wavefront errors in the open-to-atmosphere testbed. These results are used to set fabrication requirements on the starshade and constraints on the testbed environment. We use detailed measurements of the manufactured occulting mask to converge towards agreement between our modeled performance predictions and the suppression measured in the testbed, thereby building confidence in the validity of the optical models. We conclude with a discussion of the advantages and practicalities of scaling to a larger testbed to further advance the optical aspect of starshade technology.
A starshade is a specially designed opaque screen to suppress starlight and remove the effects of diffraction at the edge. The intensity at the pupil plane in the shadow is dark enough to detect Earth-like exoplanets by using direct imaging. At Princeton, we have designed and built a testbed that allows verification of scaled starshade designs whose suppressed shadow is mathematically identical to that of space starshade. The starshade testbed uses a 77.2 m optical propagation distance to realize the flight Fresnel number of 14.5. Here, we present lab result of a revised sample design operating at a flight Fresnel number. We compare the experimental results with simulations that predict the ultimate contrast performance.
A starshade or external occulter is a spacecraft flown along the line-of-sight of a space telescope to suppress starlight and
enable high-contrast direct imaging of exoplanets. Because of its large size and scale it is impossible to fully test a starshade
system on the ground before launch. Therefore, laboratory verification of starshade designs is necessary to validate the
optical models used to design and predict starshade performance. At Princeton, we have designed and built a testbed that
allows verification of scaled starshade designs whose suppressed shadow is mathematically identical to that of a
comparable space starshade. The starshade testbed uses 77.2 m optical propagation distance to realize the flight-appropriate
Fresnel numbers of 14.5. Here we present the integration status of the testbed and simulations predicting the ultimate
contrast performance. We will also present our results of wavefront error measurement and its implementation of
suppression and contrast.
Princeton University is upgrading our space occulter testbed. In particular, we are lengthening it to ~76m to achieve flightlike Fresnel numbers. This much longer testbed required an all-new enclosure design. In this design, we prioritized modularity and the use of commercial off-the-shelf (COTS) and semi-COTS components. Several of the technical challenges encountered included an unexpected slow beam drift and black paint selection. Herein we describe the design and construction of this long-travel laser enclosure.
One of the main candidates for creating high-contrast for future Exo-Earth detection is an external occulter or sharshade. A starshade blocks the light from the parent star by flying in formation along the line-of-sight from a space telescope. Because of its large size and scale it is impossible to fully test a starshade system on the ground before launch. Instead, we rely on modeling supported by subscale laboratory tests to verify the models. At Princeton, we are designing and building a subscale testbed to verify the suppression and contrast of a starshade at the same Fresnel number as a flight system, and thus mathematically identical to a realistic space mission. Here we present the mechanical design of the testbed and simulations predicting the ultimate contrast performance. We will also present progress in implementation and preliminary results.
Several computer-aided alignment (CAA) methods have been developed for the alignment of multi-element optical
systems. Most of the methods use singular value decomposition or non-linear optimization to calculate the amount of
misalignment. However, when we do the alignment of the optical system, we frequently encounter at least two problems;
one is the solution stalled in local minima that fails to align the system within requirement and the other is the field
imbalance of the system. We presume this is due to the lack of boundary conditions imposed during the optimization. In
order to overcome these problems, we propose a new CAA method using rms wavefront error (WFE) value as an
additional boundary condition in optimization. This boundary condition of target rms WFE helps to get around the local
minima and field imbalance while guaranteeing the system performance. We applied this method to the alignment of the
optical system consisting of three mirrors and four lenses. By only single trial of alignment, we obtained the rms WFE of
less than λ /20 (λ=3390 nm) at all fields and field difference less than λ /200 in off-axis field. Therefore, it is clear that
our new method is very effective and accurate, compared to the conventional CAA algorithm.
We first studied the characteristics of alignment performances of two computer-aided alignment algorithms i.e. merit
function regression (MFR) and differential wavefront sampling (DWS). The initial study shows i) that, utilizing damped
least square algorithm, MFR offers accurate alignment estimation to the optical systems with non-linear wavefront
sensitivity to changes in alignment parameters, but at the expense of neglecting the coupling effects among multiple
optical components, and ii) that DWS can estimate the alignment state while taking the inter-element coupling effects
into consideration, but at the expense of increased sensitivity to measurement error associated with experiment apparatus.
Following the aforementioned study, we report a new improved alignment computation technique benefitted from
modified MFR computation incorporating the concept of standard DWS method. The optical system used in this study is
a three-mirror anastignmat (TMA) based optical design for the next generation geostationary ocean color instrument
(GOCI-II). Using an aspheric primary mirror of 210 mm in diameter, the F/7.3 TMA design offers good imaging
performance such as 80% in 4 um in GEE, MTF of 0.65 at 65.02 in Nyquist frequency. The optical system is designed to
be packaged into a compact dimension of 0.25m × 0.55m × 1.050m. The trial simulation runs demonstrate that this
integrated alignment method show much better alignment estimation accuracies than those of standard MFR and DWS
methods, especially when in presence of measurement errors. The underlying concept, computational details and trial
simulation results are presented together with implications to potential applications.
The precise alignment of multiple element large optical system is a challenging task. In order to increase the alignment
process efficiency, computer aided alignment methods utilizing Zernike polynomial coefficients have been developed
over the last few decades. Recently, differential wavefront sampling(DWS) algorithm revealed that derivative
information about the wavefront is a very useful to separate wavefront coupling effect between optical elements of the
target system. We compared the alignment performance of the DWS, sensitivity table method and merit function
regression method. Even though DWS showed the best performance in simulation, it revealed weak points in terms of
high sensitivity to the experimental conditions when applied to the real alignment of Korsch type optical system. In this
paper, we explain three different alignment algorithms and discuss the problems in DWS method under current
experimental situation, and show the alignment result for Korsch type optical system using merit function regression
method.
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