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.
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.
This conference presentation was prepared for the Ground-based and Airborne Telescopes IX conference at SPIE Astronomical Telescopes + Instrumentation, 2022.
A Prototype of Fast-steering Secondary Mirror (FSMP) for the Giant Magellan Telescope (GMT) has been developed by the consortium consisting of institutes in Korea and the US. In 2014 the FSMP development was finalized by combining the two major sub-systems, the mirror fabricated and the mirror cell with the tip-tilt control parts. We have developed an assembly procedure in which potential difficulties, such as handling without contacting mirror surface, and optimizing bonding process, have been resolved. Supporting jigs were produced, and optimized bonding techniques have been developed. The assembled FSMP system was installed in a test tower, and stability of the system were checked. Performance of the FSMP system will be evaluated in static and dynamic environments for the validation of the FSMP system operation as the future works.
The Giant Magellan Telescope (GMT) is one of Extremely large telescopes, which is 25m in diameter featured with two Gregorian secondary mirrors, an adaptive secondary mirror (ASM) and a fast-steering secondary mirror (FSM). The FSM is 3.2 m in diameter and built as seven 1.1 m diameter circular segments conjugated 1:1 to the seven 8.4m segments of the primary. The guiding philosophy in the design of the FSM segment mirror is to minimize development and fabrication risks ensuring a set of secondary mirrors are available on schedule for telescope commissioning and early operations in a seeing limited mode. Each FSM segment contains a tip-tilt capability for fine co-alignment of the telescope subapertures and fast guiding to attenuate telescope wind shake and mount control jitter, thus optimizing the seeing limited performance of the telescope. The final design of the FSM mirror and support system configuration was optimized using finite element analyses and optical performance analyses. The optical surface deformations, image qualities, and structure functions for the gravity print-through cases, thermal gradient effects, and dynamic performances were evaluated. The results indicated that the GMT FSM mirror and its support system will favorably meet the optical performance goals for residual surface error and the FSM surface figure accuracy requirement defined by encircled energy (EE80) in the focal plane. The mirror cell assembly analysis indicated an excellent dynamic stiffness which will support the goal of tip-tilt operation.
The Giant Magellan Telescope (GMT) Fast Steering Secondary Mirror (FSM) is one of the GMT two Gregorian secondary mirrors. The FSM is 3.2 m in diameter and built as seven 1.06 m diameter circular segments. The conceiving philosophy used on the design of the FSM segment mirror is to minimize development and fabrication risks ensuring a set of secondary mirrors are available on schedule for telescope commissioning and early operations in a seeing limited mode, thereby mitigating risks associated with fabrication of the Adaptive Secondary Mirrors (ASM). This approach uses legacy design features from the Magellan Telescope secondary mirrors to reduce such risks. The final design of the substrate and support system configuration was optimized using finite element analyses and optical performance analyses. The optical performance predictions of the FSM are based on a substrate with a diameter of 1.058m (on-axis), 1.048m (off-axis), a depth of 120mm, and a face plate thickness of 20mm leading to a mass of approximately 90kg. The optical surface deformations, image qualities, and structure functions for the axial and lateral gravity print-through cases, thermal gradient effects, and dynamic performances were evaluated. The results indicated that the GMT FSM mirror and its support system will favorably meet the optical performance goals for residual surface error and the FSM surface figure accuracy requirement defined by encircled energy in the focal plane. The mirror cell assembly analysis indicated an excellent dynamic stiffness which will support the goal of 20 Hz tip-tilt motion.
The Giant Magellan Telescope (GMT) will be one of the next class of extremely large segmented mirror telescopes. The GMT will utilize two Gregorian secondary mirrors, and Adaptive Secondary Mirror (ASM) and a Fast-steering Secondary Mirror (FSM). The FSM consists of six off-axis mirrors surrounding a central on-axis circular segment. The segments are 1.1 m in diameter and conjugated 1:1 to the seven 8.4 m segments of the primary. A prototype of the FSM mirror (FSMP) has been developed, analyzed and tested in order to demonstrate the mechanical and optical responses of the mirror assembly when subjected to structural and thermal loadings. In this paper, the mechanical and thermal performances of the FSMP were evaluated by performing finite element analyses (FEA) in NX Nastran. The deformation of the mirror’s lateral flexure was measured when the FSMP was axially loaded and the temperature response of the mirror assembly was measured when exposed to a sample thermal environment. In order to validate the mirror/lateral flexure design concept, the mechanical, optical and thermal measurements obtained from the tests conducted on mirrors having two different lateral flexures were compared to the responses calculated by FEA.
The fast steering mirror (FSM) is a key element in astronomical telescopes to provide real-time angular correction of line-of-sight error due to telescope jitter and wind-induced disturbance. The Giant Magellan Telescope (GMT) will utilize a FSM as secondary mirror under unfavorable wind conditions that excites the telescope at the lowest resonance frequency around 8Hz. A flexure in the center of the mirror constrains lateral displacements, while still allowing tip-tilt motion to steer. Proper design of this central flexure is challenging to meet lateral loading capability as well as angular and axial flexibility to minimize optical surface distortion forced by redundant constraints at the flexure. We have designed the lateral flexure and estimated its performance from a variety of design case studies in a finite element analysis tool. A carefully designed finite element model at the sub-system level including the flexure, lightweight mirror and 3 point axial supports allows evaluating whether the designed flexure is qualified within specifications. In addition, distorted surface maps can be achieved as a function of forces that could be induced in telescope operation or due to misalignment errors during assembling. We have also built a test set-up to validate the finite element analysis results. Optical quality was measured by a phase shifting interferometer in various loading conditions and the measurements were decomposed by standard Zernike polynomials to concentrate specific surface shapes and to exclude low order shapes as measurement uncertainties.
FSM is a secondary mirror of the Giant Magellan Telescope (GMT), which is 3.2 m in diameter. It consists of seven
segments, each of which is 1m in diameter. The surrounding six segments are off-axis mirrors. FSM compensates image
degradations caused by wind turbulence and structure jitter by using a tip-tilt mechanism.
Korea Astronomy and Space Science Institute is developing a prototype of Fast Steering Mirror (FSM) together with
four other institutions. The prototype is a full-size FSM segment, and it has two features; an off-axis mirror and a testbed
for tip-tilt actuation. The off-axis mirror has the diameter of 1.06 m and fast focal ratio of 0.65. At present, lightweighting
is successfully finished, and polishing of the front surface is proceeding.
As for the tip-tilt, several test-beds have been assembled and the functions of tip-tilt have been checked. The third testbed
is being integrated with a dummy aluminum mirror, three axial supports, a lateral support, and a test-bed frame. It is
activated by a vacuum system. The test-bed will examine and verify the tip-tilt parameters. The FSM prototype is
expected to be completed by 2012. In this paper, system engineering and progress of the prototype development are to be
presented.
The Giant Magellan Telescope (GMT) will be a 25m class telescope currently in the design and development phase. The
GMT will be a Gregorian telescope and equipped with a fast-steering secondary mirror (FSM). This secondary mirror is
3.2 m in diameter and built as seven 1.1 m diameter circular segments conjugated 1:1 to the seven 8.4m segments of the
primary. The prototype of FSM (FSMP) development effort is led by the Korea Astronomy and Space Science Institute
(KASI) with several collaborators in Korea, and the National Optical Astronomy Observatory (NOAO) in USA. The
FSM has a tip-tilt feature to compensate image motions from the telescope structure jitters and the wind buffeting. For
its dynamic performance, each of the FSM segments is designed in a lightweight mirror. Support system of the
lightweight mirror consists of three axial actuators, one lateral support at the center, and a vacuum system. A parametric
design study to optimize the FSM mirror configuration was performed. In this trade study, the optical image qualities
and structure functions for the axial and lateral gravity print-through cases, thermal gradient effects, and dynamic
performances will be discussed.
The Giant Magellan Telescope (GMT) Fast-steering secondary mirror (FSM) is one of the GMT two Gregorian
secondary mirrors. The FSM is 3.2 m in diameter and built as seven 1.1 m diameter circular segments conjugated 1:1 to
the seven 8.4m segments of the primary. A parametric study and optimization of the FSM mirror blank and central
lateral flexure design were performed. For the optimized FSM configuration, the optical image qualities and structure
functions for the axial and lateral gravity print-through cases, thermal gradient effects, and dynamic performances will be
discussed. This paper reports performance predictions of the optimized FSM. To validate our lateral flexure design
concept, mechanical and optical tests were conducted on test mirrors installed with two different lateral flexures.
The Giant Magellan Telescope (GMT) will be a 25m class telescope which is one of the extremely large telescope
projects in the design and development phase. The GMT will have two Gregorian secondary mirrors, an adaptive
secondary mirror (ASM) and a fast-steering secondary mirror (FSM). Both secondary mirrors are 3.2 m in diameter and
built as seven 1.1 m diameter circular segments conjugated 1:1 to the seven 8.4m segments of the primary. The FSM has
a tip-tilt feature to compensate image motions from the telescope structure jitters and the wind buffeting. The support
system of the lightweight mirror consists of three axial actuators, one lateral support at the center, and a vacuum system.
A parametric study and optimization of the FSM mirror blank and central lateral flexure design were performed. This
paper reports the results of the trade study. The optical image qualities and structure functions for the axial and lateral
gravity print-through cases, thermal gradient effects, and dynamic performances will be discussed for the case of a lightweighted
segment with a center thickness of 140 mm weighing approximately 105 kg.
Giant Magellan Telescope (GMT) is one of the largest next-generation ground telescopes whose diameter is 25.4m. It
has been developed since 2003, and is expected to be finished by 2018. Korea officially joined the GMT project in 2009,
and actively participates in the development. KASI (Korea Astronomy & Space Science Institute) and Korean
astronomical society are planning several activities to enhance the capabilities in science research. Building a secondary
mirror system is another activity Korea wants to develop. A prototype of the GMT secondary is being developed.
Developing a spectrograph is another one. In this talk, I will present the plan of Korea's works for the GMT.
The simplex fitting method makes use of a geometrical figure that finds the minimum variance value in successive steps. It was developed from the idea of finding the minimum value of a function. A set of vertices are assigned at first with associated coefficients and variances. The vertex with the highest variance value moves by one of the four mechanisms of reflection, expansion, contraction, or shrinkage. By repeating this process, the vertices proceed toward the minimum value of variance. Finally, the best fit to the basis function is achieved, and appropriate coefficients can be derived. When the algorithm of the simplex fitting method was examined, it was found that one of the four mechanisms, shrinkage, may not be used normally for continuous functions. This was also confirmed by examining the usage of the mechanism in the fitting of several equations. A revised flowchart of the simplex fitting method is presented.
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