Interrogating ejecta particles launched from target materials that are undergoing dynamic shock can be done with both xray imaging and visible shadowgraph imaging. Our dynamic testing must be done inside a containment vessel with limited access ports available. We designed an imaging system to relay both types of imaging systems through a single port using the same optical relay and then splitting the images onto three separate high-speed imaging cameras outside the containment vessel. X-ray imaging provides ejecta density measurements. Shadowgraph imaging that is done at two wavelengths (blue and red) constrains ejecta particle size distributions and provides areal density measurements of the ejecta cloud. The ejecta particles are positioned 225 mm before the x-ray scintillators; this arrangement permits a folded mirror system to allow the shadowgraph data to bypass the x-ray scintillators. This configuration results in spatial separations between the intermediate image planes of the x-ray and shadowgraph images along the optical axis. At the position of the x-ray intermediate image plane, mirrors are positioned such that the shadowgraph images are kicked out and their images are sent on to different cameras. Positioning of the large doublet relay lenses keeps shrapnel from impacting the vessel containment windows.
This work explores quick predictive methods for calculating potentially risky stresses in cemented doublets underdoing temperature change that agree well with finite element analysis. We also provide guidelines for avoiding stress concentrations.
There is growing interest in using low-energy flash x-ray sources in radiographic applications to provide high-contrast
images of low-density objects. Due to the low-energy nature of the detected photons, thin bright scintillators are desired.
In order to pursue an optimum radiographic system, experimental studies have been performed of the static imaging
properties of thin microcolumnar CsI using a Platts x-ray source. The Platts source is a nominally 300 keV endpoint rod
pinch diode x-ray source with a ~35 ns pulse time. The source was used to measure the imaging properties of
microcolumnar CsI with various thicknesses and backings. The experimental setup was modeled in GEANT4, and the
images were simulated to estimate system performance. Taking into account the source photon production, radiation
transport, and system optical performance, an accurate assessment of the detection system can be deduced.
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.
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.
Thermal modeling of the Thirty Meter Telescope (TMT) was conducted for evaluations of thermal performances by finite element (FE) and optical analysis tools. The thermal FE models consist of the telescope optical assembly systems, instruments, laser facility, control and electronic equipments, and telescope structural members. A three-consecutive-day thermal environment data was implemented for the thermal boundary created by Computational Fluid Dynamics (CFD) based on the environment conditions of the TMT site. Temporal and spatial temperature distributions of the optical assembly systems and the telescope structure were calculated under the environmental thermal conditions including air convections, conductions, heat flux loadings, and radiations. With the calculated temperature distributions, the thermo-elastic analysis was performed to predict thermal deformations of the telescope structure and the optical systems. The line of sight calculation was made using the thermally induced deformations of the optics and structures. Merit function routines (MFR) were utilized to calculate the Optical Path Difference (OPD) maps after repositioning the optics based on a best fit of M1 segment deformations. The goal of this thermal modeling is to integrate the mechanical and optical deformations in order to simulate the thermal effects with the TMT site environment data from CFD.
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.
KEYWORDS: Telescopes, Convection, Thermal modeling, Thermal analysis, Finite element methods, Actuators, Mirrors, Systems modeling, Space telescopes, Thirty Meter Telescope
Thermal performances of the Thirty Meter Telescope (TMT) structure were evaluated by finite element thermal models.
The thermal models consist of the telescope optical assembly systems, instruments, laser facility, control and electronic
equipments, and structural members. Temporal and spatial temperature distributions of the optical assembly systems and
the telescope structure were calculated under various thermal conditions including air convections, conductions, heat flux
loadings, and radiations. In order to capture thermal responses faithfully, a three-consecutive-day thermal environment
data was implemented. This thermal boundary condition was created by CFD based on the environment conditions of the
corresponding TMT site. The thermo-elastic analysis was made to predict thermal deformations of the telescope
structure at every hour for three days. The line of sight calculation was made using the thermally induced structural
deformations. Merit function was utilized to calculate the OPD maps after repositioning the optics based on a best fit of
M1 segment deformations. The goal of this thermal analysis is to establish creditable thermal models by finite element
analysis to simulate the thermal effects with the TMT site environment data. These thermal models can be utilized for
estimating the thermal responses of the TMT structure. Thermal performance prediction of the TMT structure will guide
us to assess the thermal impacts, and enables us to establish a thermal control strategy and requirements in order to
minimize the thermal effects on the telescope structure due to heat dissipation from the telescope mounted equipment
and systems.
KEYWORDS: Telescopes, Convection, Finite element methods, Thermal modeling, Thermal analysis, Space telescopes, Electronics, Control systems, Systems modeling, Thirty Meter Telescope
Thermal analysis for the Thirty Meter Telescope (TMT) structure was performed using finite element analysis in
ANSYS and I-DEAS. In the thermal analysis, the telescope structural parts with simplified optical assembly systems
were modeled for various thermal conditions including air convections, conductions, heat flux loadings, and radiations.
Thermal responses of the TMT telescope structure were predicted and the temperature distributions of the optical
assembly systems were calculated under sample thermal loading conditions. The thermo-elastic analysis was made to
obtain the thermal deformation based on the resulting temperature distributions. The line of sight calculation was made
using the thermally induced structural deformations. The goal of this thermal analysis is to establish thermal models by
the FEA programs to simulate for an adequate thermal environment. These thermal models can be utilized for estimating
the thermal responses of the TMT structure. Thermal performance prediction of the TMT structure will be able to guide
us to control and maintain the system from the "seeing" effects.
Thermal analysis for the Thirty Meter Telescope (TMT) optics (the primary mirror segment, the secondary mirror, and
the tertiary mirror) was performed using finite element analysis in ANSYS and I-DEAS. In the thermal analysis, each of
the optical assemblies (mirror, mirror supports, cell) was modeled for various thermal conditions including air
convections, conductions, heat flux loadings, and radiations. The thermal time constant of each mirror was estimated
and the temperature distributions of the mirror assemblies were calculated under the various thermal loading conditions.
The thermo-elastic analysis was made to obtain the thermal deformation based on the resulting temperature distributions.
The optical performance of the TMT optics was evaluated from the thermally induced mirror deformations. The goal of
this thermal analysis is to establish thermal models by the FEA programs to simulate for an adequate thermal
environment. These thermal models can be utilized for estimating the thermal responses of the TMT optics. In order to
demonstrate the thermal responses, various sample time-dependent thermal loadings were modeled to synthesize the
operational environment. Thermal responses of the optics were discussed and the optical consequences were evaluated.
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