Performance prediction of the TMT tertiary mirror support system

Primary mirror is an important component of collimator. The surface figure error of primary mirror is a critical factor affecting the imaging quality of collimator. Besides, the support system of primary mirror of collimator must be steady, while collimator need be moved safely as an elementary optical measuring tool. The support system of the primary mirror is composed of axial support and lateral support. Due to the axis of the primary mirror is horizontal when collimator working, the lateral support of the primary mirror has a far greater impact on the figure error of the primary mirror. In this paper, static structure analysis with finite element method is carried out for a 5m collimator primary mirror with V-block support under gravity load. With the analysis, the relationship between the structure parameters in primary mirror V-block support and the deformation of the primary mirror is built. With this relationship, the optimization parameters are found out to reduce the gravity deformation of the primary mirror.

To calibrate the tracing performance of the thirty meter telescope (TMT) tertiary mirror, for the special requirement of the TMT, the laser tracker is used to verify the motion. Firstly, the deviation is divided into two parts, namely, the repeatable error and the unrepeatable part. Then, based on the laser tracker, the mearturement and evalutation methods of the rigid body motion for the mirror are established, and the Monte Carol method is used to determine the accuracy of the mothod. Lastly, the mothod is applied to the turn table of a classical telescope and the residual error is about 4 arc second. The work of this paper will guide the next desgin and construction work of the thirty meter telescope tertiary mirror.

The California Extremely Large Telescope (CELT) is a joint project of the University of California and the California Institute of Technology to build and operate a 30-meter diameter telescope for research in astronomy at visible and infrared wavelengths. The current optical design calls for a primary, secondary, and tertiary mirror with Ritchey-Chretien foci at two Nasmyth platforms. The primary mirror is a mosaic of 1080 actively stabilized hexagonal segments. This paper summarizes the recent progress on the conceptual design of this telescope.

The European Extremely Large Telescope (ELT) construction¹ is advancing and the M2, M3 and M5 cells are running the same path. The M2² and M3 mirrors are 4-meter class Zerodur® meniscus supported axially and laterally by mechanical whiffletrees. To allow low order corrections, axial support is provided with a warping harness system. Additionally, an electromechanical hexapod allows the movement in 5 degrees of freedom to optically align the telescope. The M2 Cell is ending the integration and test phase and approaching to the verification phase, where the highly demanding requirements will be checked. On the other hand, M3 cell is being assembled, taking advantage of the lessons learned during the M2 cell assembly. The M5 mirror is lightweighted silicon carbide elliptical flat mirror of 2.7 x 2.1 m², having the objective of folding the optical beams towards the Nasmyth platforms. Additionally, stabilizes the image movements induced by the telescope mechanisms and wind shaking vibrations. The M5 Cell is divided in two stages: the Tip-tilt and the Alignment Stage. The former allows to perform a fast-steering control while the latter provides active alignment capabilities to cope with the overall telescope structure misalignments The ELT M5 Cell is currently in the final design review, with qualification models for both stages successfully developed and tested. Preliminary results shown submicrometric resolutions for the Alignment Stage and around 5 nanometres for the Tip-Tilt Stage. This paper summarizes the design of the M2, M3 and M5 cells and presents its current development status.

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.

This paper describes the studies performed to establish a baseline conceptual design of the Segment Support Assembly (SSA) for the Thirty Meter Telescope (TMT) primary mirror. The SSA uses a combination of mechanical whiffletrees for axial support, a central diaphragm for lateral support, and a whiffletree-based remote-controlled warping harness for surface figure corrections. Axial support whiffletrees are numerically optimized to minimize the resulting gravityinduced deformation. Although a classical central diaphragm solution was eventually adopted, several lateral support concepts are considered. Warping harness systems are analyzed and optimized for their effectiveness at correcting second and third order optical aberrations. Thermal deformations of the optical surface are systematically analyzed using finite element analysis. Worst-case performance of the complete system as a result of gravity loading and temperature variations is analyzed as a function of zenith angle using an integrated finite element model.

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.

The Solar Optical Telescope (SOT) is designed to operate as an attached payload mounted on the Instrument Pointing System (IPS) in the cargo bay of the Shuttle Orbiter. Pointing and control of SOT is accomplished by an active Articulated Primary Mirror (APM), an active Tertiary Mirror (TM), an elaborate set of optical sensors, electromechanical actuators and programmable controllers. The structural interactions of this complex control system are significant factors in the stability of the SOT. The preliminary stability study results of the SOT dynamical system are presented. Structural transfer functions obtained from the NASTRAN model of the structure were used. These studies apply to a single degree of freedom (elevation). Fully integrated model studies will be conducted in the future.

Present day spectrographs with their excellent coatings and high quantum efficiency CCDs have reached levels of performance which cannot easily be exceeded by significant factors. To achieve still higher efficiency it is necessary to observe many objects simultaneously either with slit-mask or multi-fiber techniques. It is therefore planned to implement both techniques on the Keck 10-meter telescope. Multi-slit or slit-mask devices will be implemented on both the low-resolution and moderate-resolution instruments. Because of the limited space at the Cassegrain focus the multi-fiber mode will be implemented only on the Moderate Resolution Imaging Spectrometer (MRIS) and the high resolution instrument which are located on the Nasmyth platform. In this talk I will briefly describe the MRIS and indicate how we plan to implement the fiber mode.

The paper reports optical system of a 1 meter diameter telescope dedicated to Stellar Observations Network Group (SONG) for the National Astronomical Observatories, CAS. SONG is an international cooperative project, Optimize the design for Asteroseismology purposes. According to the prototype of SONG, Chinese SONG telescope includes Cassegrain telescope, Nasmyth platform, Coude train, Coude focal plane, Shack Hartmann wavefront sensor and spectrograph. The telescope will provide a field of view of 65 arcsec at the Nasmyth F/36.67 focus, 10 arcsec at the F/6 Coude focus. The rotating tertiary mirror directs the light to the two Nasmyth foci, one for Shack-Hartmann wavefront sensor, the other for Nasmyth platform and spectrograph.

The stability problem for the axisymmetric equilibrium states of an isorotating liquid bridge between equidimensional circular disks in a constant axial gravity field is considered. In particular, we examine the stability of bridges satisfying two constraints that are typical for the floating zone method used for materials purification and single crystal growth. First we consider the constraint that the relative volume of the bridge, V, is equal to 1. Here, V is the ratio of the actual bridge volume to that of a cylinder pinned to the edges of disks. For this case, the critical values of the slenderness (Λ) (ratio of the disk separation to the diameter) and of the free surface slopes (β1,β2) at both disks have been determined for a wide range of the Bond (B) and Weber (W) numbers. The second constraint is that the surface slope β1 at one of the disks is prescribed. The chosen values are 90° and 75° and correspond to extremes in growth angle values encountered in floating zone crystal growth. For this case, the dependencies of critical Λ and V values B and W have been calculated. In addition, both axial gravity directions are considered separately and the values of the slope angle, β2, at the other disk are also analyzed for critical states. The solution of the stability problem for any liquid bridge is discussed in detail using the case for B=W=0.1 as an example. In particular, the relationship between the general boundary of the stability region and the stability of bridges subject to the constraints outlined above is examined.

Intravascular ultrasound (IVUS) is a vascular imaging technique that is used to study atherosclerosis since it has the ability to show the lumen and the vessel wall. Cross-sectional images of blood vessels are produced and they provide quantitative assessment of the vascular wall, information about the nature of atherosclerotic lesions, as well as the plaque shape and size. Due to the ultrasound speckle, catheter artifacts, or calcification shadows, the automated analysis of large IVUS data sets represents an important challenge. A multiple interface 3D fast-marching method is presented for the detection of the lumen and external vessel wall boundaries. The segmentation is based on a combination of region and contour information, namely, the gray level probability density functions of the vessel structures and the intensity gradient. The detection of the lumen boundary is fully automatic. The segmentation method includes an interactive initialization procedure of the external vessel wall border. The segmentation method was applied to 20 in vivo IVUS data sets acquired from femoral arteries. This database contained three subgroups: Pullbacks acquired before balloon angioplasty (n=7), after the intervention (n=7), and at a 1 yr follow-up examination (n=6). Results were compared to validation contours that were manually traced by two experts on more than 1500 individual frames. For all subgroups, no significant difference was found between the area measurements of the segmentation and validation contours for the lumen and external vessel wall. Moreover, high intraclass correlation coefficients (> 0.96) between the area of the manually traced contours and detected boundaries with the fast-marching method were obtained for both vessel layers over the whole database. The segmentation performance was also evaluated with point-to-point contour distances between segmentation results and manually traced contours. A good overall accuracy was obtained with average distances < 0.13 mm and maximum distances < 0.46 mm, indicating a good performance in regions lacking information or containing artifacts. Only small differences of less than a pixel (0.02 mm) were observed between the average distance metrics of each subgroup, which prove the segmentation consistency. This new IVUS segmentation method provides accurate results that correspond well to the experts' manually traced contours, but requires much less manual interactions and is faster.

Analytical second-order drag theory with application for lifetime determination of artificial satellites in low earth orbits

For GPS satellite clocks, a nominal (hardware) frequency offset and a conventional periodic relativistic correction derived as a dot product of the satellite position and velocity vectors, are used to compensate the relativistic effects. The conventional hardware clock rate offset of 38,575.008 ns/day corresponds to a nominal orbit semi-major axis of about 26,561,400 m. For some of the GPS satellites, the departures from the nominal semi-major axis can cause an apparent clock rate up to 10 ns/day. GPS orbit perturbations, together with the earth gravity field oblateness, which is largely responsible for the orbit perturbations, cause the standard GPS relativistic transformations to depart from the rigorous relativity transformation by up to 0.2 ns/day. In addition, the conventional periodic relativistic correction exhibits periodic errors with amplitudes of about 0.1 and 0.2 ns, with periods of about 6 h and 14 days, respectively. Using an analytical integration of the gravity oblateness term (J2), a simple analytical approximation was derived for the apparent clock rate and the 6-h periodic errors of the standard GPS gravity correction. For daily linear representations of GPS satellite clocks, the improved relativistic formula was found to agree with the precise numerical integration of the GPS relativistic effects within about 0.015 ns. For most of the Block IIR satellites, the 6-h periodical errors of the GPS conventional relativistic correction are already detectable in the recent IGS final clock combinations.

This paper presents preliminary results of a broader ongoing experimental study on the seismic bond strengthening of the critical reinforcement splice region in wide reinforced concrete (RC) columns or bridge piers confined with carbon fiber reinforced polymer (FRP) laminates and having bending about their minor axis. Large lateral drifts induced by strong earthquakes may result in splitting bond failure of the spliced bars, or rapid bond degradation at the splice location, leading to possible structural failure of the columns or piers. Previous research has verified the effectiveness of external confinement using FRP composites for improving bond performance of the spliced reinforcement of columns or piers having circular cross section, or rectangular cross section subjected to cyclic loading about their major axis. The preliminary experimental program reported in this paper consists of testing two full-scale wide column specimens under extreme substandard splice detailing associated with relatively short splice length, small concrete covers, small transverse spacing between the spliced bars, and complete absence of internal steel ties within the splice region. The test results showed that, despite extreme substandard splice detailing, the use of external FRP confinement improved the bond strength of the spliced bars, delayed the bond stiffness degradation under cyclic loading, and increased the energy dissipation capacity of the wide columns. However, the corresponding improvements were not as effective as anticipated. Consequently, before a final conclusion is drawn, more tests will be carried out on similar specimens but using instead more realistic and practical splice details as well as internal transverse steel ties for satisfying the minimum detailing requirements of the ACI 318-11 for gravity load designed axial members.