No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Optimization of the ATST primary mirror support system - art. no. 62731E
Abstract
The Advanced Technology Solar Telescope (ATST) primary mirror is a 4.24-m diameter, 75-mm thick, off-axis parabola solid meniscus mirror made out of a glass or glass ceramic material. Its baseline support system consists of 120 axial supports mounted at the mirror back surface and 24 lateral supports along the outer edge with an active optics capability. This primary mirror support system was optimized for the telescope at a near horizon position to achieve the best gravity and thermal effects. To fulfill the optical and mechanical performance requirements, extensive finite element analyses using I-DEAS and optical analyses with PCFRINGE have been conducted for the support optimization. Analyses include static deformation (gravity and thermal), frequency calculations, and support system sensitivity evaluations. An influence matrix was established to compensate potential errors using an active optics system. Performances of the primary mirror support system were evaluated from mechanical deformation calculations and the optical analyses before and after active optics corrections. The performance of the mirror cell structure was also discussed.
... F z , N ι , and N r are proportional to sin θ or cos θ, where r and θ are polar coordinates with the direction θ 0 coinciding with the gravity vector. In the last decade, this conventional push-pull-shear lateral support optimization (CPLSO) was thoroughly investigated and widely used in many particular telescope projects [7][8][9][10][11]. In the above studies, the support position height, H , of the actuator positions from the bottom of the mirror along the z axis is fixed at mid-thickness, H m (or at H 0 , the height of the center of gravity for the mirror), on the outer rim of the mirror. ...
... These three amplitudes are not dependent on θ but on G (here G denotes the gravity force of primary mirror) and the number of support points [see Eqs. (11), (16), and (18)]. ...
... From Eqs. (11) and (13), if the optimal value of β is obtained, the optimization of N r and N τ is accomplished. According to the moment equilibrium and symmetrical distribution of the support locations, an equation for F Z is derived as (10) and (14), we obtain ...
We have proposed a multi-variable H-β optimization approach (MHOA). Compared with the conventional push-pull-shear lateral support optimization (CPLSO), which has only one design variable, β, MHOA adds another design variable, H, which is the support position height. By contrast, the support position height of CPLSO is usually fixed at mid-thickness, Hm (or at H0, the height of the center of gravity for the mirror), on the outer rim of the mirror blank. In addition, hybrid optimization with the sub-problem approximation method and first order method is also applied in MHOA. To verify the feasibility and the advancement, the optimization of the lateral support of the 2.5 m-wide field survey telescope (WFST) is performed with MHOA in this paper. Three designs with different supporting points, including 18 supporting points, 24 supporting points, and 36 supporting points, are obtained, and the residual half path length errors are 23.71 nm, 19.60 nm, and 17.79 nm, respectively. Furthermore, other things being equal, CPLSO with H = H0 as well as CPLSO with H = Hm are used separately to validate the H-β design idea quantitatively. The results have suggested that limiting the value of the residual half path length error, obtained by MHOA, has improved almost 20 nm compared to that of CPLSO with H = H0, and almost 10 nm compared with that of CPLSO with H = Hm.
... Push-pull-shear support, which has been successfully applied to the 3.6 m Devasthal optical telescope (DOT) [7], 4.24 m advanced technology solar telescope (ATST) [8], and 8.1 m Gemini [9], has been proposed to solve this problem. Obviously, push-pull-shear support is mostly applied in the above thin meniscus mirrors, but with the wide application of the lightweight mirrors at present, it is essential to study the push-pull-shear lateral support in the lightweight mirrors. ...
Lightweight primary mirrors are increasingly applied both in ground-based and space-based telescopes. Because the absolute stiffness of the lightweight mirror is much lower than that of the solid one, the design of lateral support becomes more difficult. Based on parallel push-pull support, we have proposed a multi-class variable F-θ optimization approach (MVFOA), where F denotes the magnitude of the support force and θ denotes the support position. Compared with conventional optimization approaches, which only have one class of design variables, F or θ, MVFOA considers the impact of F and θ simultaneously. In addition, we also study push-pull-shear lateral support and propose an unequal-angle push-pull-shear support optimization approach (UPSOA). To verify the advancement of above approaches, by means of finite element calculation, the lateral support optimization of a 2.5 m ULE honeycomb sandwich mirror is performed in this paper. For parallel push-pull support with 24 forces, three optimization approaches with different variables, including single-class variable F, single-class variable θ and multi-class variable F-θ, are compared, and the RMS of surface deformations are 17.60nm, 15.93nm and 14.81nm respectively. For push-pull-shear support with 24 forces, the optimal result by UPSOA occurs when β equals to 0.84 and the RMS of surface deformations is 10.83nm. UPSOA also solves the problem that the forces in the region x≈± R are much larger than the ones in the region x≈0 in the equal-angle push-pull-shear support optimization approach (EPSOA). Through the analysis of results, we find that optimal β of the honeycomb sandwich mirror is greater than that of the meniscus mirror in push-pull-shear support. What’s more, both in parallel push-pull support and push-pull-shear support, it also can be concluded that the position and the magnitude of optimal lateral support forces depend on the stiffness distribution of the mirror along the altitude axis rather than the mass distribution.
... M1 is actively supported by 118 axial actuators and 24 lateral supports (Cho, Price, and Moon, 2006). The active M1 support system, including the thermal control of M1 (Hansen, Bulau, and Phelps, 2008) and a cooled 4 m aperture stop, were produced by Advanced Mechanical and Optical Systems (AMOS) in Belgium. ...
We present an overview of the National Science Foundation’s Daniel K. Inouye Solar Telescope (DKIST), its instruments, and support facilities. The 4 m aperture DKIST provides the highest-resolution observations of the Sun ever achieved. The large aperture of DKIST combined with state-of-the-art instrumentation provide the sensitivity to measure the vector magnetic field in the chromosphere and in the faint corona, i.e. for the first time with DKIST we will be able to measure and study the most important free-energy source in the outer solar atmosphere – the coronal magnetic field. Over its operational lifetime DKIST will advance our knowledge of fundamental astronomical processes, including highly dynamic solar eruptions that are at the source of space-weather events that impact our technological society. Design and construction of DKIST took over two decades. DKIST implements a fast (f/2), off-axis Gregorian optical design. The maximum available field-of-view is 5 arcmin. A complex thermal-control system was implemented in order to remove at prime focus the majority of the 13 kW collected by the primary mirror and to keep optical surfaces and structures at ambient temperature, thus avoiding self-induced local seeing. A high-order adaptive-optics system with 1600 actuators corrects atmospheric seeing enabling diffraction limited imaging and spectroscopy. Five instruments, four of which are polarimeters, provide powerful diagnostic capability over a broad wavelength range covering the visible, near-infrared, and mid-infrared spectrum. New polarization-calibration strategies were developed to achieve the stringent polarization accuracy requirement of 5×10⁻⁴. Instruments can be combined and operated simultaneously in order to obtain a maximum of observational information. Observing time on DKIST is allocated through an open, merit-based proposal process. DKIST will be operated primarily in “service mode” and is expected to on average produce 3 PB of raw data per year. A newly developed data center located at the NSO Headquarters in Boulder will initially serve fully calibrated data to the international users community. Higher-level data products, such as physical parameters obtained from inversions of spectro-polarimetric data will be added as resources allow.
... A simpler type of support system consists of controlled-pressure airbags as the force actuators. These are used in, for example, [4,14], and [15]. These systems are much simpler, smaller, more lightweight, and have a much lower profile than the above mentioned. ...
Successful tests and results that confirm an efficient behavior of the new common-pull (controlled vacuum), multiple-push primary mirror cell for the 2.1 m telescope at OAN/SPM, are presented. An optical design program that reduces the information obtained from intra- and extra-focal Hartmann patterns, using the direction cosines of the rays that cross the sampled regions, is discussed. The intrinsic uncertainties of this method are evaluated.
... Since its first application to the monolithic primary of the new technology telescope (NTT) [2] by European Southern Observatory, active optics systems have been widely used in astronomical telescopes in the last two decades. Among these are the 8 m class Very Large Telescope (the successor of NTT) [3], Gemini [4] and Subaru [5], the 4 m class Telescopio Nazionale Galileo [6], Southern Astrophysical Research telescope [7], the Visible and Infrared Telescope for Astronomy [8], the Advanced Technology Solar Telescope [9], and others [10,11]. ...
In active optics systems, one concern is how to quantitatively separate the effects of astigmatic and trefoil figure errors and misalignments that couple together in determining the total aberration fields when wavefront measurements are available at only a few field points. In this paper, we first quantitatively describe the impact of mount-induced trefoil deformation on the net aberration fields by proposing a modified theoretical formulation for the field-dependent aberration behavior of freeform surfaces based on the framework of nodal aberration theory. This formulation explicitly expresses the quantitative relationships between the magnitude of freeform surfaces and the induced aberration components where the freeform surfaces can be located away from the aperture stop and decentered from the optical axis. On this basis, and in combination with the mathematical presentation of nodal aberration theory for the effects of misalignments, we present the analytic expressions for the aberration fields of two-mirror telescopes in the presence of astigmatic primary mirror figure errors, mount-induced trefoil deformations on both mirrors, and misalignments. We quantitatively separate these effects using the analytical expressions with wavefront measurements at a few field points and pointing errors. Valuable insights are provided on how to separate these coupled effects in the computation process. Monte Carlo simulations are conducted to demonstrate the correctness and accuracy of the analytic method presented in this paper.
... A simpler type of support system consists of controlled-pressure airbags as the force actuators. These are used in, for example, [4,14], and [15]. These systems are much simpler, smaller, more lightweight, and have a much lower profile than the above mentioned. ...
A new concept for push–pull active optics is presented, where the push-force is provided by means of individual airbag type actuators and a common force in the form of a vacuum is applied to the entire back of the mirror. The vacuum provides the pull-component of the system, in addition to gravity. Vacuum is controlled as a function of the zenithal angle, providing correction for the axial component of the mirror’s weight. In this way, the push actuators are only responsible for correcting mirror deformations, as well as for supporting the axial mirror weight at the zenith, allowing for a uniform, full dynamic-range behavior of the system along the telescope’s pointing range. This can result in the ability to perform corrections of up to a few microns for low-order aberrations. This mirror support concept was simulated using a finite element model and was tested experimentally at the 2.12 m San Pedro Mártir telescope. Advantages such as stress-free attachments, lighter weight, large actuator area, lower system complexity, and lower required mirror-cell stiffness could make this a method to consider for future large telescopes.
... To enable high performance optical systems, integration of the thermal analysis and structural analysis is an essential task [18]. Cho et al. [19] conducted FEA and optical analyses for support frame design. They analyzed the static deformation induced by gravity and temperature, and then established a fixturing matrix to compensate potential errors using an active optics system. ...
We aim to build an integrated fixturing model to describe the structural properties and thermal properties of the support frame of glass laser optics. Therefore, (a) a near global optimal set of clamps can be computed to minimize the surface shape error of the glass laser optic based on the proposed model, and (b) a desired surface shape error can be obtained by adjusting the clamping forces under various environmental temperatures based on the model. To construct the model, we develop a new multiple kernel learning method and call it multiple kernel support vector functional regression. The proposed method uses two layer regressions to group and order the data sources by the weights of the kernels and the factors of the layers. Because of that, the influences of the clamps and the temperature can be evaluated by grouping them into different layers.
... The supporting optimization is another important issue during the support design, including the composition of support ways, selection of support positions [18][19][20], the selection of support materials and so on [21][22]. Many researchers have focused on support optimization for the large-scale mirrors. ...
The paper overviews various supporting ways for large-size movement
mirrors, and the advantages and disadvantages of the support methods are
summarized. Some valuable optimization methods to improve support
effects are also introduced. As a case study, a radial segment-face
contact support method is proposed to solve the support problem for a
large-aperture rotating prism, and a two-step optimization method is
implemented to improve the support effects. The surface deformations
under different support separated angles are evaluated. The overview can
be as good references for large-size mirror support design in similar
opto-mechanical systems especially under movement conditions.
... One option is that the active supports normal to the back surface of the primary mirror, a case in point is the GEMINI telescope [3,4]. The other axial support scheme is defined as those supports whose resultant force is parallel to the optical axis of the primary mirror, such as SUB-ARU [5]], Telescopio Nazionale Galileo (TNG) [6], SOAR [7], VISTA [8] and ATST [9]. It can be seen that most of the meniscus primary mirrors are supported with the latter scheme. ...
Active support scheme may decide the deformation of the optical surface
figure of the primary mirror. Two main active axial support schemes are
often adopted to the thin meniscus primary mirror, one scheme is that
the axial supports normal to the mirror bottom surface, and the other is
that the active forces parallel to the optical axis. In order to compare
the performance of the two support schemes, 1-m thin meniscus primary
mirror is conducted. Finite element analysis (FEA) is employed to
analyze the optical surface figures of the primary mirror, and
optimizations are carried out by using ANSYS for each support scheme to
obtain the locations and active forces. The axial support force
sensitivities are calculated for the two support schemes in a case that
a single axial support has a force error of 0.5 N. The correction
ability of the active support system for both of the support schemes are
analyzed when an arbitrary axial support is failure. Several low order
Zernike modes are modeled with MATLAB procedure, and active optics
corrections are applied to these modes for the two active supports. The
extra mirror surface error due to thermal deformation is also corrected
with the two support schemes.
... Next, a further optimization was processed to select support forces into groups without sacrificing the RMS surface errors. This optimization process is being adopted in the Primary Mirror of the Advanced Technology Solar Telescope (ATST) Project [2] and the Secondary Mirror and Tertiary Mirror of the Thirty Mirror Telescope (TMT) Project [5] [6] . ...
The Large Synoptic Survey Telescope (LSST) is an 8.4 meter telescope with a field of view of 10 square degrees. This telescope will be capable of mapping the entire visible sky every few nights via sequential 15-second exposures, opening new windows on the universe from dark energy to time variable objects. The LSST optics calls for an annular 3.5 m diameter Secondary Mirror (M2), which is a large meniscus convex asphere (ellipse). The M2 converts the beam reflected from the f/1.2 primary mirror into a beam for the f/0.83 Tertiary Mirror (M3). The M2 has a mass of approximately 1.5 metric tons and the mirror support system will need to maintain the mirror figure at different gravity orientations. The optical performance evaluations were made based on the optimized support systems consisting of 72 axial supports, mounted at the mirror back surface, and 6 tangent link lateral supports mounted around the outer edge. The predicted print-though errors of the M2 supports are 8nm RMS surface for axial gravity and 10nm RMS surface for lateral gravity. The natural frequencies were calculated for the M2 dynamic performance. In addition, thermo-elastic analyses of M2 for thermal gradient cases were conducted. The LSST M2 support system has an active optics capability to maintain optical figure and its performance to correct low-order aberrations has been demonstrated. The optical image qualities and structure functions for the axial and lateral gravity print-through cases, and thermal gradient effects were calculated.
The present paper describes a parametric design and optimization tool [Support Optimization and Design Tool (SODT)], used to evaluate passive axial support positions on circular solid meniscus mirrors. The developed tool avoids the intrinsic limitations of methodologies of the reference literature, based on analytical formulations. A parametric finite element model of the mirror is generated from the user inputs and the support distribution is optimized in terms of the root mean square of the surface error (SFE). The optimization process is based on a
hybrid optimization algorithm combining genetic algorithms and a gradient-based approach. The results are compared to the ones presented in the literature, evidencing minor discrepancies that
can be basically attributed to differences in methodology and structural formulation, as it is discussed in the text. Finally, the finite element and optical postprocessing results are verified
against industry-grade software: MSC Nastran® and Sigmadyne SigFit®.
Workpiece deformation must be controlled in the manufacturing process and other engineering application. Fixture configuration (position), clamping force and temperature are main aspects that influence the degree and distribution of Workpiece deformation. This paper takes large optical glass as an example, develop a new multiple kernel learning method to discuss the optimal fixture design. The proposed method uses two layers regressions to group and order the data sources by the weights of the kernels and the factors of the layers. Since that, the influences of the clamps and the temperature can be evaluated by grouping them into different layers. Then, based on the proposed model, the optimal magnitude and positions of clamping forces can be obtained. The experiments show is effective for the optical element clamping optimization analysis.
A large aspheric mirror is a key component for large astronomical telescopes and high resolution satellite cameras. Since it is large and has an aspheric form, it is much more difficult to fabricate it compared to the similar size of spherical mirror. Especially, the opto-mechanical design and analysis is critical to reduce the deformation of mirror surface due to the external forces such as gravity or temperature change, as the mirror size is larger and lightweighting ratio is increased. The design requirements for the mirror are different depending on the particular ground and space applications because the environmental conditions are changed. In this paper, we explain the opto-mechanical design and analysis for ground and space applications that are among the most difficult to achieve among several technologies related to development of the large aspheric mirror.
The Very Large Telescope Survey Telescope (VST) is equipped with an active optics system in order to correct low-order aberrations. The
2.6
m
primary mirror is supported both axially and laterally and is surrounded by several safety devices for earthquake protection. We describe the mirror support system and discuss the results of the qualification test campaign.
Until now a diameter of about 4 m seemed to be the upper-size limit of telescope mirrors that still permitted cost-saving designs of lateral supports by edge forces alone. In some designs, the supporting edge forces comprised not only basic push-pull action normal to the edge but also a specific, moderate amount of tangential shear. However, this was a by-product of design economy rather than the result of understanding the potential of tangential support forces as a means of reducing mirror flexure systematically, down to residuals in the 1% region. The surprising possibility of extending the usefulness of pure edge supports is demonstrated by the example of the 8 m mirror of the ESO's VLT. Fitted with a lateral support at the outer edge alone, this thin mirror will exhibit a wavefront aberration with a calculated rms value of only 18 nm, without taking into account possible active control.