Device control software design for the active support system of GMT primary mirror segments

Laser Tomography Adaptive Optics (LTAO) is one of adaptive optics systems planned for the Giant Magellan Telescope (GMT). End-to-end simulation tools that are able to cope with the complexity and computational burden of the AO systems to be installed on the extremely large telescopes such as GMT prove to be an integral part of the GMT LTAO system development endeavors. SL95, the Fortran 95 Simulation Library, is one of the software tools successfully used for the LTAO system end-to-end simulations. The goal of SL95 project is to provide a complete set of generic, richly parameterized mathematical models for key elements of the segmented telescope wavefront control systems including both active and adaptive optics as well as the models for atmospheric turbulence, extended light sources like Laser Guide Stars (LGS), light propagation engines and closed-loop controllers. The library is implemented as a hierarchical collection of classes capable of mutual interaction, which allows one to assemble complex wavefront control system configurations with multiple interacting control channels. In this paper we demonstrate the SL95 capabilities by building an integrated end-to-end model of the GMT LTAO system with 7 control channels: LGS tomography with Adaptive Secondary and on-instrument deformable mirrors, tip-tilt and vibration control, LGS stabilization, LGS focus control, truth sensor-based dynamic noncommon path aberration rejection, pupil position control, SLODAR-like embedded turbulence profiler. The rich parameterization of the SL95 classes allows to build detailed error budgets propagating through the system multiple errors and perturbations such as turbulence-, telescope-, telescope misalignment-, segment phasing error-, non-common path-induced aberrations, sensor noises, deformable mirror-to-sensor mis-registration, vibration, temporal errors, etc. We will present a short description of the SL95 architecture, as well as the sample GMT LTAO system simulation results.

The primary mirror of the Giant Magellan Telescope (GMT) consists of seven 8.4-meter diameter borosilicate segments. While this design has optical advantages, the unmitigated seismic risk is significant. Recently added design features meet this challenge. A 2D seismic isolation system decouples the telescope from horizontal ground motion and dampers at the interface with the primary mirror segments attenuate their motion. A detailed analysis framework has been developed to justify and refine the design. Discrete analyses, in which the models are exercised at discrete seismic intensity levels, are used to generate requirements throughout the telescope via a seismic response spectrum approach. Risk-based analyses utilize a broad characterization of uncertainty to assess probability of survival of the most critical components. These tools support a general design strategy that effectively trades the cost of designing and constructing the telescope against the seismic risk.

We have developed a metrology system that is capable of measuring rough ground and polished surfaces alike, has limited sensitivity to the nominal surface shape, and can accommodate surfaces up to 8.4 m in diameter. The system couples a commercial laser tracker with an advanced calibration technique and a system of stability references to mitigate numerous error sources. This system was built to guide loose abrasive grinding and initial polishing of the off-axis primary mirror segments for the Giant Magellan Telescope (GMT), and is also being used to guide the fabrication of the Large Synoptic Survey Telescope primary and tertiary mirrors. In addition to guiding fabrication, the system also works as a verification test for the GMT principal optical interferometric test of the polished mirror segment to corroborate the measurement in several low-order aberrations. A quantitative assessment of the system accuracy is presented, along with measurement results for GMT, including a comparison to the optical interferometric test of the polished surface.8

A detailed Computational Fluid Dynamics (CFD) model for the Giant Magellan Telescope (GMT) telescope has been developed and used to simulated and analyze the aero-optical environment around the observatory. The developed model accounts for the major observatory components such as the primary (M1) and secondary (M2) mirrors, the M2 supporting truss, other subcomponents of the telescope mount, and enclosure building along with the auxiliary and site support buildings on the summit. A large topographical area around the installation site is included. This study evaluates three different lower enclosure designs; a closed soffit, an open soffit and a perforated ring-wall (partially closed soffit). Timevarying CFD simulations provide detailed flow and temperature fields along the optical path, which are subsequently used to compute optical parameters such as Optical Path Difference (OPD) maps and Point Source Sensitivity normalized (PSSn), the GMT Image Quality (IQ) metric. Results show that enclosure-induced turbulent flow patterns and refractive index variations have a greater influence on optical performance compared to flow and thermal behavior external to the enclosure. Instantaneous and mean PSSn values obtained for the three soffit configurations show minor differences, indicating that the lower enclosure design has minimal impact on observatory optical performance for the simulated operating conditions.

The Giant Magellan Telescope (GMT) is a 25-meter optical/infrared extremely large telescope that is being built by an international consortium of universities and research institutions. It will be located at the Las Campanas Observatory, Chile. The GMT primary mirror consists of seven 8.4-m borosilicate honeycomb mirror segments made at the Steward Observatory Mirror Lab (SOML). Six identical off-axis segments and one on-axis segment are arranged on a single nearly-paraboloidal parent surface having an overall focal ratio of f/0.7. The fabrication, testing and verification procedures required to produce the closely-matched off-axis mirror segments were developed during the production of the first mirror. Production of the second and third off-axis segments is underway. GMT incorporates a seven-segment Gregorian adaptive secondary to implement three modes of adaptive-optics operation: natural-guide star AO, laser-tomography AO, and ground-layer AO. A wide-field corrector/ADC is available for use in seeing-limited mode over a 20-arcmin diameter field of view. Up to seven instruments can be mounted simultaneously on the telescope in a large Gregorian Instrument Rotator. Conceptual design studies were completed for six AO and seeing-limited instruments, plus a multi-object fiber feed, and a roadmap for phased deployment of the GMT instrument suite is being developed. The partner institutions have made firm commitments for approximately 45% of the funds required to build the telescope. Project Office efforts are currently focused on advancing the telescope and enclosure design in preparation for subsystem- and system-level preliminary design reviews which are scheduled to be completed in the first half of 2013.

Segmented deployable space imaging systems represent a promising solution for future ultra-large aperture space optical systems. With the proposal of larger aperture segmented telescope designs, ultra-lightweight primary mirror (PM) segments with lower areal density have become a research hotspot. However, the lightweight structure poses more stringent challenges in maintaining a high-precision surface figure of PM segments. Active deformable PM segments with surface shape adjustment capability serve as an effective approach to address these challenges. To achieve surface figure control at the PM segments scale, accurate determination of the PM segments' surface figure error magnitude is fundamentally required. After in-orbit deployment of segmented mirror systems, deviations between the actual position and ideal position of PM segments will induce optical pupil localization errors in the system's overall pupil plane. The optical pupil localization error (OPLE) of PM segments leads to an inaccurate decoupling of wavefront errors into individual PM segments, thereby compromising the accuracy of surface figure correction. This paper proposes an active segmented mirror optical pupil localization method based on local wavefront sensitivity analysis. By utilizing the deformation capability of active optics, we establish sensitivity equations through wavefront variations within the PM segments' pupil region before and after surface shape adjustments, enabling the inverse solution for the OPLE of PM segments. The proposed method achieves micrometer-level positioning accuracy of PM segments' positional errors solely relying on focal plane information, while avoiding the introduction of additional mechanisms. Experimental validations were designed to verify the feasibility of the method.

The Giant Magellan Telescope (GMT) is an Extremely Large Telescope (ELT) class observatory set to make history as one of the largest telescopes ever built. Vast improvements in the fields of optics, control systems, and mirror fabrication technologies have facilitated correspondingly drastic increases in the size and presence of ground-based telescopes previously thought to be impossible. Size for these observatories has increased to the point where conventional approaches impart seismic demands on the telescope structure and optics that are unmanageable. With this, a refined approach involving base isolation is being designed to provide seismic protection of a sensitive, invaluable instrument that will revolutionize our understanding of the universe.

<strong>11.1 Introduction</strong> Today, large-aperture modern telescope optical systems such as the ground-based Thirty Meter Telescope (TMT) and Giant Magellan Telescope (GMT) are divided into four parts: a large precision telescope radiation collector, a metrology and wavefront sensing and control (WFSC) system, the instrument that analyzes the complex wavefronts, and the detector that converts the complex wavefronts into intensity. Smaller-aperture space telescopes such as those used by the Wide-field Infrared Survey Explorer (WISE), Kepler, Stereo, and Ice, Cloud, and land Elevation Satellite (ICESat) do not require optical metrology and wavefront sensing and control because they are sufficiently small that their rigidity is obtained using mass, since the space system mass budget will accommodate it. In this chapter we expand the classical two-part astronomical optical system comprised of telescope and instrument into the much more capable (for large apertures) new three-part optical system of (1) the telescope, (2) the metrology and WFSC system, and (3) the instrument. At the heart of this new system is the two-stage optics system1 that collects, measures, and corrects the wavefront, and focuses it onto a field stop where the radiation passes into instruments that process the input complex wavefront for spectral, spatial (image), polarization, and radiometric information. In Chapters 8 and 9, we learned how scalar complex wavefronts propagate through an optical system to create an image, and we discussed the relationship between the wavefront and image quality. In Chapter 10, we learned that interferometry is a tool for analyzing the spectral (temporal) content and spatial structure of wavefronts. In this chapter, we show how wavefronts are manipulated to compensate for the following: <ul> &#x2022; telescope fabrication errors, &#x2022; the low mechanical stiffness characteristic of the new lightweight next-generation ground and space telescopes, and &#x2022; atmospheric turbulence. </ul>

This paper presents the development of an event-driven control architecture and its implementation in a physical simulator of a computerized manufacturing system using object-oriented techniques. The architecture was developed to improve the efficiency of handling concurrent control events in the DOS environment. In the implementation, the control system of the physical simulator consists of four distinct layers of control devices: a PC/386 computer, a microcontroller, I/O modules and the system's control devices such as motors, solenoids and sensors. A control program residing in the PC/386 coordinates system-level tasks such as event scheduling, while a BASIC program running on the microcontroller handles all low-level control tasks such as sensor monitoring and motion control. The concepts and developments presented in this paper should help in implementing an efficient control system for both CIM systems and their physical simulators.

Achieving the diffraction limit with the adaptive optics system of the 25m Giant Magellan Telescope will require that the 7 pairs of mirror segments be in phase. Phasing the GMT is made difficult because of the 30-40cm gaps between the primary mirror segments. These large gaps result in atmospheric induced phase errors making optical phasing difficult at visible wavelengths. The large gaps between the borosilicate mirror segments also make an edge sensing system prone to thermally induced instability. We describe an optical method that uses twelve 1.5-m square subapertures that span the segment boundaries. The light from each subaperture is mapped onto a MEMS mirror segment and then a lenslet array which are used to stabilize the atmospherically induced image motion. Centroids for stabilization are measured at 700nm. The piston error is measured from the fringes visible in each of the 12 stabilized images at 2.2 microns. By dispersing the fringes we can resolve 2&pi; phase ambiguities. We are constructing a prototype camera to be deployed at the 6.5m Magellan Clay telescope.

GMTNIRS is a first-generation instrument for the Giant Magellan Telescope. It is a high-resolution spectrograph that will cover the 1.15-5.3 μm range in a single exposure with R=60,000 in the J, H, and K bands and R=85,000 in the L and M bands. It resides on the GMT’s rotating instrument platform and employs the facility adaptive optics system. The GMTNIRS design is evolving in response to emerging science problems, particularly in the area of exoplanet atmospheres. Our design revisions also derive lessons from GMTNIRS’ highly successful forerunner instrument, IGRINS. Technical changes also drive evolution of the design. It has proven impractical to manufacture 200mm long immersion gratings at the necessary precision. The success of primary mirror phasing efforts has removed the need for a very wide entrance slit that we would have needed to accommodate the Airy pattern of individual segments at the shortest operating wavelengths. The high efficiency of our double-side coated JWST grisms introduces the possibility of transmissive cross-dispersers at L and M. These changes move us toward a design with almost the same R as presented in our previous work but with a much more compact physical envelope. We will report on the optimization of the instrument design with these technical changes in mind. We are also producing the critical Si immersion gratings. The grating production is well under way and includes manufacture of H and K gratings and process development for the precision needed in the J band and for the manufacture of larger gratings for the L and M band. The development of GMTNIRS is on track with the results from IGRINS and the progress in the lab giving us substantial assurance that the new instrument can meet its performance goals.

The GMT-CfA, Carnegie, Catolica, Chicago Large Earth Finder (G-CLEF) is a fiber fed, optical echelle spectrograph that has undergone conceptual design for consideration as a first light instrument at the Giant Magellan Telescope. GCLEF has been designed to be a general-purpose echelle spectrograph with precision radial velocity (PRV) capability. We have defined the performance envelope of G-CLEF to address several of the highest science priorities in the Decadal Survey¹. The spectrograph optical design is an asymmetric, two-arm, white pupil design. The asymmetric white pupil design is adopted to minimize the size of the refractive camera lenses. The spectrograph beam is nominally 300 mm, reduced to 200 mm after dispersion by the R4 echelle grating. The peak efficiency of the spectrograph is &gt;35% and the passband is 3500-9500&Aring;. The spectrograph is primarily fed with three sets of fibers to enable three observing modes: High-Throughput, Precision-Abundance and PRV. The respective resolving powers of these modes are R~ 25,000, 40,000 and 120,000. We also anticipate having an R~40,000 Multi-object Spectroscopy mode with a multiplex of ~40 fibers. In PRV mode, each of the seven 8.4m GMT primary mirror sub-apertures feeds an individual fiber, which is scrambled after pupil-slicing. The goal radial velocity precision of G-CLEF is &part;V &lt;10 cm/sec radial. In this paper, we provide a flowdown from fiducial science programs to design parameters. We discuss the optomechanical, electrical, structural and thermal design and present a roadmap to first light at the GMT.

We study the application of Lyot coronagraphy to future Extremely Large Telescopes (ELTs), showing that Apodized Pupil Lyot Coronagraphs enable high-contrast imaging for exoplanet detection and characterization with ELTs. We discuss the properties of the optimal pupil apodizers for this application (generalized prolate spheroidal functions). The case of a circular aperture telescope with a central obstruction is considered in detail, and we discuss the effects of primary mirror segmentation and secondary mirror support structures as a function of the occulting mask size. In most cases where inner working distance is critical, e.g., for exoplanet detection, these additional features do not alter the solutions derived with just the central obstruction, although certain applications such as quasar-host galaxy coronagraphic observations could benefit from designs that explicitly accomodate ELT spider geometries. We illustrate coronagraphic designs for several ELT geometries including ESO/OWL, the Thirty Mirror Telescope, the Giant Magellan Telescope, and describe numerical methods for generating these designs.

An incremental tide in IoT devices prompts a centralized control system where physical controls such as buttons and knobs can become virtual and centralized via augmented reality: especially headset AR. I conduct a literature mapping to identify gaps and create a front-end based virtual control panel API tool to allow programmers and end-users to rapidly create headset augmented reality-based virtual control systems for physical devices. I probe on how an artificial intelligence back-end aids in such a system in terms of panel creation and automation as well as panel usage and control scenarios. I delve into use cases of the virtual control panel API including mass usage and specialized scenarios. Furthermore, I specify the guidelines for a requirements elicitation study for such a system along with potential points of derivation. Next, I probe into implications and limitations of such a system in terms of artificial intelligence, usage, and precision. My work has implications for programmers and users of a virtual control system backed by artificial intelligence for the purpose of controlling physical IoT devices in mass usage as well as in specialized scenarios.

This paper first analyzes the advantages and disadvantages of all kinds of compensation technology and then puts forward a integrated control strategy of the composite operation of TSC and SVG and its working principle, so we designs and develops the TSC unit and reactive compensation controller. Equipped with the man-computer interface, the main controller has the functions of password login, information acquisition, calculation, process and storage, internal and external communication, and parameter setting. The protection include over-voltage, under-voltage, phase-loss etc. The main controller determines the cooperating relationship between TSC and SVG, and TSC's switching strategy. The simulation result in RTDS can verify the precision of the validity of the control logic, and also can test the filter performance, dynamic response performance of reactive power compensation and protection functions of the protype. Device control system can meet the design requirements. The prototype of this device has finished the type test according to the national standard.