Characteristic analysis of Golay 6 multiple-mirror telescope

The multiple mirror telescope (MMT), a joint project of the University of Arizona and the Smithsonian Institution, is in many ways a pioneering instrument that helped pave the way for the new class of 8 to 10 meter optical telescopes in use today. Part of the telescope facility upgrade to a 6.5m primary mirror is improved servos for pointing and tracking of sufficient quality to support the latest generation of wide-field and adaptive-optics instruments. This discussion presents the current and future work in servo development at the MMT.

The Multiple Mirror Telescope (MMT), upgraded in 2000 to a monolithic 6.5m primary mirror from its original array of six 1.8m primary mirrors, was commissioned with axis controllers designed early in the upgrade process without regard to structural resonances or the possibility of the need for digital filtering of the control axis signal path. Post-commissioning performance issues led us to investigate replacement of the original control system with a more modern digital controller with full control over the system filters and gain paths. This work, from system identification through controller design iteration by simulation, and pre-deployment hardware-in-the-loop testing, was performed using latest-generation tools with Matlab® and Simulink®. Using Simulink's Real Time Workshop toolbox to automatically generate C source code for the controller from the Simulink diagram and a custom target build script, we were able to deploy the new controller into our existing software infrastructure running Wind River's VxWorks™real-time operating system. This paper describes the process of the controller design, including system identification data collection, with discussion of implementation of non-linear control modes and disturbance decoupling, which became necessary to obtain acceptable wind buffeting rejection.

The Modular Optical Space Telescope (MOST) project is a design tool that allows rapid generation and analysis of many unique space telescope realizations. The project uses a parametric integrated model to quantitatively analyze many dierent architectures during the conceptual design phase. MOST aims to include advanced concepts and technologies such as lightweight, deformable optics, dynamic wavefront control, and low-cost segmented mirror systems. Traditional optical performance metrics are considered alongside programmatic metrics such as cost, robustness, and mission operations, permitting an examination of these conflicting requirements at the very beginning of the project. The model has been substantially updated to include new technologies, control, and performance metrics, and the trade studies continue to provide insights into determining favorable space telescope architectures. urrent space telescopes are reaching their limits in terms of size, cost, and performance. Future systems will have larger aperatures with increasingly tight performance requirements, with line-of-sight (LOS) jitter on the order of milli-arcseconds and wavefront error (WFE) on the order of nanometers. At the same time, lower mass and lower cost systems are desired. This creates an implicit conflict for currently designed systems, thus new technologies and telescope types must be developed and implemented. Technology possibilities for these new systems include deployable mirrors or sparse apertures, structural control, and active optics. Sparse apertures and deployable optics can be deployed on orbit, eliminating the launch fairing diameter as an aperture size constraint. Also, the smaller, identical mirrors used in sparse apertures are easier and less expensive to manufacture than large monolithic mirrors. Structural control can provide a means to achieve better performance with a less massive system by counteracting the flexible dynamics of the lightweight system. Active optics can help to meet the strict performance requirements. A fast steering mirror can correct for LOS jitter, and wavefront sensing and mirror shape control can rectify both thermal and dynamic distortions of the primary mirror. These and other technologies provide a promising path to meeting both the performance and systematic requirements of future space telescopes. The challenge is in determining which combinations of technologies create favorable architectures. It is important to explore the entire tradespace of possible designs to ensure that superior designs are not overlooked. In order to assist with these important decisions and tradespace exploration, the MOST project has created a parametric modeling technique to consider the implications of design decisions during the conceptual design phase. 1,2 In the past, simple models, along with engineering judgment, have been used in the conceptual design phase where key design decisions were made. During the preliminary design phase, detailed models of the single point design were built and analyzed. If the requirements were not met, then another point design was chosen and modeled. This strategy works well if the system is based upon heritage designs and performance can be adequately predicted. However, with the addition of new technologies, there is no guarantee that the chosen point design would meet the requirements, and if the design does meet requirements, there is no assurance that it is an optimal design. Therefore, the MOST project uses a parameterized model to quickly and automatically generate and analyze many designs during the conceptual

Very large telescopes will be needed for the future of space science, space laser-com, and other interstellar or interplanetary applications. However, as telescopes' diameters increase, their weight and cost increase dramatically. An approximation for ground-based observatories is that their cost increases to the power of 2.7 of its diameter [SAO, Special Report #385 (1979), p. 9]. Large space-based telescopes become limited by the rocket size and power. Multiple telescopes are also needed for very long baseline interferometry (VLBI), which further increases cost. A solution to overcome these issues is the use of inflatable telescopes. A thin mirror material clearly has much lower mass; however, controlling its surface error or wavefront can be a challenge. Intensity interferometry is an imaging method that has a much looser sensitivity to wavefront error (WFE), and thus is an ideal match for very large inflatable telescopes. A spherical inflatable mirror is the most practical; however, it suffers from spherical aberration. This paper presents new optical designs and simulations for intensity interferometry in support of large inflatable spherical telescopes. The optical system design includes a novel five-mirror off-axis, free-form, spherical aberration corrector. The system design shown is a 10 m diameter f/1 spherical primary mirror with 1.2 arcmin (0.02°) field of view (FOV). MATLAB simulations of intensity interferometry combine signal with noise and WFE. Visibility-based VLBI image simulations are shown based on various telescope arrays. Simulations show that with a 1 GHz detector, a 1 cm RMS WFE is tolerable. So the challenge of the optical design is then more about gathering and concentrating the light down to a reasonable size detector. Further simulations of signal combined with noise indicate that the signal rate must be about 100 times higher than the noise rate for an adequate intensity interferometry measurement. Visibility-based image simulations reveal that many telescopes (5-20 per axis) are needed in a 2D array out to the first visibility minimum to adequately resolve unknown features of a distant object.

A preliminary optical design is proposed to convert the existing Multiple Mirror Telescope (MT) on Mount Hopkins to the maximum diameter, filled-aperture optical/infrared telescope that can be accommodated by the existing telescope mounting and building without substantial modification. The design utilizes a 256-inch diameter f/1.00 primary mirror which is chosen to be parabolic in order to provide adequate field of view at the required f/45.0 infrared Cassegrain focus. A 40-arcmin-diameter flat field of view is provided at an f/4.5 optical Cassegrain focus such that the resulting image scale gives a sampling factor of 3.5 (27 μ) pixels per (2/3 arcsec) spatial information element. The three-element refracting field corrector contains material for an atmospheric dispersion compensator (ADC) and it is fully color-corrected such that the entire passband from 0.33 μ to 1.60 μ can be imaged simultaneously. An f/9.0 Cassegrain focal expander-corrector with (ADC) is provided which uses the f/4.5 secondary mirror and enables the new telescope optics to be coupled to existing ancillary MMT instrumentation without substantial modification to the latter. A two-element all-spherical null-lens design is presented which provides a diffraction limited optical null-test arrangement for the unprecedentedly large f/1.00 parabolic primary mirror.

A new interim adaptive system—FASTTRAC IT—has been developed for near-infrared imaging for the Multiple Mirror Telescope (MMT), prior to upgrade to a single 6.5 m mirror. The system employs a real-time adaptive beam combiner consisting of six mirror facets which control the tip and tilt for each of the 1 .8 m primary mirrors. Since the overall piston of the mirrors is not controlled, the light from the six MMT mirrors adds incoherently at the focal plane, producing an image with the diffraction limit of a single mirror but with flux corresponding to a filled 4.5 m aperture. In operational mode the tilts over each of the 1.8 m mirrors will be sampled using a sodium laser guide star. Overall tilt is compensated using a field star imaged in the visible. We present a brief discussion of the various error sources entering into the system performance. Simulations of performance are presented showing the dependence on field star magnitude and angle. the time delay between sense and application of the required correction, and the angle between laser guide star and field position. These simulations demonstrate that FASTTRAC II should readily achieve diffraction limited imaging for a 1.8 m aperture with 6 times the light collection at near-infrared wavelengths.

We explore solutions for the optical design of the OWL 100-m telescope, and discuss their properties, advantages and drawbacks in relation to top level requirements. Combining cost, design, fabrication and functionality issues, and taking into account the scale of the telescope, we conclude that the requirements are best met with a design based on spherical primary and secondary mirrors. The combined active and adaptive correction capability envisioned for the telescope allows substantial relaxation of otherwise critical subsystems specifications. We elaborate on the telescope correction capabilities, including alignment and focusing, and derive the structure of the optical error budget.

Collimator is essential to evaluate and assemble the other telescopes. Its diameter should be larger than that of the target telescope for the correct use. We are currently developing the Cassegrain type collimator of which diameter is 0.9 m. The primary mirror is light-weighted so that its weight is only 70 kg. Due to its structure, the primary mirror can be supported only at the backside of the mirror. This mirror is tested with the combination of null Hartmann test and interferometer. The secondary mirror is tested with a Hindle method. This method requires 600 mm high quality spherical mirror. The distance between the primary and secondary mirror is maintained by the Carbon composite material. The assembly of two mirrors is carried out by the computer aided alignment method. The whole structure is designed to maintain the performance of the collimator under +/-5 degrees of temperature variation.

Technology computer-aided design simulations are revolutionizing the development of semiconductor devices, including solar cells, allowing researchers to understand device design physics, and thus, improving the device design for potential applications. We assessed the performance of simulated InGaP/GaAs solar cells, with and without intrinsic layers in the bottom cells. We employed two different intrinsic layers, separately, in the bottom cells of our two simulated InGaP/GaAs solar cells. One of our simulated InGaP/GaAs solar cells employs InP 1.6 μm intrinsic layer in the bottom GaAs cell. For this solar cell, we found open circuit voltage (VOC), short circuit current density (JSC), maximum power density (Pm), efficiency (η), and fill factor (FF) to be 2.37 V, 18.2 mA/cm2, 36.7 mW/cm2, 26.6%, and 84.7%, respectively. Another simulated InGaP/GaAs solar cell employs an InAlGaP intrinsic layer in the bottom GaAs cell for which JSC = 20.9, VOC = 2.41 V, Pm = 41.3 mW/cm2, FF = 81.7%, and η = 29.93%. These results bring us closer to understanding and creating efficient III–V solar cells for harnessing solar energy.

We present a design for an active telescope for space astronomy. The telescope is capable of both exoplanet work and general astronomy over wavelengths from ∼100 nm up to 5 μm. The primary mirror is 6 m in diameter, formed by 16 mirror segments that are precisely phased and supported on rigid body actuators and with segment optical surface figures fine-tuned using surface figure actuators. The active primary forms a large deformable mirror (DM) with wavefront error (WFE) correction at the entrance pupil. Thus the largest source of WFE can be removed at the source and is corrected over the entire field of view. This enables diffraction-limited performance at 400 nm and a more efficient optical system over a broader wavelength range than could be achieved by a small DM at a downstream relayed pupil. The telescope is passively cooled to below 100 K at Sun–Earth L2, enabling astronomical-background-limited observations out to 5 μm. Launched on a SpaceX Starship or alternatively National Aeronautics and Space Administration’s Space Launch System, the telescope requires minimal deployments. A 72-m-diameter starshade provides a contrast ratio better than 10 − 10 for exoplanet science. Near the visible region, with a 108% working bandwidth from 300 to 1000 nm, a working distance of 120 Mm provides a 51-mas inner working angle (IWA). This band can be moved to shorter or longer wavelengths by adjusting the starshade range from the telescope. Our first-ever thermal analysis of such a starshade shows that a temperature below 100 K can be achieved over a broad range of observing directions, permitting the possibility of working into the infrared. We model the yield in exoplanets that can be observed. A starshade and associated spectrograph offer significant advantages for exoplanet characterization. They enable a much broader instantaneous spectral bandwidth (here 108%) than current coronagraphs (∼10 % to 20% bandwidth), allow both polarizations to be observed simultaneously, and have higher throughput. The IWA is twice as small as can be achieved with a coronagraph and there is no outer working angle. These differences are particularly pronounced in the UV, where coronagraph performance would be strongly affected by throughput losses, wavefront aberrations, Fresnel polarization effects at surfaces, and thermal instability.

Partial shading is a commonly encountered issue in a photovoltaic (PV) system. Analytical modeling of a PV system for studying the effects of partial shading with and without bypass diode as well as different orientation of PV modules is discussed here. In this work, a new Ring Pattern (RP) configuration is proposed and compared with Series Parallel (SP), Total cross tied (TCT), Bridge linked (BL) and examined under same shading pattern on the basis of maximum power and fill factor. Those models are studied and their performances were compared on the basis of global peak under partial shading conditions (PSCs). Each network connection was analyzed taking care of the non-linearity of the PV cell which is evaluated by using Kirchhoff's voltage and current laws. The simulation and experimental study conclude that the proposed RP configuration exhibits superior performance over SP, TCT and BL configurations in terms of maximum power and fill factor.

Screen-printed CdS/CdTe solar cell of 12.8% efficiency for an active area of 0.78 cm 2

Traditionally a telescope system consists of a large collecting element, usually called the primary, located at the entrance pupil and some smaller elements to relay or convey the light to an image plane. As telescope systems become larger and larger, in order to achieve higher resolution and collect more light, a point is reached where the size of the required elements exceeds the current state of the art in fabrication and support. For telescopes larger than this, the entrance pupil must either be divided into manageable segments, or the entrance pupil is divided into an array of separate telescopes. A multiple telescope array consists of afocal collector telescopes distributed in the entrance pupil, relay optics to bring the light to the center and control tilt and piston errors, and a focal combiner telescope to form the image. Sparse telescope arrays have been designed for various applications. This paper addresses the issues and design constraints leading to a multiple telescope array with a high fill factor.

Increasing the available imaging time of a remote sensing satellite over a specified ground area can be accomplished by placing the satellite in a higher, more elliptical orbit. This, however, will also require the satellite to be farther away from the Earth, thus reducing the resolution of the images. If the aperture size of the optics can be increased proportional to the increase in the satellite's altitude, then the resolution can be maintained. Remote sensing satellites with a single, large, monolithic telescope are difficult to manufacture and costly to launch. Several smaller telescopes can be used together to capture the resolution of a single large telescope. Collectively, these small telescopes generate a sparse aperture because they do not fill the entire aperture area that they synthesize. The fill factor of the aperture is the total area of the telescopes divided by the effective aperture size. Reducing the fill factor decreases the weight, but also reduces the signal-to-noise ratio and system modulation transfer function. Image simulations are used to assess the image quality of different sparse aperture designs.

Transparent ZnO/Al/ZnO multilayer electrodes that have been fabricated by atomic layer deposition were examined. The resistivity of multilayer electrodes strongly depended on the thickness of the inter-layer aluminum thin film. As the aluminum layer became thicker the resistivity decreased. By comparing theoretical calculations to experimental data we found that the resistivity change was mainly due to the carrier scattering mechanism. The transparent multilayer electrodes showed resistivities as low as 7 × 10−4 Ω-cm for 12 nm-thick Al inter-layer. The ZnO/Al/ZnO electrodes were implanted in organic solar cell devices. The best results were obtained for the ZnO(35 nm)/Al(6 nm)/ZnO(35 nm) configuration. The maximum power conversion efficiency and fill factor were 1.6% and 51%, respectively.