We provide an update on the construction status of the Daniel K. Inouye Solar Telescope. This 4-m diameter facility is designed to enable detection and spatial/temporal resolution of the predicted, fundamental astrophysical processes driving solar magnetism at their intrinsic scales throughout the solar atmosphere. These data will drive key research on solar magnetism and its influence on solar winds, flares, coronal mass ejections and solar irradiance variability. The facility is developed to support a broad wavelength range (0.35 to 28 microns) and will employ state-of-the-art adaptive optics systems to provide diffraction limited imaging, resolving features approximately 20 km on the Sun. At the start of operations, there will be five instruments initially deployed: Visible Broadband Imager (VBI; National Solar Observatory), Visible SpectroPolarimeter (ViSP; NCAR High Altitude Observatory), Visible Tunable Filter (VTF (a Fabry-Perot tunable spectropolarimeter); Kiepenheuer Institute for Solarphysics), Diffraction Limited NIR Spectropolarimeter (DL-NIRSP; University of Hawaii, Institute for Astronomy) and the Cryogenic NIR Spectropolarimeter (Cryo-NIRSP; University of Hawaii, Institute for Astronomy). <p> </p>As of mid-2016, the project construction is in its 4th year of site construction and 7th year overall. Major milestones in the off-site development include the conclusion of the polishing of the M1 mirror by University of Arizona, College of Optical Sciences, the delivery of the Top End Optical Assembly (L3), the acceptance of the Deformable Mirror System (Xinetics); all optical systems have been contracted and are either accepted or in fabrication. The Enclosure and Telescope Mount Assembly passed through their factory acceptance in 2014 and 2015, respectively. The enclosure site construction is currently concluding while the Telescope Mount Assembly site erection is underway. The facility buildings (Utility and Support and Operations) have been completed with ongoing work on the thermal systems to support the challenging imaging requirements needed for the solar research.<p> </p> Finally, we present the construction phase performance (schedule, budget) with projections for the start of early operations.
The Visible Broadband Imager (VBI) Blue and Red channels are the first Daniel K. Inouye Solar Telescope (DKIST) instruments that have been aligned and tested in a laboratory. This paper describes the optical alignment method of the VBI as performed in the laboratory. The objective of this preliminary alignment is to test and validate the optical alignment method that will be used during final alignment on the telescope, to measure the VBI performances and to verify that it meets specification. The optical alignment method is defined by three major steps. The first step is realized by combining the optical and mechanical models into the Spatial Analyzer (SA) software, and extracting the data serving as target values during alignment. The second step is the mechanical alignment and allows to accurately position the optics in the instrument coordinate system by using a Coordinate Measurement Machine (CMM) arm and a theodolite. This step has led to a great initial positioning and has allowed reaching an initial wavefront error before optical alignment close to the specification. The last step, performed by interferometry, allows fine alignment to compensate the residual aberrations created by misalignment and manufacturing tolerances. This paper presents also an alignment method to compute the shifts and tilts of compensating lenses to correct the residual aberrations. This paper describes first results of the VBI instruments performances measured in the laboratory and confirm the validity of the alignment process that will be reproduced during final alignment on the telescope.
The DKIST wavefront correction system will be an integral part of the telescope, providing active alignment control, wavefront correction, and jitter compensation to all DKIST instruments. The wavefront correction system will operate in four observing modes, diffraction-limited, seeing-limited on-disk, seeing-limited coronal, and limb occulting with image stabilization. Wavefront correction for DKIST includes two major components: active optics to correct low-order wavefront and alignment errors, and adaptive optics to correct wavefront errors and high-frequency jitter caused by atmospheric turbulence. The adaptive optics system is built around a fast tip-tilt mirror and a 1600 actuator deformable mirror, both of which are controlled by an FPGA-based real-time system running at 2 kHz. It is designed to achieve on-axis Strehl of 0.3 at 500 nm in median seeing (r<sub>0</sub> = 7 cm) and Strehl of 0.6 at 630 nm in excellent seeing (r<sub>0</sub> = 20 cm). We present the current status of the DKIST high-order adaptive optics, focusing on system design, hardware procurements, and error budget management.
The Daniel K. Inouye Solar Telescope (DKIST, renamed in December 2013 from the Advanced Technology Solar
Telescope) will be the largest solar facility built when it begins operations in 2019. Designed and developed to meet the
needs of critical high resolution and high sensitivity spectral and polarimetric observations of the Sun, the observatory
will enable key research for the study of solar magnetism and its influence on the solar wind, flares, coronal mass
ejections and solar irradiance variations. The 4-meter class facility will operate over a broad wavelength range (0.38 to
28 microns, initially 0.38 to 5 microns), using a state-of-the-art adaptive optics system to provide diffraction-limited
imaging and the ability to resolve features approximately 25 km on the Sun. Five first-light instruments will be available
at the start of operations: Visible Broadband Imager (VBI; National Solar Observatory), Visible SpectroPolarimeter
(ViSP; NCAR High Altitude Observatory), Visible Tunable Filter (VTF; Kiepenheuer Institut für Sonnenphysik),
Diffraction Limited Near InfraRed SpectroPolarimeter (DL-NIRSP; University of Hawai’i, Institute for Astronomy) and
the Cryogenic Near InfraRed SpectroPolarimeter (Cryo-NIRSP; University of Hawai’i, Institute for Astronomy).
As of mid-2014, the key subsystems have been designed and fabrication is well underway, including the site
construction, which began in December 2012. We provide an update on the development of the facilities both on site at
the Haleakalā Observatories on Maui and the development of components around the world. We present the overall
construction and integration schedule leading to the handover to operations in mid 2019. In addition, we outline the
evolving challenges being met by the project, spanning the full spectrum of issues covering technical, fiscal, and
geographical, that are specific to this project, though with clear counterparts to other large astronomical construction
The Daniel K. Inouye Solar Telescope is a 4-meter-class all-reflecting telescope under construction on Haleakalā
mountain on the island of Maui, Hawai’i. When fully operational in 2019 it will be the world's largest solar telescope
with wavelength coverage of 380 nm to 28 microns and advanced Adaptive Optics enabling the highest spatial resolution
measurements of the solar atmosphere yet achieved. We review the first-generation DKIST instrument designs, select
critical science program topics, and the operations and data handling and processing strategies to accomplish them.
The Advanced Technology Solar Telescope (ATST) is a 4 meter class telescope for observation of the solar atmosphere
currently in the construction phase. The Visible Broadband Imager (VBI) is a diffraction limited imaging instrument
planned to be the first-light instrument in the ATST instrumentation suite. The VBI is composed of two branches, the
"VBI blue" and the "VBI red", and uses state-of-the-art narrow bandwidth interference filters and two custom designed
high speed filter wheels to take bursts of images that will be re-constructed using a Graphics Processing Unit (GPU)
optimized near-real-time speckle image reconstruction engine. At first light, the VBI instrument will produce
diffraction-limited movies of solar activity at eight discrete wavelengths with a field of view of 2 arc minutes square. In
this contribution, the VBI design team will discuss the capabilities of the VBI and describe the design of the instrument,
highlighting the unique challenges faced in the development of this unique instrument.
The National Solar Observatory’s (NSO) Advanced Technology Solar Telescope (ATST) is the first large U.S. solar telescope accessible to the worldwide solar physics community to be constructed in more than 30 years. The 4-meter diameter facility will operate over a broad wavelength range (0.35 to 28 μm ), employing adaptive optics systems to achieve diffraction limited imaging and resolve features approximately 20 km on the Sun; the key observational parameters (collecting area, spatial resolution, spectral coverage, polarization accuracy, low scattered light) enable resolution of the theoretically-predicted, fine-scale magnetic features and their dynamics which modulate the radiative output of the sun and drive the release of magnetic energy from the Sun’s atmosphere in the form of flares and coronal mass ejections. In 2010, the ATST received a significant fraction of its funding for construction. In the subsequent two years, the project has hired staff and opened an office on Maui. A number of large industrial contracts have been placed throughout the world to complete the detailed designs and begin constructing the major telescope subsystems. These contracts have included the site development, AandE designs, mirrors, polishing, optic support assemblies, telescope mount and coudé rotator structures, enclosure, thermal and mechanical systems, and high-level software and controls. In addition, design development work on the instrument suite has undergone significant progress; this has included the completion of preliminary design reviews (PDR) for all five facility instruments. Permitting required for physically starting construction on the mountaintop of Haleakalā, Maui has also progressed. This paper will review the ATST goals and specifications, describe each of the major subsystems under construction, and review the contracts and lessons learned during the contracting and early construction phases. Schedules for site construction, key factory testing of major subsystems, and integration, test and commissioning activities will also be discussed.
The 4m Advance Technology Solar Telescope (ATST) will be the most powerful solar telescope and the world's leading
ground-based resource for studying solar magnetism that controls the solar wind, flares, coronal mass ejections and
variability in the Sun's output. The project has successfully passed its final design review and the Environmental Impact
Study for construction of ATST on Haleakala, Maui, HI has been concluded in December of 2009. The project is now
entering its construction phase. As its highest priority science driver ATST shall provide high resolution and high
sensitivity observations of the dynamic solar magnetic fields throughout the solar atmosphere, including the corona at
infrared wavelengths. With its 4 m aperture, ATST will resolve features at 0."03 at visible wavelengths and obtain 0."1
resolution at the magnetically highly sensitive near infrared wavelengths. A high order adaptive optics system delivers a
corrected beam to the initial set of state-of-the-art, facility class instrumentation located in the coudé laboratory facility.
The initial set of first generation instruments consists of five facility class instruments, including imagers and spectropolarimeters.
The high polarimetric sensitivity and accuracy required for measurements of the illusive solar magnetic
fields place strong constraints on the polarization analysis and calibration. Development and construction of a fourmeter
solar telescope presents many technical challenges, including thermal control of the enclosure, telescope structure
and optics and wavefront control. A brief overview of the science goals and observational requirements of the ATST
will be given, followed by a summary of the design status of the telescope and its instrumentation, including design
status of major subsystems, such as the telescope mount assembly, enclosure, mirror assemblies, and wavefront
The high order adaptive optics (HOAO) system is the centerpiece of the ATST wavefront correction system. The ATST
wavefront correction system is required to achieve a Strehl of
S = 0.6 or better at visible wavelength. The system design
closely follows the successful HOAO implementation at the Dunn Solar Telescope and is based on the correlating
Shack-Hartmann wavefront sensor. In addition to HOAO the ATST will utilize wavefront sensors to implement active
optics (aO) and Quasi Static Alignment (QSA) of the telescope optics, which includes several off-axis elements.
Provisions for implementation of Multi-conjugate adaptive optics have been made with the design of the optical path that
feeds the instrumentation at the coudé station. We will give an overview of the design of individual subsystems of the
ATST wavefront correction system and describe some of the unique features of the ATST wavefront correction system,
such as the need for thermally controlled corrective elements.
Solar observations are performed over an extended field of view and the isoplanatic patch over which conventional
adaptive optics (AO) provides diffraction limited resolution is a severe limitation. The development of multi-conjugate
adaptive optics (MCAO) for the next generation large aperture solar telescopes is thus a top priority. The Sun is an ideal
object for the development of MCAO since solar structure provides multiple "guide stars" in any desired configuration.
At the Dunn Solar Telescope (DST) we implemented a dedicated MCAO bench with the goal of developing wellcharacterized,
operational MCAO. The MCAO system uses two deformable mirrors conjugated to the telescope
entrance pupil and a layer in the upper atmosphere, respectively. The high altitude deformable mirror can be placed at
conjugates ranging from 2km to 10km altitude. We have successfully and stably locked the MCAO system on solar
granulation and demonstrated the MCAO system's ability to significantly extend the corrected field of view. We present
results derived from analysis of imagery taken simultaneously with conventional AO and MCAO. We also present first
results from solar Ground Layer AO (GLAO) experiments.
The four-meter Advanced Technology Solar Telescope (ATST) will be the most powerful solar telescope and the
world's leading resource for studying solar magnetism that controls the solar wind, flares, coronal mass ejections and
variability in the Sun's output. Development of a four-meter solar telescope presents many technical challenges (e.g.,
thermal control of the enclosure, telescope structure and optics). We give a status report of the ATST project (e.g.,
system design reviews, PDR, Haleakalä site environmental impact statement progress) and summarize the design of the
major subsystems, including the telescope mount assembly, enclosure, mirror assemblies, wavefront correction, and
We have implemented a MCAO experiment at the Dunn Solar Telescope. The MCAO system uses 2 deformable mirrors, one conjugated to the telescope entrance pupil and other one conjugated to a layer in the upper atmosphere. For our initial experiments we have used a staged approach in which the 97 actuator, 76 subaperture correlating Shack-Hartmann solar adaptive optics system normally operated at the DST is followed by the second DM and the tomographic wavefront sensor, which used three "solar guide stars". We have successfully and stably locked the MCAO system on solar structure. We varied the height of the upper conjugate between 3km and 9 km. A large number of images were recorded in order to evaluate the performance of the system. The data analysis is still ongoing. We present preliminary results and discuss future plans.
An important part of a large solar telescope is the ability to correct, in real time, optical alignment errors caused by gravitational bending of the telescope structure and wavefront errors caused by atmospheric seeing. The National Solar Observatory is currently designing the 4 meter Advanced Technology Solar Telescope (ATST). The ATST wavefront correction system, described in this paper, will incorporate a number of interacting wavefront control systems to provide diffraction limited imaging performance. We will describe these systems and summarize the interaction between the various sub-systems and present results of performance modeling.
The Advanced Solar Technology Telescope (ATST) is a 4-m solar telescope being designed for high spatial, spectral and temporal resolution, as well as IR and low-scattered light observations. The overall limit of performance of the telescope is strongly influenced by the qualities of the site at which it is located. Six sites were tested with a seeing monitor and a sky brightness instrument for 1.5 to 2 years. The sites were Big Bear (California), Haleakala (Hawaii), La Palma (Canary Islands, Spain), Panguitch Lake (Utah), Sacramento Peak (New Mexico), and San Pedro Martir (Baja California, Mexico). In this paper we will describe the methods and results of the site survey, which chose Haleakala as the location of the ATST.
The four-meter Advanced Technology Solar Telescope (ATST) will be the most powerful solar telescope and the world's leading resource for studying solar magnetism that controls the solar wind, flares, coronal mass ejections and variability in the Sun's output. Development of a four-meter solar telescope presents many technical challenges (e.g., thermal control of the enclosure, telescope structure and optics). We give a status report of the ATST project (e.g., system design reviews, instrument PDR, Haleakala site environmental impact statement progress) and summarize the design of the major subsystems, including the telescope mount assembly, enclosure, mirror assemblies, wavefront correction, and instrumentation.
The Sun is an ideal target for the development and application of Multi-Conjugate Adaptive Optics (MCAO). A solar MCAO system is being developed by the National Solar Observatory, Adaptive Optics Project, with the purpose of extending the corrected science field of view to 1.25Arcmin. A detailed optical set-up, design and optical performance for such a system is presented and discussed here. The preliminary results for this first MCAO/DST run, are presented in more details by Langlois et al  at this conference.
We report here the preliminary results obtained with the multi-conjugate adaptive optics (MCAO) system at the Dunn Solar Telescope (DST/NSO MCAO) and the optical setup and performances are presented in more details in Moretto et al. in this proceeding. This system relies on the tomography technique, in which three WFS are used, each of them coupled to extended images of the Sun’s granulation and/or sunspots, to retrieve a 3D measurement of the turbulent volume in order to command the two DMs. We used a 5x5 subaperture Shack-Hartmann with cross correlation applied on three selected guiding regions - 18" wide- within the 1.25' full FOV. We also report on the estimation of turbulence distribution and the future MCAO performances based on a separate tomographic wavefront sensing experiment using the Dunn Solar Telescope adaptive optics system. In addition, we obtained estimates of the turbulence distribution. The results from this article provides an important step forward for building a full solar multi-conjugate adaptive optics system for the Dunn Solar Telescope and in the long term for the future 4 meter ATST telescope.
The Advance Technology Solar Telescope (ATST) has finished its conceptual design stage, submitted a proposal for construction funding and is working towards a system level preliminary design review later this year. The current concept (including integrated adaptive optics and instrumentation) will be reviewed with concentration on solutions to the unique engineering challenges for a four meter solar telescope that have been previously presented. The overall status will be given with a concentration on near term milestones and impact on final completion targeted in 2012.
The location of the Advanced Technology Solar Telescope (ATST) is a critical factor in the overall performance of the telescope. We have developed a set of instrumentation to measure daytime seeing, sky brightness, cloud cover, water vapor, dust levels, and weather. The instruments have been located at six sites for periods of one to two years. Here we describe the sites and instrumentation, discuss the data reduction, and present some preliminary results. We demonstrate that it is possible to estimate seeing as a function of height near the ground with an array of scintillometers, and that there is a distinct qualitative difference in daytime seeing between sites with or without a nearby lake.
The National Solar Observatory and the New Jersey Institute of Technology have developed two 97 actuator solar adaptive optics (AO) systems based on a correlating Shack-Hartmann wavefront sensor approach. The first engineering run was successfully completed at the Dunn Solar Telescope (DST) at Sacramento Peak, New Mexico in December 2002. The first of two systems is now operational at Sacramento Peak. The second system will be deployed at the Big Bear Solar Observatory by the end of 2003. The correlating Shack-Hartmann wavefront sensor is able to measure wavefront aberrations for low-contrast, extended and time-varying objects, such as solar granulation. The 97-actuator solar AO system operates at a loop update rate of 2.5 kHz and achieves a closed loop bandwidth (0dB crossover error rejection) of about 130 Hz. The AO system is capable of correcting atmospheric seeing at visible wavelengths during median seeing conditions at both the NSO/Sacramento Peak site and the Big Bear Solar Observatory. We present an overview of the system design. The servo loop was successfully closed and first AO corrected images were recorded. We present first results from the new, high order AO system.
The National Solar Observatory in collaboration with the High-Altitude
Observatory is developing a new solar polarimeter, the Diffraction Limited Spectro-Polarimeter. In conjunction with a new high-order adaptive optics system at the NSO Dunn Solar Telescope, the DLSP design facilitates very high angular resolution observations of solar vector magnetic fields. This project is being carried out in two phases. As a follow-on to the successful completion of the first phase, the ongoing DLSP Phase II implements a high QE CCD camera system, a ferro-electric liquid crystal modulator, and a new opto-mechanical system for polarization calibration. This paper documents in detail the development of the modulator system and its performance, and presents preliminary results from an engineering run carried out in combination with the new NSO high-order AO system.
A diffraction limited spectro-polarimeter is under construction at the National Solar Observatory in collaboration with the High Altitude Observatory. The scientific objective of the project is to measure the magnetic fields on the Sun up to the diffraction limit of the Dunn Solar Telescope. The same instrument would also measure the magnetic field of large sunspots or sunspot groups with reasonable spatial resolution. This requires a flexible image scale which cannot be obtained with the current Advanced Stokes Polarimeter (ASP) without loosing 50% of the light. The new spectro-polarimeter is designed in such a way that the image scale can be changed without loosing much light. It can work either in high-spatial resolution mode (0.09 arcsec per pixel) with a small field of view (FOV: 65 arcsec) or in large FOV mode (163 arcsec) with low-spatial resolution (0.25 arcsec per pixel). The phase-I of this project is to design and build the spectrograph with flexible image scale. Using the existing modulation, calibration optics of the ASP and the ASP control and data acquisition system with ASP-CHILL camera, the spectrograph was tested for its performance. This paper will concentrate on the performance of the spectrograph and will discuss some preliminary results obtained with the test runs.
We investigate a number of ideas about the effect of various topographical and climtatological factors on daytime seeing. Using the results of the CalTech site survey in southern California, we confirm that the presence of lakes and wind channels are beneficial for solar observing conditions. We do not find that proximity to the ocean is of benefit but is instead detrimental to seeing in the CalTech sample possibly due to the influence of the Los Angeles metropolitan area. We also study the effect of tree removal on the seeing at Sacramento Peak Observatory, and find that removing trees improved the average seeing by 25%. The effects of these and other factors will be further investigated with the ATST site survey.
Integral Field Spectroscopy (IFS) can provide two-dimensional spatial and one spectral information for spectroscopic observation simultaneously. This is important for solar observatory because of the nature of the extended object of the solar observatory. Integrated Field Unit (IFU) is the key and basic tool for IFS. An innovative IFU was designed at National Solar Observatory which will deliver good image quality at visible (0.39 - 1.0 mm) and near infrared (1.0-1.6 mm) wavelength ranges simultaneously. The IFU is realized by using image slicer and will take the full advantage of the excellent corrected image of a high order Adaptive Optics (AO) and provide powerful image spectroscopic ability for a spectrograph/ polarimeter. This may be the first time that advanced IFU will achieve at visible and near infrared simultaneously and be used for solar observatory.
A unique design is a key importance to ensure that the IFU image slicer can work at visible and near infrared wavelengths with excellent optical performance. The IFU design is discussed in detail in this paper. It is demonstrated that the IFU image slicer technique is suitable for both visible and near infrared solar observatories and will be particularly useful for 4 or 8-meter telescopes.
The National Solar Observatory (NSO) and the New Jersey Institute of Technology are jointly developing high order solar Adaptive Optics (AO) to be deployed at both the Dunn Solar Telescope (DST) and the Big Bear Solar Telescope (BBST). These AO systems are expected to deliver first light at the end of 2003.
We discuss the AO optical designs for both the DST and the BBST. The requirements for the optical design of the AO system are as follows: the optics must deliver diffraction-limited imaging at visible and near infrared over a 190"×190" field of view. The focal plane image must be flat over the entire field of view to accommodate a long slit and fast spectrograph. The wave-front sensor must be able to lock on solar structure such as granulation. Finally, the cost for the optical system must fit the limited budget.
Additional design considerations are the desired high bandwidth for tip/tilt correction, which leads to a small, fast and off-the-shelf tilt-tip mirror system and high throughput, i.e., a minimal number of optical surfaces. In order to eliminate pupil image wander on the wave-front sensor, both the deformable mirror and tip-tilt mirror are located on the conjugation images of the telescope pupil.
We discuss the details of the optical design for the high order AO system, which will deliver high resolution image at the 0.39 - 1.6 μm wavelength range.
High-resolution studies of the Sun's magnetic fields are needed for a better understanding of solar magnetic fields and the fundamental processes responsible for solar variability. The generation of magnetic fields through dynamo processes, the amplification of fields through the interaction with plasma flows, and the destruction of fields are still poorly understood. There is still incomplete insight as to what physical mechanisms are responsible for heating the corona, what causes variations in the radiative output of the Sun, and what mechanisms trigger flares and coronal mass ejections. Progress in answering these critical questions requires study of the interaction of the magnetic field and convection with a resolution sufficient to observe scales fundamental to these processes.
The 4m aperture Advanced Technology Solar Telescope (ATST) will be a unique scientific tool, with excellent angular resolution, a large wavelength range, and low scattered light. With its integrated adaptive optics, the ATST will achieve a spatial resolution nearly 10 times better than any existing solar telescope. Building a large aperture telescope for viewing the sun presents many challenges, some of the more difficult being
Heat control and rejection
Contamination and scattered light control
Control of telescope and instrument polarization
This talk will present a short summary of the scientific questions driving the ATST design, the design challenges faced by the ATST, and the current status of the developing design and siting considerations
We present a high-order adaptive optical system for the 26-inch vacuum solar telescope of Big Bear Solar Observatory. A small elliptical tip/tilt mirror is installed at the end of the existing coude optical path on the fast two-axis tip/tilt platform with its resonant frequency around 3.3 kHz. A 77 mm diameter deformable mirror with 76 subapertures as well as wave-front sensors (correlation tracker and Shack-Hartman) and scientific channels for visible and IR polarimetry are installed on an optical table. The correlation tracker sensor can detect differences at 2 kHz between a 32×32 reference frame and real time frames. The WFS channel detects 2.5 kHz (in binned mode) high-order wave-front atmosphere aberrations to improve solar images for two imaging magnetographs based on Fabry-Perot etalons in telecentric configurations. The imaging magnetograph channels may work simultaneously in a visible and IR spectral windows with FOVs of about 180×180 arc sec, spatial resolution of about 0.2 arc sec/pixel and SNR of about 400 and 600 accordingly for 0.25 sec integration time.
We present a progress report of the solar adaptive optics (AO) development program at the National Solar Observatory (NSO) and the Big Bear Solar Observatory (BBSO). Examples of diffraction-limited observations obtained with the NSO low-order solar adaptive optics system at the Dunn Solar Telescope (DST) are presented. The design of the high order adaptive optics systems that will be deployed at the DST and the BBSO is discussed. The high order systems will provide diffraction-limited observations of the Sun in median seeing conditions at both sites.
The 4m Advance Technology Solar Telescope (ATST) will be the most powerful solar telescope in the world, providing a unique scientific tool to study the Sun and possibly other astronomical objects, such as solar system planets. We briefly summarize the science drivers and observational requirements of ATST. The main focus of this paper is on the many technical challenges involved in designing a large aperture solar telescope. The ATST project has entered the design and development phase. Development of a 4-m solar telescope presents many technical challenges. Most existing high-resolution solar telescopes are designed as vacuum telescopes to avoid internal seeing caused by the solar heat load. The large aperture drives the ATST to an open-air design, similar to night-time telescope designs, and makes thermal control of optics and telescope structure a paramount consideration. A heat stop must reject most of the energy (13 kW) at prime focus without introducing internal seeing. To achieve diffraction-limited observations at visible and infrared wavelengths, ATST will have a high order (order 1000 DoF) adaptive optics system using solar granulation as the wavefront sensing target. Coronal observations require occulting in prime focus, a Lyot stop and contamination control of the primary. An initial set of instruments will be designed as integral part of the telescope. First telescope design and instrument concepts will be presented.