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The Daniel K. Inouye Solar Telescope (DKIST) will be the largest solar telescope in the world, providing a significant increase in the resolution of solar data available to the scientific community. In large ground-based telescopes, vibration of telescope optics caused by the telescope subsystems is typically the limiting factor of image resolution. 1 The impact of vibration increases with the resolution of the telescope and is therefore a much greater problem in long focal-length telescopes, such as the DKIST. In addition, vibration is a consumer of the adaptive optics image-quality error budget limiting the correction available for atmospheric seeing. In some cases, the adaptive optics might even amplify the vibration at higher frequencies. For all of these reasons, a vibration error budget is a critical component in any large telescope project, and a plan for active vibration management and mitigation is critical to the success of a large telescope project. In the design of a large telescope, finite element analysis is employed and this is historically the only effort put into understanding vibration issues. However, after the telescope mount is constructed and the instruments and ancillary equipment are more clearly defined, there are many opportunities to perform path analyses by directly measuring the low-frequency single- input-single-output (SISO) frequency response function (FRF) between vibration source locations and image motion on the focal plane. These measurements are carried out using inertial-mass shakers along with seismic accelerometers providing an accurate measurement of the image degradation that will be caused by vibration sources in various locations. This allows the designers to determine an appropriate vibration mitigation plan (if needed) long before the vibration source is attached to the telescope. These measurements have proven sensitive enough that they can be performed for equipment not mounted on the telescope structure but located in the telescope building or even in nearby buildings. In a previous paper, techniques were described for measuring vibration which is particularly challenging at frequencies below 10 Hz where accurate measurement requires several noise reduction techniques, including high-performance windows, noise-averaging, tracking filters, and spectral estimation. In this follow-up paper, the development of the DKIST vibration budget detailing the advantages of the shaker measurement technique is described, along with examples of testing performed on the DKIST structures currently under construction at the Haleakala High-Altitude Observatories site in Maui, HI.

Construction of the Daniel K. Inouye Solar Telescope (DKIST) is well underway on the Haleakalā summit on the Hawaiian island of Maui. Featuring a 4-m aperture and an off-axis Gregorian configuration, the DKIST will be the world’s largest solar telescope. It is designed to make high-precision measurements of fundamental astrophysical processes and produce large amounts of spectropolarimetric and imaging data. These data will support research on solar magnetism and its influence on solar wind, flares, coronal mass ejections, and solar irradiance variability. Because of its large aperture, the DKIST will be able to sense the corona’s magnetic field—a goal that has previously eluded scientists—enabling observations that will provide answers about the heating of stellar coronae and the origins of space weather and exo-weather. The telescope will cover a broad wavelength range (0.35 to 28 microns) and operate as a coronagraph at infrared (IR) wavelengths. Achieving the diffraction limit of the 4-m aperture, even at visible wavelengths, is paramount to these science goals. The DKIST’s state-of-the-art adaptive optics systems will provide diffraction-limited imaging, resolving features that are approximately 20 km in size on the Sun. At the start of operations, five instruments will be deployed: a visible broadband imager (VTF), a visible spectropolarimeter (ViSP), a visible tunable filter (VTF), a diffraction-limited near-IR spectropolarimeter (DLNIRSP), and a cryogenic near-IR spectropolarimeter (cryo-NIRSP). At the end of 2017, the project finished its fifth year of construction and eighth year overall. Major milestones included delivery of the commissioning blank, the completed primary mirror (M1), and its cell. Commissioning and testing of the coude rotator is complete and the installation of the coude cleanroom is underway; likewise, commissioning of the telescope mount assembly (TMA) has also begun. Various other systems and equipment are also being installed and tested. Finally, the observatory integration, testing, and commissioning (IT&C) activities have begun, including the first coating of the M1 commissioning blank and its integration within its cell assembly. Science mirror coating and initial on-sky activities are both anticipated in 2018.

The Daniel K. Inouye Solar Telescope (DKIST) will be the largest solar telescope in the world, with a 4-meter off-axis primary mirror and 16 meter rotating Coude laboratory within the telescope pier. The off-axis design requires a mount similar to an 8-meter on-axis telescope. Both the telescope mount and the Coude laboratory utilize a roller bearing technology in place of the more commonly used hydrostatic bearings. The telescope enclosure utilizes a crawler mechanism for the altitude axis. As these mechanisms have not previously been used in a telescope, understanding the vibration characteristics and the potential impact on the telescope image is important. This paper presents the methodology used to perform jitter measurements of the enclosure and the mount bearings and servo system in a high-noise environment utilizing seismic accelerometers and high dynamic-range data acquisition equipment, along with digital signal processing (DSP) techniques. Data acquisition and signal processing were implemented in MATLAB. In the factory acceptance testing of the telescope mount, multiple accelerometers were strategically located to capture the six axes-of-motion of the primary and secondary mirror dummies. The optical sensitivity analysis was used to map these mirror mount displacements and rotations into units of image motion on the focal plane. Similarly, tests were done with the Coude rotator, treating the entire rotating instrument lab as a rigid body. Testing was performed by recording accelerometer data while the telescope control system performed tracking operations typical of various observing scenarios. The analysis of the accelerometer data utilized noise-averaging fast Fourier transform (FFT) routines, spectrograms, and periodograms. To achieve adequate dynamic range at frequencies as low as 3 Hz , the use of special filters and advanced windowing functions were necessary. Numerous identical automated tests were compared to identify and select the data sets with the lowest level of external interference. Similar testing was performed on the telescope enclosure during the factory test campaign. The vibration of the enclosure altitude and azimuth mechanisms were characterized. This paper details jitter tests using accelerometers placed in locations that allowed the motion of the assemblies to be measured while the control system performed various moves typical of on-sky observations. The measurements were converted into the rigid body motion of the structures and mapped into image motion using the telescope's optical sensitivity analysis.

The Daniel K Inouye Solar Telescope (DKIST) will be the largest solar telescope in the world, providing a significant increase in the resolution of solar data available to the scientific community. Vibration mitigation is critical in long focal-length telescopes such as the Inouye Solar Telescope, especially when adaptive optics are employed to correct for atmospheric seeing. For this reason, a vibration error budget has been implemented. Initially, the FRFs for the various mounting points of ancillary equipment were estimated using the finite element analysis (FEA) of the telescope structures. FEA analysis is well documented and understood; the focus of this paper is on the methods involved in estimating a set of experimental (measured) transfer functions of the as-built telescope structure for the purpose of vibration management. Techniques to measure low-frequency single-input-single-output (SISO) frequency response functions (FRF) between vibration source locations and image motion on the focal plane are described. The measurement equipment includes an instrumented inertial-mass shaker capable of operation down to 4 Hz along with seismic accelerometers. The measurement of vibration at frequencies below 10 Hz with good signal-to-noise ratio (SNR) requires several noise reduction techniques including high-performance windows, noise-averaging, tracking filters, and spectral estimation. These signal-processing techniques are described in detail.

The Daniel K Inouye Solar Telescope (DKIST) will be the largest solar telescope in the world, and will be able to provide the sharpest views ever taken of the solar surface. The telescope has a 4m aperture primary mirror, however due to the off axis nature of the optical layout, the telescope Mount has proportions similar to an 8 metre class telescope. The Telescope Mount Assembly (TMA) includes both the telescope Mount and the 16m diameter laboratory table or Coude Rotator. The Coude Rotator supports the full instrument suite of up to 40 tonnes and has full rotation capabilities similar to the Mount azimuth axis. The TMA has been going through the design, fabrication and assembly process since 2009 with Ingersoll Machine Tool’s and this culminated with the Factory Acceptance Testing (FAT). The preparation for the FAT started not long after the Final Design Review was complete and planning continued through the assembly stages. The official Factory Acceptance testing of the Coude Rotator was conducted during May/Jun 2014 and the Mount in Feb through Apr 2015. This paper provides an overview and discussion of the testing that was carried out. The depth and extent of testing will be described with discussion on what we would do differently next time. Also details of the preparation / process that lead into the testing will be presented. Most importantly the results will be summarized and lessons learned during the testing provided as well as discussion on how this influences the planned site assembly and extent of re-test post assembly.

The Daniel K. Inouye Solar Telescope (DKIST, formerly the Advanced Technology Solar Telescope, ATST) is unique as, apart from protecting the telescope and its instrumentation from the weather, it holds the entrance aperture stop and is required to position it with millimeter-level accuracy. The compliance of the Enclosure design with the requirements, as of Final Design Review in January 2012, was supported by mathematical models and other analyses which included structural and mechanical analyses (FEA), control models, ventilation analysis (CFD), thermal models, reliability analysis, etc. During the Enclosure Factory Assembly and Testing the compliance with the requirements has been verified using the real hardware and the models created during the design phase have been revisited. The tests performed during shutter mechanism subsystem (crawler test stand) functional and endurance testing (completed summer 2013) and two comprehensive system-level factory acceptance testing campaigns (FAT#1 in December 2013 and FAT#2 in March 2014) included functional and performance tests on all mechanisms, off-normal mode tests, mechanism wobble tests, creation of the Enclosure pointing map, control system tests, and vibration tests. The comparison of the assumptions used during the design phase with the properties measured during the test campaign provides an interesting reference for future projects.

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 coude 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.

At future telescopes, adaptive optics systems will play a role beyond the correction of Earth's atmosphere. These systems are capable of delivering information that is useful for instrumentation, e.g. if reconstruction algorithms are employed to increase the spatial resolution of the scientific data. For the 4m aperture Advanced Technology Solar Telescope (ATST), a new generation of state-of-the-art instrumentation is developed that will deliver observations of the solar surface at unsurpassed high spatial resolution. The planned Visual Broadband Imager (VBI) is one of those instruments. It will be able to record images at an extremely high rate and compute reconstructed images close to the telescope's theoretical diffraction limit using a speckle interferometry algorithm in near real-time. This algorithm has been refined to take data delivered by the adaptive optics system into account during reconstruction. The acquisition and reconstruction process requires the use of a high-speed data handling infrastructure to retrieve the necessary data from both adaptive optics system and instrument cameras. We present the current design of this infrastructure for the ATST together with a feasibility analysis of the underlying algorithms.

The range of spectrometers can be extended to wavelengths shorter than 3000 A in the ultraviolet without modifications which would impair their versatility at longer wavelengths by using an intense source and filtering out the scattered light in the visible and near ultraviolet. An absorption filter composed of nickel sulfate hexahydrate and Corning 9863 glass is described which extends the range of an absolute reflectometer having over thirty reflections and employing a single-beam, double-pass monochromator to about 2400 A.